Munekazu Ohno

TiAl3 Formation in the Titanium-Aluminum Diffusion Couple

Pure titanium and aluminum sheets were used to prepare titanium-aluminum diffusion couples. The diffusion couples were heated to temperatures 550, 575, 600, 625, 640, 650 and 700°C. SEM observations of the titanium-aluminum interface and EPMA results revealed that a TiAl3 intermetallic layer has formed and thickened between the layers. Grain boundaries of the TiAl3 compound, which were revealed by back-scattered electron imaging, indicated a size distribution across the layer. Finer grains which were located close to the titanium showed that TiAl3 has nucleated at the Ti-TiAl3 interface. Thus, the former grains which had formed close to the aluminum-rich side have grown and coarsened during annealing at high temperatures. Grain coarsening of TiAl3 decreased the kinetics of the layer thickening.

Combustion synthesis of TiB2 based hard material cemented by Fe–Al intermetallics

Abstract TiB2 based hard material has been fabricated by combustion synthesis from elemental powders using Fe–Al intermetallics as the binder phase. Both the crystal orientation map and the pole figures by electron backscatter diffraction analysis showed that the TiB2 particles have no preferential orientation. Preheating of the power compact is helpful to increase the relative density and to reduce the particle size of the synthesised product, which increases the hardness of the product. The highest hardness and relative density were achieved for a composition of TiB2–20 vol..-%FeAl.

Austenite Grain Growth in Peritectic Solidified Carbon Steels Analyzed by Phase-Field Simulation

The formation of coarse columnar grains (CCGs) in the as-cast austenite structure of peritectic carbon steels is a serious problem in continuous casting processes. Recently, it was elucidated that the formation of CCGs is ascribed to a discontinuous grain growth. Furthermore, the critical condition for the discontinuous growth to occur was elicited on the basis of phase-field simulations and a theory of grain growth. In this study, by means of the phase-field simulations, the detailed investigation is carried out for the grain coarsening of the as-cast austenite structure. It is demonstrated in the two-dimensional simulations that the coarsest grain structure emerges by the discontinuous growth in the vicinity of the critical condition. In addition, a model for predicting the upper limit of grain size during the discontinuous growth is proposed. The model successfully describes the experimental result with reasonable accuracy.

Aluminum Coating on Magnesium-Based Alloy by Hot Extrusion and Its Characteristics

Although magnesium-based alloys have excellent mechanical properties, their very poor corrosion resistance limits their application. It has been considered that aluminum coating would solve this problem because aluminum has an excellent corrosion resistance. This study proposes a superior coating method based on the hot extrusion process. An aluminum plate set between the magnesium alloy billet and an extrusion die having an inversely angled face was successfully extruded together with the magnesium alloy billet and, as a result, the aluminum coated the extruded magnesium alloy with a uniform thickness. Corrosion tests based on dipping in HCl aqueous solution and potential measurement in NaCl aqueous solution showed that the extruded sample exhibited the same corrosion resistance as the aluminum. A three point bending test at room temperature resulted in fracture after plastic deformation, while at high temperatures between 100 and 300°C plastic deformation without fracture occurred. Notably, the intermetallic layer formed on the boundary between the magnesium alloy substrate and the aluminum coating layer plastically deformed without cracking at 300°C. A tensile test at room temperature resulted in a UTS of about 320 MPa and a plastic elongation of 18%.