Local deformation mechanisms of two-phase Ti alloy

Tea-Sung Jun,Giorgio Sernicola,Fionn P.E Dunne,T Benjamin Britton

doi:10.1016/j.msea.2015.09.016

Tea-Sung Jun, Giorgio Sernicola + Show 2 more

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https://doi.org/10.1016/j.msea.2015.09.016

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Abstract

This paper describes a study of local deformation mechanisms in two-phase Ti alloy, Ti–6Al–2Sn–4Zr–2Mo, by performing in-situ micropillar compression tests. A colony microstructure was examined and select grains identified for examination were chosen with EBSD measurements. These grains were chosen to isolate individual slip systems within each test. Micropillars of tri-crystal (α–β–α) structure were fabricated from four determined regions, and compression tests were performed using a displacement-controlled nanoindenter set inside a SEM, with a constant displacement rate. The results show that the α/β morphology significantly affects the local deformation behaviour. For these colony structures, Schmid's law in general enables anticipation of local slip activity, but the presence and morphology of the β phase can significantly alter the apparent yielding point and work hardening response. The role of interfaces within these tri-crystal pillars is discussed.

Highlights

High strength-to-weight ratio, corrosion resistance and excellent mechanical properties have made titanium alloys attractive to many industrial applications, in gas turbine and aerostructures
We investigate local deformation mechanisms in two-phase Ti alloys using micropillar compression focusing on how two phase structures change local slip behaviour
The elastic and plastic anisotropy inherent to α crystal leads to significant inhomogeneity in stress and strain at the microstructural level

Summary

Introduction

High strength-to-weight ratio, corrosion resistance and excellent mechanical properties have made titanium alloys attractive to many industrial applications, in gas turbine and aerostructures. Their highly anisotropic and localised deformation behaviour, when significant fractions of the α (Hexagonal Close Packed, HCP) phase are present, lead to difficulties in understanding fatigue crack nucleation and in predicting lifetime and failure of components in service [1]. In the last few decades, extensive researches have been devoted to understanding deformation mechanisms in α phase titanium (e.g., CP–Ti or Ti–Al single crystals) [2,3,4,5,6,7] These investigations have clearly shown slip/ twinning behaviours and the corresponding dislocation evaluation as a function of Al content, temperature and crystallographic orientation. Complexities on studying α/β Ti alloys arise due to the microstructure-dependent-mechanical properties, room temperature creep behaviour, microtexture and interaction between the α and β (Body Centred Cubic, BCC) phases [8,9,10,11,12]

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