Synthesis, processing and properties of nanophase aluminide

This paper presents recent results on the production and properties of compacts of ultrafine powders of γ-TiAl, Metallic vapor was produced by magnetron sputtering of a TiAl target and inert gas-mediated condensation of nanometer sized particles. After collection, the particles were compacted in situ under ultrahigh vacuum conditions. The material was characterized by X-ray diffraction and hardness as a function of sintering time and temperature. Greater than 95% density was achieved in the compacts after sintering for 2 h at 450°C at which time the average grain size was still less than 20 nm. Hardness was measured as a function of grain size, and normal Hall-Petch behavior was observed, but only at grain sizes above approximately 30 nm, at which point a hardness of 12 GPa was measured. At finer particle sizes the hardness decreased with decreasing grain size.