Mg-5.88 Zn-0.53 Cu-0.16 Zr(wt.%)alloy was solidified at 2-6 GPa using high-pressure solidification technology.The microstructure,strengthening mechanism and compressive properties at room temperature were studied usin...Mg-5.88 Zn-0.53 Cu-0.16 Zr(wt.%)alloy was solidified at 2-6 GPa using high-pressure solidification technology.The microstructure,strengthening mechanism and compressive properties at room temperature were studied using SEM and XRD.The results showed that the microstructure was refined and the secondary dendrite spacing changed from 35μm at atmospheric pressure to 10μm at 6 GPa gradually.Also,Mg(Zn,Cu)2 and Mg Zn Cu eutectic phases were distributed in the shape of network,while under high pressures the second phases(Mg(Zn,Cu)2 and Mg7 Zn3)were mainly granular or strip-like.The solid solubility of Zn and Cu in the matrix built up over increasing solidification pressure and reached 4.12%and 0.32%respectively at 6 GPa.The hardness value was HV 90 and the maximum compression resistance was 430 MPa.Therefore,the grain refinement strengthening,the second phase strengthening and the solid solution strengthening are the principal strengthening mechanisms.展开更多
Microstructure control is a great challenge in the high-temperature gradient directional solidification of eutectic composite ceramics due to the complex solidification behavior.Herein,the microstructure trans-formati...Microstructure control is a great challenge in the high-temperature gradient directional solidification of eutectic composite ceramics due to the complex solidification behavior.Herein,the microstructure trans-formation of faceted Al_(2)O_(3)/Er_(3)Al_(5)O_(12) thermal emission eutectic composite ceramics is explored over wide ranges of compositions(13.5 mol%-22.5 mol%Er_(2)O_(3))and solidification rates(2-200μm/s).Entirely cou-pled eutectics with primary phases suppressed are fabricated and the coupled zone is broadened in a wide range of 15.5 mol%-22.5 mol%Er_(2)O_(3) at low solidification rates.The competitive growth between eutectic and dendrite is evaluated on the basis of the maximum interface temperature criterion.In ad-dition,the mechanisms of irregular eutectic spacing selection and adjustment under different solidifi-cation rates are revealed based on Magnin-Kurz model.A successful prediction of lamellar to rod-like eutectics is achieved associated with the dynamic instability of lamellar eutectic and the corresponding enlarged coexistence region is mapped based on the interface undercooling.According to the well mi-crostructure tailoring,the flexural strength of Al_(2)O_(3)/Er_(3)Al_(5)O_(12) eutectic composite ceramics has improved from 508 MPa up to 1800 MPa due to the refined eutectic spacing with low fluctuation.The eutectic composite ceramics show strong selective optical absorption and the intensity increases with the refin-ing microstructure.The as-designed Al_(2)O_(3)/Er_(3)Al_(5)O_(12) composites with microstructural tailoring have great potential as integrations of structural and functional materials.展开更多
Rapid solidification in undercooled Ni-18.7 at.%Sn eutectic melts was observed in-situ by a high-speed high-resolution camera and the microstructures were characterized in detail by electron backscattering diffraction...Rapid solidification in undercooled Ni-18.7 at.%Sn eutectic melts was observed in-situ by a high-speed high-resolution camera and the microstructures were characterized in detail by electron backscattering diffraction.For the first time,the exact crystallographic orientation relations(ORs)between HCP-Ni_(3)Sn(α-Ni)subsets were analyzed.For HCP-Ni_(3)Sn,the{1121}<1126>and/or{1122}<1123>twin ORs(i.e.,HCP-Ni_(3)Sn twins)hold independently on undercooling,whereas forα-Ni,the{111}<112>twin OR is the case at low undercooling and would hold initially at intermediate and high undercooling.The roles of twinning and allotropy transformation(i.e.,FCC-Ni_(3)Sn→HCP-Ni_(3)Sn)were integrated to reveal the formation mechanism of HCP-Ni_(3)Sn twins,and a reversed OR transition analysis was carried out for rep-resentative samples from low to high undercooling.Consequently,novel twin-assisted eutectic growth was found to occur all along.On this basis,we showed that the single nucleation mode of Herlach is followed,and speculated that primary and secondary coupled eutectic dendrite growth and un-coupled growth ofα-Ni and FCC-Ni_(3)Sn might all be the origins of anomalous eutectics.This work would shed some lights on the long-time controversies about the nucleation mode and the formation mechanism of anomalous eutectics in undercooled eutectic alloys.展开更多
