L’influence de la pression uniaxiale sur la croissance des couches NbNi₃ et NbNi a été étudiée à 1000°C en utilisant des couples de niobium pur et de nickel pur. La détermination des limites de phases et des profils de composition à l’intérieur des phases a été effectuée au microanalyseur à sonde électronique pour les échantillons recuits sous les pressions optimales. Enfin, les valeurs du coefficients d’interdiffusion dans les composés intermétalliques ont été déterminées par la méthode de Kidson avec quelques hypothèses préalables.
Les résultats obtenus sont résumés comme suit:
(1) La cinétique de croissance des couches NbNi₃ et NbNi est parabolique. A 1000°C, l’épaisseur de la couche NbNi₃ croît avec la pression tant que celle-ci est inférieure à 0, 6 kg/mm². L’épaisseur de la couche décroît lorsque la pression augmente au-delà de 0, 6 kg/mm². La microstructure de la zone de diffusion se modifie en fonction de la pression appliquée.
(2) Aux températures supérieures à 900°C les deux couches, NbNi₃ et NbNi croissent. Pour les températures inférieures à 840°C seule la couche NbNi₃ se forme. Les concentrations déterminées aux limites de phases correspondent au diagramme d’équilibre établi par Svenchnikov et col. pour des températures comprises entre 900 et 1030°C.
(3) Dans cet intervalle de température, la variation avec la température des valeurs du coefficient d’interdiffusion dans la phase β (NbNi₃) et γ (NbNi) est représentée par les équations:
\ ildeD_β=3,3×10⁻⁸exp(−17000⁄RT)cm²⁄s
\ ildeD_γ=3,0×10⁻⁵exp(−39000⁄RT)cm²⁄s

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The substructure of thin foil martensite formed below room temperature was studied in Fe–6Mn–1C, Fe–5.5Mn–1C, Fe–3Mn–3Cr–1C and Fe–8Cr–1C steels using transmission electron microscopy and diffraction. In the thin foils, as with bulk materials, the martensite habit plane in the above alloys was found to be near {225}. Even though constraints are expected to be relaxed for thin foils (two-dimensional transformations) the observed substructure was found to be highly complex. Substantial evidence for accommodation distortion in thin foils was obtained.
Several morphologies of {112}_b transformation twins, and {011}_b and {123}_b stacking faults were observed, in addition to dislocations. Upon examining the crystallography of {112}_b twins in some detail, it was found that the previously reported deviation of the twin traces from {112} could arise from an incorrect assessment of the twin plane trace; the present work shows the long traces lying in the specimen plane are not necessarily twin plane traces.
Two types of twin-stacking fault interactions were observed. In one case, stacking faults which appear to be inherited from the austenite place crystallographic restrictions on the {112} twins. Only those twin variants form whose twinning direction lies in the fault plane. In the other type of interaction, post-transformation accommodation distortion appears to occur by the activation of only those {110} and {123} fault variants which can penetrate both orientations of the {112} twins without suffering deviation.

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The present study was carried out in an attempt to measure the activities of manganese in the Mn-base molten alloys at a high temperature of 1300°C by using the TIE method.
At the moment the electrolyte comes in contact with both electrodes, the concentration cell for the Mn–Sb molten alloy may be represented as follows:
Mn(l)|MnF₂+CaF₂+MgF₂(l)|Mn−Sb(l).
The measurements for the Mn–Sb, Mn–Ni, Mn–Cu and Mn–Sn alloy systems revealed the following results:
(1) The activities for the Mn-base alloys tend to form horizontal portions in the two concentration ranges.
(2) The measured activities of the Mn–Cu and Mn–Sn systems have revealed remarkable discrepancies by the e.m.f. and vapor pressure methods.
(3) It is concluded that the activity measurements at 1300°C using the TIE method can be performed with a reasonable degree of accuracy.

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The present study was carried out in an attempt to examine what factors affect the activity curves of molten alloys showing the tendency to two-phase liquid separation.
(1) It was revealed that the tendency to two-phase liquid separations in two concentration ranges becomes larger as the electric resistance of the base-element increases.
(2) It was also found that the tendency to the phase separation is governed by the condition that the component of higher atomic number has a lower melting point.
(3) From the relationship of the volume of mixing with the two-liquid separation tendency, it was concluded that the inflection point of liquidus, maximum or minimum melting point in solid solution, maximum solid solubility limit, eutectic or monotectic point and compound are the important factors for solution behavior.

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A supplementary examination of the quenched structure of an Fe-9.70 wt%Al-1.46 wt%C alloy has been carried out by means of transmission electron microscopy and diffraction, in order to clarify whether the retained austenite is ordered in the Cu₃Au type, as reported in the previous paper (Trans. JIM, 12 (1971), 386), or it is composed of the κ carbide and the disordered γ austenite, as suggested by Oshima and Wayman (Met. Trans., 3 (1972), 2163). It is again verified that the retained austenite is basically ordered in the Cu₃Au type, and a peculiar shape, which has markedly been observed in fundamental spots from the retained austenite, is shown to be due to an accompaniment of diffuse satellites with the austenite reflection spots. The appearance of satellites suggests the existence of such a modulation as that carbon atoms are concentrated in distorted regions near the second type antiphase domain boundaries. Some of the concentrated regions with carbon atoms possibly form the perovskite-type κ carbide, as suggested, since superlattice reflections from the retained austenite exhibit two kinds of intensities. The c⁄a ratio of the tetragonal martensite in this alloy is determined to be 1.14 from a definite twinned diffraction pattern.

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