Thermodynamic calculation, SEM (scanning electron microscopy), TEM(transmission electron microscopy), XRD (X-ray diffraction), phase extraction, and chemical analysiswere employed to study the phase stability and phas...Thermodynamic calculation, SEM (scanning electron microscopy), TEM(transmission electron microscopy), XRD (X-ray diffraction), phase extraction, and chemical analysiswere employed to study the phase stability and phase precipitation in a new Ni-Cr-Co basesuperalloy heat-treated at 704 and 760 ℃ for a long tune. The results show that the precipitates ofthis new alloy heat-treated at standard annealing condition and heat-treated at 704 and 760℃ for atime up to 2000 h are γ′, MC, M_(23)C_6, and M_6C, and η phase forms at grain boundaries and inmatrix of samples heat-treated at 760 ℃ as well. The mass fractions of γ′ (+η), MC, M_(23)C_6,and M_6C in all samples have no large changes with an increase in aging time, but γ′ precipitatesgrow obviously. The γ′-to-η transformation in the samples heat-treated at 760℃ took place withincreasing aging time. The η precipitates form a Widmanstaetten pattern and the γ′ phases haveremelted partly in the samples heat-treated at 760 ℃. The alloy maintains a better microstructuralstability during prolonged aging at 704 ℃, but a worse microstructural stability during prolongedaging at 760 ℃.展开更多
The energetics, electronic structure and mechanical property of Co3(Al,W) precipitates with different ratio of Al to W in Co base alloys were investigated by the method of supercell and augmented plane waves plus loca...The energetics, electronic structure and mechanical property of Co3(Al,W) precipitates with different ratio of Al to W in Co base alloys were investigated by the method of supercell and augmented plane waves plus local orbitals within generalized gradient approximation. The calculated results show that the L12 Co3(Al,W) precipitate is the most stable when the ratio of Al to W is equal to 1. When the content of W is higher than 18.5 at%, the L12 and hexagonal structures co-exist in Co3(Al,W) precipitates at 1173 K. It is also shown that the L12 ordered Co3(Al,W) precipitates have an obvious strengthening effect in the disordered fcc cobalt matrix.展开更多
Characteristics of dynamic strain aging （DSA） in a Ni-Co-base superalloy were studied by tensile tests at temperatures ranging from 250 ℃ to 550 ℃ and strain rates ranging from 3 x 10-5 to 8 x 10-4 s-1. Serrated f...Characteristics of dynamic strain aging （DSA） in a Ni-Co-base superalloy were studied by tensile tests at temperatures ranging from 250 ℃ to 550 ℃ and strain rates ranging from 3 x 10-5 to 8 x 10-4 s-1. Serrated flow in the tensile stress-strain curves was observed in the temperature range from 300 ℃ to 500 ℃. Normal DSA behavior was found at temperatures ranging from 300 ℃ to 350 ℃, while inverse DSA behavior was observed at temperatures ranging from 400 ℃ to 500 ℃. The yield strength, ultimate tensile strength, elongation, work hardening index, and fracture features were not affected by temperature and strain rates in DSA regime. Negative strain-rate sensitivity of flow stress was observed in DSA regime. The analysis suggests that the ordering of the substitutional solutes around some defects like mobile dislocations and stacking faults due to the thermal activated process may cause the serrations on the tensile curves.展开更多
In this paper,the microstructure and hydrogen embrittlement(HE) susceptibility of an Fe-Ni-Co based superalloy with different contents of trace elements,P and Mn,have been investigated.The results indicated that by lo...In this paper,the microstructure and hydrogen embrittlement(HE) susceptibility of an Fe-Ni-Co based superalloy with different contents of trace elements,P and Mn,have been investigated.The results indicated that by lowering the contents of trace elements P and Mn,the size and distribution of γ' become more homogeneous,and the precipitation of stable phase η can be retarded to longer ageing time.As a result,the hydrogen resistant properties of the alloy are obviously improved.展开更多
The rapid recurrent thermal annealing (RRTA) method has been used to amorphous Co-Nb-Zr soft magnetic thin films fabricated by DC sputtering. By using this method, in this paper, the crystalline grains with diameter o...The rapid recurrent thermal annealing (RRTA) method has been used to amorphous Co-Nb-Zr soft magnetic thin films fabricated by DC sputtering. By using this method, in this paper, the crystalline grains with diameter of about 30~90 nm are formed and the partial nanocrystallization of the films is realized. As a result, the soft magnetic properties of the Co-based nanocrystalline thin films are improved greatly after RRTA: their resistivity is a quarter decreased; the average initial permeability is enhanced from 3 500 to over 5 000; the impedance is increased form 20 ~100 ?(at 1.4 GHz); the resonance peak is moved about 200 MHz down to low frequency. The evident improvement enables the Co-based nanocrystalline thin films to be used over a much wide frequency range of 1 KHz ~1.5 GHz.展开更多
