Volume 88, Issue 7

Characterisation of the microstructure of the single crystalline nickel-base superalloy SC16 by small angle neutron scattering (SANS) is presented. Specimens heat treated to produce γ′ precipitates of different sizes were investigated. The two-dimensional SANS scattering patterns exhibited isotropic or anisotropic character depending on the heat treatment. Data analysis was carried out using a modeling method specially developed for γ′ precipitates in superalloys with high γ′ volume fractions. A diffraction peak indicating an influence of interparticle interference was observed in one case allowing to calculate the average distance between precipitates. An estimate of the γ′ volume fraction after different heat treatments was made.

The excess enthalpies of liquid alloys in the ternary system Ge-Pb-Te were determined at 1210 K in a heat flow calorimeter for five sections Ge y Pb 1− y -Te with y = 0.2,0.4, 0.5, 0.6 and 0.8 and at 1153 K for Ge 0 . 5 Pb 0 . 5 –Te. The enthalpy surface in the ternary system is determined by a valley of exothermic minima, stretching from an exothermic minimum at the composition GeTe to one at the composition PbTe in the respective binaries. The excess enthalpies in the limiting metallic binary were adapted with the Redlich-Kister formalism. For the description of the thermodynamic functions in the ternary system the equation of Bonnier was taken using ternary coefficients. The calculated curves are in good agreement with the experimental data.

Phase equilibria were established in the ternary system Mn–Y–Zr for an isothermal section at 800 °C by use of X-ray powder diffraction, light optical microscopy and quantitative EPMA. No ternary compounds were observed. Mutual solid solubilities among the binary phases were found to be generally less than ~ 2 at.%. Solubility of Mn, Y in αZr at 800 °C was 2.1 at.% Mn and 2.9 at.% Y, whereas no Mn dissolves in α Y. A reinvestigation of the binary solid solubility limits of Mn 2 Zr 1− x at 800 °C by quantitative EPMA and X-ray powder full profile analyses revealed a smaller homogeneous region, Mn 2 Zr 1− x , 0 ≤ x ≤ 0.20, than previously reported in literature. There is little solubility of Y in stoichiometric Mn 2 Zr and maximum solubility of Mn, Zr in αY was determined from as cast alloys to be 1.8 at.% Mn and 2.4 at.% Zr. Based on this experimental findings and the literature data relevant to the binary systems a thermodynamic calculation of the ternary system was attempted, requesting a significantly higher heat of formation of Mn 2 Zr than previously reported. A nearly pseudobinary section was experimentally established for the join Y–Mn 2 Zr with a maximum eutectic at 1072 ± 10°C at 57 at.% Y (calculated at 1064 °C and 58 % Y). Three ternary eutectics were defined: L⇔Mn 2 Zr + Mn 2 Y + Mn 23 Y 6 at 1090 ± 10 °C at a composition of Mn 75 Y 23 Zr 2 (calculated at 1087 °C and at Mn 72 Y 26 Zr 2 ), L ⇔ (αY) + Mn 2 Y + Mn 2 Zr at 870 ± 10 °C at a composition of Mn 40 Y 57 Zr 3 (calculated at 883 ° C and at Mn 36 Y 63 Zr 1 ) and L ⇔ (αY)+ (βZr) + Mn 2 Zr at 1054 ± 10 °C at a composition of Mn 26 Y 15 Zr 59 (calculated at Mn 24 Y 21 Zr 55 and at 992 °C).

The drawback of overthicknesses of coatings when galvanizing silicon steels may be overcome by adding titanium to the zinc bath. In order to understand reactivities between substrates and the alloyed zinc bath, the ternary phase system Fe-Zn-Ti at 450 °C was investigated using diffusion experiments. Three kinds of diffusion couples were used (solid/solid, solid/liquid and solid/vapour under controlled pressure) to describe the whole isothermal section at 450 °C. The solid–liquid reaction accurately reveals the zinc rich corner of the diagram in connection with galvanizing. The analysis of the different phases in each coating allows to determine Ti solubilities in the Fe–Zn intermetallic compounds and to new equilibria in the Fe-Zn-Ti system at 450 °C. Moreover, we show that the diagram obtained, characterized by a huge Γ 2 domain is metastable. The stable diagram, obtained with long time experiments is characterized by a more restricted Γ 2 solid solution which extends from the Γ 2 – FeZn 4 binary compound to the Γ 2 – TiFe 2 Zn 22 ternary dross.

