A Study on Material Properties of Intermetallic Phases in a Multicomponent Hypereutectic Al-Si Alloy with the Use of Nanoindentation Testing

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Article A Study on Material Properties of Intermetallic Phases in a Multicomponent Hypereutectic Al-Si Alloy with the Use of Nanoindentation Testing

Mirosław Tupaj 1,* , Antoni Władysław Orłowicz 2, Marek Mróz 2 , Andrzej Trytek 1 , Anna Janina Dolata 3,* and Andrzej Dziedzic 4 1 Faculty of Mechanics and Technology, Rzeszow University of Technology, ul. Kwiatkowskiego, 37-450 Stalowa Wola, Poland; [email protected] 2 Faculty of Mechanical Engineering and Aeronautics, Rzeszow University of Technology, al. Powsta´nców 8, 35-959 Rzeszów, Poland; [email protected] (A.W.O.); [email protected] (M.M.) 3 Faculty of Materials Engineering, Silesian University of Technology, ul. Krasi´nskiego 8, 40-019 Katowice, Poland 4 Institute of Physics, University of Rzeszow, Pigonia 1, 35-310 Rzeszow, Poland; [email protected] * Correspondence: [email protected] (M.T.); [email protected] (A.J.D.)

Received: 15 November 2020; Accepted: 7 December 2020; Published: 9 December 2020

Abstract: The paper concerns modeling the microstructure of a hypereutectic aluminum-silicon alloy developed by the authors with the purpose of application for automobile cylinder liners showing high resistance to abrasive wear at least equal to that of cast-iron liners. With the use of the nanoindentation method, material properties of intermetallic phases and matrix in a hypereutectic Al-Si alloy containing Mn, Cu, Cr, Ni, V, Fe, and Mg as additives were examined. The scanning electron microscope equipped with an adapter for chemical composition microanalysis was used to determine the chemical composition of intermetallics and of the alloy matrix. Intermetallic phases, such as Al(Fe,Mn,M)Si, Al(Cr,V,M)Si, AlFeSi, AlFeNiM, AlCuNi, Al2Cu, and Mg2Si, including those supersaturated with various alloying elements (M), were identiﬁed based on results of X-ray diﬀraction (XRD) tests and microanalysis of chemical composition carried out with the use of X-ray energy dispersive spectroscopy (EDS). Shapes of the phases included regular, irregular, or elongated polygons. On the disclosed intermetallic phases, silicon precipitations, the matrix, values of the indentation hardness (HIT), and the indentation modulus (EIT) were determined by performing nanoindentation tests with the use of a Nanoindentation Tester NHT (CSM Instruments) equipped with a Berkovich B-L 32 diamond indenter. The adopted maximum load value was 20 mN.

Keywords: hypereutectic Al-Si alloy; intermetallic phases; materials properties; nanoindentation tests

1. Introduction The research on the application of aluminum-silicon alloys for manufacturing automobile engine cylinder liners are carried out mainly by industrial laboratories. For that reason, detailed reports on such studies are rarely published in generally available scientiﬁc literature. As a result, there are gaps in the knowledge concerning the forms of microstructure development in cylinder liner castings characterized, among other things, by high resistance to abrasive wear. It follows from the available technical literature that monoblocks and/or cylinder liners for some motorcar models of Porsche, Jaguar, Mercedes, and Audi brands were or currently are manufactured using hypereutectic Al-Si alloys with a silicon content in the range of 17–27 wt.% Si with the underlying technological processes patented under trade names such as ALUSIL®, LOKASIL I®, and LOKASIL II® [1–4]. The LOKASIL concept (quasimonolithic concept) allows to obtain an appropriate microstructure in

