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INSTRUMENTED INDENTATION of Al2o3-Sic NANOCOMPOSITES

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INSTRUMENTED INDENTATION of Al2o3-Sic NANOCOMPOSITES Chem. Listy 105, s781s782 (2011) LMV 2010 Posters INSTRUMENTED INDENTATION OF Al2O3-SiC NANOCOMPOSITES ERIKA CSEHOVÁa*, JÁN DUSZAa, sistance) model4 suggested that the test-specimen resistance, APICHART LIMPICHAIPANITb, W, during indentation is not a constant, as was proposed by b Hays and Kendall, but increase linearly with the indentation and RICHARD TODD size and is directly proportional to it according to the relation- ship; a Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 043 53 Košice, Slovak Republic, b Department (4) W a1hc of Materials, University of Oxford, Oxford, United Kingdom; [email protected] and the effective indentation load and the indentation dimen- sion are therefore related as follows: Keywords: Al2O3-SiC, ISE, micro/nano-hardness 2 (5) Peff Pmax W Pmax a1hc a2hc 1. Introduction where the parameters a1 and a2 can be related to the elastic It is well known that the apparent hardness of a solid and the plastic properties of the test material. The term a2 in usually depends on the applied test load. This phenomenon, the linear fits describes the load independent hardness, so known as the indentation size effect (ISE), involves a de- called „true hardness“, H0. crease in the measured apparent hardness with increasing The coefficients of the proportional specimen resistance applied test load, i.e., with increasing indentation size. The (PSR) a1 and a2, can be evaluated through the linear regres- works focused mainly on the analyses of the micro- or macro- sion of “Pmax/hc“ versus “hc“, hardness data and little effort has been devoted to examine the Pmax (6) applicability of these equations to the nanoindentation data aah12c 1 h obtained using instrumental indentation test . c The instrumental hardness, “H“ is defined as the ratio of For the nanoindentation test with a Berkovich indenter, H0 the peak load, Pmax, to the project area of the indentation im- can be calculated: pression, Ac, (1) 2 (7) P P H 0 Pmax a1hc ) /(24.5hc ) H max max 2 A c 24.5hc Gong et al.5 suggested a modified PSR model based on the consideration of the effect of the machining-induced resid- where hc is the contact depth most often determined by Oli- ual stresses at the surface during the indentation in the form ver and Pharr method2. The most widely used empirical equation for describing 2 (8) the ISE is the Meyer’s law, in the form: Pmax a0 a1hc a2hc n (2) Pmax Ahc where a0 is a constant related to the surface residual stresses associated with the surface machining and polishing and a1 where A and n are constants that can be derived directly from and a2 are the same parameters as in the PSR model. Similar- ly, the parameters of the modified PSR were obtained by con- curve fitting of the experimental data in the relationship ln hc ventional polynomial regression of the plot P vs. d and H0- vs. ln Pmax. If n < 2 there is an ISE on hardness and when n = 2, the hardness is independent of the applied load. values were calculated according to the equation: 3 According to Hays and Kendall there exists a minimum 2 (9) level of the applied test load, W, named the test-specimen H 0 Pmax a0 a1hc ) /(24.5hc ) resistance, below which permanent deformation due to inden- tation does not initiate, and only elastic deformation occurs. The aim of the present work is to investigate the load dependence of the measured instrumental Berkovich hardness They introduced an effective indentation load, Pef f = Pmax - W, and proposed the relationship; of Al2O3-SiC composites, to examine the ISE using different models and to compare this to the ISE observed during con- P W A h 2 (3) ventional Vickers hardness test. max 1 c 2. Experimental procedure where W and A1 are constants independent of the test load for a given material. The materials used in this investigation were alumina (A) Li and Bradt in their PSR (proportional specimen re- and Al2O3-SiC composites with the addition of 5 vol.% (A5) s781 Chem. Listy 105, s781s782 (2011) LMV 2010 Posters Table I Best-fit results of the parameters Meyer´s Hays-Kendall approach PSR model Modified PSR model Law Eq. (2) Eq. (3) Eq. (6) and Eq. (7) Eq. (8) and Eq. (9) n W (mN) A1 (mN/ a1 (mN/ a2 HV0 a0 a1 (mN/ a2 HV0 nm2) nm) (mN/nm2) (GPa) (mN) nm) (mN/nm2) (GPa) A 1.62 3.03 3.53 ×10-4 0.0764 3.02 ×10-4 10.7 ±5.7 -8. 37 0.149 2.23 ×10-4 9.75 ±3.8 A5 1.70 8.84 5.82 ×10-4 0.0615 5.23 ×10-4 20.7 ±3.0 -7.39 0.129 4.41 ×10-4 20.79 ±9.1 A10 1.68 17.38 6.31 ×10-4 0.0582 5.74 ×10-4 21.3 ±2.1 -5.61 0.108 5.09 ×10-4 24.19 ±9.9 and 10 vol.