Nitriding of transition metal powders by ball milling in nitrogen gas

Abstract

Ti, Zr, Nb, Ta, Cr and Mo powders have been mechanically nitrided by ball milling in nitrogen gas. The structures of nitrided powders were examined by means of X-ray analysis and transmission electron microscopy. A kinetic analysis for the nitriding rate was also carried out. About 50 at.% of nitrogen is absorbed in the milled powders, resulting in the formation of stable or metastable NaCl-type nitrides. The nitriding rate increases with an increase in the enthalpy of nitride formation. The nitriding rate is proportional to the cube of milling cycle. This fact means that the nitrogen absorption in the milled powders occurs at the instance of ball collision and the quantity of nitrogen absorbed at one collision event is proportional to the energy supplied to the powder from colliding balls.