Materials 2020, 13, 5612; doi:10.3390/ma13245612 www.mdpi.com/journal/materials Materials 2020, 13, 5612 2 of 17 areas of extreme operating conditions and locally increase the functional properties of the engine block (i.e., wear resistance, thermal and dimensional stability). The composite inserts are obtained by the infiltration of highly porous, hollow cylindrical preforms made of ceramic fibres and silicon particles (LOKASIL I®) or only silicon particles (LOKASIL II®) with an aluminium alloy during the engine block ® casting process [1,2]. In turn, the ALUSIL technology based on the hypereutectic AlSi17Cu4Mg alloy were used to produce monolithic aluminium engine blocks. Primary Si particles precipitated during solidification, after machining and honing procedure, protect the cylinder bore surfaces and provide the expected tribological surface characteristics for proper engine operation [3,4]. Daimler-Benz have applied the SILITECTM process to apply silicon coatings in engine monoblocks made of hypereutectic aluminum-silicon alloy [5,6]. Another innovative engineering solution was implemented by BMW in a six-cylinder engine in which the block made of a magnesium alloy was used with cast-in cylinder liners of a hypereutectic aluminum-silicon alloy [7]. Research work was also carried out on the optimization of manufacturing engine monoblocks of hypoeutectic Al-Si gravitationally cast alloys, with the cylinder bearing surface made of a hypereutectic alloy. The cylinder liner surface was formed with the use of the TRIBOSILTM method. The process involved local melting of the surface with simultaneous feeding of a powder silicon-containing powder [8,9]. In the AL-CAST research concept developed by the company TRIMET Aluminium AG [10], traditional cylinder liners were replaced with new hybrid ones, the outer surfaces of which were made of near-eutectic aluminum-silicon alloy, whereas the inner surface was made of a hypereutectic Al-Si alloy containing about 30 wt.% silicon. On the other hand, authors of papers [11,12] conducted studies on the development of monolithic cylinder blocks of Al-20 wt.% Si alloy. The present authors have also developed a hypereutectic Al-Si alloy and a geometrical structure for bearing surfaces of cylinder liners service properties of which were comparable to those of cast-iron liners [13]. One advantage of replacing cast iron with a lightweight Al-Si alloy is reduction of the overall mass of a car, resulting in a further reduction of fuel consumption. Modeling the microstructure of the alloy characterized by high resistance to abrasive wear and intended for operation in conditions of lubricated friction requires the establishment of relationships between chemical composition, morphology, and mechanical properties, such as the hardness and elastic modulus of intermetallics. The effect of the morphology of intermetallic phases in aluminum-silicon alloys is usually considered from the point of view of its relationship with the decrease of resistance to loads of variable and dynamic nature. On the other hand, morphological properties of intermetallic phases depend on chemical composition of the alloy and conditions of its solidification. The presence of plate-shaped β-Al5FeSi intermetallic phases is commonly considered undesirable in view of blocking the course of liquid material supply in the course of crystallization and the resulting deterioration properties of the alloy. It is known from the literature [14] that, with the increase of iron content from 0.57 wt.% to 0.97 wt.%, the shape of intermetallics evolves from that typical for phase β-Al8Mg3FeSi6, through Chinese scripture forms of β-Al15Fe3Si2, to plate-shaped β-Al5FeSi. Precipitations of phase β-Al5FeSi, in view of its shape, favor induction of stress concentrations and nucleation of cracks in structures operated in variable load conditions. According to Warmuzek et al. [15], the increase of iron content in Al-Si-Fe alloy from 0.5 wt.% to 3.0 wt.% can be connected with evolution of shapes of intermetallic phases from plate-like forms, through Chinese script-type features, to solid polyhedrons. Introduction of an addition of 0.5–1.5 wt.% manganese at slow cooling of Al-Si-Fe alloy is favorable for development of precipitations in the form of Chinese scripture, and in case of high cooling rates, even addition as small as 0.1 wt.% Mn is sufficient to trigger occurrence of precipitations of that shape. According to the same authors, the addition of manganese and chromium and increase of Al-Si-Fe alloy cooling rate allows to avoid occurrence of plate-shaped intermetallics. Also, Manasijevic et al. [16] noted that the addition of 0.25 wt.% manganese in AlSi13Cu4Ni2Mg alloy has an effect on development of plate-shaped intermetallic phases. In turn, the authors of reports [17,18] confirm that addition of Mn in LM13 alloy containing 1.2 wt.% Fe results in a change of β-AlFeSi phase volume share to the benefit of other intermetallics with more desirable morphologies. The authors of [19] Materials 2020, 13, 5612 3 of 17 examined a hypereutectic alloy Al-17.5 wt.% Si containing 1.2 wt.% Fe and found that that addition of 0.6 wt.% Mn resulted in evolution of morphology of phase β-AlFeSi into α-Al(Fe,Mn)Si which, as a consequence, resulted in an increase of resistance of the alloy to abrasive wear. The authors of [20], by adding 0.67 wt.% Cr, were able to reduce the volume share of plate-shaped phase β-AlFeSi to the benefit of phase α-Al(Fe,Cr)Si with skeletal morphology. Timelli and Bonollo [21] demonstrated that addition of 0.15 wt.% Cr to AlSi9Cu3Fe alloy led to the development of a complex phase Alx(Fe,Mn,Cr)ySiz with a polyhedral, star-like, and blocky shape. By increasing the Cr content from 0.057 to 0.15 wt.%, they achieved a relative increase in the alloy hardness (~8% HV). The effect of chromium on the change of β-AlFeSi phase morphology into phase α is also produced by vanadium. The authors of [22] added 0.5 wt.% V and 1.0 wt.% V to Al-20Si-5Fe alloy and found the presence of Al(Fe,V)Si phase with flower-like morphology. The occurrence of the phase Al12(Fe,V)3Si besides the phase Al4.5FeSi was found by authors of [23] in the alloy AlSi20/8009. According to reports [24,25], shapes of intermetallics rich in iron depend on manganese content. At 0.35–0.40 wt.% Mn, the intermetallic phase rich in iron is characterized by plate-like shape typical for β-Al5FeSi, while at higher content of magnesium, by precipitation forms typical for β-Al8Mg3FeSi6 phase [26]. According to the authors of [27], the change of nickel content has no effect on changes to the morphology of iron-based intermetallic phases. However, the authors of paper [28] claim that, at the Fe/Ni ratio value of 0.23 (in wt.%), phase Al9FeNi appears and forms a closed or semi-closed network resulting in an increase of mechanical strength properties of Al-12Si-4Cu-1Mg (in wt.%) alloy at temperature 350 ◦C. According to the results described by Murali et al. [29], the addition of beryllium in the amount of 0.2–0.3 wt.% to Al-Si alloy containing as much as 1.0 wt.% iron changes the morphology of phase β from needle-shaped into Chinese script-like forms. In turn, Stolarz et al. [30] showed that the plate-shaped β-Al5FeSi phase precipitations play a similar role in decreasing resistance to loads of variable nature as silicon precipitations. Additions of Cu, Ni, Cr, and Mg are introduced to aluminum-silicon alloys, especially those used for engine pistons, in order to improve their mechanical properties and dimensional stability at elevated temperatures, mainly through the reinforcing effect of developing intermetallic phases [31–36]. The authors of [31] examined different variants of heat treatment for A356 alloy and found the presence of intermetallic phases with various morphologies: Mg2Si, AlFeSi, Al12Mg2Si, Al8Mg3FeSi6, Al12Si(Fe,Cr), Al3Cr, Al8Cr5, Al9Si, Al12Mg17, CrFe4, and AlCuMg. Further, the authors of the study [32], by adding Ni and Zr to Al-Si-Cu-Mg (A354) alloy, obtained phases Mg2Si, Al2Cu, Al3CuNi, Al9NiFe, Al8Mg3FeSi6, Al5Cu2, Mg2Si6, (Al,Si)2(Ti,Zr), and Al3Ni2 with needle-like, polygonal, and/or irregular shapes. They have found that one effect of adding 0.2 wt.% Zr and 0.2 wt.% Ni was the increase of strength properties of the alloy by about 30% at temperature of 300 ◦C. Some interesting results were obtained by authors of [33] who added copper in the amount of from 2.63 wt.% do 5.45 wt.% to the alloy Al-12.5Si-XCu-2Ni-1Mg (in wt.%) and found that with increasing content of the element, intermetallic phases rich in nickel, Al3Ni, and Al3CuNi transformed into the phase Al7Cu4Ni. Morphologies of the phases changed also from short-strip to reticular and then annular or semi-annular shape, respectively. That resulted in an improvement of mechanical properties of the alloy and an increase of its dimensional stability. On the other hand, the only intermetallic phases found in the alloy Al-12Si-4Cu-2Ni-2.6Mg (in wt.%) were M-Mg2Si, Al7Cu4Ni, and Al5Cu2Mg8Si6 [34]. In the two alloys, iron content was 0.19 wt.% Fe and 0.11 wt.% Fe, respectively. However, the authors of the above-quoted papers did not find presence of any intermetallic phases containing iron. In turn, Li et al. [35] added 1 wt.% Ni and 0.1–3.2 wt.% Cu to an Al-Si alloy containing about 13 wt.% Si, about 1 wt.% Mg, and about 0.3 wt.% Fe. As a result, they observed presence of intermetallic phases Al3Ni, Al3CuNi, Al7Cu4Ni, Mg2Si, and Al8FeMg3Si5 and found that phase Al3Ni had a block-like morphology, phase Al3CuNi had the strip-like morphology, and phase Al7Cu4Ni had the skeleton-like morphology. Further, they proved that the phase Al3CuNi with strip-like morphology had the predominant effect on increase of strength of the alloy at elevated temperatures. In the next studies described in [36], the authors introduced 0.8 wt.% Fe and 0.5 wt.% Cr into the alloy Materials 2020, 13, 5612 4 of 17

