The pack boriding process was used to treat pure nickel at a boriding temperature of 950 ℃ for a boriding time of 5 h. A dense and continuous borided layer with 40 μm thickness was obtained on pure nickel. Corrosion...The pack boriding process was used to treat pure nickel at a boriding temperature of 950 ℃ for a boriding time of 5 h. A dense and continuous borided layer with 40 μm thickness was obtained on pure nickel. Corrosion behavior of the borided layer was investigated in molten LiCl 10%Li 2O(mass fraction) at 750 ℃ in air. The mass loss of the boriding coating was 8.4 mg·cm -2 after being corroded for 50 h in the melt, which is about three times lower than that of unborided pure nickel. The preferential corrosion of B in borided layer effectively prevents the corrosion of nickel, which improves the corrosion resistance of pure nickel in molten LiCl Li 2O.展开更多
A plasma arc welding( PAW)-tungsten inert gas( TIG) hybrid welding process is proposed. And this paper investigated the microstructure and properties of pure nickel N6 joints by PAW-TIG hybrid welding. Compared with t...A plasma arc welding( PAW)-tungsten inert gas( TIG) hybrid welding process is proposed. And this paper investigated the microstructure and properties of pure nickel N6 joints by PAW-TIG hybrid welding. Compared with the conventional PAW method,the characteristic of PAW-TIG welding process is that there is no interaction between the two arcs.The addition of TIG can enhance the intrinsic high-efficiency peculiarity and the stability of the keyhole status of PAW. The joints made using PAW and PAW-TIG,respectively,were subjected to microstructural evaluations and tensile testing so as to analyze the effect of TIG arc energy on the microstructure and mechanical properties of these joints. The results of this investigation indicate that significant grain coarsening was observed in the weld metal( WM) and heat affected zone( HAZ)and it is found that the extent of grain coarsening increased with the addition of TIG arc. And the microstructure in hybrid joint,with wider weld width and the smooth surface,is coarser than in PAW joint. Furthermore,the microhardness and ultimate tensile strength( UTS) of hybrid joint is slightly lower than that of PAW joint. The fractograph observation shows that the fracturing mechanism of PAW joints ductile,while the hybrid welding joints exists as brittle-ductile fracture mode. The outcome of this work shows that in the condition of same deposited rate,TIG arc post-weld heat treatment can improve the welding efficiency and welding speed. The proposed PAW-TIG hybrid welding process is demonstrated to be suitable for welding nickel and its alloys in industry application.展开更多
According to the selection principle of grain refiners and calculation of planar disregistries, CeO2 and TiB2 particles were selected as the grain refiners of pure nickel. The change of grain size and refining effects...According to the selection principle of grain refiners and calculation of planar disregistries, CeO2 and TiB2 particles were selected as the grain refiners of pure nickel. The change of grain size and refining effects of different refiners under the same melting conditions were investigated. The results show that the grain size of pure nickel gradually reduces with increasing the amount of grain refiners. And with increasing the amount of CeO2 up to 0.7 wt%, the grain size of pure nickel decreases from 323.0 to 53.5 lm. In addition, when the amount of TiB2is0.7 wt%, the grain size is reduced to 41.3 lm.展开更多
The microstructural evolution of pure nickel treated by deep rolling(DR)technique with different indent depths was investigated by means of optical microscopy and transmission electron microscopy.The surface roughness...The microstructural evolution of pure nickel treated by deep rolling(DR)technique with different indent depths was investigated by means of optical microscopy and transmission electron microscopy.The surface roughness,hardness and residual stress distribution along the depth from surface were measured.Moreover,the DR-treated sample was annealed at temperatures from 300 to 700℃for 2 h.The results reveal that dislocation movements are the fundamental mechanisms of gradient grain refinement during the DR process.With increasing indent depth of the DR,the gradient microhardness on the cross section of sample significantly increases,the maximum compressive residual stress decreases,and the affecting region of residual stress increases.The results of thermal stability depict that the microstructure can be stable as temperature up to 300℃,and the abnormal grain growth and annealing twins are observed at 600℃.展开更多
文摘The pack boriding process was used to treat pure nickel at a boriding temperature of 950 ℃ for a boriding time of 5 h. A dense and continuous borided layer with 40 μm thickness was obtained on pure nickel. Corrosion behavior of the borided layer was investigated in molten LiCl 10%Li 2O(mass fraction) at 750 ℃ in air. The mass loss of the boriding coating was 8.4 mg·cm -2 after being corroded for 50 h in the melt, which is about three times lower than that of unborided pure nickel. The preferential corrosion of B in borided layer effectively prevents the corrosion of nickel, which improves the corrosion resistance of pure nickel in molten LiCl Li 2O.
