Hot Deformation Mechanisms Of O Phase Alloy Using Processing Maps

Ti₂AlNb-based alloy is a new type of high specific strength titanium aluminum intermetallic compounds designed for new aeroengine development. It's nominal composition is Ti-22Al-25Nb. Study of the hot deformation mechanisms and microstructure evolvtion is meaningful for the safety designing of components used in airplane. Considering the application background of some special high performance areoengines, this investigation is focused on the hot deformation characteristics of Ti2AlNb-based alloy at different hot deformation conditions. The relationships between microstructure and performance are analyzed. A brief introduction to the project and the main achievements are as follows:The influence of deformation temperature, strain rate and flow stress in hot deformation process are disclosed. A constitutive relationship of this alloy is formulated at three-phase region and above it. A relational expression of the grain growth is established at 1060-1100 ℃.Based on the hot compression experimental study at isothermal constant strain rate, the flow curves of this alloy exhibits obvious flow softening at low temperature with all strain rates tested or at high temperature with high strain rates. The flow stress drop increases with temperature decreasing or strain rate increasing. This phenomenon is attributed to microstructure changes of this alloy. Discontinuous yielding easily occurs at higher strain rate (10s^-1). The peak flow stress drop increases with the strain rate and the temperature increasing. It is considered that discontinuous yielding is associated with the generation of new mobile dislocations from grain boundary sources, but independent of solute-pinning.Using processing maps developed on the basis of dynamic material model (DMM). The results show that this alloy exhibit a wide instability regime due to cracking or shear band formation at a strain rate greater than 1s^-1. At lower temperatures (940-970℃), the instability was characterized by shear cracking along 45° orientation with respect to the compression axis and adiabatic shear band formation. At higher temperatures (970-1060℃), the instability was attributed to longitudinal cracking or flow localization. The others were safe regimes characterized by recrystallization.