Fabrication of in situ Ti₂AlN/TiAl composites by reaction hot pressing and their properties

Ti₂AlN/TiAl composites with different volume fractions of reinforcement were successfully fabricated by hot-pressing sintering method (reaction hot pressing) using Ti, Al and TiN powders as starting materials. The synthesis process includes four stages: first, the reactions between Al and Ti powers and between Al and TiN powders respectively occur and result in TiAl ₃ phase; secondly, Al powders in the sample are exhausted; the remaining Ti cores react with TiAl₃ layer to form Ti-Al intermetallics; moreover, a few Ti₂AlN particles precipitate from the TiAl₃ phase; thirdly, Ti-Al intermetallics react with the remaining Ti cores to form Ti₃Al and TiAl phases. TiAl phase and original TiN powers are in direct contact each other; finally, the residual TiN powers react with TiAl phase and result in a plenty of Ti₂AlN phase. Compared with TiAl matrix, the hardness, elastic modulus and high-temperature compressive strength of Ti₂AlN/TiAl composite are improved obviously and they are all enhanced with increasing the volume fraction of Ti₂AlN phase.