High temperature drop calorimetry measurements of enthalpy increment in Ti-xTa (x=5, 10, 15, 20 mass%) alloys

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• 作者：Madhusmita Behera ; Subramanian Raju ; Ganapathy Panneerselvam ; Mythili Rangachari ; Saroja Saibaba
• 关键词：A ; Ti&ndash ; Ta alloy ; C ; Calorimetry ; D ; Phase equilibria ; D ; Specific heat ; D ; Thermodynamic properties
• 刊名：Journal of Physics and Chemistry of Solids
• 出版年：February, 2014
• 年：2014
• 卷：75
• 期：2
• 页码：283-295
• 全文大小：3009 K

文摘

The enthalpy increment for a series of Ti-xTa (x=5, 10, 15, 20 mass%) alloys, having 伪(hcp)+尾(bcc) two phase microstructure has been measured using inverse drop calorimetry in the temperature range 463-1257 K. The studies clearly revealed the occurrence of 伪鈫捨?/em> diffusional phase transformation. Both the 伪鈫捨?/em> transformation onset temperatures and the measured transformation enthalpy 螖⁰H_tr ^{伪鈫?em>尾} exhibit progressively lower values with increasing Ta content. It is found that the measured enthalpy in the transformation region is constituted of two principal contributions namely, (i) the enthalpy due to untransformed 伪 and coexisting 尾 phases and (ii) the transformation enthalpy due to 伪鈫?em>尾 phase change. Since the fractional extent of 伪鈫?em>尾 transformation varies continuously with temperature, the measured enthalpy variation in the transformation domain has been modeled using Kolmogorov-Johnson-Mehl-Avrami formalism for the diffusional transformation kinetics. The thermodynamic quantities for all the alloys have been derived.