Plasma nitrocarburizing of nanocrystallized （NC） 3J33 steel were carried out at 400 and 430 ℃ for 4 h in a mixed gas of N2：3H2 and different flow rates of rare earths （RE） La and Ce reagents in this paper. Effec...Plasma nitrocarburizing of nanocrystallized （NC） 3J33 steel were carried out at 400 and 430 ℃ for 4 h in a mixed gas of N2：3H2 and different flow rates of rare earths （RE） La and Ce reagents in this paper. Effects of temperature, rare earth addition and its addition amount on the microstructure and hardness of the nitrocarburized layer of NC 3J33 steel were also investigated. Surface phase composition of the nitrocarburized samples was analyzed by X-ray diffraction. Metallurgical structure, La and Ce concentration and microhardness profiles of cross-sectional nitrocarburized samples were studied using an optical microscope, a scanning electron microscope equipped with an energy dispersive X-ray analyzer and Vickers microhardness tester, respectively. The results showed that the surfaces of the nitrocarburized samples were mainly composed of γ＇-Fe4N and α＇-Fe （α-Fe dissolved with N and C） when the NC 3J33 steel was nitrocarburized at 400 ℃. As the temperature was enhanced up to 430 ℃, the surfaces consisted of γ＇-Fe4N, α＇-Fe and low nitrogen compound FeNx （x=0.0324–0.0989）, and simple substance La was presented when RE flow rate was 0.1 L/min. The addition of La and Ce into nitrocarburized gas increased the thickness and hardness of the nitrocarburized layers. The samples nitrocarburized at 400 ℃ with RE flow rate of 0.025 L/min and 430 ℃ of 0.05 L/min possessed the thickest nitrocarburized layer, highest proportion of nitrides and hardness profile. RE elements could diffuse into the nitrocarburized layer and their concentration increased with temperature. The excess RE impeded the permeation of N, C elements and led to thinner compound layer as well as the diffusion layer.展开更多
The properties and electronic structure of Fe under pressures of 0-30GPa have been studied by flrst principles employing the density functional theory（DFT）,the ultra-soft pseudo-potentials（USPP）and the generalized...The properties and electronic structure of Fe under pressures of 0-30GPa have been studied by flrst principles employing the density functional theory（DFT）,the ultra-soft pseudo-potentials（USPP）and the generalized gradient approximation（GGA）.The calculating results show that there is a structural transition from magnetic body-centered cubic（bcc）to nonmagnetic hexagonal-close-packed（hcp）structure for Fe around 11 GPa pressure.There is a pseudogap both in the density of states（DOS）for bcc and hcp Fe.The pseudogap of bcc Fe is deeper and wider than that of hcp Fe.The elastic modulus is obtained by Voigt-Reuss-Hill averaging scheme.The results indicate that the elastic properties of bcc Fe enhance with pressure except for elastic stiffness constant C11, shear modulus G and elastic modulus E at the transition pressure,while the elastic properties of hcp Fe increase linearly with pressure.Magnetic bcc Fe is ductile,and hcp Fe becomes ductile from brittle around 25 GPa.展开更多
基金supported by the National Natural Science Foundation of China (50871035 and 51071061)Program of Excellent Team at Harbin In-stitute of Technology
文摘Plasma nitrocarburizing of nanocrystallized （NC） 3J33 steel were carried out at 400 and 430 ℃ for 4 h in a mixed gas of N2：3H2 and different flow rates of rare earths （RE） La and Ce reagents in this paper. Effects of temperature, rare earth addition and its addition amount on the microstructure and hardness of the nitrocarburized layer of NC 3J33 steel were also investigated. Surface phase composition of the nitrocarburized samples was analyzed by X-ray diffraction. Metallurgical structure, La and Ce concentration and microhardness profiles of cross-sectional nitrocarburized samples were studied using an optical microscope, a scanning electron microscope equipped with an energy dispersive X-ray analyzer and Vickers microhardness tester, respectively. The results showed that the surfaces of the nitrocarburized samples were mainly composed of γ＇-Fe4N and α＇-Fe （α-Fe dissolved with N and C） when the NC 3J33 steel was nitrocarburized at 400 ℃. As the temperature was enhanced up to 430 ℃, the surfaces consisted of γ＇-Fe4N, α＇-Fe and low nitrogen compound FeNx （x=0.0324–0.0989）, and simple substance La was presented when RE flow rate was 0.1 L/min. The addition of La and Ce into nitrocarburized gas increased the thickness and hardness of the nitrocarburized layers. The samples nitrocarburized at 400 ℃ with RE flow rate of 0.025 L/min and 430 ℃ of 0.05 L/min possessed the thickest nitrocarburized layer, highest proportion of nitrides and hardness profile. RE elements could diffuse into the nitrocarburized layer and their concentration increased with temperature. The excess RE impeded the permeation of N, C elements and led to thinner compound layer as well as the diffusion layer.
基金the National Natural Science Foundation of China(Nos.50871035 and 51071061)the Program of Excellent Team at Harbin Institute of Technology
文摘The properties and electronic structure of Fe under pressures of 0-30GPa have been studied by flrst principles employing the density functional theory（DFT）,the ultra-soft pseudo-potentials（USPP）and the generalized gradient approximation（GGA）.The calculating results show that there is a structural transition from magnetic body-centered cubic（bcc）to nonmagnetic hexagonal-close-packed（hcp）structure for Fe around 11 GPa pressure.There is a pseudogap both in the density of states（DOS）for bcc and hcp Fe.The pseudogap of bcc Fe is deeper and wider than that of hcp Fe.The elastic modulus is obtained by Voigt-Reuss-Hill averaging scheme.The results indicate that the elastic properties of bcc Fe enhance with pressure except for elastic stiffness constant C11, shear modulus G and elastic modulus E at the transition pressure,while the elastic properties of hcp Fe increase linearly with pressure.Magnetic bcc Fe is ductile,and hcp Fe becomes ductile from brittle around 25 GPa.
