Effect of multi-pass cooling compression and subsequent heat treatment on microstructural and mechanical evolution of TC4 alloys
Zhaoming Yan, Haijun Liu, Xueyan Dai, Luyao Li, Zhimin Zhang, Qiang Wang, Yong Xue
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.