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A calorimetric study of the phase transformation of vanadium hydrides VH0.06 - VH0.77
1
ii.
ABSTRACTS
OF ARTICLES
TO APPEAR
EVIDENCE FOR THE FORMATION AND TRANSFOP~ATION OF ORDERED OXYGEN D(IV~INS IN NIOBIUM
Vol.
9~ No.
ii
13. A CALORIMETRIC STUDY OF ~ PHASE TRANSFORMATION OF VANADIUM HYDRIDES VH0.06 VH0.77
K.A. JONES & R.M. ROSE
H. ASANO, Y. ABE & M. HIRABAYASHI
Dept. of Materials Science, Massachusetts Institute of Technology, Cambridge, Mass.
The Research Institute for Iron, Steels & Other Metals, Tohoku University, Sendai 980 Japan.
(Received May 23, 1974) (Revised July 30, 1975) Evidence is presented that ordered oxygen domains are formed in niobium lattice at concentrations as low as 200 ppm (wt.%) when the crystal is annealed for a sufficiently long time in a sufficiently clean vacuum (oxygen partial pressure l0 -11 torr or less) to avoid the rapid pickup of much greater quantities of oxygen. It is also hypothesized that the ordered domains can transform martensitically into a suboxide phase in order to relieve the stresses generated by the interstitial oxygen atoms in the domains. Because the suboxide phase is formed at concentrations below the accepted solubility limit, it is suggested that at least one suboxide is stable and is not a metastable phase formed during the evolution of NbO from a supersaturated solid solution. There is evidence in the literature that supports our hypothesis, and it is shown that much of the evidence that disagrees with the hypothesis can be attributed to performing experiments in a highly oxidizing atmosphere (e.g., l0 -G torr). 12.
IN ACTA MET
]'HE EFFECT OF CRYSTAL ORIENTATION ON THE STRENGTH ANOMALY IN 8 CuZn AT AROUND 200°C Y. UMAKOSHI, M. YAMAGUCHI, Y. NAMBA & K. MURAKAMI
(Received July 25, 1975) The order-disorder transformation of hydrogen in vanadium hydrides has been studied by heat capacity measurements. It is shown that B-hydrides near V2H tmdergo the two-step disordering B1-B2-~.
The structure of B1-V2H
is isomorphic with B-V2D. The B2-form becomes stable in the hydrogen-rich region on the basis of the ordered structure VH. A partial phase diagram is proposed. The observed entropy change of transformation is well accounted for from the configurational and vibrational terms; the former is calculated by the structure models and the latter is estimated from neutron scattering data 14. NATURE DE LA TRANSFORMATION DESORDRE-ORDRE DANS LES ALLIAGES FER-COBALT INFLUENCE DE L'ADDITON DE VANADIUM P. GROSBRAS, J. P. EYMERY & P. MOINE Lab. de M6tallurgie Physique L.A. 131 du CNRS, 40 Ave. du Recteur Pineau - 86022 Poitiers - France (Received June 20, 1975)
Dans les alliages fer-cobalt, tremD6s de temp6ratures sup6rieures a la temp6rature Dept. of Metallurgy, Faculty of Engineer- critique, la restauration de l'6tat d'ordre s' ing, Osaka University, Osaka, Japan effectue par croissance de domaines ordonn6s et simultanement par croissance du degr6 d'ordre (Received July 2, 1975) grande distance ~ l'int6rieur de ces domaines. Nous montrons que cette mise en ordre n'ob6it The tenmerature and orientation dependpas aux r~gles classiques des transformations ence of yield stress and slip geometry in 8 par germination-croissance, mais qu'elle peut CuZn single crystals has been investigatsd s'inter~r6ter co,me ~tant une mise en ordre over the entire temperature range 50-300 C homog~ne. La transformation est ensuite suivie where th8 anomalous strength peak occurs. d'un stade de de coalescence des domaines antiAbove 50 C the critical resolved shear stress nhases. L'addition de vanadium acc61~re les for {110}<111> slip increased abnormally a~d reached a maximum neak in the range 150-250 C. cin6tiques de mise en ordre, ce qui peut s'expliquer par la pr6sence d'une forte sursaturaThe peak temperature was orientation sensitive. tion de lacunes dans l'alliage ternaire. It was found that the CRSS law for {ii0} slip system was not obeyed below the peak temperature, i.e. CRSS for this system increased with increasing the stress component on the {112} plane on which the slip direction was in the twinning sense. The strength anomaly was interpreted in terms of the mechanism involving the effect of orientation on the cross slip of screw dislocations onto the twinning {112} plane.
ii.
