退火工艺对激光选区熔化成形Ti6Al4V合金组织及室温力学性能的影响

以Ti6Al4V球形粉末为原料,利用激光选区熔化成形方法制备了Ti6Al4V合金试样,采用光学显微镜、扫描电镜及力学性能测试等手段,研究了退火工艺对Ti6Al4V合金室温力学性能及组织的影响规律。结果表明: SLM成形沉积态Ti6Al4V合金室温抗拉强度超过1200 MPa,而平均断后伸长率仅为4.0%;在650 ℃下进行真空退火处理,合金的抗拉强度仍保持在1200 MPa左右,规定塑性延伸强度R_p0.2高于1150 MPa,但试样的断后伸长率<10%;而在750及800 ℃下进行真空退火处理,合金试样的抗拉强度降至1100 MPa左右,规定塑性延伸强度高于1050 MPa,伸长率达到甚至超过10%,材料的综合强韧性得到明显提升。随着真空退火加热温度和保温时间的增加,SLM成形Ti6Al4V合金原始β晶界逐渐变模糊,晶粒趋向于等轴化。与此同时,快速冷却转变的α′针状马氏体未出现明显地粗化。

Effect of annealing process on microstructure and room temperature mechanical properties of selective laser melted Ti6Al4V alloy

Ti6Al4V alloy specimens were prepared from Ti6Al4V spherical powder by laser selective melting (SLM) process, and effect of annealing process on the room temperature mechanical properties and microstructure of the SLM Ti6Al4V alloy were studied by means of optical microscope, scanning microscope and tensile test. The results show that the room temperature tensile strength of the alloy without heat treatment exceeds 1200 MPa, but the average fracture elongation is only 4.0%. Under the condition of vacuum annealing at 650 ℃, the tensile strength of the alloy is still around 1200 MPa, and the R_p0.2 is higher than 1150 MPa, but the percentage elongation after fracture is below 10%, the overall stvength and toughness of the material has been significemtly improved. The tensile strength of the alloy is decreased to 1100 MPa when vacuum annealed at 750 ℃ and 800 ℃, the R_p0.2(the proof strength, plastic extension) is higher than 1050 MPa and the percentage elongation after fracture is greater than 10%. Furthermore, with the increase of heating temperature and holding time of vacuum annealing, the original β grain boundary of the alloy formed by laser selective melting becomes blurred gradually and the grains tend to be equiaxed. In the meantime, the needle-like α′ martensite formed with rapid cooling transformation does not appear obviously coarsening.