Materials 2020, 13, x FOR PEER REVIEW 4 of 17 Al-13Si-3.7Cu-3.2Ni-1.1Mg (in wt.%) and found presence of Cr, Fe, and Si in phase Al3CuNi which, by precipitating at boundaries of α-Al-Al grains, might transfer stresses from the Al matrix. As a result of introducingintroducing Cr and Fe,Fe, aa 26%26% riserise ofof thethe tensiletensile strengthstrength ofof thethe alloyalloy waswas observed.observed. The presented presented review review of literature of literature reveals reveals a wide a range wide of range opportunities of opportunities to shape the to morphology shape the ofmorphology intermetallic of intermetallic phases through phases the properthrough selection the proper of both selection the chemistry of both the of thechemistry alloy (introduction of the alloy of(introduction alloying additives) of alloying and conditions additives) of and its crystallization.conditions of its To crystallization. be able to model To microstructure be able to model of an alloy,microstructure it is necessary of an to alloy, understand it is necessary the effect of to chemical understand composition the effect and of conditions chemical composition of crystallization and onconditions the microstructure of crystallization and mechanical on the microstructure properties, suchand asmechanical the hardness properties and modulus, such as of the elasticity hardness of individualand modulus phases. of elasticity To ensure of high individual resistance phases. to abrasive To ensure wear, high it is resistanceimportant tothat abrasive the knowledge wear, it on is theimportant subject is that acquired the knowledge with reference on the toall subject microstructure is acquired components with reference of aluminum-silicon to all microstructure alloys. components of aluminum-silicon alloys. 2. Materials and Methods 2. Materials and Methods 2.1. Preparation of the Test Material 2.1. PreparationThe aluminum-silicon of the Test Material alloy with chemical composition specified in Table1 was prepared in an inductionThe aluminum furnace-silicon with capacityalloy with of chemical 5 kg. Modification composition with specified copper-phosphorus in Table 1 was prepared key metal in was an madeinduction at temperature furnace with 950 capacity◦C. The of 5 liquid kg. Modification metal at temperature with copper of-phosphorus 920 ◦C was pouredkey metal into was a metalmade mouldat temperature preheated 950 up °C. to 300The◦ C.liquid The proceduresmetal at temperature for producing of 920 experimental °C was poured castings into are a alsometal described mould in [37,38]. From the plate casting with dimensions 400 mm 120 mm 40 mm, a specimen from area preheated up to 300 °C. The procedures for producing experimental× × castings are also described in A (Figure1) with dimension 40 mm 30 mm 10 mm was cut out using Labotom 3 metallographic [37,38]. From the plate casting with dimensions× × 400 mm × 120 mm × 40 mm, a specimen from area A cutter(Figure (Struers, 1) with Copenhagen,dimension 40 Denmark) mm × 30 equippedmm × 10 mm with was Supra cut TRD out 15using type Labotom water cooled 3 metallographic cutting disc. Thecutter disc (Struers, edge displacement Copenhagen, linear Denmark speed) equipped was 37.2 with m/s. Supra The metallographic TRD 15 type water section cooled was preparedcutting disc. on the specimen side with dimensions 40 mm 30 mm. After sectioning, the surface was ground and The disc edge displacement linear speed was× 37.2 m/s. The metallographic section was prepared on polishedthe specimen with side the usewith of dimensions Saphir 320E 40 metallographic mm × 30 mm. polisher After sectioning, equipped the with surface Rubin was 500 ground head (ATM, and Altenkirchen,polished with Germany).the use of Saphir The finish 320E polishing metallogr wasaphic made polisher on a discequipped covered with with Rubin suspension 500 head of ( siliconATM, oxideAltenkirchen, with grain Germany size of). 0.1 Theµm. finish polishing was made on a disc covered with suspension of silicon oxide with grain size of 0.1 μm. Table 1. Chemical composition of hypereutectic aluminum-silicon alloy [13].

Table 1. Chemical compositionElement of Contenthypereutectic (wt.%) aluminum * -silicon alloy [13]. Si Mn Cu CrElement Ni C Vontent Fe (wt.%) Mg * Ti B P Al 31.32Si 0.53Mn Cu 1.44 Cr 0.58 Ni 1.15 V 0.45 Fe 0.54 Mg 1.33 Ti0.041 0.0027B P 0.05 Al Bal. 31.32* Alloy 0.53 composition 1.44 tested0.58 by Q41.15 Tasman 0.45 emission 0.54 spectrometer 1.33 0.041 (Bruker, 0.0027 Kalkar, Germany).0.05 Bal. * Alloy composition tested by Q4 Tasman emission spectrometer (Bruker, Kalkar, Germany).

Figure 1. 1. Plate casting with dimensions 400 mm × 120 mm × 40 mm cast cast in in metal metal mold. mold. A—testA—test × × material taking area.

2.2. Chemical C Compositionomposition M Microanalysisicroanalysis The analysis of chemical composition was carried out with the use of Q4 Tasman emission spectrometer (Bruker, Kalkar, Germany).Germany). The specimen was subject to examination with the use of VEGA XMH scanning electron microscope (SEM, Tescan, Brno, Czech Republic)Republic) equipped with an energy dispersive X-ray spectrometer (EDS, Oxford Instruments, Abingdon, UK) in order to reveal intermetallic phases (Figure 2). The determination of chemical composition was carried out for

Materials 2020, 13, 5612 5 of 17 energy dispersive X-ray spectrometer (EDS, Oxford Instruments, Abingdon, UK) in order to reveal Materials 2020, 13, x FOR PEER REVIEW 5 of 17 intermetallic phases (Figure2). The determination of chemical composition was carried out for intermetallic phases and for the alloy alloy matrix. matrix. The The quoted quoted results results are are averages averages from from five ﬁve measurements measurements taken for each analyzed microstructure component.component.

(a) (b)

Figure 2. AnAn example example structure structure of of hypereutectic hypereutectic Al Al-Si-Si alloy alloy prepared prepared for for metallographic metallographic examination, examination, SEMSEM,, ( a) 500× 500 ,,( (bb)) 1000× 1000 . . × × 2.3. Examination of Material Properties of Microstructure Components by Nanoindentation Testing 2.3. Examination of Material Properties of Microstructure Components by Nanoindentation Testing In the next step, the nanoindentation nanoindentation technique was used to determine determine the indentation indentation hardness HIT and the indentation modulus EIT evaluated with the use of Nanoindentation Tester NHT (CSM HIT and the indentation modulus EIT evaluated with the use of Nanoindentation Tester NHT (CSM InstrumInstruments,ents, Peseux,Peseux, Switzerland).Switzerland). The The measurements measurements were were taken taken in linein line with with the the standard standard PN-EN PN- ISOEN 14577-1 [39]. The indentation hardness HIT, which is a measure of material resistance until permanent ISO 14577-1 [39]. The indentation hardness HIT, which is a measure of material resistance until permanentdeformation, deformation, was determined was determined from the following from the formula following [39 ,formula40]: [39,40]:

퐹F푚푎푥max H퐻IT퐼푇 == (1(1)) A퐴푝p where HITIT (MPa)(MPa) denotes the indentation hardness,hardness, Fmax (N)(N)—maximum—maximum force force applied applied to to indenter indenter,, 22 and Ap (mm(mm ))—area—area of of the the indenter indenter-tested-tested material material contact contact surface surface projection. projection. IT The v valuealue of the indentation modulus EIT waswas determined determined from from the the formula [39,40]: [39,40]: 2 1 − 푣2푠 퐸퐼푇 = 1 vs 2 EIT = 1 −1 − 푣 (2(2)) v2 푖 1− 1 i 퐸푟 −퐸푖 Er − Ei √휋 푆 퐸푟 = √π S (3) Er = 2 √p퐴푝 (3) 2 Ap where EIT (GPa) is the indentation modulus; νs—tested material Poisson number; νi—indenter where EIT (GPa) is the indentation modulus; νs—tested material Poisson number; νi—indenter material material Poisson number (for diamond indenter, νi = 0.07); Er (GPa)—tested material reduced Young’s Poisson number (for diamond indenter, νi = 0.07); Er (GPa)—tested material reduced Young’s modulus; modulus; Ei—elastic modulus of indenter material (for diamond indenter; Ei = 1141 GPa); S = dF/dh— Ei—elastic modulus of indenter material (for diamond indenter; Ei = 1141 GPa); S = dF/dh—the the slope of tangent to the load indentation curve during the unloading cycle; and Ap (mm2)—area of slope of tangent to the load indentation curve during the unloading cycle; and A (mm2)—area of the the indenter-tested material contact surface projection. p indenter-tested material contact surface projection. Nanoindentation tests were carried out using B-L 32 diamond indenter. The maximum value of Nanoindentation tests were carried out using B-L 32 diamond indenter. The maximum value of the load force was 20 mN. The indenter loading and unloading rate for all the analyzed the load force was 20 mN. The indenter loading and unloading rate for all the analyzed microstructure microstructure components was 40 mN/min. The maximum load force interaction period was 15 s. Measurements were taken for silicon precipitations, intermetallic phases, and the matrix. In the case of intermetallics and silicon precipitations, measurements were taken on precipitations with largest dimensions to minimize the effect of immersion in matrix in the course of measurement which

