Fabrication of (TiB/Ti)-TiAl composites with a controlled laminated architecture and enhanced mechanical properties

Abstract

The (TiB/Ti)-TiAl composites with a laminated structure composing of alternating TiB/Ti composite layers, α2-Ti3Al interfacial reaction layers of and γ-TiAl layers were successfully prepared by spark plasma sintering of alternately stacked TiB2/Ti powder layers and TiAl powder layers. And the influence of thickness ratio of TiB2/Ti powder layers to TiAl powder layers on microstructure evolution and mechanical properties of the resulting (TiB/Ti)-TiAl laminated composites were investigated systemically. The results showed that the thickening of α2-Ti3Al layers which originated from the reaction of Ti and TiAl was significantly hindered by introducing TiB2 particles into starting Ti powders. As the thickness ratio of TiB2/Ti powder layers to TiAl powder layers increased, the bending fracture strength and fracture toughness at room temperature of the final (TiB/Ti)-TiAl laminated composites were remarkably improved, especially for the (TiB/Ti)-TiAl composites prepared by TiB2/Ti powder layers with thickness of 800 μm and TiAl powder layers with thickness of 400 μm, whose fracture toughness and bending strength were up to 51.2 MPa·m1/2 and 1456 MPa, respectively, 293 % and 108 % higher than that of the monolithic TiAl alloys in the present work. This was attributed to the addition of high-performance network TiB/Ti composite layers. Moreover, it was noteworthy that the ultimate tensile strength at 700 °C of (TiB/Ti)-TiAl composites fabricated by 400 μm thick TiB2/Ti powder layers and 400 μm thick TiAl powder layers was as high as that at 550 °C of network TiB/Ti composites. This means the service temperature of (TiB/Ti)-TiAl laminated composites was likely raised by 150 °C, meanwhile a good combination of high strength and high toughness at ambient temperature could be maintained. Finally, the fracture mechanism of (TiB/Ti)-TiAl laminated composites was proposed.