Synthesis of TiAl-(TiB₂+Ti₂AlC)Composites Using Combustion Reaction Processing, Following Arc-melting

Abstract

To enhance the negligible low-temperature strength and ductility and low high-temperature strength of titanium aluminides, TiAl-(TiB₂+Ti₂A1C) composites were made by the combustion reaction processing using Ti, Al, and B₄C powders, and homogenized by arc melting. The alloy composition included Ti_52.2A1_45.6(B₄C)_{2, 2} in at.%. The resulting composites had about 14 vol.% (TiB₂+Ti₂AIC) in the matrix TiAl with a lamellar structure of Ti₃Al. In the homogenized specimens, such lamellar structures were not observed, therefore, the matrix after the homogenizing treatment consisted predominantly of the TiAl phase which is expected from the Ti-Al equilibrium phase diagram. On the other hand, smaller particles were visible in the matrix, and appeared to form in place of solutionizing lamellae. These particles have also identified as a Ti₂A1C phase with an average particle size of about 100-200 run. This suggested that carbon atoms in the matrix, probably in the Ti₃Al phase, formed carbide Ti₂Al particles when the lamellar Ti₃Al phase was disappeared during the homogenization treatment. It was found that the composite material has a high strength at both ambient and elevated (at 1173 K) temperatures ; about 900 and 500 MEN, respectively, and ambient-temperature ductility as large as 0.8% was obtained in bending.