High entropy alloys are the focus of current research.An accurate description of their phase-transformation path,however,is a challenge when their phase constituent and transformation process are complex.In this study...High entropy alloys are the focus of current research.An accurate description of their phase-transformation path,however,is a challenge when their phase constituent and transformation process are complex.In this study,a FeCoNiSn x eutectic high entropy alloy(EHEA)system was investigated and a novel FeCoNiSn EHEA composed of BCC+HCP phases was reported.The transition from the hypoeutectic to the fully eutectic and then to the hypereutectic microstructure with the Sn addition was characterized by the electron backscatter diffraction(EBSD)technology,and the phase-transformation path was clari-fied by crystallographic orientation relationships.The studies reveal that the primary phase of FeCoNiSn x(x=0.2,0.4)is FCC structure,and a further Sn addition induces an obvious phase-transformation from FCC to BCC in both the primary phase and eutectic lamellar,which satisfies the Kurdjumov-Sachs(K-S)or Nishiyama-Wasserman(N-W)variant orientation relationship.The mechanical results confirm that the phase structure and microstructure transition caused by Sn addition do significantly improve the strength and hardness of FeCoNiSn x EHEAs,but have serious adverse effects on plasticity.This study would be of significance to understanding the phase-transformation process in HEAs and preparing the HEAs with aimed mechanical properties.展开更多
Here we show the results of experimental observation of decomposition of the solution components into the neighboring cells. The liquid solution under crystallization first gets into the unstable state and then decomp...Here we show the results of experimental observation of decomposition of the solution components into the neighboring cells. The liquid solution under crystallization first gets into the unstable state and then decomposes. The decomposition result is fixed in the solid phase as inhomogeneous component distribution. Our experimental results enable to argue that the eutectic pattern forms due to interface instability and spinodal decomposition of non-equilibrium solution forming in front of the interface.展开更多
The effects of Mg content and cooling rate on the solidification behaviour of Al-7%Si-Mg（mass fraction） casting alloys have been investigated using differential scanning calorimetry, differential thermal analysis an...The effects of Mg content and cooling rate on the solidification behaviour of Al-7%Si-Mg（mass fraction） casting alloys have been investigated using differential scanning calorimetry, differential thermal analysis and microscopy. The Mg contents were selected as respectively 0.00%, 0.35% and 0.70%（mass fraction）. DTA curves of Al-7%Si-0.55%Mg（mass fraction） alloy at various cooling rates were accomplished and the alloy melt was cast in different cooling rates. The results indicate that increasing Mg content can lower the liquidus and binary Al-Si eutectic transformation temperatures. Large Fe-rich π-phases （Al8FeMg3Si6） are found in the 0.70% Mg alloys together with some small β-phases （Al5FeSi）; in contrast, only β-phases are observed in the 0.35% Mg alloys. The test results of the Al-7%Si-0.55%Mg alloys identify that the liquidus and binary Al-Si eutectic transformation temperatures decrease, and the quantity of ternary Al-Si-Mg2Si eutectic phase decreases as the cooling rate increases.展开更多
The paper presents the calculation results on the construction of solidus lines of phase diagrams for some binary metal systems based on cadmium, zinc and tellurium. The investigations have been carried out using the ...The paper presents the calculation results on the construction of solidus lines of phase diagrams for some binary metal systems based on cadmium, zinc and tellurium. The investigations have been carried out using the phase equilibrium thermodynamics and known liquidus lines. By the calculation method the solidus lines of phase diagrams of the Cd-Na, Cd-Tl, Te-Ga, Te-As, Te-Cu and Zn-Sn systems were constructed in the temperature range from the base component melting point to the eutectic transformation temperature. In the Cd-Tl, Te-As, Te-Cu and Zn-Sn systems a retrograde solubility of the second component in the solid phase was observed. The temperature and maximum solubility values at the retrograde behavior of solidus lines, as well as, the limiting solubility values of components at eutectic transformation in the systems based on Cd, Zn and Te were determined.展开更多
基金Projects(51675092,51775099)supported by the National Natural Science Foundation of ChinaProjects(E2018501030,E2018501033,E2018501032)supported by the Natural Science Foundation of Hebei Province,China.
