Secondary M23C6 precipitation around primary MC carbide in a directionally solidified cobalt-base saperalloy was investigated duriny aging at 850℃. The results show that it was closely related to the decomposition of...Secondary M23C6 precipitation around primary MC carbide in a directionally solidified cobalt-base saperalloy was investigated duriny aging at 850℃. The results show that it was closely related to the decomposition of the MC. Two mechanisms were suggested,i.e. the in situ reaction, MC+γ→M23C6+C, and the direct reaction, M+C→M23C6,in which MC acted as a carbon source.展开更多
Effect of revert cycles on microstructure and fatigue properties of cast cobalt base superalloy K640S has been investigated. The results show that: at 70 times of cool heat cycles, there were microcracks found in seve...Effect of revert cycles on microstructure and fatigue properties of cast cobalt base superalloy K640S has been investigated. The results show that: at 70 times of cool heat cycles, there were microcracks found in seven times revert and ten times revert. With the increasing of thermal fatigue cycles, the crack of revert grows a little faster than virgin. When the cycle time reaches 200, the crack length for both virgin and reverts have been as long as 2mm. The low cycle fatigue life has no remarkable change, with the increase of revert cycles at 815℃, 360MPa ,0 5Hz. With the times of cycles increasing, it is found that the content of impurity and gas in alloy change a little, and there is no obvious change for dendrite microstructure.展开更多
Carbon nanotubes（CNTs） were successfully synthesized through chemical vapor deposition（CVD） method over cobalt catalysts using scrap tyre rubber as carbon source.The CNTs as produced were investigated by means of ...Carbon nanotubes（CNTs） were successfully synthesized through chemical vapor deposition（CVD） method over cobalt catalysts using scrap tyre rubber as carbon source.The CNTs as produced were investigated by means of X-ray diffraction, thermogravimetric analysis,scanning electron microscope,transmission electron microscopy and Raman spectrum techniques.It was found that the obtained carbon material mainly existed in the form of CNTs.展开更多
The intrinsic relationship between the microstructure evolution and thermal fatigue behavior of a single-crystal cobalt-base superalloy has been investigated. The thermal fatigue tests are performed cyclically between...The intrinsic relationship between the microstructure evolution and thermal fatigue behavior of a single-crystal cobalt-base superalloy has been investigated. The thermal fatigue tests are performed cyclically between room temperature and 1050 ℃ using V-notch plate specimens. Three states of thermal fatigue specimens are selected： the as-cast, solutionized as well as aged states. The solution treatment is carried out at 1260 ℃ for 24 h, which results in the dissolution of most of interdendritic continuous primary carbides. The subsequent aging treatment is carried out at 1100 ℃ for 100 h after solution treatment, resulting in the precipitation of a profusion of chain- and point-like M23C6 carbides in the matrix. The results indicate that the heat treatment can improve the thermal fatigue properties of the alloy and the effect of the solution treatment is more prominent than that of the aging treatment. The coarse and continuously distributed primary carbides in the as-cast state are changed into small and discontinuous distribution by heat treatment, which is the dominant factor in the improvement of thermal fatigue property. Additionally, the effect of oxidation behavior during thermal fatigue test on the thermal fatigue behavior is also studied.展开更多
The precipitation of the lamellar-shaped M23C6 carbide within the dendritic matrix of a cobalt-base superalloy during thermal exposure at 1000 ℃ has been investigated. Such a precipitation is not commonly observed in...The precipitation of the lamellar-shaped M23C6 carbide within the dendritic matrix of a cobalt-base superalloy during thermal exposure at 1000 ℃ has been investigated. Such a precipitation is not commonly observed in cobalt-base superalloys. It is found that M23C6 particles nucleate preferentially at stacking faults （SFs） in the dendritic matrix and grow along the SFs to develop a lamellar character. Additionally, a Cr depletion zone is observed in the vicinity of the lamellar M23C6 carbide, which strongly supports the presence of Suzuki segregation.展开更多
用金相显微镜,X 射线衍射(XRD),扫描电镜(SEM),透射电镜(TEM)和 X 射线能谱(EDS)对等离子弧堆焊Co-Cr-W 系多元合金层进行了研究,结果表明,合金层基体为具有(200)晶面择优取向的 Co 基固溶体,Co 基固溶体中存在许多堆垛层错;与固溶体组...用金相显微镜,X 射线衍射(XRD),扫描电镜(SEM),透射电镜(TEM)和 X 射线能谱(EDS)对等离子弧堆焊Co-Cr-W 系多元合金层进行了研究,结果表明,合金层基体为具有(200)晶面择优取向的 Co 基固溶体,Co 基固溶体中存在许多堆垛层错;与固溶体组成共晶体的碳化物主要为具有六方点阵并含有层片状孪晶的(Cr, Fe)7C3。展开更多
Heavy duty engine valve head was prepared by Ni76Cr19AlTi alloy.It was coated by cobalt-base alloy on the surface topromote its wear-resistance.Hardness tester,metallograph,scanning microscopy,energy spectrum and X-ra...Heavy duty engine valve head was prepared by Ni76Cr19AlTi alloy.It was coated by cobalt-base alloy on the surface topromote its wear-resistance.Hardness tester,metallograph,scanning microscopy,energy spectrum and X-ray diffraction were used toanalyze the mechanical properties,the microstructure of the welds and the coated layer of cobalt-base alloy.The results show that thegrains are obviously coasened in the side of Ni76Cr19AlTi alloy in the welds and it contains a typical dentritic structure in the sidecobalt-base alloy.It is found that micro-strain in weld is stronger than that in heat-effected-zone.Micro-strain in nickel-base alloy isstronger than that cobalt-base alloy.There are not obvious imperfects in the weld.Hardness in cobalt-base alloy is more than 390HVand the major carbides in cobalt-base alloy are Cr7C3 and W2C.展开更多
文摘Secondary M23C6 precipitation around primary MC carbide in a directionally solidified cobalt-base saperalloy was investigated duriny aging at 850℃. The results show that it was closely related to the decomposition of the MC. Two mechanisms were suggested,i.e. the in situ reaction, MC+γ→M23C6+C, and the direct reaction, M+C→M23C6,in which MC acted as a carbon source.
