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RISS 인기검색어
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- 저자 : Hasan Kotan (검색결과 2 건)
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Hasan Kotan,Kris A. Darling,Tom Luckenbaugh 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6
The key requirement to consolidate high-energy mechanically alloyed nanocrystalline powders is to achieve densificationand particle bonding without impairment in the mechanical properties. Recent demonstrations of consolidation methodsinvolving high shear, pressure and temperature have shown promising results for bonding high strength particulate materialsproduced by mechanical alloying. In this study, we report the ability of multi-pass high temperature equal channel angularextrusion to produce bulk ferritic alloys from nanocrystalline Fe–Ni–Zr powders. Subsequent microstructural characterizationsindicate limited grain growth as the average grain sizes remain smaller than 100 nm after processing temperatures of600 °C and 700 °C, above which grains reach micron sizes. The compression test results reveal that the alloys exhibit highmechanical strength at room and moderately high temperatures compared to the pure Fe and Fe–Ni alloys without Zr addition.
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Gökhan Polat,Hasan Kotan 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10
Stainless steels with Fe/Cr/Ni ratios of 74/18/8, 71/17/12, and 55/20/25 were produced from elemental powders by highenergy mechanical alloying at both room and cryogenic temperatures. The effect of mechanical alloying temperature onmartensitic transformation, the reversion of deformation-induced martensite-to-austenite upon annealing, and the influenceof cooling rate on the thermal stability of reversed austenite upon cooling to room temperature were investigated in detailby in-situ and ex-situ X-ray diffraction (XRD) experiments, transmission electron microscopy (TEM) and Thermo-Calcsimulations. A relative comparison of stainless steels after room temperature mechanical alloying indicated that the lownickel-containing steel underwent an almost complete martensitic transformation. However, martensitic transformation bydeformation through mechanical alloying at room temperature would not be possible with increasing nickel contents butwas created partially at cryogenic temperature, the degree of which depended on the steel composition. The in-situ XRDstudies exhibited that the deformation-induced martensite completely transformed to austenite at elevated temperatures. Thecomplete reverse transformation temperature simulated by Thermo-Calc software was found to be lower than that of theexperimentally determined ones. Additionally, the different cooling rates from the reversed austenite demonstrated that theslower cooling increased the thermal stability of reversed austenite at room temperature.
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