The orthorhombic phase in the Ti52Al30Nb18 alloy

Several phases may appear in the ternary Ti-Al-Nb, among others : cubic β, hexagonal α, and (recently identified) orthorhombic O. The special composition Ti52Al30Nb18 has lead to one-phased orthorhombic through adequate thermal treatment. The results of observations using X-ray diffraction, transmission and scanning electron microscopy, are shown. The untreated samples are mainly B2; the samples annealed at 1100 C or 900 C, and subsequently quenched, are many-phased α2+O+possibly B2; the long annealed (340 h; 900 C) samples are completely orthorhombic. This final state O seems to be reached, both through a massive transformation B2→O and an ordering α2→O. (orig.)