Microstructure control and compressive strength of 10 mol% Ti-bearing Nb3Al/Nb-ss in-situ composites

10 mol% Ti-bearing Nb3Al(delta)/Nb-ss(beta) in-situ composites with fine an d homogeneous microstructures have been successfully fabricated by heat tre atment or thermo-mechanical processing of cast ingots. Homogenization treat ment at an extremely high-temperature of 2173 K for 1 h, which produces a B 2 single phase, plays an important role for obtaining homogeneous two-phase microstructures. delta-rich alloys annealed at 1473 K after homogenization form delta/beta colonies with unidirectionally dispersed beta filaments in delta grains. On the other hand, microstructures of delta-rich alloys isot hermally forged and annealed become fine and equiaxed. Compression tests in dicate that increase in volume content of beta phase enables plastic deform ation at lower temperatures, although it decreases yield strength at 1473 K . Nevertheless some of Nb-x mol%Al-10mol%Ti alloys, e.g. Nb-13 mol%Al-10 mo l%Ti including about 50 vol% beta, possess superior strength in the range f rom room temperature to 1473 K, making them more applicable as a structural material than conventional Ni-based superalloys. (C) 1999 Elsevier Science Ltd. All rights reserved.