TIAL-BASED HIGH-TEMPERATURE MATERIALS MADE FROM EXTREMELY DEFORMED ELEMENTAL POWDERS

Materials based on the intermetallic compound TiAl have been made from elemental powders which were extremely deformed through repeated cold -extrusion or through combination of cold-extrusion and cold-rolling. The microstructure is getting finer with increasing deformation. After HIP at 1350 degrees C under a pressure of 200 MPa for 4 hours without encapsulation, the repeatedly extruded material showed a porosity of about 2%, smaller than the porosity of simply extruded material (> 6%) . Two-step sintering experiments carried out on the repeatedly extrude d material showed that pores formed during pressureless sintering can be almost fully suppressed by an additional HIP treatment. On the cont rary, the relatively low porosity HIP'ed material becomes more porous after a post pressureless sintering. In addition, TiAl matrix composit es have been successfully prepared by pressing multilayerd rolled shee ts, sandwiched with Al2O3 fibres or Mo foils, at high temperatures.