The hot deformation experiments of ultra-low carbon steel in ferrite range were carried out in a hot simulator in order to research hot deformation behaviors of ultra-low carbon steel in ferrite range at low temperatu...The hot deformation experiments of ultra-low carbon steel in ferrite range were carried out in a hot simulator in order to research hot deformation behaviors of ultra-low carbon steel in ferrite range at low temperature. The results show that the influences of deformation parameters on flow stress are different to those in austenitic deformation. The deformation characteristic parameters were calculated for ultra-low carbon steel in ferrite region. The flow stress equation for ultra-low carbon steel in ferritic deformation at low temperature was obtained.展开更多
The effects of laser shock processing(LSP)and warm laser shock processing(WLSP)on the microstructure of surface hardening layer and high-cycle fatigue performance at room temperature and high temperature(600°C)of...The effects of laser shock processing(LSP)and warm laser shock processing(WLSP)on the microstructure of surface hardening layer and high-cycle fatigue performance at room temperature and high temperature(600°C)of IN718 alloy were investigated.It has been revealed that the grain refined hardening layer with greater residual compression stresses,higher fraction of coincidence site lattice(CSL)boundaries and dislocation densities was formed in WLSP-treated alloy than in LSP-treated alloys.Moreover,microtwins includedγ″phase/high density dislocation complex was found in the surface of WLSP-treated alloy.These characters caused the significant enhancement of the medium value fatigue strength of WLSP-treated alloy at room temperature and elevated temperature.Apparently,the microtwins includedγ″phase/high density dislocation complex formed in the surface hardening layer of LSP-treated alloy has more complicated steric structure and more stable at elevated temperature thanγ″phase/low density dislocation complex formed in LSP-treated alloy,leading to the slow recovery process.Therefore,the surface hardening layer in the WLSP-treated alloy remained more ideal strengthening effect under high-cycle fatigue at elevated temperature than that in LSP-treated alloy.This resulted in the much longer fatigue crack initiation incubation and longer high-cycle life of WLSP-treated IN718 alloy under cycling load at 600℃.This discovery provides a new cognition of fatigue resistance by WLSP treatment of precipitation strengthening superalloy.展开更多
Anisotropic bonded magnets were prepared by warm compaction using anisotropic Nd-Fe-B powder. The forming process, magnetic properties, and temperature stability were studied. The results indicate that the optimal tem...Anisotropic bonded magnets were prepared by warm compaction using anisotropic Nd-Fe-B powder. The forming process, magnetic properties, and temperature stability were studied. The results indicate that the optimal temperature of the process, which was decided by the vis-cosity of the binders, was 110°C. With increasing pressure, the density of the magnets increased. When the pressure was above 700 MPa, the powder particles were destroyed and the magnetic properties decreased. The magnetic properties of the anisotropic bonded magnets were as follows： remanence Br=0.98 T, intrinsic coercivity iHc=1361 kA/m, and maximum energy product BHmax=166 kJ/m3. The magnets had excellent thermal stability because of the high coercivity and good squareness of demagnetization curves. The flux density of the magnets was 35% higher than that of isotropic bonded Nd-Fe-B magnets at 120°C for 1000 h. The flux density of the bonded magnets showed little change with regard to temperature.展开更多
Anisotropic NdFeB/SmCoCuFeZr composite bonded magnets were prepared by warm compaction process. The effects of adding SmCoCuFeZr magnetic powder on the properties of anisotropic bonded NdFeB magnet were investigated i...Anisotropic NdFeB/SmCoCuFeZr composite bonded magnets were prepared by warm compaction process. The effects of adding SmCoCuFeZr magnetic powder on the properties of anisotropic bonded NdFeB magnet were investigated in this work. The results show that, both magnetic properties and temperature stability of the bonded magnet can be improved by adding fine SmCoCuFeZr magnetic powder. In the present study, the optimal content of SmCoCuFeZr magnetic powder was about 20 wt.%, in this case, the Br, Hcj, and（BH）maxof the NdFeB/SmCoCuFeZr composite magnet achieved 0.943 T, 1250 kA/m, and168 kJ/m^3, respectively.展开更多
With modified water glass as binder and the introduction of micro silicon powders into the coremaking process,an improvement was made to the tensile strength and collapsibility of the sand core.The potassium hydroxide...With modified water glass as binder and the introduction of micro silicon powders into the coremaking process,an improvement was made to the tensile strength and collapsibility of the sand core.The potassium hydroxide,sodium hexametaphosphate and white sugar were applied as the modifiers of water glass.The optimum proportion of the modifiers was determined through the combination of single factor test and orthogonal test.The optimum proportion of water glass,potassium hydroxide,sodium hexametaphosphate and white sugar is 1000:40:5:5(wt.).In terms of weight,modified binder and micro silicon powders accounted for 2%and 0.6%of sand,respectively.The sand core was hardened by going through a warm core box process,in which the temperature of core box was 150°C,and the compressed hot air was blown at 120°C for 40 s under a pressure of 0.2 MPa.As for the sand core bonded with modified water glass,the tensile strength is 2.46 MPa at room temperature(σ0)and 2.49 MPa at 25°C and 40%RH for 24 h(σ24),which are 2 times more than that with unmodified binder.The bonded strengths of sand core are increased as a result of the reaction between-OH groups from addition of potassium hydroxide and SiO2 particles widely distributed in the sand core.Comparing with the sand core bonded with unmodified water glass,the high temperature residual tensile strength(σr)of sand core bonded with modified water glass under 600°C for 5 min,is sharply reduced from 0.20 MPa to 0.01 MPa.By the comparison with unmodified water glass,the dynamic viscosity of the modified water glass and the flowability of molding sand using modified water glass are increased from 74 mPa·s and 2.15 g to 80 mPa·s and 2.21 g,respectively.As revealed by FT-IR analysis,new groups including PO3-,PO43-,and Si-O-C appear in the molecular structure of modified water glass,which are beneficial to the collapsibility of sand core.展开更多
基金the Education Bureau of Hubei Province of China(No.2002A01013)
文摘The hot deformation experiments of ultra-low carbon steel in ferrite range were carried out in a hot simulator in order to research hot deformation behaviors of ultra-low carbon steel in ferrite range at low temperature. The results show that the influences of deformation parameters on flow stress are different to those in austenitic deformation. The deformation characteristic parameters were calculated for ultra-low carbon steel in ferrite region. The flow stress equation for ultra-low carbon steel in ferritic deformation at low temperature was obtained.
