半固态处理对Ti基非晶复合材料的组织和力学性能影响

Effect of semi-solid heat-treatment on microstructure and mechanical properties of Ti-based bulk armorphous composites

利用"形变诱导相变机制"对非晶基体同时增强增韧,采用悬浮熔炼-铜模吸铸法制备了Ti基非晶复合材料。在此基础上,通过半固态处理工艺对凝固过程动力学控制优化组织,研究了半固态处理对试样的组织和力学行为的影响。结果表明,铸态试样组织为过冷奥氏体相、热致马氏体相和非晶复合结构,应力加载形变过程中通过形状记忆晶相TRIP效应对非晶基体增韧,表现为加工硬化行为。铸态试样的心部组织为较粗大的树枝晶,且生长不均匀;经半固态处理后,先析出相按照尖角溶解平面析出长大形式近球化,形成等轴晶,并在磁悬浮搅拌作用下均匀化,获得奥氏体相晶粒细小、圆整度高、组织致密,复合材料组织得到有效优化,(Ti0.5Ni0.48Co0.02)80Cu20合金断裂强度和塑性变形量由2 582 MPa和15%分别提高至2 745MPa和21.5%。

Ti-based bulk amorphous composites,designed by deformation induced transformation effect to en-hance the strength and plasticity,were fabricated by suspend melting under an argon atmosphere using a copper mold.And semi-solid heat-treatment was chosen to control the solidification kinetics and optimize the micro-structure.The effect of semi-solid heat-treatment on microstructure and mechanical properties of Ti-based bulk amorphous composites were investigated.The results showed that the as-cast compounds microstructure were consist of the supercooled austenite phase,thermally-induced martensite phase and amorphous phase.As load-ing,the alloys were strengthened and toughed by TRIP effect,and exhibit a strongly work-hardening behavior. The as-cast microstructure of core region contains coarse dendrites with uneven growth.Nevertheless,the semi-solid heat-treated microstructure contains equiaxed grain with higher spheroidization,smaller and more uniform size.The spheroidal grain was formed by the sharp corner solution and plane precipitation growth mechanism. Therefore the composites microstructure was effectively optimized,as well as the comprehensive mechanical properties are further improved.After semi-solid heat-treated,fracture strength and plastic deformation of (Ti0.5Ni0.48Co0.02)80Cu20 were enhanced from 2 582 MPa and 15%,to 2 745 MPa and 21.5%.