% (A10) SiC, processed at the University of Ox- measured in the peak-load range from 7.5 to 500 mN by Peng ford, United Kingdom6. et al.1. Our results show good agreement with their results in The CMCTM (Continuous Multi Cycle) method was ap- the case of Hays - Kendall model, however the values ob- plied using Nano Hardness Tester (CSM-Instruments SA) tained for W are too high, mainly for the composite with with Berkovich diamond indenter. In each test run, the indent- 10 vol.% of SiC. According to the results, both the PSR and er was driven into the specimen surface under a peak load modified PSR models underestimate the true hardness for gradually increased from 5 mN to 400 mN, unloaded gradual- alumina and overestimate the true hardness for composites. ly to 10 % of the peak load after being held at peak load for For ceramics investigated in the present work the PSR model 10 s, and then driven again into the specimen surface to applied for conventional Vickers hardness data results in the a higher value of the peak load. At least 15 test runs were best estimation of true hardness values7. recorded on each sample. 4. Conclusions 3. Results and discussion The load-dependence of the nano/micro instrumental The results of the hardness measurement and of the ap- Berkovich hardness of alumina and Al2O3-SiC composites plied ISE models are illustrated in Fig. 1 and in Table I. The has been investigated. Similar ISE was found as in the case of hardness decreased with increasing peak load and exhibited a conventional Vickers hardness test for all systems. The Hays - typical indentation size effect which was most evident for Kendall approach results in high W values and the PSR and alumina (n = 1.62). The behaviour of the composites is very modified PSR models in low true hardness for alumina and similar, (n = 1.68 and n = 1.70). These results are in good high true hardness for composites. agreement with the results of conventional Vickers hardness tests (from 1 N to 49.05 N), performed on the same materials, This work was supported by APVV LPP 0174-07, VEGA according to which the most significant ISE is in alumina 2/0088/08 and MNT-ERA.NET HANCOC. (n = 1.83) and in the composites the ISE is less pronounced (n = 1.92 and n = 1.93) (ref.7). REFERENCES By comparing these results it is visible that the ISE is 1. Peng Z., Gong J., Miao H.: J. Eur. Ceram. Soc. 24, 2193 more pronounced during the instrumental test in the lower (2004). interval of applied loads. As regards the indentation module, 2. Oliver W. C., Pharr G. M.: J. Mater. Res. 7, 1564 (1992). for alumina the values decrease with increasing load from 3. Hays C., Kendall E. G.: Metall. 6, 275 (1973). approximately 300 GPa to 100 GPa and for composites from 4. Li H., Bradt R. C.: J. Mater. Sci. 28, 917 (1993). 500 GPa to 300 GPa. The ISE of various types of ceramics 5. Gong J., Wu J., Guan Z.: J. Eur. Ceram. Soc. 19, 2625 has recently been investigated using nanoindentation data (1999). 6. Limpichaipanit A., Todd R. I.: J. Eur. Ceram. Soc. 29, 2841 (2009). 40 7. Csehova E., Dusza J., Limpichaipanit A., Todd R., Me- 35 tallic materials, in press. 30 a a b [Gpa] 25 E. Csehová *, J. Dusza , A. Limpichaipanit , and IT R. Toddb (a IMR, SAS, Košice, Slovak Republic, b Department 20 of Materials, Oxford, United Kingdom): Instrumented In- 15 dentation of Al2O3-SiC Nanocomposites 10 A10 Hardness, H Hardness, A5 5 A The load dependence of instrumental Berkovich hardness 0 has been investigated and the indentation size effect has been -50 50 150 250 350 450 analyzed during the hardness test of alumina and Al2O3-SiC Peak load, Pmax [mN] nanocomposites in the load range from 5 mN to 400 mN. As regards the load dependence of hardness the results are in agree- Fig. 1. Influence of Pmax on hardness ment with the results of conventional Vickers hardness test. s782 Chem. Listy 105, s783s784 (2011) LMV 2010 Posters INDENTATION SIZE EFFECT IN BASAL AND PRISMATIC PLANES OF Si3N4 CRYSTALS ERIKA CSEHOVÁa*, ANNAMÁRIA 3. Results and discussion DUSZOVÁa, PAVOL HVIZDOŠa, FRANTIŠEK LOFAJa, JÁN DUSZAa, The material has a bimodal grain size distribution, with b large grains up to 10 m in diameter and small ones < 1 m in and PAVOL ŠAJGALÍK diameter. a Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Košice; b Institute of Inorganic Chemis- try, Slovak Academy of Sciences, Bratislava, Slovak Republic [email protected] Keywords: Si3N4 grains, CMC Indentation Test 1.
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