Microstructure and mechanical behavior of the NiAl-TiC In situ composite

Abstract

The microstructure, interfaces, and mechanical properties of NiAl-matrix composites reinforced by 0 and 20 vol pct TiC particles have been examined. The composites were prepared by the hot-press-aided exothermic synthesis (HPES) technique. Portions of the HPES-processed samples were hot isostatically pressed (''hipped'') at 1165 degrees C/150 MPa for 4 hours or annealed at 1400 degrees C for 48 hours. In the as-fabricated state, TiC particles were generally polygonal and faceted, and the interfaces' between TiC and NiAl were atomically flat, sharp, and generally free from any interfacial phase. At least two orientation relationships between TiC and NiAl were observed. In some cases, thin amorphous layers existed at NiAl/TiC interfaces. After ''hipping,'' the TiC particles tended to become round and the TiC/NiAl interfaces became overlapped. Annealing at 1400 degrees C for 48 hours did not affect the microstructure or the interfacial structure of the composite in most cases. The compressive yield strengths (YSs) from room temperature to 1100 degrees C of the composite were considerably higher than that of the monolithic NiAl. At 980 degrees C, the tensile YS of the composite was approximately 3 times that of the monolithic NiAl. In addition, the ambient fracture toughness of the composite was 50 pct higher than that of the monolithic NiAl.