Compression behavior and interfaces of NiAl-TiB 2in situ composites

Abstract

The B2 crystal structure intermetallic NiAl is one of the most attractive materials for high temperature structural applications due to its low density, high melting point and excellent oxidation resistance. However, the problems of its poor high temperature strength and low temperature ductility have not been overcome. One possible approach to increase high temperature strength is to incorporate metallurgically stable, uniformly dispersed, hard, fine second phase particles in sufficient amount in the alloy. Recent works have shown that the elevated temperature strength of the NiAl can be effectively increased by dispersively distributed TiB[sub 2] particles. Such composites were fabricated by XD[trademark] synthesis and hot pressed to full density. The microstructure and interfaces of NiAl/TiB[sub 2] have also been investigated by analytical electron microscopy and high-resolution electron microscopy (HREM). But coherent or semi-coherent interfaces between TiB[sub 2] and NiAl were not observed via HREM, only one-dimensional lattice fringes in both the matrix and the particles were observed. If pressure could be applied during exothermic synthesis while the product mass is still at elevated temperatures, then it might be possible to synthesize and densify the product simultaneously. This paper uses a hot pressing aided exothermic synthesis (termed HPES) technique to fabricate themore » Ni-50at.%Al matrix composites containing 0 to 20 vol.%TiB[sub 2] particles. Their interfaces and the compression behavior from room temperature to 1,000 C were studied.« less