Structure and Mechanical Properties of TiAl Compact Produced by Hot Pressing of Mechanically Alloyed Powder

Abstract

The mixture of elemental powders of Ti(64 mass% (50 at%)) and Al(36 mass% (50 at%)) was offered to a mechanical alloying process. The processed powder was vacuum hot pressed at 1173 K for 3.6 ks under 100 MPa. The compact having relative density of 99.8% was obtained.The results of X-ray diffraction, TEM observation and energy dispersive X-ray analysis indicated that the compact has an ultra-fine grain (average grain diameter=0.1 μm) structure mainly consisting of TiAl intermetallic compound. Grain growth up to 1∼2 μm in diameter occurred in the compact annealed at 1473 K for 36 ks.As-hot pressed compact was extremely brittle in spite of its noticeable high compressive strength (0.2% proof stress=2770 MPa).Improved combination of high strength (0.2% proof stress=1189 MPa) and good ductility (higher than 20% reduction in height) by the compression test at room temperature was attained by annealing the compact at 1473 K for 36 ks.The compressive deformation of the compact at 1173 K was presumed to proceed by superplastic flow.