MICROSTRUCTURE AND MECHANICAL-BEHAVIOR OF THE NIAL-TIC IN-SITU COMPOSITE

The microstructure, interfaces, and mechanical properties of NiAl-matr ix composites reinforced by 0 and 20 vol pct TiC particles have been e xamined. The composites were prepared by the hot-press-aided exothermi c synthesis (HPES) technique. Portions of the HPES-processed samples w ere hot isostatically pressed (''hipped'') at 1165 degrees C/150 MPa f or 4 hours or annealed at 1400 degrees C for 48 hours. In the as-fabri cated state, TiC particles were generally polygonal and faceted, and t he interfaces' between TiC and NiAl were atomically flat, sharp, and g enerally free from any interfacial phase. At least two orientation rel ationships between TiC and NiAl were observed. In some cases, thin amo rphous layers existed at NiAl/TiC interfaces. After ''hipping,'' the T iC particles tended to become round and the TiC/NiAl interfaces became overlapped. Annealing at 1400 degrees C for 48 hours did not affect t he microstructure or the interfacial structure of the composite in mos t cases. The compressive yield strengths (YSs) from room temperature t o 1100 degrees C of the composite were considerably higher than that o f the monolithic NiAl. At 980 degrees C, the tensile YS of the composi te was approximately 3 times that of the monolithic NiAl. In addition, the ambient fracture toughness of the composite was 50 pct higher tha n that of the monolithic NiAl.