The high temperature high cycle fatigue behaviour of a directionally solidified Co-base superalloy was investigated. The alloy has saperior fatigue resistance at 900℃ and its fatigue strength is up to 295MPa. Its σ-...The high temperature high cycle fatigue behaviour of a directionally solidified Co-base superalloy was investigated. The alloy has saperior fatigue resistance at 900℃ and its fatigue strength is up to 295MPa. Its σ-Nf curve is characterized by three distinct zones. The stronger dependence of Nf on or in the high .and low stress zones results from multiple fatigue crock initiation sites produced by high stress and oxidation effect in a prolonged exposure, respectively.展开更多
The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and 1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re- sults show tha...The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and 1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re- sults show that the Y-containing cobalt base clad alloy has a finer microstructure and higher corrosion re- sistance to the salt mixture of 75% Na_2SO_4+25%NaCl at high temperature.The unique properties are ob- tained with addition of 0.875% Y for the formation of a continuous and compact oxide scale.The compact scale may act as a barrier for the inward diffusion of oxygen and sulphur and also for the outward diffusion of alloying elements.展开更多
Ni-base alloy DZ468 has been joined by transient liquid phase bonding technique with a newly developed Co-based filler. The microstructures of the Co-base filler and the joint, the effects of heat treatment on microst...Ni-base alloy DZ468 has been joined by transient liquid phase bonding technique with a newly developed Co-based filler. The microstructures of the Co-base filler and the joint, the effects of heat treatment on microstructure and hardness of the joint have been investigated by various experimental methods. Results show that the Co-base filler consists of γ, M2B, M5B3 and M23B6 phases. Because of the interdiffusion between the base metal and the filler, γ, MC, M5B3 and M23B6 phases are formed in the bonding zone. And localized liquidation of substrate occurs in the diffusion affected zone, with MC and M3B2 precipitating in this area. During heat treatment, the volume of the intermetallic phases in the bonding zone resulting from incomplete isothermal solidification decreases obviously. On the contrary, the width of the diffusion affected zone increases at the solution stage and subsequently decreases at the aging stages.展开更多
A thermal fatigue behaviour of Co-based alloy coating obtained by laser surface meltcasting on the high temperature alloy GH33 was studied.The results show that after each time of thermal cycling,the final residual st...A thermal fatigue behaviour of Co-based alloy coating obtained by laser surface meltcasting on the high temperature alloy GH33 was studied.The results show that after each time of thermal cycling,the final residual stress was formed in the melt-casting layer which is attributed to the thermal stress and structural stress.Through the first 50 times of thermal cycling,the morphology of coating still inherits the laser casting one,but the dendrites get bigger;After the second 50 times of thermal cycling,corrosion pits emerge from coating,and mostly in the places where coating and substrate meet.The fatigue damage type of coating belongs to stress corrosion.展开更多
The Co-based alloy coatings had been prepared by laser cladding and vacuum fusion sintering. Microstructures of the coatings were investigated and the performance of thermal cycling was also tested using scanning elec...The Co-based alloy coatings had been prepared by laser cladding and vacuum fusion sintering. Microstructures of the coatings were investigated and the performance of thermal cycling was also tested using scanning electron microscopy （ SEM） and X-ray diffraction （ XRD ）. The results show that the coatings and substrates combine well. The main phase compositions of laser cladding coating are T-Co, Cr23 C6 and Ni2 9 Cro. 7 Feo. 36, while vacuum fusion sintering coating consists of Co, Cr7 C3, and Ni2.9 Cro. 7 Feo. 36. After thermal cycling, the minimum hot cracking width of laser cladding coating is 14 μm; moreover, laser cladding coating maintains high hardness and hot-cracking susceptibility. Those are beneficial to high temperature wear resistance of hot work dies.展开更多
