Takeshi Nagase

Fast electron irradiation can induce the solid-state amorphization (SSA) of many intermetallic compounds. The occurrence of SSA stimulated by fast electron irradiation was found in the Al_0.5TiZrPdCuNi high-entropy alloy (HEA). The relationship between the occurrence of SSA in intermetallic compounds under fast electron irradiation and the empirical alloy parameters for predicting the solid-solution-formation tendency in HEAs was discussed. The occurrence of SSA in intermetallic compounds was hardly predicted, only by the alloy parameters of <italic>δ</italic> or Δ<italic>H</italic>_mix, which have been widely used for predicting solid-solution formation in HEAs. All intermetallic compounds with Δ<italic>H</italic>_mix ≤ -35 kJ/mol and those with <italic>δ</italic> ≥ 12.5 exhibit the occurrence of SSA. This implies that the intermetallic compounds with a largely negative Δ<italic>H</italic>_mix value and a largely positive <italic>δ</italic> parameter are favorable for the occurrence of SSA.

The Ti–Ag alloy system is an important constituent of dental casting materials and metallic biomaterials with antibacterial functions. The binary Ti–Ag alloy system is characterized by flat liquidus lines with metastable liquid miscibility gaps in the phase diagram. The ternary Ti–Ag-based alloys with liquid phase separation (LPS) were designed based on the mixing enthalpy parameters, thermodynamic calculations using FactSage and Scientific Group Thermodata Europe (SGTE) database, and the predicted ground state diagrams constructed by the Materials Project. The LPS behavior in the ternary Ti–Ag–Nb alloy was investigated using the solidification microstructure analysis in arc-melted ingots and rapidly solidified melt-spun ribbons via trans-scale observations, combined with optical microscopy (OM), scanning electron microscopy (SEM) including electron probe micro analysis (EPMA), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM). The solidification microstructures depended on the solidification processing in ternary Ti–Ag–Nb alloys; macroscopic phase-separated structures were observed in the arc-melted ingots, whereas fine Ag globules embedded in the Ti-based matrix were observed in the melt-spun ribbons.

The liquid phase separation (LPS) behavior in Co-Cr-based high-entropy alloys (HEAs) is an important target for the development of Co-Cr-based HEAs for metallic biomaterials (BioHEAs). The solidification microstructure in Ag-Co-Cr-Fe-Mn-Ni-Ag, Co-Cr-Cu-Fe-Mn-Ni-Cu, and Co-Cr-Cu-Fe-Mn-Ni-B HEAs, which were designed as the combination of the equiatomic CoCrFeMnNi with Ag, Cu, and the interstitial element of B, was investigated as the fundamental research of LPS in Co-Cr-based HEAs. Ingots of equiatomic AgCoCrFeMnNi, equiatomic CoCrCuFeMnNi, non-equiatomic CoCrCuxFeMnNi (x = 2, 3), and CoCrCuxFeMnNiB0.2 (x = 1, 2, 3) with a small amount of B were fabricated using the arc-melting process. A macroscopic phase-separated structure was observed in the ingots of the equiatomic AgCoCrFeMnNi and CoCrCuxFeMnNiB0.2 (x = 2, 3) HEAs. The addition of a small amount of B enhanced the LPS tendency in the Co-Cr-Fe-Mn-Ni-Cu HEAs. The LPS behavior was discussed through the heat of mixing and computer coupling of phase diagrams and thermochemistry (CALPHAD).