The hot deformation behavior of powder met- allurgical （PM） TiAI alloys was investigated on Gleeble- 3500 thermomechanical simulator, at a temperature range of 1050-1200 ℃ with an interval of 50℃ and a strain rate range of 0.001-1.000 s-1. The results show that the flow stress of PM TiAI alloy is sensitive to deformation tem- perature and strain rate, the peak stress decreases with the increase in deformation temperature and decrease in strain rate, and dynamic recrystallization occurs during the hot compression. The deformation active energy was calcu- lated and the flow stress model during high-temperature deformation was established based on the Arrhenius equations and Zener-Hollomon parameter. The deformed microstructure consists of refined homogeneous γ and α2/γ grains.
Na LiuZhou LiWen-Yong XuYue WangGuo-Qing ZhangHua Yuan
A quantitative cellular automaton model is used to study the cell-to-dendrite transition（CDT） in directional solidification. We give a detailed description of the CDT by carefully examining the influence of the physical parameters, including：the Gibbs–Thomson coefficient Γ, the solute diffusivity Dl, the solute partition coefficient k0, and the liquidus slope ml. It is found that most of the parameters agree with the Kurz and Fisher（KF） criterion, except for k0. The intrinsic relations among the critical velocity Vcd, the cellular primary spacing λc,max, and the critical spacing λcd are investigated.