基金supported by the Major Technology Program Foundation of Gansu(Grant No.145RTSA004)
文摘A plasma arc welding( PAW)-tungsten inert gas( TIG) hybrid welding process is proposed. And this paper investigated the microstructure and properties of pure nickel N6 joints by PAW-TIG hybrid welding. Compared with the conventional PAW method,the characteristic of PAW-TIG welding process is that there is no interaction between the two arcs.The addition of TIG can enhance the intrinsic high-efficiency peculiarity and the stability of the keyhole status of PAW. The joints made using PAW and PAW-TIG,respectively,were subjected to microstructural evaluations and tensile testing so as to analyze the effect of TIG arc energy on the microstructure and mechanical properties of these joints. The results of this investigation indicate that significant grain coarsening was observed in the weld metal( WM) and heat affected zone( HAZ)and it is found that the extent of grain coarsening increased with the addition of TIG arc. And the microstructure in hybrid joint,with wider weld width and the smooth surface,is coarser than in PAW joint. Furthermore,the microhardness and ultimate tensile strength( UTS) of hybrid joint is slightly lower than that of PAW joint. The fractograph observation shows that the fracturing mechanism of PAW joints ductile,while the hybrid welding joints exists as brittle-ductile fracture mode. The outcome of this work shows that in the condition of same deposited rate,TIG arc post-weld heat treatment can improve the welding efficiency and welding speed. The proposed PAW-TIG hybrid welding process is demonstrated to be suitable for welding nickel and its alloys in industry application.
基金financially supported by the National Natural Science Foundation of China (No. E051004)
文摘According to the selection principle of grain refiners and calculation of planar disregistries, CeO2 and TiB2 particles were selected as the grain refiners of pure nickel. The change of grain size and refining effects of different refiners under the same melting conditions were investigated. The results show that the grain size of pure nickel gradually reduces with increasing the amount of grain refiners. And with increasing the amount of CeO2 up to 0.7 wt%, the grain size of pure nickel decreases from 323.0 to 53.5 lm. In addition, when the amount of TiB2is0.7 wt%, the grain size is reduced to 41.3 lm.
基金the financial support through the National Natural Science Foundation of China (Nos.51725503, 51605164 and 51575183)111 Project+4 种基金support by Shanghai Technology Innovation Program of SHEITC (CXY-2015-001)Fok Ying Tung Education FoundationYoung Program of Yangtze River Scholarssupport by Shanghai Sailing Program (16YF1402300)Shanghai Chenguang Program (16CG34)
文摘The microstructural evolution of pure nickel treated by deep rolling(DR)technique with different indent depths was investigated by means of optical microscopy and transmission electron microscopy.The surface roughness,hardness and residual stress distribution along the depth from surface were measured.Moreover,the DR-treated sample was annealed at temperatures from 300 to 700℃for 2 h.The results reveal that dislocation movements are the fundamental mechanisms of gradient grain refinement during the DR process.With increasing indent depth of the DR,the gradient microhardness on the cross section of sample significantly increases,the maximum compressive residual stress decreases,and the affecting region of residual stress increases.The results of thermal stability depict that the microstructure can be stable as temperature up to 300℃,and the abnormal grain growth and annealing twins are observed at 600℃.
基金the Science Foundation for Distinguished Young Scholars of Gansu Province,China(No.18JR3RA134)the Lanzhou University of Technology Support Plan for Excellent Young Scholars,China(No.CGZH001)+1 种基金the National Nature Science Foundation of China(No.51665032)the Key R&D Program of Gansu Province−International Cooperation Project,China(No.20YF8WA064).
