Research On High Nb-TiAl Alloy Prepared By Hot Pressing Sintering

Due to its low density, high specific strength, high specific stiffness, excellent oxidation resistance and high temperature creep resistance. TiAl-based alloys have attracted scholars’wide attention. They are expected to become new generation of high temperature structural materials in the near future and play great potential in the field of aerospace and automotive engine. But their room temperature brittleness, difficulty in machining and deficiency in high temperature oxidation resistance above 850℃ limit their application in industrial. With the development of science and technology, researchers make the development of TiAl-based be directed at high Nb low Al through a series of experiments and innovations. High Nb containing, TiAl alloys are the most promising candidates to fulfill these demands.In this paper, the object of study is high Nb containing TiAl alloys based on the nominal composition of Ti-45Al-8Nb-0.2B-0.2W-0.1 Y for the substrate. Research the matrix alloy by vacuum hot pressing sintering process in order to determine the best sintering temperature. Matrix alloy is prepared with coarse particle powder (300 mesh number) and micron grade of small particles of powder and is machined by wire-cutting processing into our required specification. And then, the surface of samples is grinded and polished. The alloying elements are added in the matrix alloy after the sintering process is determined. The effect of alloying elements of Cr and Mo on the mechanical properties, microstructure and fracture appearance are investigated by optical microscope (OM), Vickers microhardness, thermal field emission scanning electron microscope (SEM), X-ray diffraction (XRD), backscattered electron imaging (BSE) and energy spectrum analysis (EDS). The results show that:The sample machined by different sintering temperature is analyzed to determine the best sintering process. There are two ways in the best sintering process, first, hot pressing sintering at the low temperature 620℃ for 1.5h, and second, hot pressing sintering at the high temperature 1350℃ for 2h.Matrix alloy are joined in alloy element Cr and Mo. Then sample of adding alloy elements are analyzed by mechanical properties testing and the microstructure morphology of the cross section. The sample added Cr alloy elements in make no significant in the hardness. By comparing the bending strength of the matrix alloy,2% Cr enhances the bending strength by 16.2%. Make the microstructure wee and the slice layer spacing decrease. Make the fracture form of matrix alloy change from brittle fracture to dimple fracture. When add 1% Mo, the hardness of matrix alloy is reduced, but addition of Mo also improves the bending strength of the alloy (951.49MPa), increased by 12.8%.1% Mo also refines the grain material and makes the grain boundary becomes clearer.