Conversion of titanium hydride to titanium nitride during mechanical milling

The response of a stable titanium hydride to severe mechanical milling treatments at room temperature was studied in different gaseous environments using different milling media. Structural details were monitored by Reitveld refinements using x-ray-diffraction data and hydrogen compositions were measured by decomposition at 850 ^∘{}C in a constant volume system.mMilling in an argon atmosphere produces only nanocrystalline TiHₓ with a reduction in hydrogen content proportional to the milling time. Milling in steel and Co bonded WC vials in air gave a more rapid loss of H and simultaneous formation of TiN. The lattice parameters of both the TiHₓ and the Ti formed by decomposition support a mechanism based on solid solution of N in the TiHₓ followed by partition into two phases. This resembles a chemically enhanced version of the 'solid-solution pumping' mechanism previously described for the nitrogenation of pure Ti milled in air.mExperiments with different milling media and minor additions of Fe and or Co suggest that 3d transition metal is necessary for the nitrogenation to occur, most likely by promoting dissociative chemisorption of N₂.