Nitriding reactions of Ti-Al system induced by ball milling in ammonia gas

TiN, AlN and Ti₂ AlN were synthesized by ball milling elemental TiAl powders in an ammonia atmosphere. The progress of the milling process was monitored by measurement of the vial pressure changes during milling. The vial pressure variations revealed that ammonia was absorbed on the particle surfaces during the first stage of milling and further decomposed into nitrogen and hydrogen. The average nitrogen content of the as-milled powders was determined using Rutherford backscattering spectrometry. The structural development and nitride formation were characterized by X-ray diffractometry. The incidence of the milling conditions, mixture composition and ammonia quantity on the reaction product is discussed.