Dai Fu-Ping

Formation of ζ phase in Cu-Ge peritectic alloys

Rapid growth behavior of ζ phase has been investigated in the undercooling experiments of Cu-14%Ge, Cu-15%Ge, Cu-18.5%Ge and Cu-22%Ge alloys. Alloys of the four compositions obtain the maximum undercoolings of 202 K(0.17TL), 245 K(0.20TL), 223 K(0.20TL) and 176 K(0.17TL), respectively. As the content of Ge increases, the microstructural transition of “α(Cu) dendrite + ζ peritectic phase → ζ peritectic phase → ζ dendrite + (ɛ+ζ) eutectic” takes place in the alloy at small undercooling, while the microstructural transition of “fragmented α(Cu) dendrite + ζ peritectic phase → ζ peritectic phase → ζ dendrite + ɛ phase” happens in the alloy at large undercooling. EDS analysis of the Ge content in ζ peritectic phase indicates that undercooling enlarges the solid solubility of α dendrite, which leads to a decrease in the Ge content in ζ phase as undercooling increases. In the Cu-18.5%Ge alloy composed of ζ peritectic phase, the Ge content in ζ phase increases when undercooling increases, which is due to the restraint of the Ge enrichment on the grain boundaries by high undercooling effect.

Thermophysical properties of Ni-5%Sn alloy melt

The surface tension and specific heat of Ni-5%Sn alloy melt were measured by the oscillating drop method and the drop calorimetric method using electromagnetic levitation, respectively. The temperature coefficient of surface tension is 6.43×10−4 N·m−1K−1 within the temperature regime of 1464–1931 K. The enthalpy change was measured in the temperature range from 1461 to 1986 K, and the average specific heat was obtained as 43.03 J·mol−1K−1. Some other thermophysical properties, such as viscosity, solute diffusion coefficient, density, thermal diffusivity and thermal conductivity of this alloy melt, were derived based on the experimentally measured surface tension and specific heat. Using these thermophysical parameters, the relation between solute trapping and undercooling in rapidly solidified α-Ni was calculated, and the theoretical prediction shows a good agreement with experimental data.

Crystal Growth in Al72.9Ge27.1 Alloy Melt under Acoustic Levitation Conditions

The nonequilibrium solidification of liquid Al72.9Ge27.1 hypoeutectic alloy is accomplished by using single-axis acoustic levitation. A maximum undercooling of 112K (0.16TL) is obtained for the alloy melt at a cooling rate of 50 K/s. The primary (Al) phase displays a morphological transition from coarse dendrite under a normal conditions to equiaxed grain under acoustic levitation. In the (Al)+(Ge) eutectic, the (Ge) phase exhibits a conspicuous branched growth morphology. Both the primary (Al) dendrites and (Al)+(Ge) eutectics are well refined and the solute content of the primary (Al) phase is extended under acoustic levitation. The calculated and experimental results indicate that the solute trapping effect becomes more intensive with the enhancement of bulk undercooling.

Solute Distribution within Rapidly Grown Fe–Co Single Phase

Rapid growth of Fe–Co single phase is accomplished by rapid solidification in a drop tube. (Fe,Co) grains are refined with the decrease of alloy droplet diameters. Energy dispersive spectroscopy analysis indicates that microsegregation in (Fe,Co) single phase becomes lower with the reduction of droplet diameters. The experimental results with theoretical calculation reveal that the microsegregation is efficiently suppressed with the increase of undercooling. The free energies of intrinsic segregation for Fe-30 wt.%Co, Fe-40 wt.%Co and Fe-50 wt.%Co alloys are -47.17, -27.57 and -6.57 kJ/mol, respectively. The dependence of free energy of segregation on composition and undercooling has been deduced.