A consistent thermodynamic data set for the V–N system is obtained by a computer-aided least squares method applied to all of the experimental phase diagram and thermodynamic data available from the literature. The sublattice model V 1 (N, Va) a is used to model the phases: fcc ( a = 1), bcc (a = 3), and hcp (a = 0.5). The liquid phase is described by the Redlich-Kister formula, and the gas phase is treated as an ideal gas. Special attention is paid to the modeling of the fcc phase with its exceptional bulk of experimental data. This phase is first analyzed by an ideal solution, then by a regular, and finally by a subregular interaction in the nitrogen sublattice. The other solution phases are analyzed with similar modeling procedures. This step-by-step analysis procedure permits insight into reliable estimations for the parameters at each of the higher level models. Comparisons between the calculated and measured phase diagram and thermodynamic quantities show that most of the experimental information is satisfactorily accounted for by the thermodynamic calculation. Inconsistent experimental information is identified and ruled out. The thermo-dynamic property of the fcc phase in the V–N system is compared with those in the Cr–N and Ti–N systems and related to the Neumann-Kopp’s rule.

Die Schmelzfläche, das Reaktionsschema der Phasengleichgewichte mit Beteiligung der Schmelze, isotherme Schnitte bei 1100 und 1050°C und 13 Temperatur-KonZentration-Schnitte wurden für das Teilsystem Al-AlCo-AlNi ausgearbeitet. Als Untersuchungsmethoden wurden die Differentialthermoanalyse, die magnetothermische Analyse, lichtmikroskopische Metallographie und Röntgenbeugung herangezogen. Elektronenmikroskopische Bilder anderer Untersuchungen an identischen Proben bestätigten die Phasenidentifikation. 9 Vierphasenebenen mit Beteiligung der Schmelze wurden gefunden, und zwei Vierphasenreaktionen im festen Zustand wurden in das Diagramm aufgenommen.

Al–Mg alloys containing Mg in the range between 0.5 and 5 % were cold rolled to 95 % reduction in thickness and the effect of Mg on the formation of shear bands was investigated metallographically in detail. It was found that shear banding was strongly influenced by the Mg concentration. At medium rolling reductions, shear bands were observed only in specimens containing Mg above a critical concentration of about 2.5 %. In specimens with lower Mg concentrations, shear bands could be observed only after 95 % cold rolling. Detailed investigations on Al-5 % Mg alloys revealed that the mechanism of the formation of shear bands in polycrystals is different from that proposed in the case of single crystals. In polycrystals, nucleation of shear bands occurred preferentially at grain boundary offsets. Such grain boundary offsets seem to be formed since normal deformation to accomodate compatibility conditions at grain boundaries is strongly suppressed by the interactions between dislocations and Mg atoms.

In order to investigate the effect of Mg in the development of the rolling and recrystallization textures in Al, Al–Mg alloys containing Mg in the range between 0.5 and 5 % were cold rolled 95 % and subsequently annealed at 300 °C up to complete recrystallization. It was found that, in the rolling texture, the addition of Mg above 3 % significantly reduced the orientations in the range between {112}〈111〉 and {123}〈634〉 lying along the β fiber. This was attributed to frequent shear banding, which was enhanced by Mg atoms in grains of these orientations. Intensities of the {110}〈112〉 rolling texture component were not affected by the Mg addition. In the recrystallization textures, the {123}〈634〉 orientation was reduced by the addition of Mg. The {100}〈001〉 orientation, on the other hand, increased remarkably with the increasing amount of Mg addition. At the Mg content above 3 %, however, the {100}〈001〉 orientation decreased appreciably with the increase in Mg content. This decrease in the {100}〈001〉 orientation seems to be correlated with the decrease in the β fiber rolling texture component positioning between {112}〈111〉 and {123}〈634〉.

The susceptibility to disbonding which occurs at the interface of 2.25 Cr-1 Mo steel overlay welded with austenitic stainless steel can be drastically improved by modified postweld heat treatments (Mod PWHT, heat treatment at 963 K for 25.2 ks followed by annealing at 8l3 K for 54 ks and subsequent air cooling (after overlay welding). Severe disbonding tests under hydrogen atmosphere have revealed that the Mod PWHT steel produced hardly cracks at the interface; whereas, the conventional PWHT steel developed large cracks. This was due to the fact that the Mod PWHT suppresses the appearance of high carbon fresh martensite, which increases the susceptibility to disbonding significantly.

The effect of vanadium addition on disbonding of 2.25Cr–1Mo steel overlay welded with austenitic stainless steel has been studied with the aim of decreasing the susceptibility to disbonding at the interface of the base and weld metals. Vanadium added 2.25Cr– 1Mo steel overlay welded did not produce disbonding cracks at all, while vanadium free 2.25Cr–lMo steel overlay welded lead to large disbonding cracks. This is attributed to the fact that low carbon martensite was formed on the weld metal side of the interface instead of high carbon martensite which increased the susceptibility to disbonding. This is due to the fact that vanadium carbide precipitation reduced carbon diffusion from the base metal to the weld metal.