Rapid Consolidation Mechanism of Titanium Aluminide Solid Compact via Electric Discharging Through Elemental Ti and Al Powder Mixture

Elemental Ti and Al powders were milled and mixed as starting materials for the synthesis of titanium aluminide solid compacts by using the electric discharge sintering (EDS) technique. The polycrystalline compact with near full-density (>99.6%) and the main phase of Ti3Al was produced in 170s by the EDS. In the early stage of electric discharging, the generated heat at the interface of metal and oxide film created an explosive force, inducing a dielectric breakdown of inherent oxide film. Once the oxide film was removed and the metals were melt, the formation of necks at the clean contact points occurred and the inter-diffusion between Ti and Al in liquid phase was initiated at the metallic contact areas with sequent alloying into an amorphous Ti3Al. During the full alloying and substantial neck growth, the heat dissipated through the mold, causing the crystallization of Ti3Al. During the EDS, pinch pressure (24-68 MPa) was also generated, which can densify the EDS compact. The fine microstructure, higher density, and greater hardness of EDS compact were results of the shorter exposure time to a high temperature and the generated pinch pressure, causing a higher densification and constrained grain growth, compared to conventional powder metallurgy methods.