文摘Effect of revert cycles on microstructure and fatigue properties of cast cobalt base superalloy K640S has been investigated. The results show that: at 70 times of cool heat cycles, there were microcracks found in seven times revert and ten times revert. With the increasing of thermal fatigue cycles, the crack of revert grows a little faster than virgin. When the cycle time reaches 200, the crack length for both virgin and reverts have been as long as 2mm. The low cycle fatigue life has no remarkable change, with the increase of revert cycles at 815℃, 360MPa ,0 5Hz. With the times of cycles increasing, it is found that the content of impurity and gas in alloy change a little, and there is no obvious change for dendrite microstructure.
基金supported by the National Basic Research Program of China(973 Program,No2011CB201202) the Fundamental Research Funds for the Central Universities(No2010SCU22010)
文摘Carbon nanotubes（CNTs） were successfully synthesized through chemical vapor deposition（CVD） method over cobalt catalysts using scrap tyre rubber as carbon source.The CNTs as produced were investigated by means of X-ray diffraction, thermogravimetric analysis,scanning electron microscope,transmission electron microscopy and Raman spectrum techniques.It was found that the obtained carbon material mainly existed in the form of CNTs.
基金supported by the National Natural Science Foundation of China (Nos.51331005,51601192,51671188 and 11332010)the High Technology Research and Development Program of China (No.2014AA041701)
文摘The intrinsic relationship between the microstructure evolution and thermal fatigue behavior of a single-crystal cobalt-base superalloy has been investigated. The thermal fatigue tests are performed cyclically between room temperature and 1050 ℃ using V-notch plate specimens. Three states of thermal fatigue specimens are selected： the as-cast, solutionized as well as aged states. The solution treatment is carried out at 1260 ℃ for 24 h, which results in the dissolution of most of interdendritic continuous primary carbides. The subsequent aging treatment is carried out at 1100 ℃ for 100 h after solution treatment, resulting in the precipitation of a profusion of chain- and point-like M23C6 carbides in the matrix. The results indicate that the heat treatment can improve the thermal fatigue properties of the alloy and the effect of the solution treatment is more prominent than that of the aging treatment. The coarse and continuously distributed primary carbides in the as-cast state are changed into small and discontinuous distribution by heat treatment, which is the dominant factor in the improvement of thermal fatigue property. Additionally, the effect of oxidation behavior during thermal fatigue test on the thermal fatigue behavior is also studied.
基金supported by the National Natural Science Foundation of China (Nos. 51331005, 51601192, 51671188 and 11332010)the High Technology Research and Development Program of China (No. 2014AA041701)
文摘The precipitation of the lamellar-shaped M23C6 carbide within the dendritic matrix of a cobalt-base superalloy during thermal exposure at 1000 ℃ has been investigated. Such a precipitation is not commonly observed in cobalt-base superalloys. It is found that M23C6 particles nucleate preferentially at stacking faults （SFs） in the dendritic matrix and grow along the SFs to develop a lamellar character. Additionally, a Cr depletion zone is observed in the vicinity of the lamellar M23C6 carbide, which strongly supports the presence of Suzuki segregation.
文摘用金相显微镜,X 射线衍射(XRD),扫描电镜(SEM),透射电镜(TEM)和 X 射线能谱(EDS)对等离子弧堆焊Co-Cr-W 系多元合金层进行了研究,结果表明,合金层基体为具有(200)晶面择优取向的 Co 基固溶体,Co 基固溶体中存在许多堆垛层错;与固溶体组成共晶体的碳化物主要为具有六方点阵并含有层片状孪晶的(Cr, Fe)7C3。
文摘Heavy duty engine valve head was prepared by Ni76Cr19AlTi alloy.It was coated by cobalt-base alloy on the surface topromote its wear-resistance.Hardness tester,metallograph,scanning microscopy,energy spectrum and X-ray diffraction were used toanalyze the mechanical properties,the microstructure of the welds and the coated layer of cobalt-base alloy.The results show that thegrains are obviously coasened in the side of Ni76Cr19AlTi alloy in the welds and it contains a typical dentritic structure in the sidecobalt-base alloy.It is found that micro-strain in weld is stronger than that in heat-effected-zone.Micro-strain in nickel-base alloy isstronger than that cobalt-base alloy.There are not obvious imperfects in the weld.Hardness in cobalt-base alloy is more than 390HVand the major carbides in cobalt-base alloy are Cr7C3 and W2C.