Laser engineered net shaping(LENS) process was investigated using Co-based superalloy powder with a high power continuous wave CO2 laser. Thin wall part with smooth surface was obtained by LENS of layer-by-layer depos...Laser engineered net shaping(LENS) process was investigated using Co-based superalloy powder with a high power continuous wave CO2 laser. Thin wall part with smooth surface was obtained by LENS of layer-by-layer deposition of the powder materials. This thin wall sample was tested for metallographic examinations, micro-hardness, X-ray diffraction and mechanical property test. Microstructural results show that the layers possess rapid solidification microstructural feature, fine dendritic crystal and M7C3-type carbides (essentially chromium-rich carbide) dispersed in theγ(Co,Cr) phase matrix. Dendrite spacing as well as the solidification mode can be controlled through control process parameters. In addition, this microstructural feature of the as-formed Co-base sample leads to an evident hardening and a superior tensile strength and toughness.展开更多
The effect of potassium-decoration was studied on the activity of water-gas shift （WGS） reaction over the Co-Mo-based catalysts supported on active carbon （AC）, which was prepared by incipient wetness co-impregnat...The effect of potassium-decoration was studied on the activity of water-gas shift （WGS） reaction over the Co-Mo-based catalysts supported on active carbon （AC）, which was prepared by incipient wetness co-impregnation method. The decoration of potassium on active carbon in advance enhances the activities of the CoMo-K/AC catalysts for WGS reaction. Highest activity （about 92% conversion） was obtained at 250 ？ C for the catalyst with an optimum K 2 O/AC weight ratio in the range from 0.12 to 0.15. The catalysts were characterized by TPR and EPR, and the results show that activated carbon decorated with potassium makes Co-Mo species highly dispersed, and thus easily reduced and sulfurized. XRD results show that an appropriate content of potassium-decoration on active carbon supports may favors the formation of highly dispersed Co 9 S 8 -type structures which are situated on the edge or a site in contact with MoS 2 , K-Mo-O-S, Mo-S-K phase. Those active species are responsible for the high activity of CoMo-K/AC catalysts.展开更多
The ultrafine particles of a new style Fe-Cu-based catalysts for CO hydrogenation were prepared by impregnating the organic sol of Fe（OH）3 and Cu（OH）2 onto the activated Al2O3, in which the organic sol of Fe（OH）...The ultrafine particles of a new style Fe-Cu-based catalysts for CO hydrogenation were prepared by impregnating the organic sol of Fe（OH）3 and Cu（OH）2 onto the activated Al2O3, in which the organic sol of Fe（OH）3 and Cu（OH）2 were prepared in the microemulsion of dodecylbenzenesulfonic acid sodium（S）/n-butanol（A）/toluene（O）/water with V（A）/V（O） = 0.25 and W（A）/W（S） = 1.50. This catalyst was characterized by particle size analysis, XRD and TG. The results of particle size analysis showed that Fe（OH）3 particles with a mean size of 17.1 nm and Cu（OH）2 particles with an average size of 6.65 um were obtained. TG analysis and XRD patterns suggested that 673 K is the optimal calcination temperature. CO hydrogenation produced C＋OH with a high selectivity above 58 wt% by using the ultrafine particles as catalyst, and the total alcohol yield of 0.250 g·ml^-1 ·h^-1 was obtained when the contents of Al2O3 and K were 88.61 wt% and 1.60 wt%, respectively.展开更多
Highly dispersed Cu-base catalyst has been prepared via thermal decomposition of layered double hydroxides precursors. The XRD pattern and the HRTEM images of the as prepared catalyst confirmed the high dispersion of ...Highly dispersed Cu-base catalyst has been prepared via thermal decomposition of layered double hydroxides precursors. The XRD pattern and the HRTEM images of the as prepared catalyst confirmed the high dispersion of Cu and Fe ions. Results show that the catalyst has a relatively high selectivity of alkanes at low temperature.展开更多
文摘Thermodynamic calculation, SEM (scanning electron microscopy), TEM(transmission electron microscopy), XRD (X-ray diffraction), phase extraction, and chemical analysiswere employed to study the phase stability and phase precipitation in a new Ni-Cr-Co basesuperalloy heat-treated at 704 and 760 ℃ for a long tune. The results show that the precipitates ofthis new alloy heat-treated at standard annealing condition and heat-treated at 704 and 760℃ for atime up to 2000 h are γ′, MC, M_(23)C_6, and M_6C, and η phase forms at grain boundaries and inmatrix of samples heat-treated at 760 ℃ as well. The mass fractions of γ′ (+η), MC, M_(23)C_6,and M_6C in all samples have no large changes with an increase in aging time, but γ′ precipitatesgrow obviously. The γ′-to-η transformation in the samples heat-treated at 760℃ took place withincreasing aging time. The η precipitates form a Widmanstaetten pattern and the γ′ phases haveremelted partly in the samples heat-treated at 760 ℃. The alloy maintains a better microstructuralstability during prolonged aging at 704 ℃, but a worse microstructural stability during prolongedaging at 760 ℃.
