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 composite containing about 10 vol. % of AlN particles. This is the result of a reaction milling process, where nitrogen incorporated into the matrix during cryomilling reacts with Al during subsequent thermomechanical processing to form the composite. Compressive testing at 1300 K of such materials densified by 1505 K extrusion or isostatic pressing at 1323 K or 1623 K indicated that strength at relatively fast strain rates ($GR10-7 s-1) is slightly dependent on the method of consolidation. At slower rates, however, no clear dependency on densification technique appears to exist, and four different consolidation methods possessed similar creep strengths. In all cases deformation at 1300 K occurred by two distinct mechanisms: at high strain rates the stress exponent is greater than 11 while at slower rates (<10-7 s-1) a much lower stress exponent (approximately 6) was found. Comparison of density compensated creep strengths reveals that the properties of NiAl-Aln are similar to those of the single crystal Ni-base superalloy NASAIR 100.