Effect of Strain-Path Reversal on Microstructure Evolution and Cavitation during Hot Torsion Testing of Ti-6Al-4V

Abstract

Hot torsion testing comprising multiple twist reversals was used to establish the effect of strain-path changes on concurrent dynamic globularization and cavitation of Ti-6Al-4V with a colony-alpha starting microstructure. Optical microscopy was used to quantify the cavity area fraction and the effect of globularization on cavitation. The deformation of the hard and soft colonies surrounding the largest cavities and self-consistent-model calculations of strain partitioning were used to estimate the macroscopic and local strains at which colonies with different strengths globularize. It was found that both hard and soft colonies undergo dynamic globularization at the same local strain (i.e., strain within the colony). In addition, cavitation behavior during torsion with multiple strain-path changes was interpreted by taking into account the break up of the colonies into a globular structure. It was found that cavity growth (or shrinkage) persisted as long as there was a flow-stress difference in adjacent regions/colonies surrounding a given cavity. When the microstructure became uniform (as in the case of full globularization), the cavity area fraction did not measurably change with subsequent additional deformation.