1300-K compressive properties of a reaction milled NiAl-AlN composite

Abstract

Cryomilling (high intensity mechanical ball milling in aliquid nitrogen bath) of the B2 crystal structure nickel aluminide leads to a NiAl-AlN composite containing about 10 vol pct second phase which is dispersed as very small diameter (<50 nm) AlN particles in a mantle surrounding particle-free NiAl grains. The AlN particles are the result of reaction milling, where nitrogen incorprated into the matrix during cryomilling reacts with Al during subsequent thermomechanical processing to form a composite. Compressive testing at 1300 K of such materials densified by either hot extrusion or hot isostatic pressing have indicated that strengh at relatively fast strain rates. In addition deformation at 1300 K occurs by two distinct mechanism, where at high strain rates the stress exponent is greater than 13 while at slower rates (<10-7 s-1) a much lower stress exponent (-6) was found.