Search

Recently, metal additive manufacturing (AM) has enabled a wide range of control over metallurgical structures. Originally, the unique manufacturing method of stacking tiny melted sections to fabricate products with complex shapes with high precision provided geometrically defined solidification units with specific solidification directions and steep cooling, which in turn enabled the control of the metallurgical microstructure. This article describes the work of the author’s research group on crystallographic texture control via laser powder bed fusion (LPBF), including (1) the influence of powder properties on the formation of dense products, which is essential for crystallographic texture formation; (2) the influence of melt pool shape and crystallographic characteristics of the materials on single crystal formation and determination of crystal orientation; and (3) the success of “Alloy Design” for a highly functional single crystalline bio-high-entropy alloy (BioHEA) considering specific solidification fields under LPBF. [ABSTRACT FROM AUTHOR]

Me-substituted W-type ferrites (AMe2Fe16O27 with A = Sr, Ba, …, and Me = Co, Ni, Zn, Mg, …) can be obtained by standard solid state reaction but always contain secondary phases. Phase stability of SrMe2Fe16O27 with Me = Co, Ni, Zn, and Mg sintered in various oxygen pressures of pO2 = 0.2, 1, 10 and 387 atm were investigated using X-ray diffraction analysis, wavelength-dispersive X-ray (WDX) analysis, and transmission electron microscopy (TEM). WDX analysis revealed that the W-type ferrites are described as SrMe2-δFe16+δO27 because Fe3+ is partially reduced to Fe2+ even when synthesis is initiated from SrMe2Fe16O27. Increasing the oxygen pressure suppresses the reduction of Fe3+ and the formation of the secondary phases. In addition, TEM analysis shows that the SrCo2Fe16O27 single crystal is free of stacking faults. We conclude that the single-phase formation of the Mesubstituted W-type ferrites is hampered by the discrepancy between initial and actual chemical composition caused by the appearance of Fe2+. [ABSTRACT FROM AUTHOR]

Relaxor-type lead-perovskite piezoelectric single crystals (SCs) are ABO3-type piezoelectric materials with lead (Pb) at the A site and composite oxides such as magnesium (Mg), zinc (Zn), indium (In), niobium (Nb), and titanium (Ti) at the B site. The development and application of these materials have been pursued in earnest since the 1980s. The piezoelectric constant d33 and electromechanical coupling coefficient k33 of these SCs are much higher than those of conventional PZT ceramics. Currently, eight companies around the world are mass producing and selling these SC transducers, and in particular, more than 1 million units of this SC transducers have already been put into practical use for medical ultrasound probes, and in recent years, the range of its use has been further expanded. In this article, the history, current status, and future progress of lead-perovskite piezoelectric SCs are chronologically introduced, including not only published papers but also patents. In particular, the major topics of the past few years, low-cost solid state crystal growth (SSCG) process, textured ceramics process, and innovative AC poling technology are discussed in detail. [ABSTRACT FROM AUTHOR]

The itinerant ferromagnetism is reported in A2T12P7 (A = lanthanoid, Group 2-4 element, T = transition metal) with Zr2Fe12P7-type structure. In order to investigate the behavior of electrons in this structure, we have synthesized single crystals of (Ca1-xMgx)2Co12P7 and measured magnetizations. From magnetic susceptibility, we found that Ca2Co12P7 shows a ferromagnetic transition at TC = 78 K, which is attributed to the Co-3d itinerant electrons. We also found the Curie temperature decreases and eventually disappears around x~0.6, when Ca is substituted by Mg. It has been suggested that the electronic density of states changes and the magnetic state of this system crosses the quantum critical point due to the positive chemical-pressure effect of the Ca substitution by Mg [ABSTRACT FROM AUTHOR]

The quasi-skutterudite superconductor La3Co4Sn13 with the Yb3Rh4Sn13-type cage-structure presents structural transition at T* = 152 K. As in the case with isostructural compound Sr3Rh4Sn13, it has been shown that T* can be suppressed to 0 K by applying external physical pressure in La3Co4Sn13. In order to investigate chemical pressure effect on La3Co4Sn13, we have synthesized single crystals of La1−xAx)3Co4Sn13 (A = Sr, Ca) and measured magnetic susceptibilities and specific heats. From magnetic susceptibility and specific heat measurements, it has been suggested that T* can change sensitively to the composition. [ABSTRACT FROM AUTHOR]