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

研究了短时双相热处理对Ti-6Al-4V合金组织、力学性能和疲劳强度的影响。对60 S进行1203K固溶处理，40 S进行753~953K水淬时效处理。对热处理后的材料进行了详细的金相分析，包括光学显微镜和透射电子显微镜观察、X射线衍射和选区电子衍射测量以及硬度测量、拉伸试验和疲劳试验。上述热处理显著提高了合金的静强度和疲劳强度。特别是在1203K固溶处理60 S，803K时效处理40 S的热处理条件下，合金的抗拉强度和疲劳强度的改善率分别达到29%和22%左右。认为这种强化是由于短时固溶处理后淬火形成的α‘马氏体相和短时时效过程中残留的α相中析出细小的β相所致，尽管强度有了显著的提高，但热处理材料的塑性仍保持在未处理材料的水平上，这很可能是因为应变诱导马氏体相变发生在β相中，即使在短时时效后仍保留了该相。

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.