Phase Equilibria in the Fe-Mo-Ti Ternary System at 1173 K (900 °C) and 1023 K (750 °C)

Alloys with fine-scale eutectic microstructures comprising Ti-based A2 and TiFe B2 phases have been shown to have excellent mechanical properties. In this study, the potential of alloys with further refined A2-B2 microstructures formed through solid-state precipitation has been explored by analyzing a series of six alloys within the Fe-Mo-Ti ternary system. Partial isothermal sections of this system at 1173 K (900 °C) and 1023 K (750 °C) were constructed, from which the ternary solubility limits of the A2 (Ti, Mo), B2 TiFe, D8$_5$ Fe$_7$Mo$_6$ , and C14 Fe$_2$Ti phases were determined. With these data, the change in solubility of Fe in the A2 phase with temperature, which provides the driving force for precipitation of B2 TiFe, was determined and used to predict the maximum potential volume fraction of B2 TiFe precipitates that may be formed in an A2 (Ti, Mo) matrix.Rolls-Royce/EPSRC Strategic Partnership (EP/H022309/1, EP/H500375/1, and EP/M005607/1

Determination of the phase diagram of the MoCo system using diffusion couples

The phase diagram of the MoCo system between 800 and 1300°C has been investigated by microscopy, X-ray diffraction and electron-probe micro-analysis, using diffusion couples consisting of the pure metals or their alloys. The μ (Mo6Co7) phase has a constant homogeneity range of 7 at.% (51.5-58.5 at.% Co). The θ phase (discovered by Quinn and Hume-Rothery2) is stable between 1018 and 1200°C. Its Mo-rich boundary is found at 81 at.% Co. The Co-rich boundary shifts from 83 at.% Co at 1050°C to 81 at.% Co at 1200°C. The K phase found up to 1000°C has a homogeneity range of 75-76.5 at.% Co. The σ phase is found at and above 1000°C at a composition of about 36 at.% Co. The σ layers were too thin for an accurate determination of the phase boundary concentrations. Co can dissolve 19.5 at.% Mo, and Mo only 1.5 at.% Co at 1300°C

Determination of the phase diagram of the molybdenum-nickel system using diffusion couples and equilibrated alloys

The phase diagram of the Mo-Ni system at 800-1295 Deg was studied by microscopy and electron-probe microanal. Equilibrated 2-phase Mo-Ni alloys contg. 7.9-83.0 at. % Ni and diffusion couples consisting of pure metals or their alloys were used to compare both methods. In both cases identical phase diagrams were found, which differ in details from those given by R. E. W. Casselton and W. Hume-Rothery (1964). The homogeneity range of the d-MoNi phase extends from 47.8-51.8 at. % Ni. The soly. limit of Mo in Ni is 28 at. % Mo at 1318 Deg and decreases with temp. by 2.3 at. %/100 Deg. The homogeneity region of the g-MoNi3 phase exists at compns. >75 at. % Ni. Exact boundary concns. are absent also for the b-MoNi4 phase. The soly. of Ni in Mo is .apprx.2 at. % Ni at 1295 Deg. [on SciFinder (R)

The influence of carbon on the layer formation during Interdiffusion of Mo and Fe

Experiments have been carried out between 800 and 1300° C with diffusion couples prepared from iron containing 0·09 wt.-% carbon and pure molybdenum. At all annealing temperatures an η carbide, Mo 3 Fe 3 C, is formed with a very narrow homogeneity range, viz., ∼ 3 at.-% Fe. The formation of the carbide is very fast, but stops at a certain layer thickness. During heating at temperatures from 800 to 1000° C a two-phase layer is also formed, probably consisting of Mo 2 C and the η carbide. The solid-solution layer of Mo in Fe grows parabolically above 1000° C. Below 1000° C it reaches the equilibrium concentration only after the disappearance of the two-phase layer. The diffusion behaviour in this system is compared with the results obtained in the Mo–Ni–C system

The use of standards in the quantitative electron probe micro analysis of binary metal systems

For the binary metal systems investigated, the Ziebold-Ogilvie relation has been found to be valid. It has been shown that polyphase alloys may be used as calibration standards if some specific conditions are fulfilled. In connection with a long-term instability of the microprobe apparatus, the Ziebold-Ogilvie constant of the calibration curve may vary with time. There is no reason for assuming that this instability is restricted to the particular instrument used. Therefore it is recommended that one or two standard alloys be used together with the pure reference metal to determine that constant every time concentration measurements have to be performed. The effect of the long-term instability can hardly be taken into account in the usual theoretically-based correction procedures.Für die hier untersuchten binären Metallsysteme hat sich die von Ziebold und Ogilvie angegebene Beziehung als gültig erwiesen. Wie sich zeigen ließ, kann man mehrphasige Legierungen als Eichstandards verwenden, wenn gewisse Voraussetzungen erfüllt sind. In Zusammenhang mit der Langzeit-Instabilität der Mikrosonde kann es sein, daß sich die Konstante der Ziebold-Ogilvie-Kurve mit der Zeit ändert. Es besteht kein Grund zur Annahme, daß diese Instabilität auf das eine benutzte Instrument beschränkt ist. Daher wird empfohlen, ein oder zwei Standardlegierungen zusammen mit dem reinen Bezugsmetall zu verwenden, um jederzeit die Gewähr für einwandfreie Meßergebnisse zu haben. Die Auswirkung der Langzeit-Instabilität kann bei dem üblichen, theoretisch ermittelten Korrekturverfahren nur schwer in Rechnung gestellt werden. Fulltext Previe