Kyushu University · Engineering
Professor Shigeto Yamasaki's research lab specializes in the development and characterization of advanced high-temperature structural materials, with a focus on heat-resistant alloys and steels for extreme environments. The lab investigates microstructure-property relationships in materials such as aluminum, nickel-based, and ferritic heat-resistant steels produced via additive manufacturing or advanced processing techniques. Key research directions include creep deformation mechanisms, dislocation evolution, and the role of precipitates and solute elements (e.g., nitrogen, iron, silicon) in enhancing high-temperature strength and stability. The lab employs advanced characterization techniques such as electron backscatter diffraction (EBSD), serial sectioning with electron channeling contrast imaging (ECCI), and 3D dislocation reconstruction to understand deformation and fracture at the microscale.
Figures are computed from collected data and may differ slightly.
The effect of Fe addition on the high-temperature mechanical properties of heat-resistant aluminum alloys produced by selective laser melting (SLM) was investigated in relation to the alloy microstructures. Fe is generally detrimental to the properties of cast aluminum alloys; however, we found that Fe-containing alloys produced by SLM had improved high-temperature strength and good ductility. Microstructural observations revealed that the increase in the high-temperature strength of the alloys
We performed the three-dimensional visualization of dislocations through serial sectioning and use of SEM electron channeling contrast (ECC) images for a crept nickel-based alloy. We successfully reconstructed a volume of approximately 7.5 μm3, including dislocation arrangements, by performing calculations based on the continuous tomograms of ECC images. By incorporating the information on crystal orientation obtained by the electron back-scattered diffraction, we verified that the three-dimensi
New ferritic heat-resistant steels with high nitrogen content were prototyped and their microstructures and mechanical properties at high temperature were evaluated. The addition of 0.3 mass% N into ferritic steels was achieved without the formation of blowholes by applying pressurized melting methods under an atmosphere of up to 4.0 MPa. The high-nitrogen ferritic heat-resistant steels contained several kinds of nitrides within the lath martensitic structure. V-rich coarse particles were identi
The transition of the creep deformation mechanism in the low-stress region of Grade P92 high Cr ferritic heat-resistant steel was investigated by a helicoid spring creep test. Specifically, the effect of variation in the microstructure of steel on creep deformation behavior was evaluated by subjecting samples to thermal aging for 1000, 3000, 5000, and 10000 h at 700°C over a wide stress range. In addition, stress exponents were determined from the stress dependence of the minimum strain rate in
The causes of the change in creep rupture ductility with the creep test temperature in Alloy 617 were investigated. The rupture ductility in the creep test was low at 700℃, whereas it was high at 800℃. Although the rupture ductility depended on the creep test temperature, creep fracture occurred due to cavity formation at the grain boundaries under all the creep conditions. In the sample crept at 800℃, subgrains developed with creep deformation. However, the crept sample at 700℃ fractured before
Creep strain in SUS347HTB austenitic heat-resistant steel and Ni-based heat-resistant alloys was evaluated by electron backscattered diffraction (EBSD). Localized crystallographic misorientations in the crept samples were quantified by using misorientation indicators such as kernel average misorientation and grain reference orientation deviation. In most crept samples, the misorientation indicators increased with creep deformation. However, this trend was not observed for alloys with dense dispe
The creep deformation behavior and microstructure of a N-containing steel expected to exhibit high creep strength and excellent oxidation resistance were investigated. Even for steel with a high W content, it was possible to form a martensitic microstructure by adding a sufficient amount of N. Comparison of the microstructures of the N-containing steel and a C-containing steel confirmed that the two steels have the same crystal orientation relationship. The N-containing steel precipitated with t
In this study, the cleavage fracture of the C14 Fe2W Laves phase was investigated by first-principles calculations and crystal orientation analysis using scanning electron microscopy. Trace analysis of the orientations of cleavage planes revealed that cleavage fracture occurred in five types of crystal planes: (0001), {1100}, {1120}, {1101}, and {1122}. Among these fractures, the fracture at (0001) is the most preferable. From, the first-principle calculations of the surface energy for fracture,
New ferritic heat resistant steels with high nitrogen content were developed and these microstructure and the mechanical properties at high temperature were evaluated. 0.3 mass% N could be added into ferritic steels without blow holes by applying pressurized melting methods with pressurized atmosphere up to 4.0 MPa. The high nitrogen ferritic heat resistant steels contained several kind of nitrides within the lath martensitic structure. V-rich coarse particles were identified as crystallized VN.
Microscopic stress-strain curves were obtained by applying stress measurements using the HR-EBSD method and strain measurements using the DIC method to the same field of view in SEM in-situ tensile tests. From the analysis of these microscopic stress-strain curves, yield stress map and work hardening rate map were successfully produced. The relationship between these mechanical property value maps and the microstructure is investigated. The yield stress maps confirm the tendency of the local yie
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