Cold dwell behaviour of Ti6Al alloy:Understanding load shedding using digital image correlation and dislocation based crystal plasticity simulations  

作　　者：Yi Xiong NicolòGrilli Phani S.Karamched Bo-Shiuan Li Edmund Tarleton Angus J.Wilkinson 

机构地区：[1]Department of Materials,University of Oxford,Parks Road,Oxford,OX13PH,United Kingdom [2]Department of Mechanical Engineering,University of Bristol,Queen’s Building,University Walk,Bristol,United Kingdom [3]Department of Engineering Science,University of Oxford,Parks Road,Oxford,OX13PJ,United Kingdom

出　　处：《Journal of Materials Science & Technology》2022年第33期254-272,共19页材料科学技术（英文版）

基　　金：the financial support provided by the Henry Royce Institute(No.EP/R010145/1);financial support of the China Scholarship Council(CSC);support through Fellowship grant(No.EP/N007239/1)。

摘　　要：Digital image correlation(DIC)and dislocation based crystal plasticity simulation were utilised to study cold dwell behaviour in a coarse grain Ti-6Al alloy at 3 different temperatures up to 230℃.Strains extracted from large volume grains were measured during creep by DIC and were used to calibrate the crystal plasticity model.The values of critical resolved shear stresses(CRSS)of the two main slip systems(basal and prismatic)were determined as a function of temperature.Stress along paths across the boundaries of four grain pairs,three“rogue”grain pairs and one“non-rogue”grain pair,were determined at different temperatures.Large load shedding was observed in one of the“rogue”grain pairs,where a stress increment during the creep period was found in the“hard”grain.A minor load shedding mechanism was observed in two non-typical“rogue”grain pairs,in which the plastic deformation is nonuniform inside the grains and geometrically necessary dislocations accumulate in the centre of the grains.At elevated temperatures,120℃was found to be the worst case scenario as the stress difference at the grain boundaries of these four grain pairs was found to be the largest among the three temperatures analysed.The origin of this critical temperature is debated in the literature and it is investigated for the first time in the present work by analysing the simultaneous effects of the geometrically necessary dislocations(GND)and the strain rate sensitivity(SRS)of the slip systems.The analysis shows that the combined effects of the peak SRS of both prismatic and basal slip systems at 80℃and of the increase of the spread of the GND distribution around the grain boundary at higher temperatures are the origin of the observed worst case scenario.

关 键 词：Cold dwell fatigue Digital image correlation Crystal plasticity Load shedding Titanium alloy 

分 类 号：TG146.23[一般工业技术—材料科学与工程] TP391.41[金属学及工艺—金属材料]