Determination of Ti-6242 α and β slip properties using micro-pillar test and computational crystal plasticity

T Benjamin Britton,Fionn P.E Dunne,Zhen Zhang,Tea-Sung Jun

doi:10.1016/j.jmps.2016.06.007

T Benjamin Britton, Fionn P.E Dunne + Show 2 more

Open Access

https://doi.org/10.1016/j.jmps.2016.06.007

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Abstract

The properties and behaviour of an α−β colony Ti-6242 alloy have been investigated at 20°C utilising coupled micro-pillar stress relaxation tests and computational crystal plasticity. The β-phase slip strength and intrinsic slip system strain rate sensitivity have been determined, and the β-phase shown to have stronger rate sensitivity than that for the α phase. Close agreement of experimental observations and crystal plasticity predictions of micro-pillar elastic-plastic response, stress relaxation, slip activation in both α and β-phases, and strain localisation within the α−β pillars with differing test strain rate, β morphology, and crystal orientations is achieved, supporting the validity of the properties extracted. The β-lath thickness is found to affect slip transfer across the α−β−α colony, but not to significantly change the nature of the slip localisation when compared to pure α-phase pillars with the same crystallographic orientation. These results are considered in relation to rate-dependent deformation, such as dwell fatigue, in complex multiphase titanium alloys.

Highlights

Dual phase ( -β) titanium alloys have been widely utilised in aerospace and energy industries owing to their high strength to weight ratio, excellent fracture toughness and corrosion resistance (Banerjee and Williams, 2013; Boyer, 1996)
A key feature of their microstructure is the Burgers orientation relationship (BOR) which defines the crystallographic relationship between the hcp alpha ( ) and bcc beta ( ) phases and is found largely to be invariant (Bhattacharyya et al, 2003)
A critical factor in the -β titanium alloys is argued to be that of their rate-sensitive response under strain and stress-controlled loading, with the former leading to stress relaxation and the latter to creep, both of which occur even at low (20oC and lower) temperature and under low stresses (Adenstedt, 1949; Chu, 1970; Neeraj et al, 2000)

Summary

Introduction

Dual phase ( -β) titanium alloys have been widely utilised in aerospace and energy industries owing to their high strength to weight ratio, excellent fracture toughness and corrosion resistance (Banerjee and Williams, 2013; Boyer, 1996). The direct determination of phase properties from dual phase titanium alloys such as Ti6242 is challenging since the colony structures comprise laths which are very thin (~2 m or less), thereby making the manufacture of mechanical specimens, eg by FIB of micro-pillar samples, in alone difficult. Recent integrated experimental and crystal plasticity modelling studies (Jun et al., 2016b; Zhang et al, 2016b) have shown that the strain rate sensitivities for phase basal and prismatic slip systems in Ti-6242 are different. Crystal plasticity modelling is utilised primarily in this study to quantify the strain rate sensitivities of the -β pillars. Recent studies by the authors (Jun et al, 2016b; Zhang et al, 2016b) show that these external compliances are significant and have to be explicitly recognised in order to separate structural response, often including the indentation frame, from implicit material rate sensitivity

Crystal plasticity modelling with updated lattice rotation

Coupled micro-pillar test and crystal plasticity modelling

Findings

Slip trace analysis and slip transfer in -β colonies