Improvement of Strength and Ductility of α+β Titanium Alloy by Stress Induced Transformation and Fining Microstructure

研究了短时间双相热处理对Ti-6Al-4V合金组织、力学性能和疲劳强度的影响。该热处理由1203k固溶处理60 s和753 ~ 953 K水淬+时效40 s组成。对热处理后的材料进行了详细的金相检查，包括光学显微镜和透射电镜的显微组织观察、x射线衍射和选定区域电子衍射测量、硬度测量、拉伸试验和疲劳试验。经上述热处理后，合金的静强度和疲劳强度均有显著提高。特别是在1203 K固溶60 s和803 K时效40 s条件下，合金的抗拉强度和疲劳强度的提高率分别达到29%和22%左右。分析认为，这种强化是由于短时间固溶后淬火形成α′马氏体相，短时间时效时在保留的β相中析出细小的α相所致。尽管强度有显著提高，但热处理材料的塑性仍高于未处理材料的水平，这很可能是由于β相发生应变诱导马氏体转变，即使在短时间时效后仍保持不变。

The effect of short-time duplex heat treatment on the microstructure, mechanical properties and fatigue strength of Ti-6Al-4V alloy was investigated. This heat treatment consisted of solution treatment at 1203 K for 60 s and subsequent water-quenching plus aging at 753〜953 K for 40 s. For the heat-treated materials, we carried out detailed metallographic examinations including the observations of microstructures by an optical microscope and TEM, X-ray diffraction and selected area electron diffraction measurements as well as the hardness measurements, tensile test and fatigue test. The static strengths and fatigue strength of the alloy were significantly increased by the above heat treatments. Especially, when the alloy was heat-treated with the conditions of the solution treatment at 1203 K for 60 s and aging at 803 K for 40 s, the improvement rates of the tensile strength and fatigue strength reached about 29% and 22% respectively. It was thought that this strengthening was caused by the formation of α'martensite phase with quenching after the short-time solution treatment and the precipitation of fine αphase in the retained βphase during the short-time aging. In spite of the remarkable improvement in the strengths, the ductility of the heat-treated materials remained above the level of the untreated material, most likely because strain-induced martensite transformation occurred in β phase which was retained even after the short-time aging.