Cavitation during hot tension testing of Ti–6Al–4V

Abstract

Abstract Cavity initiation, growth, and coalescence phenomena during the hot tension testing of Ti–6Al–4V with several different transformed β-microstructures were established to obtain an understanding of the failure process during subtransus hot working. Samples with either a colony-type microstructure (containing grain-boundary α) or a martensitic, acicular α-microstructure were pulled to failure at strain rates between 0.01 and 3 s−1 and various subtransus temperatures ranging from 540 to 955°C. Metallographic analysis of sectioned tension samples with colony microstructures revealed that cavity initiation occurred at very low strains (≾0.2) irrespective of strain rate at temperatures below 900°C due to an apparent incompatibility of deformation between the grain-boundary α-layer and the Widmanstatten side plates. Initiation strains were somewhat higher (∼0.2–0.5) for samples with the acicular α-microstructure tested at temperatures below 900°C; however, failure was still intergranular. Subsequent cavity growth was more rapid for colony microstructures than that for the martensitic α-microstructure at these temperatures. Above 900°C, however, substantially higher cavity initiation strains and lower cavity growth rates were obtained for both microstructures. These latter behaviors were ascribed to the presence of a large volume fraction of ductile β-phase and moderate values of the strain-rate sensitivity of the flow stress, respectively.