Microstructure of spark sintered titanium-aluminide compacts

The microstructural properties have been investigated for titanium-aluminide (Ti-53mol%Al) compacts spark sintered at four temperatures: 1573, 1623, 1648, and 1673 K after pulsed electrical discharge. The microstructure changes with sintering temperature and is classified into two groups. (1) Group 1: for specimens spark sintered at 1573-1648 K, the structure consists of three different grains which represent the core grain (core consisting of alpha-Ti and Tl3Al, surrounding grain consisting of Tl3Al), lamellar grain (Ti3Al/TiAl) and equiaxed grain (TiAl). The structure of the core grain is the same as that of the as-received pre-alloy powder produced by combustion synthesis. (2) Group 2: for specimens spark sintered at 1673 K, the structure consists of two different grains which represent the lamellar (Ti3Al/TiAl) and equiaxed (TiAl) grains. The grain growth is prevented during spark sintering. Vickers microhardness values of each phase in the spark sintered specimens are almost the same as those in specimens produced by other manufacturing methods. A simple rule of mixtures can be applied for the hardness of Ti3Al/TiAl lamellar grains in spark sintered specimens. Specimens with high densities and approaching the equilibrium state can be obtained in a shorter time by spark sintering than conventional sintering. Such shorter high temperature exposure is important to prevent grain growth. Copyright (C) 1996 Elsevier Science Ltd