Preparation of cBNp/NiCrAl nanostructured composite powders by a step-fashion mechanical alloying process

Abstract

When mechanical alloying process is employed to synthesize composite powders strengthened by particle dispersion, the powders tend to fracture into small segments, especially when high content of ceramic particles is added. In the present work, a step-fashion mechanical alloying (MA) method was developed to synthesize 40vol.% cBNp/NiCrAl composite powders with both cBNp uniform dispersion in the metal alloy matrix and desirable particle size distribution. The effect of MA time on the particle size, microstructure, grain size and microhardness of the composite powder was investigated. The morphology and cross-sectional microstructure evolution of composite powders during milling were characterized by scanning electron microscopy (SEM). The change of the grain size of the alloy matrix phase with milling time was estimated based on X-ray diffraction analysis (XRD). It was found that after 40h of milling the nanostructured composite powder with a mean particle size of ~22μm and a narrow distribution was obtained. Moreover, the SEM examination showed that cBN particles were uniformly distributed in the nanostructured NiCrAl matrix. Finally, the milling mechanism of the proposed step-fashion MA was discussed.