Abstract
The effect of microstructure in Ti-6Al-4V alloy on low-cycle fatigue behavior at elevated temperature was studied. Three kinds of microstructure in Ti-6Al-4V alloy were prepared under different heat treatment conditions; that is, equiaxed α structure, lenticular α structure and bimodal (mixed of equiaxed α and lenticular α) structure. Total strain controlled low-cycle fatigue test was performed at 773K in air. Crack initiation was investigated by D.C. potential method. The following conclusions were obtained.(1) The highest low-cycle fatigue strength was obtained for the bimodal structure, followed by the equiaxed α structure and the lowest was the lenticular α structure.(2) The crack initiation life of the lenticular α structure was smaller than those of other structures.(3) The effect of microstructure on crack propagation life was small as compared with that on crack initiation life.(4) Cracks initiated inside of grains of the equiaxed α structure and the bimodal structure. Cracks of the lenticular α structure initiated at the interface between α layer precipitated at grain boundary and lenticular α structure.
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