文摘Mg-5.88 Zn-0.53 Cu-0.16 Zr(wt.%)alloy was solidified at 2-6 GPa using high-pressure solidification technology.The microstructure,strengthening mechanism and compressive properties at room temperature were studied using SEM and XRD.The results showed that the microstructure was refined and the secondary dendrite spacing changed from 35μm at atmospheric pressure to 10μm at 6 GPa gradually.Also,Mg(Zn,Cu)2 and Mg Zn Cu eutectic phases were distributed in the shape of network,while under high pressures the second phases(Mg(Zn,Cu)2 and Mg7 Zn3)were mainly granular or strip-like.The solid solubility of Zn and Cu in the matrix built up over increasing solidification pressure and reached 4.12%and 0.32%respectively at 6 GPa.The hardness value was HV 90 and the maximum compression resistance was 430 MPa.Therefore,the grain refinement strengthening,the second phase strengthening and the solid solution strengthening are the principal strengthening mechanisms.
基金supported by the National Natural Science Foundation of China (Nos.52130204,52174376,and 51822405)the Guangdong Basic and Applied Basic Research Foundation (No.2021B1515120028)+2 种基金the Science and Technology Innovation Team Plan of Shaan Xi Province (No.2021TD-17)the Youth Innovation Team of Shaanxi Universities,Fundamental Research Funds for the Central Universities (No.D5000210902)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University (Nos.CX2021056,CX2021066,and CX2022033),China.
文摘Microstructure control is a great challenge in the high-temperature gradient directional solidification of eutectic composite ceramics due to the complex solidification behavior.Herein,the microstructure trans-formation of faceted Al_(2)O_(3)/Er_(3)Al_(5)O_(12) thermal emission eutectic composite ceramics is explored over wide ranges of compositions(13.5 mol%-22.5 mol%Er_(2)O_(3))and solidification rates(2-200μm/s).Entirely cou-pled eutectics with primary phases suppressed are fabricated and the coupled zone is broadened in a wide range of 15.5 mol%-22.5 mol%Er_(2)O_(3) at low solidification rates.The competitive growth between eutectic and dendrite is evaluated on the basis of the maximum interface temperature criterion.In ad-dition,the mechanisms of irregular eutectic spacing selection and adjustment under different solidifi-cation rates are revealed based on Magnin-Kurz model.A successful prediction of lamellar to rod-like eutectics is achieved associated with the dynamic instability of lamellar eutectic and the corresponding enlarged coexistence region is mapped based on the interface undercooling.According to the well mi-crostructure tailoring,the flexural strength of Al_(2)O_(3)/Er_(3)Al_(5)O_(12) eutectic composite ceramics has improved from 508 MPa up to 1800 MPa due to the refined eutectic spacing with low fluctuation.The eutectic composite ceramics show strong selective optical absorption and the intensity increases with the refin-ing microstructure.The as-designed Al_(2)O_(3)/Er_(3)Al_(5)O_(12) composites with microstructural tailoring have great potential as integrations of structural and functional materials.
基金This work was financially supported by the National Natural Science Foundation of China(No.51975474)the Fundamental Research Funds for the Central Universities(No.3102019JC001)Haifeng Wang is very grateful to Prof.D.M.Herlach(1949-2022)for his inspiring suggestions and continuous support on the work of rapid solidification.
文摘Rapid solidification in undercooled Ni-18.7 at.%Sn eutectic melts was observed in-situ by a high-speed high-resolution camera and the microstructures were characterized in detail by electron backscattering diffraction.For the first time,the exact crystallographic orientation relations(ORs)between HCP-Ni_(3)Sn(α-Ni)subsets were analyzed.For HCP-Ni_(3)Sn,the{1121}<1126>and/or{1122}<1123>twin ORs(i.e.,HCP-Ni_(3)Sn twins)hold independently on undercooling,whereas forα-Ni,the{111}<112>twin OR is the case at low undercooling and would hold initially at intermediate and high undercooling.The roles of twinning and allotropy transformation(i.e.,FCC-Ni_(3)Sn→HCP-Ni_(3)Sn)were integrated to reveal the formation mechanism of HCP-Ni_(3)Sn twins,and a reversed OR transition analysis was carried out for rep-resentative samples from low to high undercooling.Consequently,novel twin-assisted eutectic growth was found to occur all along.On this basis,we showed that the single nucleation mode of Herlach is followed,and speculated that primary and secondary coupled eutectic dendrite growth and un-coupled growth ofα-Ni and FCC-Ni_(3)Sn might all be the origins of anomalous eutectics.This work would shed some lights on the long-time controversies about the nucleation mode and the formation mechanism of anomalous eutectics in undercooled eutectic alloys.
