The application of combustion synthesis reactions in Ni-Ti system in the joining of steel to tungsten carbide

In this study, the possibility of establishing steel/tungsten carbide joints via a novel method based on combustion synthesis process was studied. An experimental setup was designed for rapid heating and ignition of a cylindrical sample composed of compressed, exothermic mixture of Ni and Ti powders. The sample was placed as the bonding intermediate between steel-WC parts. The combustion reaction resulted in the formation of NiTi intermetallic compound, which was melted down and attached to both steel and WC parts. To prepare the green samples, Ni and Ti powders were weighed out to a molar ratio of Ni:Ti=1:1, and cold-pressed. The heating and ignition of the samples were carried out using inductive heating. After the joining was accomplished, the samples were cut in halves and characterized using XRD and SEM-EDS techniques. The analyses showed the formation of NiTi as the main phase as the product of synthesis. The elemental composition profile across the interfacial regions proved the diffusion of tungsten and cobalt elements in NiTi bonding layer and interdiffusion of titanium and nickel. Examination of X-ray maps within the joint confirmed the accumulation of nickel and tungsten in the carbide/NiTi joint and titanium and iron elements in the steel/NiTi joint due to high process temperature, accelerated diffusion, and bond formation at the joint. The results showed that by using the combustion synthesis reactions for the formation of NiTi compound, it is possible to establish acceptable joints between tungsten carbide and steel via an intermediate layer of NiTi.