Phase equilibria between 750 °C and 1100 °C in the Co-rich portion of the Co-Al-W ternary system are investigated via isothermal annealing of five ternary alloy compositions. At temperatures of 900 °C and below, the phase diagram is dominated by a three-phase tie-triangle between γ, D0, and B2. The 1000 °C section contains two three-phase tie-triangles, γ+D0+μ and γ+B2+μ; while only one, γ+B2+μ, exists at 1100 °C. Results at 950 °C suggest that it is possible that γ' is in equilibrium, with four out of five compositions exhibiting microstructures supporting its thermodynamic stability, and the fifth composition containing only a very small amount of a fourth phase indicating its possible instability. However, if true, the temperature range of γ' stability would be quite small, and it is more likely that the kinetics of γ' dissolution are the cause of its persistence at 950 °C. At 850 °C, γ' is observed to dissolve more rapidly than at 900 °C where dissolution exceeds 8000 h. A time-temperature-transformation diagram constructed from the combined results exhibits a classic nose-shape indicative of the tradeoff between thermodynamics and kinetics. This further supports a small driving force as the reason for the persistence of γ' in the microstructures of Co-Al-W alloys at 900 °C and 950 °C. The measured equilibrium phase compositions and five corresponding isothermal sections of the phase diagram will provide essential data for constructing a new thermodynamic description of ternary Co-Al-W.

Various topics taken from the author's research portfolio that involve multicomponent alloy solidification are reviewed. Topics include: ternary eutectic solidification and Scheil-Gulliver paths in ternary systems. A case study of the solidification of commercial 2219 aluminum alloy is described. Also described are modifications of the Scheil-Gulliver analysis to treat dendrite tip kinetics and solid diffusion for multicomponent alloys.

The partial and integral enthalpies of mixing of liquid ternary Ni-Sn-Zn alloys were determined. The system was investigated along two sections / ≈ 1:9, / ≈ 1:6 at 1073 K and along two sections / ≈ 9:1, / ≈ 4:1 at 873 K. The integral enthalpy of mixing at each temperature is described using the Redlich-Kister-Muggianu model for substitutional ternary solutions. In addition, the experimental results were compared with data calculated according to the Toop extrapolation model. The minimum integral enthalpy of approx. -20000 J mol corresponds to the minimum in the constituent binary Ni-Sn system, the maximum of approx. 3000 J mol is equal to the maximum in the binary Sn-Zn system.

Standard enthalpies of formation of ternary phases in the Cu-Ni-Sn system were determined along sections at 25, 41 and 45.5 at.% Sn applying tin solution drop calorimetry. Generally, the interaction of Ni with Sn is much stronger than that of Cu with Sn. Along all sections the enthalpy of formation changes almost linearly with the mutual substitution of Cu and Ni within the respective homogeneity ranges. Thus no additional ternary interaction promoting the formation of further Cu-Ni-Sn phases can be assumed. The results are discussed and compared with literature values relevant to this system.

The electrical conductivity of nanocomposite Sn-3.0Ag-0.5Cu alloys with two different weight percentages of Ni nanoparticles (1.0 and 2.0 wt.%) was measured over a wide temperature range. The samples were produced using a cold pressing method: Sn-3.0Ag-0.5Cu powder and Ni nanopowder were mechanically mixed and pressed into 8 mm diameter rods. Ni nanoparticles were synthesized via a chemical reduction method and characterized by a core/shell structure. Temperature dependencies of the electrical conductivity revealed a hysteresis between the heating and cooling curves in a wide temperature range above the melting temperature. This fact is connected with structure transformations accompanied by a dissolution of Ni nanoparticles, which should be retarded due to an oxide/hydroxide shell on the surface of the nanoparticles. A microstructure analysis of the samples in the solid state showed a fine distribution of intermetallic compounds in the Sn-based matrix. The Ni atoms substituted for Cu atoms in the CuSn compound forming a (Cu,Ni)Sn phase.

The binary bismuth-rhodium (Bi-Rh) phase diagram was reinvestigated from 23 to 60 at.% Rh with focus on the BiRh phase, applying powder-x-ray diffraction (XRD), high temperature powder-XRD, differential thermal analyses and scanning electron microscopy. The phase boundaries of the BiRh phase at 750 °C and the temperature of its peritectic decomposition were refined. In addition, the existence of the two phases BiRh and BiRh (in two modifications depending on temperature) could be confirmed. Most of the reaction temperatures reported in the literature could be verified within a range of about ± 10 °C. Nevertheless, a few temperatures had to be revised, such as those of the peritectic reactions L + Rh   BiRh at 979 °C and L + BiRh   -BiRh at 785 °C. No evidence could be found for the presence of a stable BiRh phase in well annealed samples; from the present results it must be concluded that BiRh is actually metastable. On the other hand, a new orthorhombic phase BiRh was discovered which crystallizes in the MnP structure type (Pmna). It was found that the temperatures of the transition between the low-temperature modification -BiRh and its high-temperature form -BiRh depend considerably on the presence or absence of metastable BiRh and stable BiRh, respectively.