Metastable monotectic phase separation in Co–Cu alloys

The liquid phase separation behaviour of metastable monotectic Co–Cu alloys was investigated as a function of cooling rate using a 6.5 m drop-tube facility. A range of liquid phase separated morphologies were observed including stable two-layer core–shell, evolving core–shell and dendritic structures. It was found that in the core–shell structures the core was always in the higher melting point (Co-rich) phase, irrespective of the core and shell volume fraction. In Cu–50 at% Co alloy, high cooling rates were observed to yield two episodes of liquid phase separation, corresponding to binodal, followed by spinodal decomposition. The resulting structure comprised a core–shell structure in which the Co-rich core contained a very fine dispersion of Cu-rich particles with a Cu-rich shell which may, or may not, contain a similar dispersion of Co-rich particles

Surface tension and viscosity of the Ni-based superalloys LEK94 and CMSX-10 measured by the Oscillating Drop Method on board a parabolic flight

The surface tension and viscosity of the Ni-based superalloys LEK94 and CMSX-10 were measured by the oscillating drop method in a containerless electromagnetic processing device on board a parabolic flight airplane. Surface oscillations were recorded by 150 and 200 Hz Frame rate digital cameras positioned in two perpendicular directions and by the inductive coupling between the oscillating sample surface and the oscillating circuit of the radio frequency heating and positioning generator. The surface tension as a function of temperature of LEK94 and CMSX-10 was obtained as r(T) = 1.73 � 4.51 9 10�4 [T—1656 K (1383 �C)] Nm�1 and r(T) = 1.71 � 5.80 9 10�4 [(T—1683 K (1410 �C)] Nm�1, respectively. The viscosity at the liquidus temperatures as 9.8 and 7.8 mPa.s, respectively. In addition, some basic thermophysical properties such as solidus and liquidus temperatures, densities at room temperature, and thermal expansion in the solid phase are reported

Surface Properties of Liquid Al-Ni Alloys: Experiments Vs Theory

The present study is an overview of the surface properties of liquid Al-Ni alloys, which are of great importance for the design and development of new Al-Ni and Ni-based industrial alloys, widely used as functional and structural materials. The solidification and thus, the microstructural evolution are directly dependent on the interface/surface properties of metallic melts. Therefore, numerical simulation of microstructure evolution requires reliable property data as input to such models. Taking into account the experimental difficulties related to a high reactivity of liquid Al-Ni alloys and the effects of impurities on their surface properties, the surface tension over the whole concentration range has been determined in the frameworks of three international research projects. Namely, the surface tension measurements have been carried out by both traditional container-based and as an alternative, containerless methods within the ESA-MAP ThermoProp and ESA-MAP Thermolab Projects and also under the EU FP6- IMPRESS Project. The obtained datasets were analysed and subsequently compared with the model predicted values as well as with the literature data. A strong exothermic mixing characterises the Al-Ni system and the presence of a few intermetallic compounds in the solid state leads to the formation of short range ordered elements or complexes in the liquid phase, at least near the melting temperature, which significantly affects the surface properties of alloy melts. Aiming to estimate the effects of short range ordering on these properties, the Compound Formation Model (CFM) and the Quasi Chemical Approximation (QCA) for regular solution were applied