Koji Hagihara 교수

The unusual increase in the strength by extrusion is a unique feature of recently developed Mg alloys containing the LPSO phase. In this study, we first elucidated the detailed mechanisms that induce this drastic strengthening. The dependencies of the deformation behavior of a Mg88Zn4Y7 extruded alloy, which contains ∼86-vol% LPSO phase, on the temperature, loading orientation, and extrusion ratio were examined. It was found that the yield stress of the alloy is drastically increased by extrusio

We investigated the influence of a change in the stacking sequence of the close-packed plane in a Mg12ZnY long-period stacking ordered (LPSO) phase on its mechanical properties. A 14H-typed LPSO-phase crystal was fabricated by annealing a directionally solidified (DS) crystal with a 18R-typed LPSO-structure at 525°C for 3 days, and the temperature dependence and orientation dependence of the yield stress were examined via compression tests. (0001)〈11\\bar20〉 basal slip was identified as a domina

The mechanical properties of the Mg-based LPSO-phase are expected to be strongly affected by the microstructure due to its anisotropic crystal structure. However, the fine details have not been sufficiently understood yet. This study first clarified the detailed microstructural factors that govern the strength of the LPSO-phase by examining alloys with microstructures that were significantly varied via directional solidification and extrusion processes. Refining the microstructure is significant

Mg–Zn–Y ternary alloys containing the long-period stacking ordered (LPSO) phase exhibit superior mechanical properties. This is believed to be originating from the LPSO phase acting as the strengthening phase. However, we first clarify that the mechanical properties of the matrix Mg solid solution in the Mg/LPSO two-phase alloy are significantly different from those of pure Mg. The yield stress of a Mg99.2Zn0.2Y0.6 single crystal (matrix Mg solid solution) is almost the same as that of an LPSO s

Abstract Additive manufacturing (AM) enables the production of complex, net-shape geometries. Additionally, in AM of metal and ceramics, which has received less attention, the microstructure and texture of the product can be arbitrarily controlled by selecting appropriate process parameters, thereby enabling unprecedented superior properties. This paper discusses recent progress pertaining to texture evolution mechanisms and control methods, with an emphasis on selective laser melting. One of th

MoSi2 is one of the promising candidates for ultrahigh-temperature structural materials. However, its product fabrication has been limited owing to its significant brittleness until now. As an approach to overcome this, we have first successfully fabricated MoSi2 samples via additive manufacturing (AM). Control of the thermal expansion coefficient of the start plate for AM is important for building a three-dimensional MoSi2 product with a low deformability. Moreover, unidirectional laser scannin

Non-basal slip systems in the Mg12ZnY long-period stacking ordered (LPSO) phase, the operational frequency of which is increased at high-temperatures and affects the mechanical properties, were clarified. The {1\bar{1}00}<11\bar{2}0> prism slip was identified in both 18R and 14H LPSO phases, even though they have the different lattice systems. This behavior is different from that observed in a Ni-based LPSO phase. The peculiar chemical modulation in the Mg12ZnY LPSO phase may affect the selectio