Application of PLD-Fabricated Thick-Film Permanent Magnets

Isotropic Nd-Fe-B thick-film magnets have been prepared using a pulsed laser deposition (PLD) method with the control of laser energy density (LED) followed by post-annealing. The characteristics of the method are a high deposition rate up to several tens of microns per hour together with a reliability of magnetic properties due to the good transfer of composition from an Nd-Fe-B target to a film. Several micro-machines comprising the isotropic Nd-Fe-B films such as a miniaturized DC motor and a swimming machine in liquid were demonstrated. Furthermore, the deposition of isotropic Nd (or Pr)-Fe-B thick-film magnets on a Si or glass substrate was carried out to apply the films to various micro-electro-mechanical-systems (MEMS). We also introduced the preparation of isotropic Sm-Co, Fe-Pt, and nano-composite Nd-Fe-B+α-Fe film magnets synthesized using the PLD

Development of Co-Cr-Mo-Fe-Mn-W and Co-Cr-Mo-Fe-Mn-W-Ag high-entropy alloys based on Co-Cr-Mo alloys

Co-Cr and Co-Cr-Mo-based alloys are commercially used in the industry especially for high wear resistance and superior chemical and corrosion performance in hostile environments. These alloys were widely recognized as the important metallic biomaterials. Here, the first development of Co-Cr-Mo-Fe-Mn-W and Co-Cr-Mo-Fe-Mn-W-Ag high-entropy alloys (HEAs) based on Co-Cr-Mo metallic biomaterials is reported. Ingots of six-component Co₂.₆Cr₁.₂Mo₀.₂FeMnW₀.₂₇ (Co₄₁.₅Cr₁₉.₁Mo₃.₂Fe₁₆Mn₁₆W₄.₃, at%) HEAs with a minor σ phase and of seven-component Co₄.₂₂₅Cr₁.₉₅Mo₀.₂FeMnW₀.₂Ag₀.₅ (Co₄₆.₆Cr₂₁.₅Mo₂.₂Fe₁₁Mn₁₁W₂.₂Ag₅.₅, at%) and Co₂.₆Cr₁.₂Mo₀.₁FeMnW₀.₁Ag₀.₁₈ (Co₄₂.₁Cr₁₉.₄Mo₁.₆Fe₁₆.₂Mn₁₆.₂W₁.₆Ag₂.₉, at%) HEAs without an · phase were fabricated. The alloy was designed by a taxonomy of HEAs based on the periodic table, a treelike diagram, predicted phase diagrams constructed by Materials Project, and empirical alloy parameters for HEAs. The · phase formation prevented the formation of solid solutions in Co-Cr-Mo-based HEAs without a Ni element. The · phase formation in as-cast ingots was discussed based on the composition dependence and valence electron concentration theory.Nagase T., Todai M., Nakano T. Development of Co-Cr-Mo-Fe-Mn-W and Co-Cr-Mo-Fe-Mn-W-Ag high-entropy alloys based on Co-Cr-Mo alloys. Materials Transactions 61, 567 (2020); https://doi.org/10.2320/matertrans.MT-MK2019002

Liquid phase separation in Ag-Co-Cr-Fe-Mn-Ni, Co Cr-Cu-Fe-Mn-Ni and Co-Cr-Cu-Fe-Mn-Ni-B high entropy alloys for biomedical application

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).Nagase T., Todai M., Nakano T.. Liquid phase separation in Ag-Co-Cr-Fe-Mn-Ni, Co Cr-Cu-Fe-Mn-Ni and Co-Cr-Cu-Fe-Mn-Ni-B high entropy alloys for biomedical application. Crystals, 10, 6, 1. https://doi.org/10.3390/cryst10060527

Development of Ti–Zr–Hf–Y–La high-entropy alloys with dual hexagonal-close-packed structure

TiZrHfYLa0.2 high-entropy alloys (HEAs) with dual hexagonal-closed-packed (HCP) structures were designed based on the concept of liquid phase separation (LPS) and segregation for enhancing the immiscibility of the constituent elements. The LPS leads to a particular solidification microstructure on the free surface side and Cu-hearth contacted area in the ingots. The dual HCP structures with equi-axis Ti–Zr–Hf dendrite and Y-La-rich interdendrite were observed at most regions of the arc-melted ingots. The mixing enthalpy among the constituent elements and predicted phase diagrams constructed by the Materials Project were effective for the alloy design of the HEAs with dual HCP structures.Nagase T., Todai M., Nakano T.. Development of Ti–Zr–Hf–Y–La high-entropy alloys with dual hexagonal-close-packed structure. Scripta Materialia, 186, 242. https://doi.org/10.1016/j.scriptamat.2020.05.033

