Study On Hot Deformation Behavior Of TC11Titanium Alloys

TC11titanium alloy is mainly used to produce aircraft engine compressor disks, drums, leaves, etc. structural components. Owing to the narrow range of the hot deformation temperature for the TC11titanium alloy, the influence of hot deformation parameters on the microstructure and properties of the alloy is more complicated. This leads to the difficulty in forming and obtaining uniform microstructure, and that severely affects the stability of product quality. Thus, an investigation of hot deformation behavior and microstructure evolution of TC11alloy has an important influence on high temperature forging and thermal processing of the alloy.In this paper, TC11titanium alloy with coarse lamellar structure is selected. The alloy is subjected to hot compression load at950℃but different strain rate (0.1s-1、1s-1、10s-1、50s-1) and strain (from50%to80%). A study on the evolution of microstructures of the alloy after hot deformation and stress-strain response is conducted. SEM, TEM and laser confocal microscope were used to characterize hot deformation behavior and microstructures. Rolling deformation behavior of the alloy was studied by using wedge-shape TC11plate, which introduce continuous strain along the hot-rolled plate. The relationship between the formation of inner cracks and local strain/strain rate is examined. The findings are given below.(1) With increasing strain, the flow stress increased rapidly, and then the flow softening happened after the flow stress reached the peak stress instantly in the hot compression tests. The peak stress increased gradually with the increase in strain rate, and the peak stress increased about30-60MPa while the strain rate rose ten times. Then the flow stress decreased rapidly due to the soften phenomenon appeared.(2) Along the rolling direction, the strain increased gradually in the hot-rolling test. The thick inflexion point b of was also the strain rate inflexion of the sample. Passing the point, the strain rate increased explosively, but the strain rate of the two sections before and after b decreased with the increasing of the strain. The deformed zones were divided into three deformation zones, i.e. the dead zone, the small weakly-deformed zone and the large heavily-deformed zone, were formed in the hot-deformed sample. In the dead zone, the grains were bigger than the other two zones; the a phase and the β phase crossed each other and wide angles were found between the lamellar structure and the axial direction. In the small weakly-deformed zone, the grains were smaller than those in the dead zone and the structure started to refine; the a phase and the β phases arranged prone to parallel to and were at small angles were found between the lamellar structure and with the loading axial direction; kinks were found in some area. In the large heavily-deformed zone, the configuration of the grains were not obvious and the structure became refined to a big heavily extent; the a phase and the P phase were almost paralleled to each other and were perpendicular to the axial loading direction; the trace of the dynamic recrystallization were found at high amplified observation. Cracks were not found outside of the dead zone; edge cracks were found outside of the weakly-deformed zone; cracks were not found in the heavily-deformed zone; extrusions and epibolic cracks were found in the border land among the three zones of the samples.(3) There exists a critical thickness at which strain rate increases rapidly, which below or above which strain rate in the sample decreases along the rolling direction. There are not inner cracks within the small strain zone in the hot-rolled samples, while micro-cracks were formed within the mediate strain zone, and long cracks within the large strain zone in the hot-rolled sample. The length of micro-cracks decreases and the number of micro-cracks increases with increasing strain. When the strain increases to a certain value, the number and the scale of the micro-cracks and long cracks become saturated. The small slant cracks were formed under rolling-induced normal and shear stresses and propagated to cause the final fracture of the wedge plate. Based on the present investigation, it is suggested that forging of the TCI1alloy can be conducted at950℃and low strain rate.