The magnesium-lithium （Mg-Li） alloy exhibits two phase structures between 5.7wt% and 10.3wt% Li contents, consisting of the a （hcp） Mg-rich and the β （bcc） Li-rich phases, at room temperature. In the experimen...The magnesium-lithium （Mg-Li） alloy exhibits two phase structures between 5.7wt% and 10.3wt% Li contents, consisting of the a （hcp） Mg-rich and the β （bcc） Li-rich phases, at room temperature. In the experiment, Mg-5Li-2Zn, Mg-9Li-2Zn, Mg-16Li-2Zn, Mg-22Li-2Zn, Mg-5Li-2Zn-2Ca, Mg-9Li-2Zn-2Ca, Mg-16Li-2Zn-2Ca, and Mg-22Li-2Zn-2Ca （wt%） were melted. During the melting process, the flux, which was composed of lithium chloride （LiCl） and lithium fluoride （LiF） in the proportion of 3：1 （mass ratio） and argon gas were used to protect the alloys from oxidation. The microstructure, mechanical properties, and cold-rolling workability of the wrought alloys were studied. The crystal grain of the alloys （adding Ga） is fine . The hardness of the studied alloys decreases with an increase in element Li. The density of the studied alloys is in the range of 1.187 to 1.617 g/cm^3. The reduction of the Mg-16Li-2Zn and Mg-22Li-2Zn alloys can exceed 85% at room temperature. The Mg-9Li-2Zn-2Ca alloy was heat treated at 300℃ for 8, 12, 16, and 24 h, respectively. The optimum heat treatment of the Mg-9Li-2Zn-2Ca alloy is 300℃×12h by metallographic observation and by studying the mechanical properties of the alloys.展开更多
With the means of electron backscattered diffraction(EBSD),mechanical properties test and digital eddy current metal conductivity,the single crystal copper cold-welded joint was tested and analyzed,the structure chang...With the means of electron backscattered diffraction(EBSD),mechanical properties test and digital eddy current metal conductivity,the single crystal copper cold-welded joint was tested and analyzed,the structure change of cold-welded joint and the effect of heat treating on the structure and property of cold-welded joint were discussed.The results show that:The deformation area of the single crystal copper cold welded joint is broken,the crystalline grain at the interface of the joint is refined,and the single crystal structure is still maintained in the base metal area.The hardness of the deformation area increases greatly,the conductivity of the joint does not change much,and the tensile strength of the joint reaches about 70%of that of the base metal.At the interface of the heat treating joint,the single crystal structure of the deformation area and the base metal area are destroyed,and the grains grow up at the interface and the orientation is different.The hardness of the joint interface is much lower than that of the non-heat treating joint,the electrical conductivity of the joint is good,and the tensile strength of the joint is higher than that of the base metal.展开更多
The effect of vacuum heat treatment on the microstructure and microhardness of cold-sprayed Cu-4%Cr-2%Nb alloy coating was investigated. The heat treatment was conducted under the temperatures from 250 ℃ to 950 ℃ wi...The effect of vacuum heat treatment on the microstructure and microhardness of cold-sprayed Cu-4%Cr-2%Nb alloy coating was investigated. The heat treatment was conducted under the temperatures from 250 ℃ to 950 ℃ with a step of 100 ℃ for 2 h. It was found that a dense thick Cu-4Cr-2Nb coating could be formed by cold spraying. After heat treatment, a Cr2Nb phase was uniformly distributed in the matrix, which was transferred from the gas-atomized feedstock. A little grain growth of Cr2Nb phase was observed accompanying with the healing-up of the incomplete interfaces between the deposited particles at the elevated temperatures. The coating microhardness increases a little with increasing the temperature to 350 ℃, and then decreases with further increasing temperature up to 950 ℃. This fact can be attributed to the microstructure evolution during the heat treatment.展开更多
