Self-propagating high-temperature synthesis mechanisms within the Ti–C–Ni system: A time resolved X-ray diffraction study

An experimental study on direct formation of TiC–Ni composite by self-propagating high-temperature synthesis (SHS) was conducted using a Ti–C–xNi systems (x = 5, 10, 15 wt.%). Composites of this kind are known to exhibit interesting structural and mechanical properties (high strength in shear and compression, high service temperature capabilities), thanks to the combination of metallic (ductility and toughness) and ceramic (high strength, modulus and hardness) properties. X-ray powder diffraction (XRPD) experiments performed on the combustion–synthesized products have shown that the main products were always TiC and Ni acting as a binding phase, but that the reaction might be incomplete in some cases, and the formation of a small amount of Ni–Ti compounds and metastable Ni3C was observed. To understand the chemical pathway, a time resolved X-ray diffraction experiment (TRXRD) using synchrotron radiation (ESRF ID-11, Materials Science Beamline) was performed to follow the reaction in situ on a time scale of ~ 35 ms. This analysis showed that TiC was the first phase to form through solid-state diffusion of C into β-Ti, followed by Ti–Ni melt and finally the simultaneous appearance of metallic Ni and Ni3Ti, suggesting an eutectic reaction during the cooling stage. Using Rietveld refinement, some critical temperatures were estimated via thermal expansion/contraction of the lattice parameter of TiC during the combustion reaction.