Comparison of the Dwell Fatigue Behavior of Ti6242 And Ti6246

Abstract

The dwell effects of Ti624x (x=2 to 6) alloys, including dwell fatigue life debit, fracture mode and strain accumulation, were characterized and compared. The different dwell fatigue behaviors of Ti6242 and Ti6246 were attributed on the fundamental level to the dual effects of Mo: It decreases the transus of titanium and, as a slow diffuser, reduces the rate of phase transformation from to . A higher Mo content encourages nucleation of multiple variants of laths and promotes the transition from aligned colonies to basketweave microstructure during cooling after forging. As a result both the grain size and microtexture intensity of grains in the two-phase processed and heat treated microstructure are reduced. Smaller grain size of the alloys with higher Mo content produces smaller slip band spacing and reduces accumulated strain during dwell fatigue, thus reducing propensity for crack initiation.

Understanding the Role of Local Texture Variation on Slip Activity in a Two-Phase Titanium Alloy

“…The slip mode activity has been quantified previously for several alloys using the Electron Back Scattered Diffraction (EBSD) based slip trace analysis technique, which correlates theoretical slip trace angles with measured slip trace angles from either secondary or backscattered electron micrographs [22][23][24][25][26][27][28][29][30][31] or strain maps recorded using High Resolution Digital Image Correlation (HRDIC) [32][33][34][35][36][37][38] . However, this does not always provide a unique solution, particularly in hexagonal materials where there can be several slip modes that have a similar slip angle projection depending on the orientation of the grain [ 39 , 40 ].…”