Deep mining is an inevitable tendency in the development of coal industry. There are many heat damage problems with the increase of mining depth. The technology of using doublet wells, together with Heat Exchange Mach...Deep mining is an inevitable tendency in the development of coal industry. There are many heat damage problems with the increase of mining depth. The technology of using doublet wells, together with Heat Exchange Machine Systems (HEMSs), to store cold energy is a key to solve the heat damage problems in deep mines. Based on the geological conditions, thermodynamic and hydraulic parameters of Jiahe Mine, the isotherms in the period of cold energy storage and refrigeration and the volumes of cold water within different temperature ranges of the cold energy storage well were numerically analyzed. The results show that 1) with the same pumped and injected water volumes, the lower the temperature of injected water is, the larger the volume of cold water in the cold energy storage well is. With the larger volume, the effect of cold energy storage is better. 2) the larger the volumes of pumped and reinjected water are, the larger the volume of cold water from the cold energy storage well is. With the larger volume, the effect of refrigeration is better. And 3) without disturbance, the volume and temperature of cold water in the cold energy storage well can keep unchanged or have only a little change for a long time. Therefore the technology of doublet wells for cold energy storage is feasible and the cold energy storage aquifers can meet the requirement of the technology.展开更多
The electromotive force (EMF) changes in type K heavy gauge sheathed thermocouple cables was investigated. To cope with this discrepancy owing to EMF steep reduction and understand the difference between type K heavy ...The electromotive force (EMF) changes in type K heavy gauge sheathed thermocouple cables was investigated. To cope with this discrepancy owing to EMF steep reduction and understand the difference between type K heavy gauge sheathed thermocouple cables and small ones, the affects of EMF from sheath pipe, drawing times, annealing temperature, annealing time and annealing way were mainly studied and appropriately analyzed. The results show the change in the thermal EMF is related with the residual stress and crystal defects, which are imparted by cold work during manufacture. The affects of cold work can be removed by annealing. Finally, a feasible way of fabricating heavy gauge sheathed thermocouples was suggested according to practical situation.展开更多
The elastic limit of single-phase alloy Nb-2Mo-2Zr-1Ti is higher as recovered state in comparison with as cold-rolled or recrystallized one.For Nb-40Ti-5.5AI alloy of age-hardening type,the elastic limit is lower as c...The elastic limit of single-phase alloy Nb-2Mo-2Zr-1Ti is higher as recovered state in comparison with as cold-rolled or recrystallized one.For Nb-40Ti-5.5AI alloy of age-hardening type,the elastic limit is lower as cold-rolled state,but increases considerably after proper aging.However,its elastic modulus changes no more,so the stored-energy (σ_e^2/E)may raise significantly.The temperature dependence on elastic modulus for pure Nb as intensely cold-worked or recrystallized state is anomalous.This anomaly may disap- pear after recovered treatment of intensely cold-worked state at 600℃ for 4 h.and may change no more after that of recrystallized state.The anomalous behaviour of elasticity was also discussed on the non-magnetic Nb.展开更多
Directed energy deposition-arc(DED-Arc)technology has the advantages of simple equipment,low manufacturing cost and high deposition rate,while the use of DED-Arc has problems of microstructure inhomogeneity,position d...Directed energy deposition-arc(DED-Arc)technology has the advantages of simple equipment,low manufacturing cost and high deposition rate,while the use of DED-Arc has problems of microstructure inhomogeneity,position dependence of macroscopic mechanical properties and anisotropy.Therefore,it is necessary to carry out a subsequent heat treatment to improve its microstructure uniformity,mechanical properties and superelasticity.In this investigation,the DED-Arc 15-layer NiTi alloy thin-walled parts with the solution treatment at different process parameters were studied to analyze the effects of solution heat treatment on microstructure,phase composition,phase transformation,microhardness,tensile and superelasticity.The temperature range of solution treatment is 800-1050℃,and the treatment time range is 1-5.5 h.The results show that after solution treatment at 800℃/1 h,the content of precipitated phase decreases,the grain is refined,the microhardness increases,and the mechanical properties in the 0°direction are improved.The strain recovery rate after 10 tensile cycles has increased from 37.13%(as-built)to 49.25%(solid solution treatment).This research provides an effective post treatment method for high-performance DED-Arc NiTi shape memory alloys.展开更多
