Alloys with long-period stacking ordered structures(LPSO)have good properties and are highly regarded.Mg-Zn-Y alloy containing LPSO phase was prepared by the traditional casting method,and the aging heat treatment was...Alloys with long-period stacking ordered structures(LPSO)have good properties and are highly regarded.Mg-Zn-Y alloy containing LPSO phase was prepared by the traditional casting method,and the aging heat treatment was performed at different temperatures and times.The microstructure and phase constitutions of the alloy were observed by means of optical microscopy and scanning electron microscopy methods.Results show the microstructure of as-cast Mg95.5Zn1.5Y3 mainly consists ofα-Mg,W phases and LPSO phases.During the aging treatment,fine lamellar-shaped 14H-LPSO phase is formed at the grain boundaries and precipitates from the supersaturated magnesium matrix,and the volume fraction increases as the aging time increases.By controlling the aging time,Mg-Zn-Y alloys with different volume fractions of 14H-LPSO phase were prepared.The aging kinetics equation of the 14H-LPSO phase is summarized,that is f=1-exp(-0.2705 t 0.6368).The phase transformation mechanism of 14H-LPSO in Mg95.5Zn1.5Y3 alloy can be described as the change of dislocation energy.展开更多
Isothermal aging behaviours of a CuZnAl shape memory alloy have been investigated by means of dilatometry.The length of the specimens during isothermal aging from 190 to 280℃ increases with the aging time at each tem...Isothermal aging behaviours of a CuZnAl shape memory alloy have been investigated by means of dilatometry.The length of the specimens during isothermal aging from 190 to 280℃ increases with the aging time at each temperature.The isothermal aging kinetics fits in Avrami equation and the time exponent n decreases with the increase in aging temperature.The apparent activation energy for the isothermal aging process was measured to be 109.0kJ/mol,which is about equal to that of a relaxation internal friction peak at about 200℃ (f≈1 Hz) in the alloy.展开更多
This paper reports the kinetic process of Ag ion exchange for the polycrystalline Na-β'-Al2O3.The interdiffusion coefficients in the process of Ag+ and Na+ ion exchange have been calculated with an 'one dimen...This paper reports the kinetic process of Ag ion exchange for the polycrystalline Na-β'-Al2O3.The interdiffusion coefficients in the process of Ag+ and Na+ ion exchange have been calculated with an 'one dimensional double side diffusion model'. Microstructures of the samples were observed and analysed by XRD, EMPA, SEM. The results of the conductivity measurements for samples with Na+, Ag+ and Na+-Ag+ mobile ions are presented and explained展开更多
To study the influence of aging heat treatments on the microstructure of single crystal superalloys with high content of refractory elements and optimal the aging heat treatment regimes, a single crystal superalloy co...To study the influence of aging heat treatments on the microstructure of single crystal superalloys with high content of refractory elements and optimal the aging heat treatment regimes, a single crystal superalloy containing 22 wt% refractory elements was investigated.Results show that for the experimental alloy, even the homogenization-solution heat treatment for 25 h cannot homogenize the alloying elements completely. During primary aging heat treatment, γ＇ phase grows larger and turns to regular cubes. Higher aging temperature induces larger γ＇ cubes. For specimens with primary aging heat treated at 1120 ℃,γ＇ morphology does not change apparently during secondary aging heat treatment. For specimens with primary aging heat treatment at 1150 ℃,γ＇phase in interdendrite grows obviously comparing with that in dendrites. By analyzing the precipitating kinetics of γ＇phase, it is found that owning to the dendrite segregation and different aging heat treatment temperatures, γ＇ phase at different regions grows under the control of different factors at different aging heat treatment stages. The two controlling factors that are driving forces of phase transformation and element diffusion rate induce obviously different growth rates of γ＇ phase. As a result, the γ＇-precipitating behaviors are variable based on different solute concentrations and aging temperatures. For advanced single crystal superalloys that are supposed to be used at relatively high temperatures, the final γ＇ size after aging heat treatment is suggested to be close to the crossing point of diffusion controlling curve and driving force controlling curve corresponding to the serving temperature. And then,high-temperature properties can be improved.展开更多
In this paper,the evolutions of microstructure and mechanical properties of Cu-l.9Be-0.3Ni-0.15Co alloy were studied.The alloys in the condition of the solution treated（soft state） and 37% cold rolled（hard state） ...In this paper,the evolutions of microstructure and mechanical properties of Cu-l.9Be-0.3Ni-0.15Co alloy were studied.The alloys in the condition of the solution treated（soft state） and 37% cold rolled（hard state） were aged at 320 ℃for different time,respectively.The mechanical properties,electrical conductivity and microstructure of the alloy aged for different time were analyzed.Additionally,the precipitation kinetics of Cu-1.9Be-0.3Ni-0.15Co alloys was investigated.X-ray diffraction and transmission electron microscopy results reveal that both continuous precipitation and discontinuous precipitation existed in the hard-state Cu-l.9Be-0.3Ni-0.15Co alloy during the whole aging process;the sequence of continuous precipitation is G.P.zone →γ″→γ′→γ.Furthermore,the precipitation transformation mechanism of softstate alloy is homogeneous nucleation,while hard-state alloy shows the heterogeneous nucleation（interface nucleation）with the nucleation rate of both states decaying rapidly to zero during aging at 320 ℃.展开更多
基金financially supported by the National Natural Science Foundation of China(51665012)the Jiangxi Province Science Foundation for Outstanding Scholarship(20171BCB23061,2018ACB21020)Primary Research&Development Plan of Jiangxi Province(20192BBEL50019)
文摘Alloys with long-period stacking ordered structures(LPSO)have good properties and are highly regarded.Mg-Zn-Y alloy containing LPSO phase was prepared by the traditional casting method,and the aging heat treatment was performed at different temperatures and times.The microstructure and phase constitutions of the alloy were observed by means of optical microscopy and scanning electron microscopy methods.Results show the microstructure of as-cast Mg95.5Zn1.5Y3 mainly consists ofα-Mg,W phases and LPSO phases.During the aging treatment,fine lamellar-shaped 14H-LPSO phase is formed at the grain boundaries and precipitates from the supersaturated magnesium matrix,and the volume fraction increases as the aging time increases.By controlling the aging time,Mg-Zn-Y alloys with different volume fractions of 14H-LPSO phase were prepared.The aging kinetics equation of the 14H-LPSO phase is summarized,that is f=1-exp(-0.2705 t 0.6368).The phase transformation mechanism of 14H-LPSO in Mg95.5Zn1.5Y3 alloy can be described as the change of dislocation energy.
