Martensite and reverse transformation temperatures of TiAu-based and TiIr-based intermetallics

Abstract

Dependence of transformation temperatures of TiAu- and TiIr-based Intermetallics on Valence Electron Ratio (VER), number of valence electrons (ev) and average atomic number of the alloys (Z) were investigated. The alloys mostly have medium numbers of valence electrons (6.5 ≤ ev ≤ 7.3) near 7 with a limited number of TiAu-based alloys belonging to high valence electron group with ev more than 7.50 and relatively narrow range of average atomic numbers (Z = 41–53). The forward and reverse phase transformation temperatures, Ms and As of AuTi-based alloys sharply increase with the average atomic number of the alloys. The investigated TiIr alloy compositions have almost similar average atomic numbers (49.5–50.2). Clear correlations between transformation temperatures and VER were found. Ms and As both decrease from around 1550 °C to as low as 17 °C respectively, with increasing VER from 0.131 to 0. 174. The dependence of transformation temperatures on valence electron ratio is discussed based on the variations of elastic properties and atomic bonding due to composition change in these alloys.