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RISS 인기검색어
- 검색키워드
- 저자 : El-Tahawy, Moustafa (검색결과 3 건)
- 무료
- 기관 내 무료
- 유료
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El-Tahawy, Moustafa,Huang, Yi,Choi, Hyelim,Choe, Heeman,Lá,bá,r, Já,nos L.,Langdon, Terence G.,Gubicza, Jenő Elsevier 2017 Materials science & engineering. properties, micro Vol.682 No.-
<P><B>Abstract</B></P> <P>Differential scanning calorimetry (DSC) was used to study the thermal stability of the microstructure and the phase composition in nanocrystalline 316L stainless steel processed by high-pressure torsion (HPT) for ¼ and 10 turns. The DSC thermograms showed two characteristic peaks which were investigated by examining the dislocation densities, grain sizes and phase compositions after annealing at different temperatures. The first DSC peak was exothermic and was related to recovery of the dislocation structure without changing the phase composition and grain size. The activation energies for recovery after processing by ¼ and 10 turns were ~163 and ~106kJ/mol., respectively, suggesting control by diffusion along grain boundaries and dislocations. The second DSC peak was endothermic and was caused by a reverse transformation of α’-martensite to γ-austenite. The hardness of annealed samples was determined primarily by the grain size and followed the Hall–Petch relationship. Nanocrystalline 316L steel processed by HPT exhibited good thermal stability with a grain size of ~200nm after annealing at 1000K and a very high hardness of ~4900MPa.</P>
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El-Tahawy, Moustafa,Um, Teakyung,Nam, Ho-Seok,Choe, Heeman,Gubicza, Jenő Elsevier 2019 Materials science & engineering. properties, micro Vol.739 No.-
<P><B>Abstract</B></P> <P>The effects of hydrogen charging on the evolution of strain-induced lattice defects and phase transformation were investigated in 316L stainless steel. The initial material was obtained by cold rolling to a thickness reduction of 20%. The surfaces of some of the initial samples were cathodically charged with hydrogen. Afterward, both the charged and uncharged samples were subjected to tension until failure. The dislocation density and twin-fault probability in the charged and uncharged specimens during tension were compared. We found that hydrogen charging reduced the degree of increase in the dislocation density and twin-fault probability during the application of tension to the same strain level. Significant martensitic phase transformation was observed in the uncharged samples tested to the strain of 10% or higher. In the hydrogen-charged samples, only a slight increase in the martensite phase fraction was detected. A correlation between the α′-martensite fraction and the dislocation density was found for the studied samples, suggesting that the lower degree of martensitic phase transformation in the charged 316L steel was caused by the smaller amount of stress developed due to the lower dislocation density. In accordance with the differences observed in the phase composition and defect densities, the hydrogen-charged material exhibited lower surface hardness.</P>
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El-Tahawy, Moustafa,Pereira, Pedro Henrique R.,Huang, Yi,Park, Hyeji,Choe, Heeman,Langdon, Terence G.,Gubicza, Jenő Elsevier 2018 Materials letters Vol.214 No.-
<P><B>Abstract</B></P> <P>An investigation was conducted to evaluate the effect of annealing at different temperatures on the tensile properties of ultrafine-grained 316L stainless steel processed by high-pressure torsion (HPT). A “moderate-temperature” annealing at 740 K resulted in reduced strength and elongation due to the annihilation of mobile dislocations. A “high-temperature” annealing at 1000 K yielded a remarkably good combination of yield strength (∼1330 MPa) and elongation to failure (∼43%) which can be attributed to the almost full reversion of α′-martensite formed during HPT into γ-austenite while the grain size remained very fine with a value of about 200 nm.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 316L steel with a nanocrystalline microstructure was processed by HPT. </LI> <LI> The effect of annealing on the tensile properties was studied. </LI> <LI> Annealing to 740 K yielded a pronounced embrittlement and a strength reduction. </LI> <LI> Annealing to 1000 K led to a good combination of strength and elongation to failure. </LI> <LI> The excellent tensile behavior was caused by the very fine austenitic microstructure. </LI> </UL> </P>
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