Hot Deformation Mechanism and Ring Rolling Behavior of Powder Metallurgy Ti2AlNb Intermetallics

Powder metallurgy (PM) Ti-22Al-24Nb-0.5Mo (at.%) alloys were prepared by hot isostatic pressing. In order to study the feasibility of PM ? ring rolling combined process for preparing Ti2AlNb rings, thermal mechanical simulation tests of PM Ti2AlNb alloys were conducted and two rectangular PM rings (150 mm in height, 75 mm in thickness, 350 mm in external diameter) were rolled as a validation experiment. Experimental results show that the flow stress of Ti2AlNb alloys exhibited a significant drop at the very beginning of the deformation (true strain <0.1), and became stable with the increase in strain. Stress instability phenomenon of PM Ti2AlNb alloys was more obvious than that of wrought alloy. Flow stress fluctuation at the initial stage of deformation is related to phase transition of Ti2AlNb alloys which strongly depends on heat treatment and thermal mechanical deformation process. Processing windows during initial stage of ring rolling process is very crucial. A sound PM Ti2AlNb rectangular ring blank (height = 150 mm, thickness = 30 mm, external diameter = 750 mm) was successfully rolled in two passes by using the improved heat preservation method and optimized rolling parameters. Tensile properties of PM Ti2AlNb alloy were improved, and the porosity was reduced after ring rolling.