Reaction Steps in the Combustion Synthesis of NiAl/TiB2 Composites

The reaction steps in the formation of NiAl/TiB2 composites produced by reaction synthesis have been determined using differential thermal analysis (DTA). The DTA technique reveals that the formation of NiAl/TiB2 composites occurs in a two-step reaction. NiAl forms first at approximately 550°C, followed by TiB2, which forms at approximately 1050°C. Both X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) were performed on composites produced by reaction synthesis in a hot-press facility using the same heating rate used in the DTA experiments. It was found that the formation of NiAl and TiB2 is preceded by the formation of intermediate compounds such as Ni3Al, TiAl, Ti3Al, Ti2Ni, and TiB. The relative density measured in the composites with 0, 0.25, 0.50, and 0.75 volume fractions of TiB2 was in excess of 96 pct of the theoretical density, since, during synthesis, NiAl is a transient liquid that acts as a binder phase for the TiB2 particles.