Influence of the Processing Route in the Microstructure and Mechanical Properties of NiAl/TiB₂ Composites Produced by Combustion Synthesis

In this work, dense NiAl/TiB₂ composites with varying amounts of TiB₂ were produced by combustion synthesis routes. The morphology of the TiB₂ phase in the composite has been modified by changing the reactants in the initial powder mixture. In the first processing route, NiAl and TiB₂ phases were obtained from Ni, Al, Ti, and B elemental powders. In the second processing route, TiB₂ was added, instead of Ti and B, along with Ni and Al to produce NiAl and TiB₂ phases. The XRD performed on the products of both processing routes confirmed that the synthesized phases were indeed TiB₂ and NiAl. The NiAl grain size is smaller for the composites obtained in the first processing route. In addition, the first processing route leads to clusters of TiB₂ submicron particles in which the matrix is either TiB₂ or NiAl depending on the starting composition. The second processing route results in less dense composites in which the matrix is the NiAl and the TiB₂ exists as dispersed platelets. The hardness (H) and Young’s modulus (E) were observed to be higher for composites produced by the first processing route. This difference in the mechanical properties is caused by the difference in microstructure, as well as the difference in porosity between the two processing routes.