Materials 2020, 13, 5612 6 of 17 components was 40 mN/min. The maximum load force interaction period was 15 s. Measurements were taken for silicon precipitations, intermetallic phases, and the matrix. In the case of intermetallics and

Materialssilicon precipitations,2020, 13, x FOR PEER measurements REVIEW were taken on precipitations with largest dimensions to minimize6 of 17 the eﬀect of immersion in matrix in the course of measurement which results in underestimation of resultsvalues ofin theunderestim analyzedation material of values properties. of the Exampleanalyzed viewsmaterial of indentsproperties. made Example on a silicon view precipitation,s of indents madeintermetallics,Materials on a20 silicon20, 13 and, x FORprecipitation, the PEER matrix REVIEW are intermetallics, shown in Figure and3 .the matrix are shown in Figure 3. 6 of 17 results in underestimation of values of the analyzed material properties. Example views of indents made on a silicon precipitation, intermetallics, and the matrix are shown in Figure 3.

intermetallic phase intermetallic phase

Al-Si matrix Si precipitation

Alal-Siloy m atrix Si precipitation alloy Figure 3. An example view of indents made in a silicon precipitation, in intermetallic phases, and in theFigure matrix 3. with An example the use viewof Nanoindentation of indents made in Tester a silicon NHTNHT precipitation, (CSM(CSM Instruments).Instruments). in intermetallic phases, and in the matrix with the use of Nanoindentation Tester NHT (CSM Instruments). Results of material properties (nanoindentation) tests tests are are presented in in the f formorm of variability ranges forResults five five ofmeasurements. material properties (nanoindentation) tests are presented in the form of variability ranges for five measurements. 2.4. X X-ray-ray D Diiffractionffraction 2.4. X-ray Diffraction The phase composition analysis was performed performed using a a Bruker Bruker D8 D8 Advance Advance X X-ray-ray diffractometer diffractometer The phase compositionα analysis was performed using a Bruker D8 Advance X-ray diffractometer with the the Cu Cu lamp lamp (K (Kα11 = 1.5406= 1.5406 Å). ToÅ ). solve To solve the resulting the resulting diffractograms, diffractograms, a base of a ICCD base PDF of ICCD standards PDF with the Cu lamp (Kα1 = 1.5406 Å ). To solve the resulting diffractograms, a base of ICCD PDF standardswas used. was Angle used. and Angle spot intensity and spot matching intensity werematching analyzed were using analyzed the EVAusing software. the EVA software. standards was used. Angle and spot intensity matching were analyzed using the EVA software. 3. Results and Discussion 3. Results3. Results and and Discussion Discussion 3.1. Identification of Alloy Microstructure Components 3.1.3.1. Identification Identification of of A Alloylloy M Microstructureicrostructure CComponentsomponents On the metallographic section surface, distribution of alloying elements was mapped results of whichOn areOn the shownthe metallographic metallographic in Figure4 section.section To determine surface, distribution chemicaldistribution composition of of alloying alloying elements of elements microstructural was was mapped mapped components results results of toof whichnecessarywhich are are accuracy,shown shown in in pointFigure Figure analysis 4. 4. ToTo determine was carried chemical chemical out (Figure composition composition5). Example of microstructuralof microstructural results of EDScomponents components diagrams to and to necessary accuracy, point analysis was carried out (Figure 5). Example results of EDS diagrams and necessaryquantitative accuracy, point analysis point analysis of chemical was compositioncarried out (Figure for individual 5). Example microstructure results of EDS components diagrams of and the quantitative point analysis of chemical composition for individual microstructure components of the quantitativealloys are presented point analysis in Figures of chemical6–12. To composition identify intermetallic for individual phases microstructure in the examined components alloy, the X-rayof the alloysalloys are are presented presented in in Figures Figures 66––12. To identifyidentify intermetallic intermetallic phases phases in thein the examined examined alloy, alloy, the X the-ray X -ray diffraction (XRD) method was also used. Results of X-ray phase analysis are shown in Figure. 13. diffractiondiffraction (XRD) (XRD) method method was was alsoalso used. ResultsResults of of X X-ray-ray phase phase analysis analysis are areshown shown in Figure in Figure 13 13.

(a) (b) (c) (d) (a) (b) (c) (d) Figure 4. Cont.

Materials 2020, 13, 5612 7 of 17 Materials 2020, 13, x FOR PEER REVIEW 7 of 17 Materials 2020, 13, x FOR PEER REVIEW 7 of 17 Materials 2020, 13, x FOR PEER REVIEW 7 of 17

(e) (f()f ) (g()g ) (h)( h) (e) (f) (g) (h )

(i) (j()j ) (k()k ) (i) (j) (k) FigureFigureFigure 4. 4.SEM SEM micrograph,micrograph, CAMEO CAMEO image image (a ( ()aa )) and and and mappi mappi mappingngng of of ofelemental elemental elemental distribution distribution distribution (b – (kb)– ( bk of–) k of) of hypereutectichypereutectichypereutecticFigure 4. aluminum-siliconSEM aluminum micrograph,--siliconsilicon alloy.alloy. CAMEOalloy. image (a) and mapping of elemental distribution (b–k) of hypereutectic aluminum-silicon alloy.

Figure 5. Microstructure of hypereutectic aluminum-silicon alloy with the characteristic FigureFiguremicrostructuralFigure 5. Microstructure 5. 5.Microstructure Microstructure components of hypereutectic of of various of hypereutectic hypereutectic chemical aluminum-silicon composition, aluminumaluminum alloy-silicon -SEM,silicon with secondary alloy thealloy characteristic with withelectrons the the (SE). characteristicmicrostructural characteristic componentsmicrostructuralmicrostructural of various components components chemical of ofvarious composition, various chemical chemical SEM, composition, composition, secondary SEM, electronsSEM, secondary secondary (SE). electrons electrons (SE).(SE). Element Weight% Atomic% ElementElementAl Weight%59.52Weight% 69.64Atomic%Atomic% SiAl Al 12.7259.5259.52 14.3069.6469.64 VSi Si 1.6112.7212.72 1.0014.3014.30 CrV V 5.411.611.61 3.281.001.00 MnCrCr 5.885.415.41 3.383.283.28 FeMnMn 14.865.885.88 8.403.383.38

FeFe 14.8614.86 8.408.40

Figure 6. EDS diagram and chemical composition at point no. 1 of Figure 5. Figure 6. EDS diagram and chemical composition at point no. 1 of Figure5. FigureFigure 6. EDS6. EDS diagram diagram and and chemical chemical composition composition at at point point no. no. 1 1 of of Figure Figure 5.5.