Conventionally manufactured 35CrMo cold heading steel must undergo spheroidization annealing before the cold heading process In this paper, different types of deformation processes with various controlled cooling peri...Conventionally manufactured 35CrMo cold heading steel must undergo spheroidization annealing before the cold heading process In this paper, different types of deformation processes with various controlled cooling periods were operated to achieve on-line spheroidal cementite using the Gleeble-3500 simulation technique. According to the measured dynamic ferrite transformation temperature （Ad3）, the deformation could be divided into two types： low temperature deformation at 810 and 780℃; ＂deformation-induced ferrite transformation＂ （DIFT） deformation at 750 and 720℃. Compared with the low temperature deformation, the DIFT deformation followed by accelerated cooling to 680℃ is beneficial for the formation of spheroidal cementite. Samples subjected to both the low-temperature deformation and DIFT deformation can obtain granular bainite by accelerated cooling to 640℃; the latter may contribute to the formation of a fine dispersion of secondary constituents. Granular bainite can transform into globular pearlite rapidly during subcritical annealing, and the more the disperse phase, the more homogeneously distributed globular cementite can be obtained.展开更多
This work studied the feasibility of producing a dual-phase aluminium bronze alloy and the use of selected treatments to manipulate the mechanical properties of the produced alloy using local techniques, as a potentia...This work studied the feasibility of producing a dual-phase aluminium bronze alloy and the use of selected treatments to manipulate the mechanical properties of the produced alloy using local techniques, as a potential replacement for con- ventional structural materials, particularly steels. Sand casting was used and was found to be effective based on its ad- vantages of low cost, ease of use and flexibility in the production of a dual-phase aluminium bronze alloy with pre-selected composition of 11% Al content. Cold deformation of 10 and 20% degrees and selected heat treatments were used on the cast alloy to influence its mechanical properties. The selected heat treatments are solution heat treat- ment, normalising, and ageing. The results showed that normalising gave the optimum mix of tested mechanical proper- ties with ultimate tensile strength in the range of 325 MPa, elongation of around 60% and Rockwell hardness values of 46.5 - 63.7 HRc, making this alloy suitable as alternatives to steel in low/medium strength structural applications.展开更多
Cold-rolling workability, heat treatment characteristics and mechanical properties of Mg-5%-22%Li-2%Zn(mass fraction) wrought alloys were studied. Density of alloys is between 1.19 and 1.62 g/cm^3. The limit of reduct...Cold-rolling workability, heat treatment characteristics and mechanical properties of Mg-5%-22%Li-2%Zn(mass fraction) wrought alloys were studied. Density of alloys is between 1.19 and 1.62 g/cm^3. The limit of reduction for cold rolling of the β phase alloys at 16% and 22%Li exceeds 90% at room temperature. The properties and microstructures of Mg-Li-Zn alloys were studied, which were homogenized, cold rolled, then annealed at different temperatures. Recrystallization behaviors of the alloys were investigated through microstructures observing and hardness measuring. The results show that the cast billets are suitable for rolling after homogenization at 573K for 12 h for Mg-9Li-2Zn-2Ca alloy and at 523K for 24 h for Mg-9Li-2Zn-2Ca alloy. The cold rolled plates were completely recrystallizated by annealing at 573K for 1 h.展开更多
Fe-6.5wt%Si alloy has excellent soft magnetic properties,but it is hard to be cold-rolled due to appearance of ordered phases in this alloy.In this paper we report that ultra thin Fe-6.5wt%Si sheet of 0.05 mm thick wa...Fe-6.5wt%Si alloy has excellent soft magnetic properties,but it is hard to be cold-rolled due to appearance of ordered phases in this alloy.In this paper we report that ultra thin Fe-6.5wt%Si sheet of 0.05 mm thick was obtained by heavily cold rolling.By means of optical microscope,micro-hardness indenter,instron,SEM and X-ray diffraction,the effect of heat treatment on mechanical properties of this alloy sheet was investigated.The heavily cold-rolled sheet exhibits some extent of ductility.The ultimate tensile strength reaches 1.93 GPa.After heat treatment,micro-hardness is decreased and the ductility is lost,especially at temperature above 650℃ when recrystallization takes place.The reason for decreasing the ductility lies in the ordered DO3 phase transformation.展开更多
