We have studied on the problems and improvement on producing large casting with solid solution strengthened ferritic spheroidal graphite cast irons (hereafter Hi-Si). As the matrix of Hi-Si material becomes hardened with silico-ferrite, hardness, tensile strength and yield strength increase when silicon content increases. But elongation and impact value decrease conversely. If silicon content increases or if the cooling rate decreases due to heavy section, as silicon segregation progresses, the elongation and impact value are remarkably reduced. When increasing the graphite nodule count with optimum inoculation and setting chiller, the segregation of silicon decreases and then the mechanical properties are recovered. In addition, when Hi-Si reaches around 400℃, its elongation decreases largely, which is called 400℃ embrittlement. This high temperature embrittlement can be prevented with setting the ratio of Mg/P less than 1.5 and reducing the free Mg, because the grain boundary fracture occurs due to the free Mg not fixed as Mg₃P₂ at the grain boundary.

  Permanent mold casting specimens of (MnFeCoNi)₈₉Cu₁₁ alloy with 0 to 5.5 at% (1.19 mass%) carbon as a fcc-based high entropy alloy were prepared, and influence of solid solution strengthening with carbon on the alloy was discussed from evaluations of microstructure, crystal structure, hardness, and tensile properties at room temperature and liquid nitrogen temperature. In addition, heat treatment was performed to investigate the presence of supersaturated solid solution of carbon in the as cast specimens, and change in lattice constant was examined.

  The microstructures of the as cast samples showed a single-phase microstructure, and graphite and manganese oxide precipitates were observed in the carbon-containing samples after heat treatment. In the XRD patterns, small peaks similar to bcc other than fcc were detected. With increasing carbon content, only the peaks only from fcc were detected and the lattice constant increased. Hardness and room temperature strength increased with increasing carbon content, and ductility decreased. At liquid nitrogen temperature, strength was greater than at room temperature, and ductility decreased.

  High-entropy alloys (HEAs) are generally multicomponent solid-solution alloys with five or more elements that are close to the isoatomic composition ratios. HEAs are solid solution alloys whose entropy (the configuration entropy, ΔS_conf., the same as the entropy of mixing in ideal and regular solutions, ΔS_mix) is equal to or above 1.5R (R is the gas constant). HEAs are metallic materials that are designed based on “elemental multiplicity and heterogeneity,” rather than on “the characteristics of a single element”. From the perspective of mixing a wide variety of constituent elements at the atomic level, the melting and solidification techniques, in the other words “casting,” is the basic method used in the preparation of specimens and engineering products, therefore, HEAs can be recognized as a new type of casting metallic material. In this review, we introduce some examples of the research on and development of high-entropy casting alloys, especially with respect to public research and testing institutes in Japan.

  Metal additive manufacturing (AM) is regarded as a new manufacturing process suited for low-volume products with new design features. Powder bed fusion (PBF) is categorized as the major metal AM method characterized by layer-by-layer production and local fuse and solidification process performed by the scanning of focused heat sources. This rapid solidification attracts material scientists to create novel alloys that do not adapt to conventional cast and wrought processes. Authors applied PBF to form CoCrFeNiTiMo multiple principal element alloy (MPEA) with excellent mechanical and corrosion resistant properties. The pre-alloyed powder feedstock was obtained by vacuum gas atomizing. Laser powder bed fusion (LPBF) process inhibited the precipitation of intermetallics during solidification and improved the mechanical properties of the products. Solution heat treatment (ST) and aging heat treatment (AG) were applied to control the grain morphologies and nano-scale precipitates formed in the matrix. Improvements in chemical compositions and post heat treatments achieved a series of superior mechanical and corrosion resistant properties to those of Ni-based superalloy.