MaterialsMaterials2020 2020, 13, 1,3 5612, x FOR PEER REVIEW 8 of8 of17 17 Materials 2020, 13, x FOR PEER REVIEW 8 of 17 MaterialsMaterials 20202020,, 1133,, xx FORFOR PEERPEER REVIEWREVIEW 88 ofof 1717 Element Weight% Atomic% Element Weight% Atomic% ElementElementAl Weight%Weight%8.47 Atomic%Atomic%11.09 Al 8.47 11.09 AlSiAl 46.588.478.47 11.0958.5611.09 Si 46.58 58.56 TiSiSi 46.5846.581.97 58.5658.561.46 Ti 1.97 1.46 TiVTi 11.361.971.97 1.467.881.46 V 11.36 7.88 CrVV 11.3620.4911.36 13.917.887.88 Cr 20.49 13.91 MnCrCr 20.4920.496.79 13.9113.914.37 Mn 6.79 4.37 MnMnFe 6.794.336.79 4.372.744.37 Fe 4.33 2.74 FeFe 4.334.33 2.742.74

Figure 7. EDS diagram and chemical composition at point no. 2 of Figure 5. Figure 7. EDS diagram and chemical composition at point no. 2 of Figure 5. FigureFigureFigure 7. 7.7.EDS EDSEDS diagram diagramdiagram and andand chemical chemicalchemical compositioncomposition at at pointpoint no.no. no. 22 2 ofof of FigureFigure Figure 5.5.5 . Element Weight% Atomic% Element Weight% Atomic% ElementElementAl Weight%Weight%63.92 Atomic%Atomic%67.07 Al 63.92 67.07 AlSiAl 63.9229.2163.92 67.0729.4567.07 Si 29.21 29.45 FeSiSi 29.2129.216.87 29.4529.453.48 Fe 6.87 3.48 FeFe 6.876.87 3.483.48

Figure 8. EDS diagram and chemical composition at point no. 3 of Figure 5. FigureFigure 8. 8.EDS EDS diagramdiagram andand chemical composition at at point point no. no. 3 3of of Figure Figure 5.5 . FigureFigure 8.8. EDSEDS diagramdiagram andand chemicalchemical compositioncomposition atat pointpoint no.no. 33 ofof FigureFigure 5.5. Element Weight% Atomic% Element Weight% Atomic% ElementElement Weight%Weight% Atomic%Atomic%

Al 56.54 71.43 Al 56.54 71.43 AlSiAl 56.5456.545.55 71.4371.436.74 Si 5.55 6.74 FeSiSi 5.555.835.55 6.743.566.74 Fe 5.83 3.56 NiFeFe 24.045.835.83 13.963.563.56 Ni 24.04 13.96 CuNiNi 24.0424.048.04 13.9613.964.31 Cu 8.04 4.31 CuCu 8.048.04 4.314.31

FigureFigure 9. 9.EDS EDS diagram diagram andand chemicalchemical composition at at point point no. no. 4 4of of Figure Figure 5.5 . Figure 9. EDS diagram and chemical composition at point no. 4 of Figure 5. FigureFigure 9.9. EDSEDS diagramdiagram andand chemicalchemical compositioncomposition atat pointpoint no.no. 44 ofof FigureFigure 5.5. Element Weight% Atomic% Element Weight% Atomic% ElementElementAl Weight%Weight%43.26 Atomic%Atomic%63.54 Al 43.26 63.54 Al 43.26 63.54 Al 43.26 63.54 Ni 20.58 13.89 Ni 20.58 13.89 CuNiNi 20.5836.1720.58 13.8922.5613.89 Cu 36.17 22.56 CuCu 36.1736.17 22.5622.56

Figure 10. EDS diagram and chemical composition at point no. 5 of Figure5. Figure 10. EDS diagram and chemical composition at point no. 5 of Figure 5. Figure 10. EDS diagram and chemical composition at point no. 5 of Figure 5. FigureFigure 10.10. EDSEDS diagramdiagram andand chemicalchemical compositioncomposition atat pointpoint no.no. 55 ofof FigureFigure 5.5.

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Element Weight% Atomic% Element Weight% Atomic% Al 58.93 77.17 Al 58.93 77.17 Cu 41.07 22.83 Cu 41.07 22.83

Figure 11. EDS diagram and chemical composition at point no. 6 of Figure 5. FigureFigure 11. 11.EDS EDS diagram diagram and and chemical chemical compositioncomposition at point no. 6 6 of of Figure Figure 5.5.

Element Weight% Atomic% Element Weight% Atomic% Mg 53.77 57.33 Mg 53.77 57.33 Si 46.23 42.67 Si 46.23 42.67

FigureFigure 12. 12.EDS EDS diagram diagram and and chemical chemical composition composition at at point point no. no. 7 7 of of FigureFigure5 5.. Figure 12. EDS diagram and chemical composition at point no. 7 of Figure 5.