基金the Natural Science Foundation of China(No.51975474)the Fundamental Research Funds for the Central Universities(No.3102019JC001)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX201907).
文摘High entropy alloys are the focus of current research.An accurate description of their phase-transformation path,however,is a challenge when their phase constituent and transformation process are complex.In this study,a FeCoNiSn x eutectic high entropy alloy(EHEA)system was investigated and a novel FeCoNiSn EHEA composed of BCC+HCP phases was reported.The transition from the hypoeutectic to the fully eutectic and then to the hypereutectic microstructure with the Sn addition was characterized by the electron backscatter diffraction(EBSD)technology,and the phase-transformation path was clari-fied by crystallographic orientation relationships.The studies reveal that the primary phase of FeCoNiSn x(x=0.2,0.4)is FCC structure,and a further Sn addition induces an obvious phase-transformation from FCC to BCC in both the primary phase and eutectic lamellar,which satisfies the Kurdjumov-Sachs(K-S)or Nishiyama-Wasserman(N-W)variant orientation relationship.The mechanical results confirm that the phase structure and microstructure transition caused by Sn addition do significantly improve the strength and hardness of FeCoNiSn x EHEAs,but have serious adverse effects on plasticity.This study would be of significance to understanding the phase-transformation process in HEAs and preparing the HEAs with aimed mechanical properties.
文摘Here we show the results of experimental observation of decomposition of the solution components into the neighboring cells. The liquid solution under crystallization first gets into the unstable state and then decomposes. The decomposition result is fixed in the solid phase as inhomogeneous component distribution. Our experimental results enable to argue that the eutectic pattern forms due to interface instability and spinodal decomposition of non-equilibrium solution forming in front of the interface.
基金Project (G2000067202) supported by the National Major Basic Research Program of China
文摘The effects of Mg content and cooling rate on the solidification behaviour of Al-7%Si-Mg（mass fraction） casting alloys have been investigated using differential scanning calorimetry, differential thermal analysis and microscopy. The Mg contents were selected as respectively 0.00%, 0.35% and 0.70%（mass fraction）. DTA curves of Al-7%Si-0.55%Mg（mass fraction） alloy at various cooling rates were accomplished and the alloy melt was cast in different cooling rates. The results indicate that increasing Mg content can lower the liquidus and binary Al-Si eutectic transformation temperatures. Large Fe-rich π-phases （Al8FeMg3Si6） are found in the 0.70% Mg alloys together with some small β-phases （Al5FeSi）; in contrast, only β-phases are observed in the 0.35% Mg alloys. The test results of the Al-7%Si-0.55%Mg alloys identify that the liquidus and binary Al-Si eutectic transformation temperatures decrease, and the quantity of ternary Al-Si-Mg2Si eutectic phase decreases as the cooling rate increases.
文摘The paper presents the calculation results on the construction of solidus lines of phase diagrams for some binary metal systems based on cadmium, zinc and tellurium. The investigations have been carried out using the phase equilibrium thermodynamics and known liquidus lines. By the calculation method the solidus lines of phase diagrams of the Cd-Na, Cd-Tl, Te-Ga, Te-As, Te-Cu and Zn-Sn systems were constructed in the temperature range from the base component melting point to the eutectic transformation temperature. In the Cd-Tl, Te-As, Te-Cu and Zn-Sn systems a retrograde solubility of the second component in the solid phase was observed. The temperature and maximum solubility values at the retrograde behavior of solidus lines, as well as, the limiting solubility values of components at eutectic transformation in the systems based on Cd, Zn and Te were determined.
