NITRIDING REACTIONS OF TI-AL SYSTEM INDUCED BY BALL-MILLING IN AMMONIA GAS

TiN, AlN and Ti2AlN were synthesized by ball milling elemental Ti-Al p owders in an ammonia atmosphere. The progress of the milling process w as monitored by measurement of the vial pressure changes during millin g. The vial pressure variations revealed that ammonia was absorbed on the particle surfaces during the first stage of milling and further de composed into nitrogen and hydrogen. The average nitrogen content of t he as-milled powders was determined using Rutherford backscattering sp ectrometry. The structural development and nitride formation were char acterized by X-ray diffractometry. The incidence of the milling condit ions, mixture composition and ammonia quantity on the reaction product is discussed.