Mechanical alloying and spark plasma sintering of Ni-Al-Ti-B powders for fabricating nanocrystalline (TiB+TiB₂)/Ni₃(Al, Ti) composite

This study investigated the feasibility of preparing intermetallic-matrix composite powders (Ni₃Al/TiB) by mechanical alloying of Ni, Al, Ti and B elemental powder mixtures with various compositions of (Ni ₃Al)_100-x(TiB)_x (x=0, 10, 20 and 30) for 30 hours. The as-milled powders were consolidated by the spark plasma sintering technique which is capable of sintering powders rapidly to its full density at a relatively lower temperature compared to the conventional furnace sintering method. The as-milled powders and the phases of the as-compacted materials were examined by X-ray diffraction. The densities of the materials after sintered were tested by the Archimedes method. It has been demonstrated that (TiB+TiB₂)/Ni₃(Al, Ti) composites were synthesized instead of Ni₃Al/TiB due to the diffusion of Ti into Ni and inhomogeneous reaction of Ti and B. It is possible to produce, using this technique, (TiB+TiB₂)/Ni₃(Al, Ti) composites with less than 5% residual porosity and less impurities. As-compacted material exhibits grain sizes between 30 and 50nm and relative density between 95 and 98% of the theoretical density, increasing with increasing compaction temperature as a result of reduced porosity.