Synthesis of nanostructured chromium nitrides through mechanical activation process

High energy milling prior to nitriding chromium metals has led to the forma tion of nanostructured CrN. Furthermore, high energy milling has substantia lly enhanced the chromium nitridation process. Under the same nitridation c ondition, nearly 100% CrN is formed for Cr powder milled in NH, for 24 hour s prior to nitridation, whereas little CrN is produced for Cr powder withou t milling. More nitrides are formed as milling time increases. The enhanced nitridation process is believed to be primarily related to the enhanced re action kinetic of the milled powder due to the presence of the sorbed nitro gen (when milled in NH,), the reduced crystallite size, large grain boundar y areas associated with ultrafine grains, the reduced correlation length of ordered stacking, and possibly the increased defect concentration induced by high energy milling. (C) 1999 Acta Metallurgica Inc.