基金Supported by the Natural National Science Foundation of China (50571063)
文摘The energetics, electronic structure and mechanical property of Co3(Al,W) precipitates with different ratio of Al to W in Co base alloys were investigated by the method of supercell and augmented plane waves plus local orbitals within generalized gradient approximation. The calculated results show that the L12 Co3(Al,W) precipitate is the most stable when the ratio of Al to W is equal to 1. When the content of W is higher than 18.5 at%, the L12 and hexagonal structures co-exist in Co3(Al,W) precipitates at 1173 K. It is also shown that the L12 ordered Co3(Al,W) precipitates have an obvious strengthening effect in the disordered fcc cobalt matrix.
基金partly supported by "Hundred of Talents Projects"the National Basic Research Program (973 Program) of China under grant No. 2010CB631206the National Natural Science Foundation of China (NSFC) under Grant Nos. 51171179, 51128101 and 51271174
文摘Characteristics of dynamic strain aging （DSA） in a Ni-Co-base superalloy were studied by tensile tests at temperatures ranging from 250 ℃ to 550 ℃ and strain rates ranging from 3 x 10-5 to 8 x 10-4 s-1. Serrated flow in the tensile stress-strain curves was observed in the temperature range from 300 ℃ to 500 ℃. Normal DSA behavior was found at temperatures ranging from 300 ℃ to 350 ℃, while inverse DSA behavior was observed at temperatures ranging from 400 ℃ to 500 ℃. The yield strength, ultimate tensile strength, elongation, work hardening index, and fracture features were not affected by temperature and strain rates in DSA regime. Negative strain-rate sensitivity of flow stress was observed in DSA regime. The analysis suggests that the ordering of the substitutional solutes around some defects like mobile dislocations and stacking faults due to the thermal activated process may cause the serrations on the tensile curves.
文摘In this paper,the microstructure and hydrogen embrittlement(HE) susceptibility of an Fe-Ni-Co based superalloy with different contents of trace elements,P and Mn,have been investigated.The results indicated that by lowering the contents of trace elements P and Mn,the size and distribution of γ' become more homogeneous,and the precipitation of stable phase η can be retarded to longer ageing time.As a result,the hydrogen resistant properties of the alloy are obviously improved.
文摘The rapid recurrent thermal annealing (RRTA) method has been used to amorphous Co-Nb-Zr soft magnetic thin films fabricated by DC sputtering. By using this method, in this paper, the crystalline grains with diameter of about 30~90 nm are formed and the partial nanocrystallization of the films is realized. As a result, the soft magnetic properties of the Co-based nanocrystalline thin films are improved greatly after RRTA: their resistivity is a quarter decreased; the average initial permeability is enhanced from 3 500 to over 5 000; the impedance is increased form 20 ~100 ?(at 1.4 GHz); the resonance peak is moved about 200 MHz down to low frequency. The evident improvement enables the Co-based nanocrystalline thin films to be used over a much wide frequency range of 1 KHz ~1.5 GHz.
文摘The high temperature high cycle fatigue behaviour of a directionally solidified Co-base superalloy was investigated. The alloy has saperior fatigue resistance at 900℃ and its fatigue strength is up to 295MPa. Its σ-Nf curve is characterized by three distinct zones. The stronger dependence of Nf on or in the high .and low stress zones results from multiple fatigue crock initiation sites produced by high stress and oxidation effect in a prolonged exposure, respectively.
基金Research Project supported by the Corrosion Science Laboratory,Academia Sinica
文摘The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and 1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re- sults show that the Y-containing cobalt base clad alloy has a finer microstructure and higher corrosion re- sistance to the salt mixture of 75% Na_2SO_4+25%NaCl at high temperature.The unique properties are ob- tained with addition of 0.875% Y for the formation of a continuous and compact oxide scale.The compact scale may act as a barrier for the inward diffusion of oxygen and sulphur and also for the outward diffusion of alloying elements.
基金supported by the National Base Research Program of China
文摘Ni-base alloy DZ468 has been joined by transient liquid phase bonding technique with a newly developed Co-based filler. The microstructures of the Co-base filler and the joint, the effects of heat treatment on microstructure and hardness of the joint have been investigated by various experimental methods. Results show that the Co-base filler consists of γ, M2B, M5B3 and M23B6 phases. Because of the interdiffusion between the base metal and the filler, γ, MC, M5B3 and M23B6 phases are formed in the bonding zone. And localized liquidation of substrate occurs in the diffusion affected zone, with MC and M3B2 precipitating in this area. During heat treatment, the volume of the intermetallic phases in the bonding zone resulting from incomplete isothermal solidification decreases obviously. On the contrary, the width of the diffusion affected zone increases at the solution stage and subsequently decreases at the aging stages.
