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A senary ScYLaTiZrHf alloy was investigated for its ability to form a solid solution with an hcp structure, also known as a high-entropy alloy (HEA). X-ray diffraction analysis of the ScYLaTiZrHf alloy produced by arc-melting method confirmed this hcp structure. The microstructure of the ScYLaTiZrHf was composed of dual phases that were enriched in (Y, La) or (Ti, Zr, Hf), with Sc distributed evenly across both phases. The positive mixing enthalpy of 11.4 kJ mol−1 derived from Miedema's model, and the immiscible tendencies of its constituent binary phase diagrams help to explain the presence of dual phases in the ScYLaTiZrHf alloy. When formed into dual hcp solid solutions, the ScYLaTiZrHf alloy can be more accurately described as a multi-principal-element alloy (MPEA) rather than as a HEA, since the ScYLaTiZrHf alloy is a solid solution that is enthalpy-driven instead of entropy driven. The results also disclosed another procedure to stabilize solid solutions excepting for high-entropy scheme.

Pettifor map for binary compounds with 1:1 stoichiometry was utilized as an alloy design for high-entropy alloys (HEAs) with exact or near equi-atomicity in multicomponent systems. Experiments started with selecting GuGd binary compound with CsCl structure from Pettifor map, followed by its extensions by selecting the binary compounds with the same CsCl structure to CuDyGdTbY equi-atomic quinary alloy and to Cu4GdTbDyY and Ag4GdTbDyY quinary alloys and Cu2Ag2GdTbDyY senary alloy in sequence. X-ray diffraction revealed that CuDyGdTbY alloy was formed into a HEA with mixture of bcc, fcc and hcp structures, whereas the Cu2Ag2GdTbDyY HEA was a single CsCl phase. The results suggest a potential of Pettifor map for the development of HEAs by utilizing its information of crystallographic structures. The further analysis was performed for composition diagrams of multicomponent systems corresponding to simplices in a high dimensional space. The present results revealed that a strategy of equi-mole of compounds instead of conventional equi-atomicity also works for the development of HEAs.

Fatigue tests were carried out on ultra-high strength Co- and Fe-based bulk metallic glasses (BMGs), and the fatigue results were investigated together with the ones which had already been obtained from the fatigue tests on the super-high strength Ni-based BMG and the high strength Ti- and Cu-based BMGs. The test alloy rods with a diameter of 2 mm were prepared in [(Co 0.6 Fe 0.4 ) 0.75 B 0.2 Si 0.05 ] 96 Nb 4 , (Fe 0.5 Co 0.5 ) 72 B 20 Si 4 Nb 4 , Ti 41.5 Zr 2.5 Hf 5 Cu 42.5 Ni 7.5 Si 1 , Ni 60 Zr 20 Nb 15 Al 5 and Cu 60 Zr 30 Ti 10 at% systems by the copper mold casting method. The test specimens were machined to hourglass shape type with a minimum diameter of 0.9 mm. The specimens were tested at a stress ratio of 0.1 and a frequency of 10 Hz. The fatigue limits in the Co- and Fe-based BMGs exceeded 2 GPa, and those in the Ni- and Ti-based BMG surpassed about 1.5 GPa. Fatigue ratios in all BMGs were found to be about 0.5. Exceptionally, only the Ti-based BMG showed the high ratio, which may indicate the possibility that the BMG does not cause the fatigue phenomenon. In front of the fatigue crack initiation sites, fracture surfaces showed a radial ridges and valleys morphology as well as a striation like pattern. Unstable fracture surfaces consisted of facets with vein patterns. As the facet and vein pattern sizes increase, the strength and fatigue limit decreased, whereas the fracture toughness increased. Fracture surfaces in front of the fatigue cracks in strong BMGs showed the clear elastic wave traces.

In this paper, ion-implantation technique was applied to improve corrosion resistance of a newly developed La-based bulk metallic glass with poor corrosion resistance. It is found that the alloys after ion implantation with doses ranging 6 × 1016–1 × 1017 Nb/cm2 have a remarkable enhancement of corrosion resistance in chloride containing environments and acid solution with respect to the alloy without the surface treatment while the implanted alloys still have high glass forming ability. The improvement of corrosion resistance for the implanted alloys is attributed to the high passivating ability of the Nb-containing surface layer. These results obtained here clearly demonstrate that the ion-implantation technique could be a useful method to improve the corrosion resistance of bulk metallic glasses without losing glass forming ability of alloys.