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采用硬度测试、金相显微镜、X射线衍射、扫描电镜、透射电镜和能谱分析技术,研究热处理工艺对V55Ti30Ni15合金组织和硬度的影响.不同热处理温度和时间下的合金显微组织对合金硬度有很大影响.研究结果表明:铸态合金由过饱和钒基固溶体以及非平衡的NiTi和NiTi2相组成.合金在750和800℃热处理时,细小NiTi粒子从过饱和钒基固溶体中析出,随着保温时间延长,NiTi粒子析出增多.NiTi粒子析出降低了钒基固溶体的晶格畸变度,合金硬度降低.合金在850和900℃热处理时,NiTi析出粒子逐步回溶到钒基固溶体中,晶格畸变度升高,合金硬度升高.在900℃热处理初期,合金硬度下降是由于铸造应力的消除,晶格畸变度降低.而随后由于NiTi2相在相界上聚集球化,使得合金的硬度开始升高.
The effects of heat treatment on the microstructure and hardness of V55Ti30Ni15 alloy were studied by hardness test, optical microscope, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy. The microstructures of V55Ti30Ni15 alloy under different heat treatment temperatures and time The results show that the as-cast alloy is composed of supersaturated vanadium-based solid solution and non-equilibrium NiTi and NiTi2 phases.The fine NiTi particles are precipitated from the supersaturated vanadium-based solid solution at 750 and 800 ℃, The NiTi particles precipitated more when the holding time was longer.The precipitation of NiTi particles reduced the lattice distortion of the vanadium-based solid solution and decreased the hardness of the alloy.The NiTi precipitated particles gradually dissolved into the vanadium-based solid solution at 850 and 900 ℃, The degree of distortion increases and the hardness of the alloy increases.At the initial stage of heat treatment at 900 ℃, the decrease of the hardness of the alloy is due to the elimination of the casting stress and the decrease of the lattice distortion, and then the hardness of the alloy starts to increase due to the aggregation of the NiTi2 phase on the phase boundary Rise.