Effect of multi-pass cooling compression and subsequent heat treatment on microstructural and mechanical evolution of TC4 alloys

Abstract

Three passes of hot compression tests of hot isostatic pressed Ti-6Al-4V alloys are carried out on a Gleeble-1500D thermo-mechanical simulator with a temperature-drop of 950–900-850 °C, constant strain rate of 0.01∼1 s−1, and the height reduction from 20% to 70%. Then, the subsequent solution and aging treatments are conducted on a heat treatment furnace. The corresponding results of microstructures and mechanical properties show: In the process of multi-pass deformation, dynamic recrystallization with spheroidization of lamellar α phases are the main characteristics affecting flow behaviors. With the increasing strain, lamellar α phases gradually transform from a bimodal distribution to a single peak state perpendicular to the compression direction. The decreasing length and rising thickness of lamellar α phases in the transformation process facilitate the formation of spheroidized α phases. During the heat treatment, the proportion of spheroidized α phases increases, and the spheroidization phenomenon promotes the reduction of lamellar α phases in length and increment in thickness. Lamellar α phases mainly dominate the contribution of microhardness in the hot compression process, and the equiaxed α phases and β transformation structures are combined to influence the mechanical properties of heat-treated Ti-6Al-4V alloys. Notably, β transformation structures contribute primarily at a higher solution temperature.