文摘Isothermal aging behaviours of a CuZnAl shape memory alloy have been investigated by means of dilatometry.The length of the specimens during isothermal aging from 190 to 280℃ increases with the aging time at each temperature.The isothermal aging kinetics fits in Avrami equation and the time exponent n decreases with the increase in aging temperature.The apparent activation energy for the isothermal aging process was measured to be 109.0kJ/mol,which is about equal to that of a relaxation internal friction peak at about 200℃ (f≈1 Hz) in the alloy.
文摘This paper reports the kinetic process of Ag ion exchange for the polycrystalline Na-β'-Al2O3.The interdiffusion coefficients in the process of Ag+ and Na+ ion exchange have been calculated with an 'one dimensional double side diffusion model'. Microstructures of the samples were observed and analysed by XRD, EMPA, SEM. The results of the conductivity measurements for samples with Na+, Ag+ and Na+-Ag+ mobile ions are presented and explained
基金financially supported by the Foundation of Beijing Institute of Aeronautical Materials (No.KJSJ150109)
文摘To study the influence of aging heat treatments on the microstructure of single crystal superalloys with high content of refractory elements and optimal the aging heat treatment regimes, a single crystal superalloy containing 22 wt% refractory elements was investigated.Results show that for the experimental alloy, even the homogenization-solution heat treatment for 25 h cannot homogenize the alloying elements completely. During primary aging heat treatment, γ＇ phase grows larger and turns to regular cubes. Higher aging temperature induces larger γ＇ cubes. For specimens with primary aging heat treated at 1120 ℃,γ＇ morphology does not change apparently during secondary aging heat treatment. For specimens with primary aging heat treatment at 1150 ℃,γ＇phase in interdendrite grows obviously comparing with that in dendrites. By analyzing the precipitating kinetics of γ＇phase, it is found that owning to the dendrite segregation and different aging heat treatment temperatures, γ＇ phase at different regions grows under the control of different factors at different aging heat treatment stages. The two controlling factors that are driving forces of phase transformation and element diffusion rate induce obviously different growth rates of γ＇ phase. As a result, the γ＇-precipitating behaviors are variable based on different solute concentrations and aging temperatures. For advanced single crystal superalloys that are supposed to be used at relatively high temperatures, the final γ＇ size after aging heat treatment is suggested to be close to the crossing point of diffusion controlling curve and driving force controlling curve corresponding to the serving temperature. And then,high-temperature properties can be improved.
基金supported by Materials Forming Processing Control and Simulation Laboratory in University of Science and Technology BeijingCNMC Ningxia Orient Group Co.,Ltd.
文摘In this paper,the evolutions of microstructure and mechanical properties of Cu-l.9Be-0.3Ni-0.15Co alloy were studied.The alloys in the condition of the solution treated（soft state） and 37% cold rolled（hard state） were aged at 320 ℃for different time,respectively.The mechanical properties,electrical conductivity and microstructure of the alloy aged for different time were analyzed.Additionally,the precipitation kinetics of Cu-1.9Be-0.3Ni-0.15Co alloys was investigated.X-ray diffraction and transmission electron microscopy results reveal that both continuous precipitation and discontinuous precipitation existed in the hard-state Cu-l.9Be-0.3Ni-0.15Co alloy during the whole aging process;the sequence of continuous precipitation is G.P.zone →γ″→γ′→γ.Furthermore,the precipitation transformation mechanism of softstate alloy is homogeneous nucleation,while hard-state alloy shows the heterogeneous nucleation（interface nucleation）with the nucleation rate of both states decaying rapidly to zero during aging at 320 ℃.