ABSTRACTS
OF ARTICLES
TO APPEAR
EVIDENCE FOR THE FORMATION AND TRANSFOP~ATION OF ORDERED OXYGEN D(IV~INS IN NIOBIUM
Vol.
9~ No.
ii
13. A CALORIMETRIC STUDY OF ~ PHASE TRANSFORMATION OF VANADIUM HYDRIDES VH0.06 VH0.77
K.A. JONES & R.M. ROSE
H. ASANO, Y. ABE & M. HIRABAYASHI
Dept. of Materials Science, Massachusetts Institute of Technology, Cambridge, Mass.
The Research Institute for Iron, Steels & Other Metals, Tohoku University, Sendai 980 Japan.
(Received May 23, 1974) (Revised July 30, 1975) Evidence is presented that ordered oxygen domains are formed in niobium lattice at concentrations as low as 200 ppm (wt.%) when the crystal is annealed for a sufficiently long time in a sufficiently clean vacuum (oxygen partial pressure l0 -11 torr or less) to avoid the rapid pickup of much greater quantities of oxygen. It is also hypothesized that the ordered domains can transform martensitically into a suboxide phase in order to relieve the stresses generated by the interstitial oxygen atoms in the domains. Because the suboxide phase is formed at concentrations below the accepted solubility limit, it is suggested that at least one suboxide is stable and is not a metastable phase formed during the evolution of NbO from a supersaturated solid solution. There is evidence in the literature that supports our hypothesis, and it is shown that much of the evidence that disagrees with the hypothesis can be attributed to performing experiments in a highly oxidizing atmosphere (e.g., l0 -G torr). 12.
IN ACTA MET
]'HE EFFECT OF CRYSTAL ORIENTATION ON THE STRENGTH ANOMALY IN 8 CuZn AT AROUND 200°C Y. UMAKOSHI, M. YAMAGUCHI, Y. NAMBA & K. MURAKAMI
(Received July 25, 1975) The order-disorder transformation of hydrogen in vanadium hydrides has been studied by heat capacity measurements. It is shown that B-hydrides near V2H tmdergo the two-step disordering B1-B2-~.
The structure of B1-V2H
is isomorphic with B-V2D. The B2-form becomes stable in the hydrogen-rich region on the basis of the ordered structure VH. A partial phase diagram is proposed. The observed entropy change of transformation is well accounted for from the configurational and vibrational terms; the former is calculated by the structure models and the latter is estimated from neutron scattering data 14. NATURE DE LA TRANSFORMATION DESORDRE-ORDRE DANS LES ALLIAGES FER-COBALT INFLUENCE DE L'ADDITON DE VANADIUM P. GROSBRAS, J. P. EYMERY & P. MOINE Lab. de M6tallurgie Physique L.A. 131 du CNRS, 40 Ave. du Recteur Pineau - 86022 Poitiers - France (Received June 20, 1975)
Dans les alliages fer-cobalt, tremD6s de temp6ratures sup6rieures a la temp6rature Dept. of Metallurgy, Faculty of Engineer- critique, la restauration de l'6tat d'ordre s' ing, Osaka University, Osaka, Japan effectue par croissance de domaines ordonn6s et simultanement par croissance du degr6 d'ordre (Received July 2, 1975) grande distance ~ l'int6rieur de ces domaines. Nous montrons que cette mise en ordre n'ob6it The tenmerature and orientation dependpas aux r~gles classiques des transformations ence of yield stress and slip geometry in 8 par germination-croissance, mais qu'elle peut CuZn single crystals has been investigatsd s'inter~r6ter co,me ~tant une mise en ordre over the entire temperature range 50-300 C homog~ne. La transformation est ensuite suivie where th8 anomalous strength peak occurs. d'un stade de de coalescence des domaines antiAbove 50 C the critical resolved shear stress nhases. L'addition de vanadium acc61~re les for {110}<111> slip increased abnormally a~d reached a maximum neak in the range 150-250 C. cin6tiques de mise en ordre, ce qui peut s'expliquer par la pr6sence d'une forte sursaturaThe peak temperature was orientation sensitive. tion de lacunes dans l'alliage ternaire. It was found that the CRSS law for {ii0}