This study was conducted to investigate the heterogeneous nucleation of spheroidal graphite on eutectic spheroidal graphite cast iron. A specimen, whose composition had been adjusted as a standard cast iron, was cast in a sand mold by graphite spheroidization and inoculation treatments. The specimen was then mirror-polished, and the matrix microstructure, spheroidal graphite, and nucleus were evaluated by SEM and TEM observations and EDS analysis.

  Spheroidal graphite nucleates during eutectic solidification and the various nuclei, which contain alloying elements such as Mg-Si-Al-N, Mg-Si-O, or Si-C, are observed in the graphite by SEM-EDS analysis. In TEM studies, the HAADF image shows an interfacial layer between the SiC nucleus and spherical graphite, which is recognized as the FeO of the NaCl-type structure, according to the EDS and diffraction pattern analyses. We therefore calculated the planer disregistry, which is the difference of crystalline lattice arrangement between FeO and graphite. On the matched (120) FeO // (0001) Gr planes, it is estimated at 1.51%. Generally, it is said that significant nucleation can occur when the planer disregistry is lower than 6%. Therefore, it is anticipated that FeO on SiC particle could possibly be a nucleus for graphite formation.

  Structure and mechanical properties of SiC fabricated by the reaction sintering method have been investigated by varying the blending composition of Si, C and SiC powders. First, specimens of the first-sintered body were formed at 473 K under a pressure of 20 MPa in a metallic mold and then sintered by heating at 973 K for 3.6 ks in Ar gas atmosphere. The first-sintered specimens were next put into a graphite mold to set Fe-75mass%Si alloy, which is often used as an inoculation agent, on the specimens and then held at 1693 K for 900 s in a vacuum furnace under a pressure of 10-1 Pa. Finally, SiC was successfully performed as a second-sintered body through the infiltration of Fe-75%Si alloy melt into the porous first-sintered body, which was followed by their mutual reaction. The microstructure and distributions of Fe and Si elements were observed using laser microscope and EPMA respectively. The hardness and fracture toughness were measured using a micro-Vickers hardness tester.

  The results indicate good infiltration of Fe-75%Si alloy melt into the first sintered body and that the second sintered body had a small amount of porosity. Iron carbides could not be found in the sintered structure but finely distributed iron silicides of FeSi and FeSi₂ were found. Furthermore, the fracture toughness of the body increased with increasing C content in the first sintered body. The mechanical properties were improved more than that of conventional sintered SiC when Fe-Si alloy was employed. The improvement in the properties is thought to be due to the uniform and fine distribution of FeSi, FeSi₂ and SiC in the matrix.

  Alloy designs of light-weight high and medium entropy alloys (LW-HEA and LW-MEA, respectively) are discussed in relation to solving the problem of the empirical alloy parameter, ΔH_mix, and the difficulties of the fabrication process. The ingots of newly-designed Al-Mg-Li-Ca LW-MEAs were fabricated by the conventional casting process via crucible melting without using a vacuum furnace, and cast under air atmosphere. The ΔH_mix parameter is the average value of the mixing enthalpy of ΔH_i-j between the two components, i-j, in multicomponent alloys, and the dispersion of ΔH_i-j cannot be evaluated. The parameter δ (ΔH_mix) was suggested for the evaluation of the dispersion of ΔH_i-j. The Al-Mg-Li-Ca LW-MEAs were designed based on empirical alloy parameters, including δ (ΔH_mix). The alloy ingots of equiatomic AlMgLiCa, non-equiatomic Al₂MgLiCa, and AlMgLiCa_0.3 were successfully obtained by the conventional casting process. The solidification microstructure of the ingots in the Al₂MgLiCa LW-MEA was investigated, with particular focus on the position dependences of the chemical composition, constituent phases, solidification microstructure, and hardness. The present study clarified that LW-HEAs and LW-MEAs containing Al, Mg, Li, and Ca can be obtained by the conventional casting process under air atmosphere, without specific expensive casting equipment.

  Unidirectional solidified Al-1.6, 1.9, 3.0% Fe alloy wires of 6 mm diameter were produced using the Ohno Continuous Casting (OCC) process at casting speeds of 1.67, 5.0, and 8.3 mm/s. The relationship between the solidification structure and mechanical properties of OCC wires was studied and compared with those of wires produced by cooled mold casting. The structure of the Al-3.0% Fe alloy OCC wire produced at a casting speed of 1.67 mm/s consisted of only eutectic structures. The other OCC wires consisted of α-aluminum dendrites aligned in the casting direction and eutectic structures. With the increase in casting speeds, the α-aluminum dendrite and eutectic structures of OCC wires became finer, and the tensile elongation of OCC wires increased simultaneously. The tensile strength and elongation of OCC wires produced at higher casting speeds (5.0 and 8.3 mm/s) were superior to those of the conventional wires. Al-3.0% Fe alloy OCC wire cast at 5.0 mm/s exhibited tensile elongation of 7% and tensile strength of 254 MPa, which was 1.4 times higher than that of conventional wires.

  Effects of reduced pressure and casting design on changes in mold filling due to coat permeability in the expendable pattern casting process of aluminum alloy were investigated experimentally. The effect of coat permeability on the melt velocity of molten aluminum alloy in the expendable pattern casting process was investigated experimentally under the conditions of the reduced pressure and top pouring. Aluminum alloy plates were cast under conditions of the reduced pressure and top pouring, using eight kinds of coats with different permeabilities. The melt velocity was measured and the results showed that the difference in the melt velocity was not large depending on the casting design. The application of the reduced pressure condition and use of high permeability coats led to higher melt velocities. However in the high coat permeability region, the melt velocity did not increase much, even when the coat permeability increased. The experimental values of the melt velocity were compared with the calculated values based on the mold filling model used in the previous study. When the coat permeability was low, the experimental values were in relatively good agreement with the calculated values. However in the high coat permeability region, the experimental values of the melt velocity were lower than the calculated values. By considering the heat transfer resistance of the liquid resin at the EPS surface to the mold filling model, even in the high coat permeability region, the experimental values of melt velocity showed more or less good correlation with the calculated values.