In this study,the effects of annealing and solution aging heat treatment on the microstructure and mechanical properties of cold spray additive manufactured(CSAMed)AA2024/Al_(2)O_(3) composite were investigated.The re...In this study,the effects of annealing and solution aging heat treatment on the microstructure and mechanical properties of cold spray additive manufactured(CSAMed)AA2024/Al_(2)O_(3) composite were investigated.The results showed that both annealing and solution aging enhanced the interfacial bonding between the deposited AA2024 particles in the composite.The tensile properties of CSAMed AA2024/Al_(2)O_(3) composite were significantly improved by 13.8%for ultimate tensile strength and 47.8%for elongation after solution aging.Microstructural examination and fractographic analysis showed that the fracture mechanism between the adjacent AA2024 particles changed from brittle to ductile-dominant mode after heat treatment.However,the interfacial bonding between the AA2024 and Al_(2)O_(3) particles cannot be improved.For the improvement of mechanical properties,the solution aging was slightly better than annealing.In addition,low-temperature annealing greatly reduced the anisotropy of the mechanical properties of CSAMed AA2024/Al_(2)O_(3) composite.展开更多
文摘The magnesium-lithium （Mg-Li） alloy exhibits two phase structures between 5.7wt% and 10.3wt% Li contents, consisting of the a （hcp） Mg-rich and the β （bcc） Li-rich phases, at room temperature. In the experiment, Mg-5Li-2Zn, Mg-9Li-2Zn, Mg-16Li-2Zn, Mg-22Li-2Zn, Mg-5Li-2Zn-2Ca, Mg-9Li-2Zn-2Ca, Mg-16Li-2Zn-2Ca, and Mg-22Li-2Zn-2Ca （wt%） were melted. During the melting process, the flux, which was composed of lithium chloride （LiCl） and lithium fluoride （LiF） in the proportion of 3：1 （mass ratio） and argon gas were used to protect the alloys from oxidation. The microstructure, mechanical properties, and cold-rolling workability of the wrought alloys were studied. The crystal grain of the alloys （adding Ga） is fine . The hardness of the studied alloys decreases with an increase in element Li. The density of the studied alloys is in the range of 1.187 to 1.617 g/cm^3. The reduction of the Mg-16Li-2Zn and Mg-22Li-2Zn alloys can exceed 85% at room temperature. The Mg-9Li-2Zn-2Ca alloy was heat treated at 300℃ for 8, 12, 16, and 24 h, respectively. The optimum heat treatment of the Mg-9Li-2Zn-2Ca alloy is 300℃×12h by metallographic observation and by studying the mechanical properties of the alloys.
文摘With the means of electron backscattered diffraction(EBSD),mechanical properties test and digital eddy current metal conductivity,the single crystal copper cold-welded joint was tested and analyzed,the structure change of cold-welded joint and the effect of heat treating on the structure and property of cold-welded joint were discussed.The results show that:The deformation area of the single crystal copper cold welded joint is broken,the crystalline grain at the interface of the joint is refined,and the single crystal structure is still maintained in the base metal area.The hardness of the deformation area increases greatly,the conductivity of the joint does not change much,and the tensile strength of the joint reaches about 70%of that of the base metal.At the interface of the heat treating joint,the single crystal structure of the deformation area and the base metal area are destroyed,and the grains grow up at the interface and the orientation is different.The hardness of the joint interface is much lower than that of the non-heat treating joint,the electrical conductivity of the joint is good,and the tensile strength of the joint is higher than that of the base metal.
文摘The effect of vacuum heat treatment on the microstructure and microhardness of cold-sprayed Cu-4%Cr-2%Nb alloy coating was investigated. The heat treatment was conducted under the temperatures from 250 ℃ to 950 ℃ with a step of 100 ℃ for 2 h. It was found that a dense thick Cu-4Cr-2Nb coating could be formed by cold spraying. After heat treatment, a Cr2Nb phase was uniformly distributed in the matrix, which was transferred from the gas-atomized feedstock. A little grain growth of Cr2Nb phase was observed accompanying with the healing-up of the incomplete interfaces between the deposited particles at the elevated temperatures. The coating microhardness increases a little with increasing the temperature to 350 ℃, and then decreases with further increasing temperature up to 950 ℃. This fact can be attributed to the microstructure evolution during the heat treatment.