基金This work was supported by the National Natural Science Foundation of China(Nos.51874090 and U1708253)the National Research Council of Science and Technology Major Project(No.2017-VI-0002).
文摘The effects of laser shock processing(LSP)and warm laser shock processing(WLSP)on the microstructure of surface hardening layer and high-cycle fatigue performance at room temperature and high temperature(600°C)of IN718 alloy were investigated.It has been revealed that the grain refined hardening layer with greater residual compression stresses,higher fraction of coincidence site lattice(CSL)boundaries and dislocation densities was formed in WLSP-treated alloy than in LSP-treated alloys.Moreover,microtwins includedγ″phase/high density dislocation complex was found in the surface of WLSP-treated alloy.These characters caused the significant enhancement of the medium value fatigue strength of WLSP-treated alloy at room temperature and elevated temperature.Apparently,the microtwins includedγ″phase/high density dislocation complex formed in the surface hardening layer of LSP-treated alloy has more complicated steric structure and more stable at elevated temperature thanγ″phase/low density dislocation complex formed in LSP-treated alloy,leading to the slow recovery process.Therefore,the surface hardening layer in the WLSP-treated alloy remained more ideal strengthening effect under high-cycle fatigue at elevated temperature than that in LSP-treated alloy.This resulted in the much longer fatigue crack initiation incubation and longer high-cycle life of WLSP-treated IN718 alloy under cycling load at 600℃.This discovery provides a new cognition of fatigue resistance by WLSP treatment of precipitation strengthening superalloy.
文摘Anisotropic bonded magnets were prepared by warm compaction using anisotropic Nd-Fe-B powder. The forming process, magnetic properties, and temperature stability were studied. The results indicate that the optimal temperature of the process, which was decided by the vis-cosity of the binders, was 110°C. With increasing pressure, the density of the magnets increased. When the pressure was above 700 MPa, the powder particles were destroyed and the magnetic properties decreased. The magnetic properties of the anisotropic bonded magnets were as follows： remanence Br=0.98 T, intrinsic coercivity iHc=1361 kA/m, and maximum energy product BHmax=166 kJ/m3. The magnets had excellent thermal stability because of the high coercivity and good squareness of demagnetization curves. The flux density of the magnets was 35% higher than that of isotropic bonded Nd-Fe-B magnets at 120°C for 1000 h. The flux density of the bonded magnets showed little change with regard to temperature.
基金Project supported by the Natural Science Foundation of Jiangsu Province,China(BK20171408)the Graduate Student Innovation Foundation of Jiangsu Province(201711276005Z)Scientific Foundation of Nanjing Institute of Technology(CKJB201402,and YKJ201506)
文摘Anisotropic NdFeB/SmCoCuFeZr composite bonded magnets were prepared by warm compaction process. The effects of adding SmCoCuFeZr magnetic powder on the properties of anisotropic bonded NdFeB magnet were investigated in this work. The results show that, both magnetic properties and temperature stability of the bonded magnet can be improved by adding fine SmCoCuFeZr magnetic powder. In the present study, the optimal content of SmCoCuFeZr magnetic powder was about 20 wt.%, in this case, the Br, Hcj, and（BH）maxof the NdFeB/SmCoCuFeZr composite magnet achieved 0.943 T, 1250 kA/m, and168 kJ/m^3, respectively.
文摘With modified water glass as binder and the introduction of micro silicon powders into the coremaking process,an improvement was made to the tensile strength and collapsibility of the sand core.The potassium hydroxide,sodium hexametaphosphate and white sugar were applied as the modifiers of water glass.The optimum proportion of the modifiers was determined through the combination of single factor test and orthogonal test.The optimum proportion of water glass,potassium hydroxide,sodium hexametaphosphate and white sugar is 1000:40:5:5(wt.).In terms of weight,modified binder and micro silicon powders accounted for 2%and 0.6%of sand,respectively.The sand core was hardened by going through a warm core box process,in which the temperature of core box was 150°C,and the compressed hot air was blown at 120°C for 40 s under a pressure of 0.2 MPa.As for the sand core bonded with modified water glass,the tensile strength is 2.46 MPa at room temperature(σ0)and 2.49 MPa at 25°C and 40%RH for 24 h(σ24),which are 2 times more than that with unmodified binder.The bonded strengths of sand core are increased as a result of the reaction between-OH groups from addition of potassium hydroxide and SiO2 particles widely distributed in the sand core.Comparing with the sand core bonded with unmodified water glass,the high temperature residual tensile strength(σr)of sand core bonded with modified water glass under 600°C for 5 min,is sharply reduced from 0.20 MPa to 0.01 MPa.By the comparison with unmodified water glass,the dynamic viscosity of the modified water glass and the flowability of molding sand using modified water glass are increased from 74 mPa·s and 2.15 g to 80 mPa·s and 2.21 g,respectively.As revealed by FT-IR analysis,new groups including PO3-,PO43-,and Si-O-C appear in the molecular structure of modified water glass,which are beneficial to the collapsibility of sand core.
