Fabrication of (Ti-Al-Si)/(Ti-C)/Ti – layered alloy by SHS pressing

Abstract

A metal-carbide-intermetallic material based on combustion products of the layer system (Ti-Al-Si)/(Ti-C)/Ti was for the first time obtained with the help of self-propagating high-temperature synthesis (SHS) combined with pressing. Exothermic synthesis from elementary powders was carried out at a pressure of 10 MPa, and pressing of the hot synthesis product was carried out at a pressure of 100 MPa. It has been shown that SHS pressing contributes to the formation of permanent joints of «metal/carbide/intermetallic» layers. The main features of microstructure formation, phase composition, and strength properties of transition zones at the boundary between reacting SHS compositions, Ti-C and Ti-Al-Si and Ti-metal substrate are investigated. It is shown that during SHS reaction, a homogeneous microstructure of Ti-C and Ti-Al-Si layers with an insignificant content of cracks and pores is formed. The thickness of the transition zone between the layers was at least 15 µm. The main phase formed in the combustion product of Ti-Al-Si layer is, according to the results of X-ray phase analysis, triple phase Ti20Al3Si9, the content of which, calculated by the Rietveld method, was at least 87 wt. %. In addition, the combustion product contains a secondary phase of Ti3Al in the amount of 13 wt. %. The energy dispersion analysis revealed that diffusion of aluminium through the titanium carbide layer into the titanium substrate to a depth of approx. 30 µm is observed. Microhardness value of the combustion product of Ti-Al-Si layer was about 10 GPa. The rectilinear nature of crack propagation in the synthesized combustion product of Ti-Al-Si layer, as well as the Palmquist crack resistance coefficient varying within 5.1-5.7 MPa·m1/2, indicate the fragility of the material.