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首页> 外文期刊>Physica, B. Condensed Matter >Thermodynamics of α″ → β phase transformation and heat capacity measurements in Ti-15 at% Nb alloy
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Thermodynamics of α″ → β phase transformation and heat capacity measurements in Ti-15 at% Nb alloy

机译：Ti-15 at％Nb合金中α''→β相变的热力学和热容测量

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摘要

The phase stability of Ti-15 at% Nb alloy has been studied in the temperature range 466-1258 K using inverse drop calorimetry. In the annealed condition, the alloy consists of orthorhombic a"-martensite and bcc b phases. The calorimetry experiments indicated the occurrence of two phase changes upon heating. They are (i) precipitation of hexagonal o phase at 582±2 K followed by (ii) α″ → β in the temperature domain 836-985 ± 2 K. The enthalpy change due to o formation is small; however, the α″ → β phase transformation is associated with a measurable enthalpy effect of 57 ± 3Jg～1. Since α″ → β phase change occurs over a temperature interval, the measured enthalpy in the transformation domain derives from two principal contributions, namely, the matrix contribution coming from untransformed a00-martensite and b phase mix and another transformational component arising from continuous α″ → β phase change. Since the fractional extent of α″ → β transformation varies continuously with temperature the transformation enthalpy also exhibits similar temperature dependence. This aspect is modeled using Kolmogorov-Johnson-Mehl-Avrami formalism for treating the diffusional transformation kinetics. Further, the measured enthalpy variation with temperature has been subjected to standard analytical treatment to obtain a comprehensive thermodynamic description of entire α″ + β region.
机译：使用逆滴热法研究了Ti-15 at％Nb合金在466-1258 K温度范围内的相稳定性。在退火条件下，该合金由正交晶的a”-马氏体相和bcc b相组成。量热实验表明，加热时会发生两个相变。它们是：（i）在582±2 K时析出六方晶相，然后（ ii）在温度域836-985±2 K上的α''→β。由于o形成而引起的焓变很小;然而，α''→β相变与可测量的57±3Jg〜1的焓效应有关。由于α''→β相变是在一个温度区间内发生的，因此在变换域中测得的焓来源于两个主要贡献，即，来自未变换的α-马氏体和b相混合的基质贡献，以及来自连续α''的另一个变换成分→β相变。由于α''→β相变的分数范围随温度连续变化，因此相变焓也表现出相似的温度依赖性。这方面的建模采用Kolmogorov-Johnson-M ehl-Avrami形式主义，用于处理扩散转化动力学。此外，对测得的焓随温度的变化进行了标准分析处理，以获得对整个α''+β区域的综合热力学描述。

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