Abstract
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 ex-tracted 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 sys-tems(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 deter-mined 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 shed-ding 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 tempera-tures 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.
基金项目
Henry Royce Institute(EP/R010145/1)
国家留学基金委项目()
ET acknowledges EPSRC for support through Fellowship grant(EP/N007239/1)
NETL
NSTL
维普
万方数据