Study On The Microstructure And Properties Of TaCr₂/Ta Composite Materials Prepared By Mechanical Alloying And Hot Pressing

Laves-phase TaCr2 intermetallics compounds have great potential as high temperature structural materials for areo-engine applications, due to their high melting, high strength, good oxidation resistance and appreciable creep resistance at elevated temperatures. However, the extremely brittleness at ambient temperature is the main obstacle, which prohibits their commercial applications.Tantalum is very ductile, and has high melting point as well. Therefore, it will be an efficient method to overcome the extremely brittleness of TaCr2 intermetallics compounds, by reasonable design the composition of Ta in TaCr2/Ta composite materials.The-200 mesh high purity Ta and Cr powders were used as the raw materials. Nominal compositions of samples were Cr-40 Ta, Cr-50 Ta, Cr-62.5Ta, Cr-75 Ta, Cr-85 Ta, repectively. The contents of Laves-phase TaCr2 were 87.5%, 70%, 50%, 31.8%, 18.4%, repectively. The TaCr2/Ta composites were prepared by mechanical alloying and hot pressing. And combined the fine-grained toughening and the soft second-phase toughening, in-situ reaction synthesized Laves-phase TaCr2 during the powder densifying. Acquired TaCr2/Ta composites with different Laves phase contents, which were consist of two-phase. The microstructure and properties of TaCr2/Ta composites were investigated using OM, XRD, SEM and EDS. Moreover, the effect of different components of Ta in composites and hot pressing processes on microstructure and properties of TaCr2/Ta composites were analyzed.The results show that the Laves-phase TaCr2 could be synthesized completely in prepared TaCr2/Ta composites at 1350? for 180 min. Relative densities of all hot pressed samples were over 94%. The microstructure revealed the two-phase each separated and uniform distributed. The relative density, fracture toughness, ultimate strength and plastic strain of TaCr2/Ta composites increased gradually with the increasing of Ta content. The highest relative density(98.5%) was obtained in Cr-85 Ta sample, which fracture toughness was more than 6.12 MPa ? m1/2. When compared with single-phase TaCr2 alloy(1MPa ? m1/2) prepared by casting, its fracture toughness was improved obviously. Ultimate strength and plastic strain of the Cr-85 Ta sample were 3752 MPa, 28.57%, respectively. Eventually, the Cr-85 Ta sample was considered as the best design composition of Ta in TaCr2/Ta composites.With increasing of hot pressing temperature and hot pressing time, the relative density, ultimate strength and plastic strain of Cr-85 Ta samples were increased gradually. The highest relative density, ultimate strength and plastic strain of the Cr-85 Ta sample prepared at 1350 ? for 180 min, were 98.5%, 3752 MPa and 28.6%, respectively. With increasing of hot pressing temperature, the Vickers hardness increased gradually, while the yield strength decreased gradually. With increasing of hot pressing time, the Vickers hardness and yield strength decreased gradually after 120 min. The Cr-85 Ta sample prepared at 1350 ? for 120 min obtained the highest Vickers hardness and yield strength were 7.7 GPa and 2097 MPa, respectively. The variation trend of fracture toughness was similar to the Vickers hardness. The fracture toughness value of Cr-85 Ta sample prepared at 1300? for 120 min was 6.12 MPa ? m1/2, then decreased with the increasing of hot pressing time. The samples prepared at 1350? were not observed pointed cracks. Therefore, the fracture toughness values were speculated more than 6.12 MPa ? m1/2. Eventually, the Cr-85 Ta sample prepared by hot pressed at 1350? for 120 min was considered as the best optimum process parameters of TaCr2/Ta composites.