Formation and characteristics of nanocrystalline composites γ–TiAl + Ti2AlN by mechanical alloying and subsequent annealing treatment

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Abstract
Formation of nanocrystalline composites γ-TiAl + Ti2AlN by mechanically alloying (MA) Ti50Al50 in a N2 atmosphere and subsequent annealing treatment are investigated. The development of the microstructure was monitored by x-ray diffraction, and differential thermal analysis and transmission electron microscopy. The amorphous phase could be obtained after milling for 30 h in a nitrogen atmosphere. The TEM results show that some nanocrystalline solid solution of Al in Ti also existed in the amorphous matrix. The results of annealing treatments at different temperatures for 0.5 h on the amorphous phase obtained by MA in N2 gas for 30 h show the formation of γ-phase (TiAl) and a nitride of titanium and aluminum (Ti2AlN). Available annealing treatments could produced nanocrystalline composites of γ-TiAl and Ti2AlN with a grain size less than 20 nm. With increasing annealing temperature, the crystalline sizes of γ-TiAl and Ti2AlN increase, but the values of microhardness increase slightly.