形变影响TC4钛合金组织和性能演变的温度依赖性

Temperature-Dependent Effect of Deformation on Microstructure and Properties of TC4 Titanium Alloy

通过等应变速率高温拉伸试验,研究了TC4钛合金在不同形变温度下微观组织和性能的演变行为,着重探讨了形变对钛合金组织演化、相变的影响作用及其随温度的变化规律。结果表明,在α+β两相区变形,随形变温度升高,峰值应力及所需应变降低。形变对微观组织演化的影响作用随形变温度变化而改变:两相区中低温段(900℃以下),形变促进初生α相再结晶,细化初生α相尺寸;两相区高温段(900℃以上),形变促进次生α相球化,其作用随温度升高先增强后减弱。形变影响β→α相变进程,提高次生α相形核率,尤以两相区中低温段变形更为显著,从而使得片层状次生α相数量增加、间距明显细化。随形变温度升高,组织中α相总量先下降后上升,导致硬度先降低后升高,耐蚀性先升高后下降。其中900℃变形时,TC4钛合金α相总量最少(约57%),硬度略有降低而耐蚀性达到最优。

The effect of deformation temperature on the evolution of microstructure and properties of TC4 alloy was studied by a constant-strain rate tensile test at high temperature.The results show that both the peak stress and its required strain decrease with increasing temperature in the α+β dual-phase field.The deformed microstructure exhibits a strong temperature-dependent evolution.Deformation leads to an accelerated recrystallization and refinement of primary α phase at a lower temperature of α+β phase field(below 900 ℃),whereas it results in a significant spheroidization of secondary α phase at a higher temperature(above 900 ℃).Additionally,deformation also affects the nucleation and growth process of β→α transformation,resulting in a larger amount of secondary α phase.With the increasing deformation temperature,the volume fraction of α phase firstly decreases and then increases,and thus hardness has a good consistence.However,the corrosion resistance displays a reverse evolution with the amount of α phase.TC4 alloy exhibits the lowest volume fraction of α phase of 57% at the deformation temperature of 900 ℃ and the best corrosion resistance in a NaCl solution,while it shows a slightly lowered hardness.