TheThe authors authors of papersof papers [22 [22,41,42],41,42] proved proved that, that for, for intermetallic intermetallic phases phases in in whichwhich thethe shareshare in the The authors of papers [22,41,42] proved that, for intermetallic phases in which the share in the alloyalloy was was less less than than 5 5 vol.%, vol.%, thethe sensitivity of of the the X- X-rayray diffraction diffraction (XRD) (XRD) method method was too was low too to low detect to alloy was less than 5 vol.%, the sensitivity of the X-ray diffraction (XRD) method was too low to detect detectand and identify identify them. them. Still, Still,another another approach approach was adopted was adopted by the byauthors the authors of [43] who of [43 marked] who markedsome of and identify them. Still, another approach was adopted by the authors of [43] who marked some of somepeaks of peaks on diffraction on diffraction patterns patterns as unknow as unknown,n, which may which be evidence may be evidence of the unavailability of the unavailability of databases of peaks on diffraction patterns as unknown, which may be evidence of the unavailability of databases databasesconcerning concerning multicomponent multicomponent intermetallic intermetallic phases. phases. By analyzing By analyzing the cooling the cooling curvescurves and their and concerning multicomponent intermetallic phases. By analyzing the cooling curves and their theirderivatives derivatives for fora AlSi a AlSi9Cu93FeCu alloy3Fe alloycontaining containing additions additions of Cr, Mo, of Cr,V, and Mo, W, V, the and authors W, the of authors the paper of derivatives for a AlSi9Cu3Fe alloy containing additions of Cr, Mo, V, and W, the authors of the paper the paper[44] found [44] found the presence the presence of a of quadruple a quadruple eutectic, eutectic, one one component component of of which which was was the the phase [44] found the presence of a quadruple eutectic, one component of which was the phase AlSiCuFeMgMnNiX, with X denoting alloying elements (Cr, Mo, V, W) or their combinations. This AlSiCuFeMgMnNiAlSiCuFeMgMnNiXX, with, withX Xdenoting denoting alloying alloying elementselements (Cr, Mo, V, W) or their combinations. combinations. This This evidences that a multicomponent silumin may comprise complex intermetallic phases which cannot evidencesevidences that that a multicomponent a multicomponent silumin silumin may may comprise comprise complex complex intermetallic intermetallic phases phases which which cannot cannot be be identified correctly with the use of the X-ray diffraction (XRD) method. Elements with similar identifiedbe identified correctly correctly with thewith use the of theuse X-rayof the di Xff-ractionray diffraction (XRD) method.(XRD) method. Elements Elements with similar with valuessimilar of values of atomic radii may change both morphology and stoichiometry of intermetallic phases [45]. atomicvalues radii of atomic may change radii may both change morphology both morphology and stoichiometry and stoichiometry of intermetallic of intermetallic phases [45 phases]. That [45]. is the That is the reason why many authors of research papers dealing with identification of intermetallics reasonThat whyis the many reason authors why many of research authors papers of research dealing papers with dealing identification with identification of intermetallics of intermetallics composed of composed of more than three elements refrain from quoting complete stoichiometry of the phases morecomposed than three of more elements than refrainthree elements from quoting refrain complete from quoting stoichiometry completeof stoichiometry the phases [ 21of, 46the,47 phases]. Such [21,46,47]. Such an approach is also adopted in the present work. an[21,46,47]. approach Such is also an adopted approach in is the also present adopted work. in the present work. The phase analysis was carried out with the use of results of both EDS (Figures 6–12) and XRD TheThe phase phase analysis analysis was was carried carried out out with withthe the useuse ofof resultsresults of both EDS EDS (Figures (Figures 66––12)12) and and XRD XRD (Figure 13). Based on results of the tests, the following were identified: (1) an intermetallic phase (Figure(Figure 13 ).13). Based Based on on results results of of the the tests, tests, the the following following werewere identified:identified: (1) (1) an an intermetallic intermetallic phase phase Al(Fe,Mn,M)Si with the shape of large polygons, often merged with each other, supersaturated with Al(Fe,Mn,Al(Fe,Mn,M)SiM)Si with with the the shape shape of of large large polygons, polygons, oftenoften mergedmerged with each each other, other, supersaturated supersaturated with with chromium and vanadium (M = Cr, V); (2) an intermetallic phase Al(Cr,V,M)Si, polygonal in shape, chromiumchromium and and vanadium vanadium ( M(M= =Cr, Cr, V);V); (2)(2) anan intermetallicintermetallic phase Al(Cr,V, Al(Cr,V,MM)Si,)Si, polygonal polygonal in in shape, shape, supersaturated with manganese, iron, and titanium (M = Mn, Fe, Ti); (3) Si crystals; (4) an supersaturatedsupersaturated with with manganese, manganese, iron, iron, and titanium and titanium (M = Mn, (M Fe,= Mn, Ti); (3) Fe, Si Ti); crystals; (3) Si (4) crystals; an intermetallic (4) an intermetallic phase Al4.5FeSi with the shape of elongated polygons; (5) intermetallic phase AlFeNiM phaseintermetallic Al FeSi phase with theAl4.5 shapeFeSi with of elongated the shape polygons;of elongated (5) polygons; intermetallic (5) intermetallic phase AlFeNi phaseM in AlFeNi the formM in the4.5 form of elongated polygons, supersaturated with copper and silicon (M = Cu, Si), (6) an ofin elongated the form polygons, of elongated supersaturated polygons, supersaturated with copper and with silicon copper (M and= siliconCu, Si), (M (6) = an Cu, intermetallic Si), (6) an intermetallic phase Al7Cu4Ni with the shape of irregular elongated polygons; (7) an intermetallic phaseintermetallic Al Cu Ni phase with Althe7Cu shape4Ni with of irregular the shape elongated of irregular polygons; elongated (7) an polygons; intermetallic (7) an phase intermetallic Al Cu in phase7 Al24Cu in the form of irregular elongated polygons; and (8) an intermetallic phase Mg2Si having2 phase Al2Cu in the form of irregular elongated polygons; and (8) an intermetallic phase Mg2Si having the formthe shape of irregular of irregular elongated polygons. polygons; and (8) an intermetallic phase Mg2Si having the shape of irregularthe shape polygons. of irregular polygons.

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FigureFigure 13. 13.XRD XRD patterns patterns of of Al-30 Al-30wt.% wt.% SiSi withwith Mn,Mn, Cu, Cr, Ni, V, Fe and Mg additions. additions.

InIn turn, turn, the the chemical chemical composition of of the the matr matrixix varied varied in the in range the range of 96.82 of– 96.82–97.8997.89 wt.% Al, wt.% 1.02 Al,– 1.02–1.731.73 wt.% wt.% Cu, Cu, 0.97 0.97–1.41–1.41 wt.% wt.% Si, 0.0 Si,– 0.0–0.440.44 wt.% wt.% Mg, Mg,and and0.0–0.12 0.0–0.12 wt.% wt.% Ni. Ni. TheThe authors authors of of papers papers [48 [48–50–50]] underline underline the the favorablefavorable eeffectffect of alloying elements elements dissolved dissolved in in matrixmatrix on on its its reinforcement. reinforcement. That That is is importantimportant in in view view of of development development of of deformation deformation and and then then microcracksmicrocracks on on boundaries boundaries between between the the matrix matrix and and hard hard and and brittle brittle silicon silicon crystals crystals or or intermetallics intermetallics as a resultas a result of existence of existence of loads of loads with with variable variable directions directions and and values. values. The The issueissue is widely analyzed analyzed with with referencereference to to the the nucleation nucleation and and development development of of fatigue fatigue crackscracks inin silumins [30]. [30]. Therefore, Therefore, enrichment enrichment of theof the matrix matrix in in silicon, silicon, copper, copper, and and magnesium magnesium demonstrated demonstrated in in the the course course of of tests tests shouldshould resultresult inin a decreasea decrease of its of susceptibility its susceptibility to the to nucleationthe nucleation of cracks of cracks on the on matrix-intermetallicsthe matrix-intermetallics boundaries boundaries as well as as inwell a decrease as in a ofdecrease susceptibility of susceptibility to the propagation to the propagation of cracks through of cracks the throughmatrix between the matrix precipitations. between preThecipitations. obtained research results indicate that the newly developed chemical composition of the The obtained research results indicate that the newly developed chemical composition of the strongly hypereutectic silumin for cylinder liners [13] and the applied conditions of cooling enabled the strongly hypereutectic silumin for cylinder liners [13] and the applied conditions of cooling enabled crystallization of intermetallic phases with complex chemical compositions. The applied cooling rate the crystallization of intermetallic phases with complex chemical compositions. The applied cooling prevented crystallization of large primary silicon precipitates and intermetallics which is favorable in rate prevented crystallization of large primary silicon precipitates and intermetallics which is view of variable stress states which occur in engine cylinder liners in the course of operation. Another favorable in view of variable stress states which occur in engine cylinder liners in the course of significant circumstance is also the enrichment of the silumin matrix with alloying elements, which operation. Another significant circumstance is also the enrichment of the silumin matrix with alloying resultselements in its, which reinforcement. results in its reinforcement. 3.2. The Nanoindentation Test 3.2. The Nanoindentation Test Displacement of the indenter face in the course of indentation testing individual microstructure Displacement of the indenter face in the course of indentation testing individual microstructure componentscomponents of theof the examined examined silumin silumin is shownis shown in in plots plots of of Figure Figure 14 14,, whereas whereas the the bar bar charts charts of of Figures Figures 15 and 16 represent values of hardness H and modulus E for the examined microstructure components 15 and 16 represent values of hardnessIT HIT and modulusIT EIT for the examined microstructure of hypereutecticcomponents of (Al-30% hypereutectic Si) aluminum-silicon (Al-30% Si) aluminum alloy. Nanoindentation-silicon alloy. Nanoindentation tests were not tests carried were out not for thecarried phase Mgout2 forSi because the phase of smallMg2Si dimensionsbecause of small of its precipitationsdimensions of andits precipitations the indenter load and valuethe indenter (20 mN) adoptedload value throughout (20 mN) the adopted study. throughout the study. NanoindentationNanoindentation tests tests were were carried carried out out on on unetched unetched specimens specimens in in order order to to minimize minimize plastic plastic responseresponse of of matrix matrix material material to to the the load load applied applied to to crystals. crystals. TheThe indentation indentation test test with with the the use use of aof Berkovich a Berkovich indenter indenter revealed revealed a di aff differenceerence in thein the course course of plotof linesplot representing lines representing indenter indenter loading and loading unloading and unloading in the case in of the individual case of microstructure individual microstructure components. Thecomponents. difference was The causeddifference by thewas elastic caused and by the plastic elastic response and plastic of the response material of constitutingthe material constituting the analyzed microstructurethe analyzed features.microstructure features.

