A quantitative measure of the stability of a glass as compared to its corresponding crystalline state can be obtained by calculating the thermodynamic parameters, such as the Gibbs free energy difference (𝛥𝐺), entropy difference (𝛥𝑆) and the enthalpy difference (𝛥𝐻) between the super-cooled liquid and the corresponding crystalline phase. 𝛥𝐺 is known as the driving force of crystallization. The driving force of crystallization (𝛥𝐺) provides very important information about the glass-forming ability (GFA) of metallic glasses (MGs). Lesser the driving force of crystallization more is the GFA. The 𝛥𝐺 varies linearly with the critical size (𝑑𝑐). According to Battezzati and Garonne the parameter 𝛾 ( = (1−(𝛥𝐻𝑥/𝛥𝐻𝑚))/(1−(𝑇 𝑥/𝑇 𝑚))) in the expression for 𝛥𝐺 should be a constant (i.e., 0.8), but its uniqueness is not observed for all MGs. The thermal stability of various alloy compositions is studied by their undercooled liquid region (𝛥𝑇 = 𝑇 𝑥 − 𝑇 𝑔). Large 𝛥𝑇 𝑥 implies greater stability against crystallization of the amorphous structure. Other GFA parameters are also calculated and correlated with critical size (𝑑𝑐).
Volume 42 | Issue 6
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