Microstructures and mechanical properties of TiB2 particle reinforced TiAl composites by plasma arc melting process

Using the plasma are melting process, TiB2 particle reinforced Ti-34 mass%Al composites were produced with varying volume fraction of TiB2 and size of starting TiB2 powders. The effects of the TiB2 fractions and distributions on the properties of the composites were investigated. The composite containing 5 vol.% TiB2 with fine powder of TiB2, 45-53 mu m in size, had the best tensile strength of 550 MPa, which was similar to 140 MPa greater than that of the unreinforced Ti-34 mass%Al. The degradation of the tensile strengths occurred in the composites containing more than 5 vol.% TiB2 and in the composites produced using coarse TiB2 powder, 90-150 mu m in size. This is believed to be attributed to higher population of touching TiB2 particles, which act as crack initiation and propagation sites, in these composites. The composites containing the volume fractions of TiB2 ranging from 5 to 7 vol.% exhibited greater proof strengths by 45-65 MPa at 1173 K and 55-70 MPa at 1273 K, and also had greater plastic elongations of 9-12% at these temperatures than the unreinforced Ti-34 mass%Al. (C) 1997 Elsevier Science S.A.