等离子电火花烧结TiAl-Nb复合材料的显微组织与断裂韧性

摘要

将钛铝预合金粉末和铌粉按照摩尔比9∶1混合均匀,再采用等离子电火花烧结技术在1250℃、50MPa下烧结5 min制备细晶钛铝基复合材料.采用X射线衍射、电子扫描、透射以及电子探针探讨烧结样品中显微组织、相成分的分布及晶粒度.结果表明:合金的显微组织主要由大量的层片γ相、O相、Nbss(Nb固溶相)以及B2相组成；室温烧结样品的断裂韧性高达28.7 MPa·m1/2,韧性铌固溶相在裂纹尖端以塑性延伸的方式吸收断裂能,从而提高了合金的断裂韧性；B2相以也会促进裂纹的侨联和分叉.对合金各相的显微硬度也进行了测试.%A TiAl-Nb composite was prepared by spark plasma sintering (SPS) at 1250 ℃ and 50 MPa for 5 min from prealloyed TiAl powder and elemental Nb powder in a molar ratio of 9∶1 for improving the fracture toughness of TiAl alloy at room temperature.The microstructure,phase constitute,fracture surface and fracture toughness were determined by X-ray diffractometry,electron probe micro-analysis,scanning and transmission electron microscopy and mechanical testing.The results show that the sintered samples mainly consist of γ phase,O phase,niobium solid solution (Nbss) phase and B2 phase.The fracture toughness is as high as 28.7 MPa·m1/2 at room temperature.The ductile Nbss phase plays an important role in absorbing the fracture energy in front of the cracks.Moreover,B2 phase can branch the propagation of the cracks.The microhardness of each phase of the composite was also tested.