激光选区熔化Ti-6Al-4V合金纳米压痕蠕变研究

目的研究原始态和退火态激光选区熔化Ti-6Al-4V合金的室温压痕蠕变特性。方法利用光学显微镜观察原始态和退火态激光选区熔化Ti-6Al-4V合金的显微组织。基于纳米压痕技术结合恒载荷法,测量原始态和退火态合金在室温下的最大压痕深度、蠕变位移和蠕变速率敏感指数等压痕蠕变参数,并分析两种状态下合金的蠕变机理。结果原始态合金的显微组织几乎全为α相,退火态合金的显微组织为网篮组织。荷载分别为200、300、400 mN时,加载阶段原始态合金的最大压痕深度比退火态合金的最大压痕深度分别提高43%、42%、34%;保载阶段,原始态合金的蠕变位移比退火态合金的蠕变位移分别提高129%、128%、139%。原始态合金的蠕变速率敏感指数m值分别为0.054、0.050、0.046,退火态合金的m值分别为0.041、0.032、0.022,相同荷载下原始态的m值均大于退火态的m值。结论退火处理形成的网篮组织,使退火态合金的蠕变速率敏感指数m值降低,从而使其蠕变抗力增强。原始态和退火态激光选区熔化Ti-6Al-4V合金的蠕变机理均为位错蠕变。

Nanoindentation Creep of Ti-6V-4V Alloy Prepared by Selective Laser Melting

The work aims to study the indentation creep properties of Ti-6Al-4V alloy by laser selective melting in the primitive and annealed states.The microstructure of the Ti-6Al-4V alloy by selective laser melting in the primitive state and annealed state was observed by optical microscope and the indentation creep parameters of primitive and annealed alloys at room temperature were measured by nanoindentation technique combined with constant load method,such as maximum indentation depth,creep displacement and creep strain rate sensitivity.Then,the creep mechanism of alloys in two states was analyzed.The microstructure of primitive alloys was almost composed ofαphase,and the microstructure of annealed alloys was basket tissue.When the loads were 200 mN,300 mN and 400 mN respectively,the maximum indentation depth of primitive alloy increased by 43%,42%and 34%compared with that of annealed state alloy at loading stage,and the creep displacement of primitive state alloy increased by 129%,128%and 139%compared with that of annealed state alloy at holding stage;the creep strain rate sensitivity m values corresponding to the primitive state alloys were 0.054,0.050 and 0.046 respectively,and the m values of annealed alloys were 0.041,0.032 and 0.022 respectively.The m value of the primitive state was greater than the m value of the annealed state under the same load.The basket structure formed by annealing reduced the creep rate sensitive index m of the annealed state,thus enhancing the creep resistance.The creep mechanism of Ti-6Al-4V alloy prepared by selective laser melting in the primitive and annealed state is dislocation creep.