Synthesis and characterization of SHS bonded Ti5Si3 on Ti substrates

The simultaneous synthesis and bonding of titanium silicide, Ti5Si3, to pure Ti has been investigated using self-propagating high-temperature synthesis (SHS). Ti and Si reactants were ignited in a self-sustaining reaction, liberating sufficient heat to first synthesize then bond Ti5Si3 to a Ti substrate. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the bond interface, while phase identification was performed using X-ray diffraction (XRD). The bond interface was shown to contain a uniform and continuous eutectic region, approximately 75 μm thick. Using back-scattered electron (BSE) imaging and quantitative phase analysis (QPA), the coating overlay was shown to consist of a two-phase mixture of 97 wt% Ti5Si3 with 3 wt% Ti segregated to the silicide grain-boundaries. It is proposed that the overall reaction sequence was initiated by the rapid SHS reaction, 5Ti+3Si→Ti5Si3+ΔHf=−579kJ/mol prior to a secondary reaction with the Ti substrate in which the eutectic region was formed.