Martensite formation in titanium alloys: Crystallographic and compositional effects

Madeleine Bignon,Emmanuel Bertrand,Pedro E.J Rivera-Díaz-Del-Castillo,Franck Tancret

doi:10.1016/j.jallcom.2021.159636

Abstract

An explanation is proposed to martensite inhibition beyond characteristic concentration thresholds in titanium binary alloys. The method combines the phenomenological theory of martensite crystallography (PTMC) and thermodynamic calculations (TCs) to describe the conditions under which martensite formation is favourable. It is shown that martensite can be crystallographically prevented while being thermodynamically favourable. The PTMC is implemented by taking into account the influence of composition. After a comprehensive comparison to experiments, two twinning systems and two glide systems are inferred to be able to produce the lattice invariant shear. The critical concentrations above which martensite cannot form are computed and compared to experimental results on binary and ternary systems, showing good agreement. The proposed method may be used as a guide to design titanium alloys for controlled martensitic behaviour.

Highlights

Martensitic transformation is responsible for some of the most in teresting mechanical properties of titanium alloys
Summary A set of two glide systems and two twinning systems are selected as candidates to accomplish the lattice invariant shear
It can be noted that the experimental compositions at which martensite forms some times slightly overlap with those at which martensite is inhibited, due to the experimental results being collected from different sources

Summary

Introduction

Martensitic transformation is responsible for some of the most in teresting mechanical properties of titanium alloys. In the past few years, there has been an increasing interest in designing titanium alloys displaying martensitic transformation. In order to improve design methods, it is useful to understand the com position dependency of martensite formation. The present work aims at showing how the composition-dependent geometric accommodation of martensite can control the occurrence of the transformation. Binary titanium alloys are known to undergo martensitic trans formation under a variety of conditions [8] (Fig. 1). Martensite displays hexagonal close-packed (hcp) α’ or orthorhombic α” struc ture, depending on composition [8].

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Discussion

Conclusion