Obtention de la phase orthorhombique dans l'alliage Ti52Al30Nb18

Several phases may appear in the ternary Ti-Al-Nb, among others : cubic ß, 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