Combustion Synthesis of a Functionally Graded NiTi-TiCx Composite

Abstract

Combustion synthesis (CS) is an alternative technique for producing advanced materials and is dependent upon a highly exothermic chemical reaction to become self-sustaining after only a short energy pulse is applied to initiate the reaction. A NiTi-TiCx functionally graded material (FGM) was investigated that combines superelastic and shape memory capabilities of NiTi with the high hardness, wear, and corrosion resistance of TiCx. CS was employed to produce a FGM from 100% TiCx ceramic to 100% NiTi intermetallic. Temperature and burning velocity data of the CS reaction were recorded. XRD of the final product layers was conducted to determine phase composition. The combustion temperature, burning velocity, and cooling rate in each layer decreased with increasing NiTi content. Large blowholes were present in the high NiTi content layers as a result of outgassing of volatile species from the reactant powders. XRD analysis revealed the presence of Ni-Ti intermetallics along with a substoichiometric TiC (TiC0.7). Production of a NiTi-TiCx FGM is possible through use of a CS reaction employing the propagating mode (SHS). The material layers were observed as functionally graded in both composition and porosity.