Solidification microstructures of the ingots obtained by arc melting and cold crucible levitation melting in TiNbTaZr medium-entropy alloy and TiNbTaZrX (X = V, Mo, W) high-entropy alloys

The solidification microstructures of the TiNbTaZr medium-entropy alloy and TiNbTaZrX (X = V, Mo, and W) high-entropy alloys (HEAs), including the TiNbTaZrMo bio-HEA, were investigated. Equiaxed dendrite structures were observed in the ingots that were prepared by arc melting, regardless of the position of the ingots and the alloy system. In addition, no significant difference in the solidification microstructure was observed in TiZrNbTaMo bio-HEAs between the arc-melted (AM) ingots and cold crucible levitation melted (CCLM) ingots. A cold shut was observed in theAMingots, but not in theCCLMingots. The interdendrite regions tended to be enriched in Ti and Zr in the TiNbTaZrMEAand TiNbTaZrX (X=V, Mo, and W) HEAs. The distribution coefficients during solidification, which were estimated by thermodynamic calculations, could explain the distribution of the constituent elements in the dendrite and interdendrite regions. The thermodynamic calculations indicated that an increase in the concentration of the low melting-temperature V (2183 K) leads to a monotonic decrease in the liquidus temperature (TL), and that increases in the concentration of high melting-temperature Mo (2896 K) and W (3695 K) lead to a monotonic increase in TL in TiNbTaZrXx (X = V, Mo, and W) (x = 0 - 2) HEAs.Nagase T., Mizuuchi K., Nakano T.. Solidification microstructures of the ingots obtained by arc melting and cold crucible levitation melting in TiNbTaZr medium-entropy alloy and TiNbTaZrX (X = V, Mo, W) high-entropy alloys. Entropy, 21, 5, 483. https://doi.org/10.3390/e21050483

Synthesis and physical properties of (Pb0.5M0.5)(Sr,La)2CuOz (z~5; M = Fe, Co, Cu, and Zn)

(Pb0.5Cu0.5)(Sr0.5La0.5)2CuOz (abbreviated as (Pb,Cu)-"1-2-0-1") with superconducting transition temperature (Tc) of 25 K is a member (n = 1) of one of the homologous series of cuprate superconductors, (Pb4+,Cu2+)(Sr2+,Ln3+)2(Y3+,Ca2+)n-1Cu2+nO2-2n+3 (n = 1-4; Ln: lanthanoid elements). For the (Pb,Cu)-"1-2-0-1", substitution effects of 3d transition metal elements M (M = Fe, Co, and Zn) for the Cu site in the (Pb,Cu)-O charge-reservoir layer (labelled as Cu(1)) are systematically investigated. Because Fe, Co and Ni ions exist as divalent or trivalent in ionic crystals, the Sr2+/La3+ ratio in the (Sr,Ln) site is adjusted to satisfy charge neutrality, assuming that they are in a trivalent state. This results in the successful synthesis of new materials with nominal compositions of (Pb0.5M0.5)(Sr0.75La0.25)2CuOz (M = Fe and Co). This observation suggests that Fe and Co are trivalent in "1-2-0-1". For M = Zn, the nominal composition of (Pb0.5Zn0.5)(Sr0.5La0.5)2CuOz was found to yield a nearly single "1-2-0-1" phase. Temperature dependence of electrical resistivity and magnetization were measured, and superconductivity was confirmed only for the case of M = Zn with a Tc of 19.7 K. For these three materials, the distribution of Fe, Co and Zn between Cu(1) and another Cu site in the Cu-O2 plane labelled as Cu(2) was investigated employing transmission electron microscopy, which showed that Fe, Co, and Zn occupy both the Cu(1) and Cu(2) sites.Comment: 26 pages, 10 figure

The Effects of Molecular Crowding on the Structure and Stability of G-Quadruplexes with an Abasic Site

Both cellular environmental factors and chemical modifications critically affect the properties of nucleic acids. However, the structure and stability of DNA containing abasic sites under cell-mimicking molecular crowding conditions remain unclear. Here, we investigated the molecular crowding effects on the structure and stability of the G-quadruplexes including a single abasic site. Structural analysis by circular dichroism showed that molecular crowding by PEG200 did not affect the topology of the G-quadruplex structure with or without an abasic site. Thermodynamic analysis further demonstrated that the degree of stabilization of the G-quadruplex by molecular crowding decreased with substitution of an abasic site for a single guanine. Notably, we found that the molecular crowding effects on the enthalpy change for G-quadruplex formation had a linear relationship with the abasic site effects depending on its position. These results are useful for predicting the structure and stability of G-quadruplexes with abasic sites in the cell-mimicking conditions