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The Correlation Between Reduced Glass Transition Temperature and Glass Forming Ability of Bulk Metallic Glasses Z.P http://www.paper.edu.cn Scripta mater. 42 (2000) 667–673 www.elsevier.com/locate/scriptamat THE CORRELATION BETWEEN REDUCED GLASS TRANSITION TEMPERATURE AND GLASS FORMING ABILITY OF BULK METALLIC GLASSES Z.P. Lu, H. Tan, Y. Li* and S.C. Ngϩ Department of Materials Science, National University of Singapore, Singapore 119260, People’s Republic of China ϩDepartment of Physics, National University of Singapore, Singapore 119260, People’s Republic of China (Received October 4, 1999) (Accepted November 9, 1999) Keywords: Differential thermal analysis (DTA); Metallic glasses; Melt-spinning; Glass forming ability (GFA) 1. Introduction Based on theoretical work on crystal nucleation in undercooled liquid metals, Turnbull [1] proposed that the glass-forming tendency should increase with the reduced glass transition temperature, Trg, which was defined by Tg/Tl. Here, Tg is the glass transition temperature and Tl is the liquidus temperature. Later work of Uhlmann, Davies and others on the crystal nucleation further identified this dimension- less parameter as a crucial figure of merit in determining glass forming ability (GFA) [2–4]. There are many reported values of Trg in the literature [5], but unfortunately most of them were calculated using Tg/Tm (Tm: onset melting point) with minimal report of Tg/Tl [6,7]. Tg/Tm and Tg/Tl were used for evaluation of Trg interchangeably by most of researchers. Also many used crystallization temperature Tx instead of Tg, since for most of the metallic glass, these two were regarded as the same [3]. In this study, onset temperature (solidus), Tm and offset temperature (liquidus) Tl of melting of a series of bulk glass forming alloys based on Zr, La, Mg, Pd and rare-earth elements were measured by studying systematically the melting behaviour of these alloys using DTA or DSC. The significance of Trg based on Tg/Tm or Tg/Tl and the correlation between resulting Trg and glass forming ability of the bulk glass forming alloys is discussed. 2. Experimental Details All the alloys were produced either by arc-melting or by induction melting mixtures of constituent pure elements under an argon atmosphere. Their nominal compositions are indicated in Table 1. Pieces of resulting ingots were sealed in quartz tubings with external diameter of 3 mm to minimize the oxidation during the DTA melting process. These tubes were evacuated and then back filled with argon. Tm and Tl of these alloys were obtained by a DTA at a heating rate of 20K/min. The melting behaviour of alloys with low melting point was also determined using a conventional DSC at a heating rate of 20 K/min *Corresponding author. 