热积累对激光直接成形Ti-6Al-4V组织和性能的影响

为了研究激光直接成形Ti-6Al-4V中热积累效应对其微观组织和力学性能的影响,采用对比试验的方法,制备了直径分别为5mm和10mm的两个圆柱试样及两组对比拉伸试样。直径为5mm的试样成形时热积累效应明显,底部和顶部的晶粒内部以马氏体'组织为主,中部的晶粒内部以针状组织为主;直径为10mm的试样热积累效较弱,自底部至顶部均以马氏体'组织为主。热积累效应强烈的一组拉伸试样拉伸强度略低于热积累效应不明显的一组试样,但塑性约为其3倍。结果表明,激光直接成形Ti-6Al-4V时强烈的热积累效应会降低冷却速率,使微观组织从马氏体'组织转变为针状组织,从而使其拉伸强度稍有降低,但塑性提高很多。

Influence of heat accumulation on microstructure and property of Ti-6Al-4V in laser direct forming

In order to study effect of heat accumulation on microstructure and mechanical property of Ti -6Al-4V, two cylindrical samples and two tensile samples in 5mm and 10mm diameters of were made by means of laser direct forming .Heat accumulation was intense while forming 5mm sample.Martensite α′was found inside βgrains at the bottom and top positions , while acicular αwas found inside βgrains in the middle position .Heat accumulation was weak while forming 10mm sample. Martensiteα′was found from the bottom to the top position .The samples of intense heat accumulation had a slightly weak tensile strength and three times of tensile plasticity .Experiment results show that intense heat accumulation while forming Ti-6Al-4V would make cooling rate decreased and microstructure would transform from martensite α′to acicularαso that the tensile strength decreases and the tensile plasticity increases .