TENSILE PROPERTIES OF W NI3AL COMPOSITES AT ELEVATED-TEMPERATURES/

In order to assess Ni3Al matrix composites as potential high-temperatu re structural material, the tensile properties of polycrystalline Ni3A l reinforced with continuous tungsten fibers were investigated. Model composites were fabricated by isothermal forging of sandwiched tungste n fibers between boron-doped Ni3Al plates at temperatures from 1373 K to 1473 K. It was found that the use of cold rolled Ni3Al plates for h ot forging enables better consolidation and a lower forging temperatur e than the use of recrystallized Ni3Al plates. Optical and scanning el ectron microscopy showed that complete metallurgical bonding between N i,AI plates is attained, the cross-section shape of the tungsten fiber s is unchanged after hot forging, and no fiber-matrix reaction zone fo rms. Hot forged Ni3Al grains in the composites are distributed finely (20 mu m) and homogeneously. The yield stresses of the composites are higher than those of Ni3Al matrix at temperatures ranging from ambient temperature to 1323 K; at 1323 especially, the strength of the compos ites is remarkably higher than that of the matrix. Fractography showed that at ambient temperature no fiber pull-out occurs, indicating good bonding between fibers and matrix until failure occurs. The tensile p roperties are discussed on the basis of experimental results on bondin g strength and interface reaction of diffusion bonded tungsten and Ni3 Al.