1359-6462/00/$–see front matter. © 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved. PII: S1359-6462(99)00417-0 转载 中国科技论文在线 http://www.paper.edu.cn 668 BULK METALLIC GLASSES Vol. 42, No. 7 TABLE 1 Results of the Glass Transition Temperature (Tg), Crystallization Temperature (Tx) Obtained by DSC and Onset Melting Temperature (Tm) and Offset Melting Temperature (Tl) Obtained by DTA at a Heating Rate of 20 K/min in Mg, Zr, Pd and Rare-Earth Based Amorphous Alloys Alloy Tg (K) Tm (K) Tl (K) Structure Mg80Ni10Nd10 454.2 725.8 878.0 off eutectic Mg75Ni15Nd10 450.0 717.0 789.8 near eutectic Mg70Ni15Nd15 467.1 742.5 844.3 off eutectic Mg65Ni20Nd15 459.3 743.0 804.9 near eutectic Mg77Ni18Nd5 429.4 723.4 886.9 off eutectic Mg90Ni5Nd5 426.2 725.9 918.8 off eutectic Mg65Cu25Y10 424.5 727.9 770.9 eutectic Zr66Al8Ni26 672.0 1188.5 1251.0 off eutectic Zr66Al8Cu7Ni19 662.3 1117.3 1200.8 off eutectic Zr66Al8Cu12Ni14 655.1 1109.1 1172.1 off eutectic Zr66Al9Cu16Ni9 657.2 1110.9 1170.6 off eutectic Zr65Al7.5Cu17.5Ni10 656.5 1108.6 1167.6 near eutectic Zr57Ti5Al10Cu20Ni8 676.7 1095.3 1145.2 near eutectic Ti34Zr11Cu47Ni8 698.4 1119.0 1169.2 near eutectic La55Al25Ni20 490.8 711.6 941.3 off eutectic La55Al25Ni15Cu5 473.6 659.7 899.6 off eutectic La55Al25Ni10Cu10 467.4 662.1 835.0 off eutectic La55Al25Ni5Cu15 459.1 663.4 878.1 off eutectic La55Al25Cu20 455.9 672.1 896.1 off eutectic La55Al25Ni5Cu10Co5 465.2 660.9 822.5 off eutectic Pd40Cu30Ni10P20 576.9 741.5 836.0 near eutectic Pd81.5Cu2Si16.5 633.0 1008.8 1097.3 off eutectic Pd79.5Cu4Si16.5 635.0 1019.3 1086.0 off eutectic Pd77.5Cu6Si16.5 637.0 1019.4 1058.1 near eutectic Pd77Cu6Si17 642.4 1019.7 1128.4 near eutectic Pd73.5Cu10Si16.5 645.0 1019.3 1135.9 off eutectic Pd71.5Cu12Si16.5 652.0 1019.6 1153.6 off eutectic Pd64.5Cu19Si16.5 640.0 1167.1 1234.3 near eutectic Pd56.5Cu27Si16.5 — 1167.3 1248.4 off eutectic Nd60Fe30Al10 591.0 929.3 958.0 eutectic Pr60 Fe30Al10 575.0 873.4 950.1 off eutectic Sm60Fe30Al10 593.0 905.2 946.6 off eutectic Y60Fe30Al10 572.0 1075.9 1225.4 off eutectic Pd40Ni40P20 580.0 [8] 855.0 [7,8] 991.0 [7,8] off eutectic Nd60Al15Ni10Cu10Fe5 430 [9] 709 [9] 779 [9] off eutectic Nd61Al11Ni8Co5Cu15 445 [9] 729 [9] 744 [9] near eutectic Zrd41.2Ti13.8Cu12.5Ni10Be22.5 638.0 [10] 937.0 [10] 993.0 [10] near eutectic with Al pans. Two to five runs were carried out to obtain an average melting temperature value. Glass formation was obtained by melt-spinning using a single roller melt-spinner. The corresponding glass transition temperature Tg and crystallization temperature Tx were measured with a DSC at the same heating rate of 20 K/min. 3. Results Figure 1 shows the representative melting curves of Pd based Pd-Si-Cu alloys with Si content fixed at around 16.5 at %, exhibiting a sharp initial melting at Tm, followed by a relatively wide melting interval. 中国科技论文在线 http://www.paper.edu.cn Vol. 42, No. 7 BULK METALLIC GLASSES 669 Figure 1. Melting curves of Pd based glass forming alloys obtained by DTA under a constant heating rate of 20 K/min. All Pd-Si-Cu alloys display two melting peaks indicating that they are off-eutectic. When the copper content increased from 2 to 6 at %, the intensity of the second melting peak decreased. While the copper content increased further from 6 to 12 at %, the intensity of the second melting peak increased again. This indicates that the Pd77.5Cu6Si16.5 alloy is very near to a eutectic point. The near invariance of the onset melting points of these alloys at around 1019K pointed out that the eutectic temperature could be at this temperature. It is also noted that the melting temperatures for Pd40Cu10Ni10P40 are the lowest among the Pd based alloys studied. All the values of Tm,Tl and the types of the melting reaction for the alloys studied are summarised in Table 1 together with their corresponding glass transition temperature Tg defined by the inflection point and crystallization temperature Tx. The reduced glass transition temperature given by Tg/Tl or Tg/Tm for all the present alloys together with the values of Tg/Tm for the same alloy from the literature are given in Table 2. 