1300 K Compressive Properties of a Reaction Milled NiAl-AlN Composite

Abstract

Cryomilling (high intensity mechanical ball milling in a liquid 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 incorporated 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 strength at relatively fast strain rates (>10⁻⁷ s⁻¹ ) is dependent on the method of consolidation; however no clear dependency on densification technique appears to exist at slower rates. In addition deformation at 1300 K occurs by two distinct mechanisms, 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.