Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10714309 | Physica B: Condensed Matter | 2011 | 10 Pages |
Abstract
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 αâ³-martensite and bcc β phases. The calorimetry experiments indicated the occurrence of two phase changes upon heating. They are (i) precipitation of hexagonal Ï phase at 582±2 K followed by (ii) αâ³âβ in the temperature domain 836-985±2 K. The enthalpy change due to Ï formation is small; however, the αâ³âβ phase transformation is associated with a measurable enthalpy effect of 57±3 J gâ1. Since αâ³âβ 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 αâ³-martensite and β phase mix and another transformational component arising from continuous αâ³âβ phase change. Since the fractional extent of αâ³âβ 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 αâ³+β region.
Related Topics
Physical Sciences and Engineering
Physics and Astronomy
Condensed Matter Physics
Authors
A. Josephine Prabha, S. Raju, B. Jeyaganesh, Arun Kumar Rai, Madhusmita Behera, M. Vijayalakshmi, G. Paneerselvam, I. Johnson,