激光选区熔化制备NiTi合金显微组织与压缩性能研究

Study on Microstructural Evolution and Compression Performances of Selective Laser Melting NiTi Alloy

采用激光选区熔化技术进行不同能量密度下的高致密NiTi合金制备,研究了基体相与沉淀相等显微组织特性对静态压缩与高应力超弹性性能的影响规律。结果表明,在55.56~66.67J/mm3能量密度下可获得高质量沉积表面,且随能量密度递增而趋于平整。沉淀相显微组织均为粗大柱状B2奥氏体晶粒内分布着细小致密的B19'马氏体,纳米级颗粒状Ti2Ni沉淀相在B19'马氏体晶界及晶内呈弥散态析出。在细晶强化与弥散强化共同作用下获得了较高的压缩强度,失效模式为快速剪切断裂。合金在压缩卸载阶段因存在纯弹性回弹与马氏体变体回弹而具有较好超弹性功能。NiTi合金SLM件在合适的可变工艺窗口下表现出良好的显微组织与压缩性能稳定性。

Selective laser melting(SLM)technology was adopted to manufacture dense NiTi alloys with different energy densities.The influence rules of the microstrcture characteristics of the matrix phase and precipitation phase on the quasi-static compression and high-stress super-elasticity were studied.The results show that high-quality deposition surface is acquired at 55.56-66.67 J/mm3,and the surface roughness is gradually improved with the energy density increasing.The as-deposited microstructure is characterized by coarse columnar B2 austenite containing dense needle-like B19'martensite.Besides,nano-sized Ti2Ni phases are precipitated at the martensitic grain boundaries and the grain interiors.The enhanced compression stress is ensured due to the combined strengthening mechanisms of grain refinement and phase precipitation.The compression failure behavior is regarded as rapid shear fracture mode.The excellent super-elasticity performance is acquired,which is attributed to both elastic rebound and martensitic rebound during the unloading period.Conclusively,the excellent microstructural and compressive stability of SLM NiTi parts is ensured within the appropriate processing window.