4. Discussion Ն According to Turnbull’s analysis [1], the liquid with Trg 2/3, could only crystallize within a very narrow temperature range and the homogeneous nucleation rate can not be measured practically. The values of Trg based on Tg/Tl for the present bulk metallic glass forming alloys are all larger than 0.5, but consistently less than the value of 2/3, except for Pd40Ni10Cu20P40 alloy which has a slightly higher value of 0.690 (Table 2). These values are quite comparable with their concomitant glass forming ability for the corresponding alloys (Table 2). On the other hand, the values of Trg given by Tg/Tm are somewhat high, some of them are even greater than 2/3. Figure 2(a), 2(b) and 2(c) show the critical cooling rates for glass formation as a function of Trg based on Tg/Tl or Tg/Tm for La, Mg and Zr based alloys respectively. It is clear from these figures that Trg based on Tg/Tl increases continuously with continuous decrease of critical cooling rate for glass formation, while the Trg based on Tg/Tm does not show such a trend. For example, the value of Tg/Tl for Mg-Ni-Nd alloys increased from 0.464 to 0.571 continuously as the critical cooling rate for glass ϫ 4 formation decreased continuously from 5.2 10 to 30 K/s, while the value of Tg/Tm increased continuously from 0.587 to 0.629 as the critical cooling rate for glass formation decreased from ϫ 4 ϫ 3 5.2 10 to the minimum value of 30 K/s and then increased to 1.3 10 . Figure 3 shows Tm,Tl,Tg, 中国科技论文在线 http://www.paper.edu.cn 670 BULK METALLIC GLASSES Vol. 42, No. 7 TABLE 2 Summary of Tg/Tm,Tg/Tl, Critical Section Thickness (Zmax) and Critical Cooling Rate (Rc) for Glass Formation for Mg, Zr, La, Pd and Rare-Earth Based Amorphous Alloys Alloy Tg/Tm Tg/Tm (ref.) Tg/Tl Zmax (mm) Rc (K/s) Mg80Ni10Nd10 0.626 0.64 [11] 0.517 0.6 [11] 1251.4 Mg75Ni15Nd10 0.628 0.63 [11] 0.570 2.8 [11] 46.1 Mg70Ni15Nd15 0.629 0.65 [11] 0.553 1.5 [11] 178.2 Mg65Ni20Nd15 0.618 0.63 [11] 0.571 3.5 [11] 30.0 [12] Յ ϫ 4 Mg77Ni18Nd5 0.594 0.64 [11] 0.484 0.1 [11] 4.9 10 Յ ϫ 4 Mg90Ni5Nd5 0.587 0.62 [11] 0.464 0.1 [11] 5.3 10 Mg65Cu25Y10 0.583 0.58 [13] 0.551 4.0 [13] 50 [14] 7.0 [5] Zr66Al8Ni26 0.565 0.56 [16] 0.537 66.6 [16] Zr66Al8Cu7Ni19 0.593 0.58 [16] 0.552 22.7 [16] Zr66Al8Cu12Ni14 0.591 0.58 [16] 0.559 9.8 [16] Zr66Al9Cu16Ni9 0.592 0.59 [16] 0.561 4.1 [17] Zr65Al7.5Cu17.5Ni10 0.583 0.58 [18] 0.566 16 [19] 1.5 [19] Zr57Ti5Al10Cu20Ni8 0.618 0.63 [20] 0.591 10.0 [21] 10.0 [20] 20.0 [22] ϳ Ti34Zr11Cu47Ni8 0.624 0.61 [23] 0.597 4 5 [23,24] 100.0 [24] Ͻ250 [23] La55Al25Ni20 0.690 0.71 [25] 0.521 3 [25] 67.5 [26,27] La55Al25Ni15Cu5 0.718 — 0.526 34.5 [26] La55Al25Ni10Cu10 0.706 0.70 [25] 0.560 5 [25] 22.5 [26] La55Al25Ni5Cu15 0.692 — 0.523 35.9 [26] La55Al25Cu20 0.678 0.68 [25] 0.509 3 [25] 72.3 [26] Ͼ La55Al25Ni5Cu10Co5
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