✍ Scribed by M Ron; M.M Stupel; B.Z Weiss
No coin nor oath required. For personal study only.
By means of h4ljssbauer spectroscopy, the w-phase was found to form as a result of the plastic deformation of an xTi(0.25 wt.% Fe) alloy in which the O-phase was present. The B-w and U-Y transitions were observed upon cold work, whereas the reverse I -+ B and Ed-+ 0 transitions were observed after aging. A combined effect, of a decrease in specific volume AV# < 0 associated with the r-8 transition and of a small displacement of atoms caused by the plastic deformation, was suggested as the mechanism for r-0 --+w transition. The formation of the w-phase explains the known fact that both the toughness and the ductility of rTi(Fe) decrease upon cold working.
The iron concentrations were found to be: C, = 0.22 wt.%, CB = 0.55 wt.",. C, = 0.95 wt.?& the latter increasing upon aging to C, = 2.35 wt.?& The decomposition of the rTit0.25 kt.% Fe) solid solution can be described by the spinodal decomposition mode. A change, upon cold work, in the isomeric shift of the line related to the z-phase was interpreted as having been caused by the accommodation of Fe atoms to lower energy positions in the compressive stress fields of dislocations. An appropriate line-broadening was also observed.
R&sum&-On a montri par spectroscopic Mossbauer que la phase or) se formait sous l'effet de la deformation pgastique dans un alliage Ti(0,25% Fe en poids) x, dans lequel la phase 6 etait presente. On observait les transitions B-W et B --+x par ecrouissage, alors que I'on observait les transitions inverses z + 0 et w-t 8 par neillissement. On a suggere. comme micanisme de la transition r -+ f3 --t w. l'effet combine dune diminution du volume spicifique AK, < 0 associee i la transition r-8 et d'un petit dtplacement des atomes produit par la deformation plastique. La formation de la phase w explique le fait bien connu que la resistance et la ductilite du Ti(Fe)r augmentent toutes ies deux au tours d'un Ccroissage.
On a trouve les concentrations en fer suivantes: C, = 0,220/,, C, = 0.5j00 et C, = 0.95% (en poids). cette demiere augmentant au tours du vieillissement jusqu'a 2.35%. On peut d&ire la decomposition de la solution solide Ti(O,25% Fe en poidsb comme une decomposition spinodale. On a interprite un changement du deplacement isomerique de la raie lice a la phase r comme db a l'accommodation d'atomes de fer dans des positions d'energie inferieure dans le champ de contraintes de compression des dislocations. On a egalement observe I'elargissement correspondant de la raie.
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