THE PREPARATION OF TIAL-BASED INTERMETALLICS FROM ELEMENTAL POWDERS THROUGH A 2-STEP PRESSURELESS SINTERING PROCESS

Pressureless sintering is not considered feasible for the preparation of TiAl-based intermetallics from elemental powders due to the Kirkend all effect. When the compacts are sintered without pressure, swelling and surface cracking occur in the billets. Porous billets are obtained , which cannot be further used. Nevertheless, pressureless sintering i s still worth investigating because of lower cost and easier operation . In this study, a two-step pressureless sintering process was develop ed to prepare the TiAl-based intermetallic preforms, The first step wa s to eliminate the aluminum particles in the billets through a solid-s tate sintering procedure to prevent the aluminum from melting and to s uppress the formation of the Kirkendall pores by sintering with a cons trained mold. The second step was to make the billets homogenized and densified by a high-temperature sintering procedure. Results show that the billets sintered with constrained molds are dense and crack free after the first step. Then, the billets are densified in the second st ep. Therefore, the application of constrained molds makes pressureless sintering feasible in the preparation of the TiAl-based intermetallic s from the elemental powders. The microstructure is fully transformed from the aluminum and titanium compacts to the TiAl-based intermetalli cs after this two-step pressureless sintering process.