In-situ high-energy X-ray diffraction and material modeling are used to investigate the strainrate dependence of the strain-induced martensitic transformation and the stress partitioning between austenite and a¢ martensite in a metastable austenitic stainless steel during tensile loading. Moderate changes of the strain rate alter the strain-induced martensitic transformation, with a significantly lower a¢ martensite fraction observed at fracture for a strain rate of 10 À2 s À1 , as compared to 10 À3 s À1 . This strain-rate sensitivity is attributed to the adiabatic heating of the samples and is found to be well predicted by the combination of an extended Olson-Cohen strain-induced martensite model and finite-element simulations for the evolving temperature distribution in the samples. In addition, the strain-rate sensitivity affects the deformation behavior of the steel. The a¢ martensite transformation at high strains provides local strengthening and extends the time to neck formation. This reinforcement is witnessed by a load transfer from austenite to a¢ martensite during loading.
Small-angle x-ray scattering was used to study in situ decomposition of an arc evaporated TiAlN coating into cubic-TiN and cubic-AlN particles at elevated temperature. At the early stages of decomposition particles with ellipsoidal shape form, which grow and change shape to spherical particles at higher temperatures. The spherical particles grow at a rate of 0.18 Å/°C while coalescing.
Carbothermal reduction–nitridation (CRN) of SiO2–Al2O3–CaO powders was performed under various firing conditions to investigate the formation process of Ca‐α sialon hollow balls composed of nanosized particles. Scanning electron microscopy and transmission electron microscopy observations of the samples obtained at different firing temperatures confirmed that solid spherical particles were formed at the early stage of the reaction, and nanosized particles were subsequently produced on the surface of these solid balls. From X‐ray diffraction and energy‐dispersive spectrometry analyses, it was found that the solid balls initially formed at 1450°C were mainly amorphous and contained Si, Al, Ca, O, and a small amount of N. Further nitridation at 1450°C gradually converted the solid balls into Ca‐α sialon hollow balls over time. The results revealed that the formation of Ca‐α sialon hollow balls depends on the formation of solid balls from the Si–Al–Ca–O liquid phase at the initial stage of the CRN process.
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