基金Project 50490270 supported by Key Project of National Natural Science Foundation of China
文摘Deep mining is an inevitable tendency in the development of coal industry. There are many heat damage problems with the increase of mining depth. The technology of using doublet wells, together with Heat Exchange Machine Systems (HEMSs), to store cold energy is a key to solve the heat damage problems in deep mines. Based on the geological conditions, thermodynamic and hydraulic parameters of Jiahe Mine, the isotherms in the period of cold energy storage and refrigeration and the volumes of cold water within different temperature ranges of the cold energy storage well were numerically analyzed. The results show that 1) with the same pumped and injected water volumes, the lower the temperature of injected water is, the larger the volume of cold water in the cold energy storage well is. With the larger volume, the effect of cold energy storage is better. 2) the larger the volumes of pumped and reinjected water are, the larger the volume of cold water from the cold energy storage well is. With the larger volume, the effect of refrigeration is better. And 3) without disturbance, the volume and temperature of cold water in the cold energy storage well can keep unchanged or have only a little change for a long time. Therefore the technology of doublet wells for cold energy storage is feasible and the cold energy storage aquifers can meet the requirement of the technology.
文摘The electromotive force (EMF) changes in type K heavy gauge sheathed thermocouple cables was investigated. To cope with this discrepancy owing to EMF steep reduction and understand the difference between type K heavy gauge sheathed thermocouple cables and small ones, the affects of EMF from sheath pipe, drawing times, annealing temperature, annealing time and annealing way were mainly studied and appropriately analyzed. The results show the change in the thermal EMF is related with the residual stress and crystal defects, which are imparted by cold work during manufacture. The affects of cold work can be removed by annealing. Finally, a feasible way of fabricating heavy gauge sheathed thermocouples was suggested according to practical situation.
文摘The elastic limit of single-phase alloy Nb-2Mo-2Zr-1Ti is higher as recovered state in comparison with as cold-rolled or recrystallized one.For Nb-40Ti-5.5AI alloy of age-hardening type,the elastic limit is lower as cold-rolled state,but increases considerably after proper aging.However,its elastic modulus changes no more,so the stored-energy (σ_e^2/E)may raise significantly.The temperature dependence on elastic modulus for pure Nb as intensely cold-worked or recrystallized state is anomalous.This anomaly may disap- pear after recovered treatment of intensely cold-worked state at 600℃ for 4 h.and may change no more after that of recrystallized state.The anomalous behaviour of elasticity was also discussed on the non-magnetic Nb.
基金The study was supported by the National Natural Science Foundation of China(No.52105396).The authors thank the State Key Laboratory of Materials Processing and Die&Mould Technology,and the Analytical&Testing Center,Huazhong University of Science&Technology for the extensive experiments.
文摘Directed energy deposition-arc(DED-Arc)technology has the advantages of simple equipment,low manufacturing cost and high deposition rate,while the use of DED-Arc has problems of microstructure inhomogeneity,position dependence of macroscopic mechanical properties and anisotropy.Therefore,it is necessary to carry out a subsequent heat treatment to improve its microstructure uniformity,mechanical properties and superelasticity.In this investigation,the DED-Arc 15-layer NiTi alloy thin-walled parts with the solution treatment at different process parameters were studied to analyze the effects of solution heat treatment on microstructure,phase composition,phase transformation,microhardness,tensile and superelasticity.The temperature range of solution treatment is 800-1050℃,and the treatment time range is 1-5.5 h.The results show that after solution treatment at 800℃/1 h,the content of precipitated phase decreases,the grain is refined,the microhardness increases,and the mechanical properties in the 0°direction are improved.The strain recovery rate after 10 tensile cycles has increased from 37.13%(as-built)to 49.25%(solid solution treatment).This research provides an effective post treatment method for high-performance DED-Arc NiTi shape memory alloys.
文摘Conventionally manufactured 35CrMo cold heading steel must undergo spheroidization annealing before the cold heading process In this paper, different types of deformation processes with various controlled cooling periods were operated to achieve on-line spheroidal cementite using the Gleeble-3500 simulation technique. According to the measured dynamic ferrite transformation temperature （Ad3）, the deformation could be divided into two types： low temperature deformation at 810 and 780℃; ＂deformation-induced ferrite transformation＂ （DIFT） deformation at 750 and 720℃. Compared with the low temperature deformation, the DIFT deformation followed by accelerated cooling to 680℃ is beneficial for the formation of spheroidal cementite. Samples subjected to both the low-temperature deformation and DIFT deformation can obtain granular bainite by accelerated cooling to 640℃; the latter may contribute to the formation of a fine dispersion of secondary constituents. Granular bainite can transform into globular pearlite rapidly during subcritical annealing, and the more the disperse phase, the more homogeneously distributed globular cementite can be obtained.
