Abstract
TiAl alloy has become a key element in aerospace and automotive engine development due to its favorable high temperature mechanical properties and low density. In this paper, high performance TiAl alloy was prepared using atomized Ti-48Al-2Cr-8Nb powder by spark plasma sintering. This paper analyzed the variation of density, microstructure, Vickers hardness, and fracture strength of TiAl alloys prepared with spherical pre-alloyed powder (named as SP powder) and pre-alloyed powder after 12 h of ball milling (named as MP powder) at different sintering temperatures. The results indicate that the density, Vickers hardness, and room temperature (25 °C) bending strength of Ti-48Al-2Cr-8Nb alloy sintered using MP powder, are significantly higher than that of TiAl alloy sintered using SP powder. Specifically, the densification temperature of the MP powder sintered specimen is reduced by 100 °C, the Vickers hardness is increased by 15%, and the room temperature bending strength is increased by 51.9% at a sintering temperature of 1250 °C. The microstructure analysis shows that the Ti-48Al-2Cr-8Nb alloy has the best bending strength when it has a fine grain phase structure.
Highlights
TiAl alloys are ideal materials for aerospace and automotive engines because of their low density, good high temperature strength, creep resistance, and oxidation resistance [1,2,3]
Poor plasticity at room temperature and relatively low strength at high temperature severely limit the practical application of TiAl alloys [4,5,6]
Due to the high melting point of Nb (2468 ◦ C) [19], high contents of Nb can lead to an increased melting point, and detrimental inhomogeneity and segregation may appear in the microstructures of the TiAl alloy making
Summary
TiAl alloys are ideal materials for aerospace and automotive engines because of their low density, good high temperature strength, creep resistance, and oxidation resistance [1,2,3]. The mechanical milling process can significantly improve the mechanical properties of TiAl alloys by reducing the sintering temperature, decreasing the size of the pre-alloyed particles, and increasing the reactivity and the degree of alloying. Guyon [22] found that after ball milling, the pre-alloyed powder has a high defect density, smaller particle size, and jagged particle surface These results are due to the high strength plastic deformation causing the densification temperature to be 200 ◦ C lower than that of the spherical pre-alloyed powder. Sanjay [24] found that pre-alloyed powder after milling has a significantly accelerated diffusion process during sintering This causes the coarse dendritic structure to disappear, forming a fine microstructure with a specific phase distribution, where the material becomes lamellar and equiaxed and has a higher fracture strength and ductility. The bending strength and fracture mechanism of the prepared Ti-48Al-2Cr-8Nb alloys at different bending test temperatures were analyzed to see the effect of the powder state on these properties
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