基金Project Sponsored by Committee on Science and Technology of Guizhou Province(943068)
文摘A thermal fatigue behaviour of Co-based alloy coating obtained by laser surface meltcasting on the high temperature alloy GH33 was studied.The results show that after each time of thermal cycling,the final residual stress was formed in the melt-casting layer which is attributed to the thermal stress and structural stress.Through the first 50 times of thermal cycling,the morphology of coating still inherits the laser casting one,but the dendrites get bigger;After the second 50 times of thermal cycling,corrosion pits emerge from coating,and mostly in the places where coating and substrate meet.The fatigue damage type of coating belongs to stress corrosion.
文摘The Co-based alloy coatings had been prepared by laser cladding and vacuum fusion sintering. Microstructures of the coatings were investigated and the performance of thermal cycling was also tested using scanning electron microscopy （ SEM） and X-ray diffraction （ XRD ）. The results show that the coatings and substrates combine well. The main phase compositions of laser cladding coating are T-Co, Cr23 C6 and Ni2 9 Cro. 7 Feo. 36, while vacuum fusion sintering coating consists of Co, Cr7 C3, and Ni2.9 Cro. 7 Feo. 36. After thermal cycling, the minimum hot cracking width of laser cladding coating is 14 μm; moreover, laser cladding coating maintains high hardness and hot-cracking susceptibility. Those are beneficial to high temperature wear resistance of hot work dies.
基金Project(51461010101JB3501) supported by National Key Laboratory for High Energy Density Beam Processing Technology Foundation of China
文摘Laser engineered net shaping(LENS) process was investigated using Co-based superalloy powder with a high power continuous wave CO2 laser. Thin wall part with smooth surface was obtained by LENS of layer-by-layer deposition of the powder materials. This thin wall sample was tested for metallographic examinations, micro-hardness, X-ray diffraction and mechanical property test. Microstructural results show that the layers possess rapid solidification microstructural feature, fine dendritic crystal and M7C3-type carbides (essentially chromium-rich carbide) dispersed in theγ(Co,Cr) phase matrix. Dendrite spacing as well as the solidification mode can be controlled through control process parameters. In addition, this microstructural feature of the as-formed Co-base sample leads to an evident hardening and a superior tensile strength and toughness.
文摘The effect of potassium-decoration was studied on the activity of water-gas shift （WGS） reaction over the Co-Mo-based catalysts supported on active carbon （AC）, which was prepared by incipient wetness co-impregnation method. The decoration of potassium on active carbon in advance enhances the activities of the CoMo-K/AC catalysts for WGS reaction. Highest activity （about 92% conversion） was obtained at 250 ？ C for the catalyst with an optimum K 2 O/AC weight ratio in the range from 0.12 to 0.15. The catalysts were characterized by TPR and EPR, and the results show that activated carbon decorated with potassium makes Co-Mo species highly dispersed, and thus easily reduced and sulfurized. XRD results show that an appropriate content of potassium-decoration on active carbon supports may favors the formation of highly dispersed Co 9 S 8 -type structures which are situated on the edge or a site in contact with MoS 2 , K-Mo-O-S, Mo-S-K phase. Those active species are responsible for the high activity of CoMo-K/AC catalysts.
文摘The ultrafine particles of a new style Fe-Cu-based catalysts for CO hydrogenation were prepared by impregnating the organic sol of Fe（OH）3 and Cu（OH）2 onto the activated Al2O3, in which the organic sol of Fe（OH）3 and Cu（OH）2 were prepared in the microemulsion of dodecylbenzenesulfonic acid sodium（S）/n-butanol（A）/toluene（O）/water with V（A）/V（O） = 0.25 and W（A）/W（S） = 1.50. This catalyst was characterized by particle size analysis, XRD and TG. The results of particle size analysis showed that Fe（OH）3 particles with a mean size of 17.1 nm and Cu（OH）2 particles with an average size of 6.65 um were obtained. TG analysis and XRD patterns suggested that 673 K is the optimal calcination temperature. CO hydrogenation produced C＋OH with a high selectivity above 58 wt% by using the ultrafine particles as catalyst, and the total alcohol yield of 0.250 g·ml^-1 ·h^-1 was obtained when the contents of Al2O3 and K were 88.61 wt% and 1.60 wt%, respectively.
文摘Highly dispersed Cu-base catalyst has been prepared via thermal decomposition of layered double hydroxides precursors. The XRD pattern and the HRTEM images of the as prepared catalyst confirmed the high dispersion of Cu and Fe ions. Results show that the catalyst has a relatively high selectivity of alkanes at low temperature.