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FigureFigureFigure 14. 14. Plots Plots representing representing indenter indenterindenter face face displacement displacement in inin the thethe course course course of of of loading loading loading and and and unloading unl unloadingoading in in the in the course of indentation tests of: (1)—Al(Fe,Mn,M)Si; (2)—Al(Cr,V,M)Si; (3)—Si crystals; (4)— thecourse course of indentation of indentation tests of: tests (1)—Al(Fe,Mn, of: (1)—Al(Fe,Mn,M)Si; (2)—Al(Cr,V,M)Si; (2)—Al(Cr,V,M)Si; (3)—SiM)Si; crystals; (3)—Si crystals; (4)—Al4.5 (4)FeSi;— Al4.54.5FeSi; (5)—AlFeNiM (6)—Al77Cu44Ni; (7)—Al22Cu; and (8)—the matrix. Al(5)—AlFeNiFeSi; (5)—MAlFeNi(6)—AlM7Cu (6)4—Ni;Al (7)—AlCu Ni;2 Cu;(7)— andAl Cu; (8)—the and (8) matrix.—the matrix.

Figure 15. Values of indentation hardness HIT for primary silicon crystals, intermetallic phase crystals, Figure 15. Values of indentation hardness HIT for primary silicon crystals, intermetallic phase crystals, Figureandand matrix matrix 15. Values of of hypereutectic hypereutectic of indentation siluminsilumin hardness determined HIT for withprimary with the the usesilicon use of of indentation indentationcrystals, intermetallic technique. technique. phase crystals, and matrix of hypereutectic silumin determined with the use of indentation technique.

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Figure 16. Values of indentation modulus E for primary silicon crystals, intermetallic phase crystals, Figure 16. Values of indentation modulus EITIT for primary silicon crystals, intermetallic phase crystals, andand matrix matrix of of hypereutectic hypereutectic silumin silumin determineddetermined with the use of of indentation indentation technique. technique.

InIn case case of of the the Al(Fe,Mn, Al(Fe,Mn,MM)Si)Si intermetallicintermetallic phase (1), (1), the the steepest steepest course course of of the the loading loading-unloading-unloading curve was observed which evidences that H and E assume highest values within the group of curve was observed which evidences that HITIT and EITIT assume highest values within the group of analyzedanalyzed microstructure microstructure components.components. It can be found found interesting interesting that that two two intermetallic intermetallic phases phases (1,2) (1,2) werewere characterized characterized by by high high values values of of hardness hardnessH HITIT and modulus modulus EEITIT comparedcompared to to those those demonstrated demonstrated byby silicon silicon precipitations. precipitations. In In casecase ofof the Al(Fe,Mn, MM)Si)Si intermetallic intermetallic phase phase (1), (1), the the indenter indenter penetration penetration depthdepth was was 282 282 nm. nm. On On thethe otherother hand, in case case of of the the Al(Cr,V, Al(Cr,V,MM)Si)Si intermetallic intermetallic phase phase (2), (2), the the indenter indenter penetrationpenetration depth depth waswas 291291 nm. In In the the case case of of phase phase (1) (1) Al(Fe,Mn Al(Fe,Mn,,M)Si,M )Si,HIT HvalueIT value was included was included in the in therange range 15,947 15,947–12,637–12,637 MPa, MPa, whereas whereas the range the range of EIT of valuesEIT values was 222 was–183 222–183 GPa. The GPa. intermetallic The intermetallic phase phase(2) Al(Cr,V, (2) Al(Cr,V,M)Si Mwas)Si characterized was characterized with H withIT valuesHIT fallingvalues into falling the intorange the 15,306 range–12,887 15,306–12,887 MPa and MPaEIT andvaluesEIT values in the range in the 213 range–178 213–178 GPa. The GPa. authors The authors of [22] added of [22] 0.5 added wt.% 0.5 V wt.%and 1.0 V andwt.% 1.0 V wt.%to the V alloy to the alloyAl-20Si Al-20Si-5Fe-5Fe (in wt.%) (in wt.%) and found and found that vanadium that vanadium atoms can atoms partially can partially or entirely or entirelysubstituted substituted the iron in the ironthe in phase the phaseAl4FeSi Al2 4formingFeSi2 forming thus the thus phase the Al phase4(Fe,V)Si Al4 (Fe,V)Sicharacterized characterized with lower with free lower energy free values. energy IT values.The effect The was effect a reduction was a reduction of the Young’s of the Young’s modulus modulus value for value the alloy. for the Lower alloy. E Lower valuesEIT forvalues the phase for the phase(2) Al(Cr,V, (2) Al(Cr,V,M)SiM compared)Si compared to the to the phase phase (1) (1) Al(Fe,Mn, Al(Fe,Mn,M)SiM can)Si can be be attributed attributed to tohigh high content content of of vanadiumvanadium in in the the phase phase (2). (2). InIn the the case case of primary of primary silicon silicon crystals crystals (3), the (3), indenter the indenter penetration penetration depth was depth 312 was nm. 312 The nm. unloading The portionunloading of the portion penetration of the graph penetration features graph a prominent features a drop. prominent This occurrence drop. This canoccurrence be explained can be by explained by metastable reconstruction of its crystalline structure and development of amorphous metastable reconstruction of its crystalline structure and development of amorphous allotropic form allotropic form in the course of deformation under indenter pressure [50,51]. According to Hu et al. in the course of deformation under indenter pressure [50,51]. According to Hu et al. [52], such [52], such reconstruction requires the pressure value of 11.2–12.0 GPa. As a result of lattice reconstruction requires the pressure value of 11.2–12.0 GPa. As a result of lattice reconstruction, phase reconstruction, phase Si-I transforms into phase Si-II crystalline form which is accompanied by Si-I transforms into phase Si-II crystalline form which is accompanied by density increase by 22% [53]. density increase by 22% [53]. The authors of [54] evaluated the effect of the load applied to the The authors of [54] evaluated the effect of the load applied to the indenter on the indentation hardness indenter on the indentation hardness value of silicon precipitations. The nanoindentation testing was valuecarried of siliconout with precipitations. the use of Vickers The nanoindentationindenter and load testing force values was carried in the range out with 200– the800 use mN. of It Vickers was indenterfound that and, with load an force increasing values inload the force range value, 200–800 the hardness mN. It was value found decreases. that, with The an authors increasing explain load forcethe effect value, by the occurrence hardness of value excessive decreases. plastic Thedeformations authors explain in the matrix the eff inect the by form occurrence of pile-ups of excessivearound plasticthe examined deformations precipitation in the matrix and byin an the increase form of silicon pile-ups precipitation around the volume examined due precipitationto interaction andwith by anthe increase indenter. of siliconThat resulted precipitation in the development volume due of to crack interactions in subsurface with the areas indenter. of silicon That p resultedrecipitations in the developmentwhich, by merging of cracks with in subsurfaceeach other, were areas the of siliconcause of precipitations crumbling silicone which, particles by merging in the with area each around other, werethe theindenter. cause of crumbling silicone particles in the area around the indenter.

