Kyoto University · Materials Science
Professor Si Gao's research lab specializes in the microstructure-property relationships of advanced metallic materials, with a focus on ultrafine-grained and nanostructured steels, intermetallic compounds, and metastable austenitic alloys. The lab employs advanced characterization techniques such as electron tomography, in situ X-ray diffraction, and mechanical testing to investigate deformation mechanisms, yielding behavior, and strengthening effects at the nanoscale. Key research directions include the Hall–Petch relationship in fine-grained materials, the Bauschinger effect in ultrafine-grained metals, and the role of intermetallic phases in enhancing both strength and ductility. The lab also develops innovative processing routes—such as accumulative roll bonding and two-step cold rolling and annealing—to tailor microstructures for improved mechanical performance.
Figures are computed from collected data and may differ slightly.
Knowing the three-dimensional structural information of materials at the nanometer scale is essential to understanding complex material properties. Electron tomography retrieves three-dimensional structural information using a tilt series of two-dimensional images. In this paper, we report an alternative combination of electron ptychography with the inverse multislice method. We demonstrate depth sectioning of a nanostructured material into slices with 0.34 nm lateral resolution and with a corre
Interstitial free (IF) steel specimens with different mean grain sizes ranging from 0.4 to 12 µm were fabricated by the accumulative roll bonding (ARB) process and subsequent annealing. Tensile tests at room temperature have revealed that by decreasing the mean grain size down to an ultra-fine range, the yielding behavior gradually changes from the continuous yielding to the discontinuous yielding, accompanying a yield drop phenomenon. It has been found that the yield stress of specimens having
Bauschinger test in uniaxial tension-compression mode was carried out for the first time on the pure Al specimens having homogeneous ultra-fine grained (UFG) microstructures fabricated by equal-channel angular pressing (ECAP) and subsequent annealing processes. Significant Bauschinger stress (transient softening), Bauschinger energy parameter and their strong dependences on the tensile plastic pre-strain at the very early stage of the tensile deformation were measured in the UFG specimens, in sh
High purity iron specimens containing 11 ppm carbon and 8 ppm nitrogen with different grain sizes were fabricated by cold rolling and subsequent annealing. It was found that the specimens exhibited entirely different yielding behavior in tensile tests depending on different cooling processes after annealing. The water-cooled specimens exhibited continuous yielding while the air-cooled ones exhibited discontinuous yielding. It was found that the Hall–Petch slope, ky, significantly changed dependi
Metastable austenitic steels having ultrafine grained (UFG) microstructures can be fabricated by conventional cold rolling and annealing processes by utilizing the deformation-induced martensitic transformation during cold rolling and its reverse transformation to austenite upon annealing. However, such processes are not applicable when the austenite has high mechanical stability against deformation-induced martensitic transformation, since there is no sufficient amount of martensite formed duri
Intermetallic compounds are usually considered as deleterious phase in alloy designing and processing since their brittleness leads to poor ductility and premature failure during deformation of the alloys. However, several studies recently found that some alloys containing large amounts of NiAl-type intermetallic particles exhibited not only high strength but also good tensile ductility. To clarify the role of the intermetallic particles in the excellent tensile properties of such alloys, the te
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