EFFECTS OF TIN ADDITION ON MICROSTRUCTURE AND CRYSTAL-STRUCTURE OF TIAL-BASE ALLOYS

Microstructures, mechanical properties, and crystal structures of Ti-( 50-52)mol%Al alloys containing Sn up to 5mol% as a third element have been studied by using an optical microscope, a transmission electron m icroscope, a micro-Vickers hardness tester, and an X-ray diffractomete r. Results obtained are as follows: The amount of Ti3Al (alpha2) phase existing in as-cast alloys was decreased by addition of Sn and it dis appeared by an annealing for 604.8ks at 1273K. But the Ti3Sn phase for med in the cast alloys containings Sn did not disappear by the anneali ng. The Ti6Sn5 phase was formed in the Ti-50mol%Al-5mol%Sn alloy by th e annealing. Both of the lattice parameter c and the axial ratio c/a o f the Ll0-type Al-rich intermetallic compound TiAl (gamma phase) incre ased with increasing Sn content. Tin atoms in the gamma phase occupy p redominantly in the Ti site. The amount of mutual exchanges of Ti and Al atoms in lattice sites increased with increasing Sn content in the gamma phase.