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Results of indentation hardness and indentation modulus measurements indicate that primary silicon crystals were characterized by an HIT value in the range 12,626–11,579 MPa and EIT value in the range 171–148 GPa. The results can be regarded as comparable with results reported by authors of [55] who observed values of indentation hardness HIT in the range from 11,500–12,500 MPa and EIT values in the range from 160 GPa to 165 GPa. In the case of the Al4.5FeSi intermetallic phase (4), the indenter penetration depth was 316 nm. Values of HIT were included in the range 13,234–10,691 MPa and the range of EIT values was 188–159 GPa. Crystals of that intermetallic phase were characterized by indentation hardness HIT values close to those obtained for primary silicon crystals. However, in that case, the obtained values of the indentation modulus EIT were higher compared to values observed for primary silicon crystals, the fact being observed also in [55], where the same load force of 20 mN was adopted. The indenter loading and unloading rates were not quoted. Values of HIT are directly correlated with the indenter penetration depth (indenter loading curve in Figure7), whereas EIT values are correlated with elastic response of the material (unloading curve in Figure7). The analysis of the loading-unloading plot for the silicone precipitation reveals a notch on the unloading curve connected with metastable restructuring of the crystal lattice [50–53]. This can be considered a rationale behind lower EIT values observed for silicon crystals compared to intermetallic phases (1) Al(Fe,Mn,M)Si, (2) Al(Cr,V,M)Si, and (4) Al4.5FeSi. The literature on the subject describes attempts to establish a relationship between the temperature of crystallization and the enthalpy and material properties of intermetallics. The authors of [56] have found that, in the case of multicomponent silumins, presence of iron, manganese, cobalt, chromium, molybdenum, and tungsten favor the crystallization of intermetallic phases at temperatures higher than the α+β eutectic crystallization temperature, whereas nickel, copper, and magnesium support the crystallization of intermetallics at temperatures lower than the eutectic crystallization temperature. Vanadium and chromium are linked to the reduction of size of the needle-shaped phase β-AlFeSi precipitations [57] and a decrease of its volume fraction at expense of α–Al(Fe,M)Si phase precipitations in the form of Chinese script or polygons [58]. According to Lin et al. [58], an addition of 0.8 wt.% V to the alloy A356 with elevated content of Fe (about 1.5 wt.%) resulted in reduction of volume fraction of the phase β-Al5FeSi through its partial replacement with precipitations of the phase α–Al15(Fe,V)3Si2 with Chinese script-like morphology. According to Yang et al. [20], an addition of 0.67 wt.% Cr to the alloy Al-12.5Si-5Cu-2Ni-0.8Mg-0.5Fe (in wt.%) results in the replacement of the needle-shaped phase β-Al5FeSi with the fishbone-shaped phase α–Al(Fe,Cr)Si. The authors of [59] explain the phenomenon by higher temperature of crystallization of the phase α–Al(Fe,M)Si which, by bonding Fe, hinders the development of the needle-like phase β-AlFeSi crystallizing at lower temperatures. The higher crystallization temperature requires higher enthalpy which is connected with higher value of ETI [55]. For the intermetallic phase (5) AlFeNiM, the indenter penetration depth was 320 nm, while for the intermetallic phase (6) Al7Cu4Ni, the depth increased to as much as 380 nm. From among all the examined crystals, the most gentle course of the loading-unloading plot line was observed for crystals of the intermetallic phase (7) Al2Cu. In that case, the indenter penetration depth was the largest and amounted to 407 nm. In case of crystals of the last three intermetallics, values of indentation hardness HIT and indentation modulus EIT were definitely lower compared to values obtained for silicon crystals. Crystals of intermetallics rich in copper were characterized by lowest values of hardness HIT and modulus EIT, which is consistent with results reported in [55]. Based on published data concerning intermetallic phases Al9FeNi, Al3Ni, and Al2Cu, of which the first crystallizes at higher temperature and is characterized by higher value of the enthalpy and higher value HIT hardness and EIT modulus values, authors of [55] suggest that intermetallics development of which was connected with higher value of the enthalphy are characterized by stronger atomic bonds. It should be expected that the phase AlFeNiM (5) (HIT = 12,503–8575 MPa, EIT = 184–135 GPa) will crystallize before the phase Al7Cu4Ni (6) (HIT = 7682–5486 MPa, EIT = 157–115 GPa) and before the phase (7) Al2Cu (HIT = 6078–3918 MPa, EIT = 132–119 GPa). Materials 2020, 13, 5612 14 of 17

The displacement of indenter face in the matrix during its loading and unloading is accompanied by plastic deformation of the material. A slight elastic deformation occurs in the course of unloading which can be explained by interaction of dislocations developing in the matrix material in the course of its plastic deformation. Such activity of dislocations is blocked by alloying elements reinforcing the matrix, which results in its plastic instability [55,60].

4. Conclusions 1. A new multicomponent hypereutectic silumin is developed for application in the process of manufacturing automobile cylinder cast-in liners. 2. The adopted chemical composition and conditions of solidiﬁcation enabled crystallization of the intermetallic phase Al(Fe,Mn,M)Si, where M = Cr and V; the phase Al(Cr,V,M)Si where M = Mn, Fe, and Ti; the phase Al4.5FeSi; the phase AlFeNiM where M = Cu and Si; the phase Al7Cu4Ni; and phases Al2Cu and Mg2Si. 3. The addition of chromium, vanadium, and manganese partially blocked the development of AlFeSi phase, replacing iron in its composition and developing phases Al(Fe,Mn,M)Si and Al(Cr,V,M)Si characterized with HIT and EIT values higher than those observed for silicon crystals, which will be a feature of special importance for the service properties of cylinder liners. 4. It turned out that the intermetallic phase Al(Fe,Mn,M)Fe as well as the intermetallic Al(Cr,V,M)Si are characterized by lower susceptibility to the penetration of a diamond indenter compared to silicon crystals, and therefore better or comparable resistance to scratching with hard particles. This conﬁrms usefulness of the newly developed silumin as a material suitable for automobile cylinder cast-in liners.

Author Contributions: Conceptualization, M.T., A.W.O., M.M., A.T., and A.J.D.; methodology, M.T., A.W.O., M.M., and A.T.; software, M.T.; validation, M.T., A.W.O., M.M., and A.T.; formal analysis, M.T., A.W.O., M.M., and A.T.; investigation, M.T. and A.D.; resources, M.T., A.W.O., M.M., and A.T.; data curation, M.T.; writing—original draft preparation, M.T., A.W.O., and A.J.D.; writing—review and editing, M.T., A.W.O., and A.J.D.; visualization, M.T. and A.J.D.; supervision, M.T. and A.W.O. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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