文摘This work studied the feasibility of producing a dual-phase aluminium bronze alloy and the use of selected treatments to manipulate the mechanical properties of the produced alloy using local techniques, as a potential replacement for con- ventional structural materials, particularly steels. Sand casting was used and was found to be effective based on its ad- vantages of low cost, ease of use and flexibility in the production of a dual-phase aluminium bronze alloy with pre-selected composition of 11% Al content. Cold deformation of 10 and 20% degrees and selected heat treatments were used on the cast alloy to influence its mechanical properties. The selected heat treatments are solution heat treat- ment, normalising, and ageing. The results showed that normalising gave the optimum mix of tested mechanical proper- ties with ultimate tensile strength in the range of 325 MPa, elongation of around 60% and Rockwell hardness values of 46.5 - 63.7 HRc, making this alloy suitable as alternatives to steel in low/medium strength structural applications.
基金Project supported by National High Tech Research Programof China (2001AA335010)
文摘Cold-rolling workability, heat treatment characteristics and mechanical properties of Mg-5%-22%Li-2%Zn(mass fraction) wrought alloys were studied. Density of alloys is between 1.19 and 1.62 g/cm^3. The limit of reduction for cold rolling of the β phase alloys at 16% and 22%Li exceeds 90% at room temperature. The properties and microstructures of Mg-Li-Zn alloys were studied, which were homogenized, cold rolled, then annealed at different temperatures. Recrystallization behaviors of the alloys were investigated through microstructures observing and hardness measuring. The results show that the cast billets are suitable for rolling after homogenization at 573K for 12 h for Mg-9Li-2Zn-2Ca alloy and at 523K for 24 h for Mg-9Li-2Zn-2Ca alloy. The cold rolled plates were completely recrystallizated by annealing at 573K for 1 h.
基金supported by the National Basic Research Program of China ("973" Project)(Grant No 2006CB605205-2)the National Natural Science Foundation of China (Grant No 50771018)
文摘Fe-6.5wt%Si alloy has excellent soft magnetic properties,but it is hard to be cold-rolled due to appearance of ordered phases in this alloy.In this paper we report that ultra thin Fe-6.5wt%Si sheet of 0.05 mm thick was obtained by heavily cold rolling.By means of optical microscope,micro-hardness indenter,instron,SEM and X-ray diffraction,the effect of heat treatment on mechanical properties of this alloy sheet was investigated.The heavily cold-rolled sheet exhibits some extent of ductility.The ultimate tensile strength reaches 1.93 GPa.After heat treatment,micro-hardness is decreased and the ductility is lost,especially at temperature above 650℃ when recrystallization takes place.The reason for decreasing the ductility lies in the ordered DO3 phase transformation.
基金supported by the National Natural Science Foundation of China (No.51875471)the Research Fund of the State Key Laboratory of Solidification Processing (NPU),China (No.2021TZ-01)。
文摘In this study,the effects of annealing and solution aging heat treatment on the microstructure and mechanical properties of cold spray additive manufactured(CSAMed)AA2024/Al_(2)O_(3) composite were investigated.The results showed that both annealing and solution aging enhanced the interfacial bonding between the deposited AA2024 particles in the composite.The tensile properties of CSAMed AA2024/Al_(2)O_(3) composite were significantly improved by 13.8%for ultimate tensile strength and 47.8%for elongation after solution aging.Microstructural examination and fractographic analysis showed that the fracture mechanism between the adjacent AA2024 particles changed from brittle to ductile-dominant mode after heat treatment.However,the interfacial bonding between the AA2024 and Al_(2)O_(3) particles cannot be improved.For the improvement of mechanical properties,the solution aging was slightly better than annealing.In addition,low-temperature annealing greatly reduced the anisotropy of the mechanical properties of CSAMed AA2024/Al_(2)O_(3) composite.
