Fabrication of Functionally Gradient Materials by a MA-PS (Plasma Sintering) Technique

Abstract

A novel P/M processing is developed, which consists of plasma sintering with the aid of an applied stress and a temperature gradient and a high quality powder production of amorphous TiAI by mechanical alloying, for the fabrication of a functionally gradient materials(FGM) of zirconia-titanium aluminide system. Our processing makes it possible to obtain a FGM of FSZ/TiAl without a visible crack-like discontinuity throughout an overall cross section with a short-time sintering of 300 s and a relatively low applied stress ranging from 29 to 59 MPa. Plasma sintering leads to a full dense compaction, mainly via viscous flow in amorphous TiAl matrix, in layers between TiAI and 50%-TiAl/FSZ, and a relatively high hardness of 807 Hv for 7-phase TiAl including a small amount. of α₂(Ti₃Al) and at the maximum, 1016 Hv at 25 %FSZ/TiAl. These higher levels are explained by strengthening mechanisms of nano-meter scaled grain and FSZ particle dispersion respectively. Two-step plasma sintering with a greater temperature gradient realizes the enhanced hardness and relative density of FSZ-rich layers.