Microstructure and mechanical properties of TiNbFeCoAl alloys prepared by semi-solid sintering assisted by thermo-mechanical field

In this study, the semi-solid sintering of TiNbFeCoAl amorphous powder was carried out by hot isostatic pressing (HIP) and spark plasma sintering (SPS), both of which are assisted by thermo-mechanical field, and finally two alloys with eutectic structure were prepared. The results show that the SPSed and HIPed alloys are composed of hypoeutectic (local ultra-fine lamellar eutectic beta-Ti + TiFe and residual spherical beta-Ti) and equiaxed Ti2Co phase. However, the size of hypoeutectic structure in SPSed alloy is about one third of that in HIPed alloy, and the size of the Ti2Co phase is not much different. Moreover, the Ti2Co phase in SPSed alloy is uniformly dispersed, while that in HIPed alloy is more likely to gather at the beta-Ti grain boundaries. In addition, compared with the HIPed alloy, there is an obvious orientation relationship between the eutectic lamellae of SPSed alloy, which exhibits higher yield strength (1580 +/- 6 MPa) and larger plastic strain (26.2 +/- 0.6%). The failure analysis shows that eutectic structure can effectively prevent the propagation of micro cracks and mainly contribute to the yield strength of the alloys, while the stable phase boundaries, spherical beta-Ti and dispersed Ti2Co particles mainly contribute to the strength and plasticity of the alloy.