Due to positive mixing heat between Fe and Mg,it is difficult to diffuse for Fe-Mg at the interface of steel/Mg laminated composites,resulting in the inability to achieve high-strength metallurgical bonding.In this pa...Due to positive mixing heat between Fe and Mg,it is difficult to diffuse for Fe-Mg at the interface of steel/Mg laminated composites,resulting in the inability to achieve high-strength metallurgical bonding.In this paper,20#steel/Mg laminated composites were prepared by large deformation rolling and subse-quent diffusion heat treatment process.The interfacial bonding strength was improved by constructing high-density crystal defects at the interface to promote element diffusion.The mechanisms of interface morphology evolution and element diffusion were analyzed by finite element simulation and theoretical calculation.The results show after diffusion heat treatment,the bond strength of the large deformation rolled interface was increased from 14 to 30 MPa.Fe-Mg transition layer with about 80 nm thickness as well as high-density vacancies,dislocations and grain boundaries were formed in the large deforma-tion rolled interface region.During diffusion heat treatment,Mg elements diffused into grain interior and grain boundary regions of 20#steel under the effect of heat-force coupling,and the thickness of Fe-Mg transition layer increased to 150 nm,forming an Fe-based supersaturated solid solution.The in-terface with high-density defects constituted a non-equilibrium interface.The 20#steel internal energy in the non-equilibrium interface is able to overcome positive mixing heat of immiscible Fe-Mg system and provide the driving force for Mg elements diffusion.Promoting elemental diffusion by constructing high-density defects can be a new concept to achieve metallurgical bonding at the interface of immiscible metal laminated composites.展开更多
Garnet is an essential phase in a wide range of metamorphic grades. Ratios of Fe and Mg concentrations in garnet have been widely used as a geothermometer for the crystallization, cooling rate and tectonic uplift rate...Garnet is an essential phase in a wide range of metamorphic grades. Ratios of Fe and Mg concentrations in garnet have been widely used as a geothermometer for the crystallization, cooling rate and tectonic uplift rate because garnets in natural rocks always show a variety of Fe-Mg compositional partition. Normally, Fe-Mg concentrations of natural garnets vary widely and the Fe-Mg exchange reactions usually occur in a complex chemical system. Effect of pressure and temperature on Fe-Mg compositions of garnet in natural pelitic system was studied experimentally at temperatures of 700 to 780 ℃ and pressures from 21 to 29.4 kbar. The concentrations of FeO and MgO of garnet in the run products showed a linear relation with experimental temperatures. The result provided experimental evidence of Fe-Mg partition trend with temperature in a complex natural rock and therefore improved our understanding in the determinations of metamorphic temperature calculated by garnet geothermometer. Although the accurate geological application of our results requires the knowledge of the effects of other components upon [D(Mg)] and [D(Fe)] which is largely unknown currently, the data provided in this study are useful to build the relation between FeO-MgO contents and temperature, which is useful in the metamorphic temperatures determine of rocks with pelitic composition.展开更多
The kinetics of Fe-Mg interdiffusion in nominally dry polycrystalline olivine was investigated at 6 GPa and 1373-1673 K using diffusion couples of forsterite(Fo_(100))and olivine(Fo_(90))aggregates.Diffusion profiles ...The kinetics of Fe-Mg interdiffusion in nominally dry polycrystalline olivine was investigated at 6 GPa and 1373-1673 K using diffusion couples of forsterite(Fo_(100))and olivine(Fo_(90))aggregates.Diffusion profiles were measured by electron microprobe,and diffusion data were analyzed by the Boltzmann-Matano method.Our results show that the Fe-Mg interdiffusion coefficient(D_(Fe-Mg))depends on the iron content(with X_(Fe)ranging from 0 to 0.1).The temperature dependence of D Fe-Mg in olivine can be described by the Arrhenius relation.By combining the present data and a simple model,it is found that the length scale over which the chemical heterogeneities are homogenized by Fe-Mg interdiffusion in the upper mantle is very limited at the geological time scale,only through solid-state diffusion.展开更多
基金supported by the National Key R&D Program of China (No.2018YFA0707300).
文摘Due to positive mixing heat between Fe and Mg,it is difficult to diffuse for Fe-Mg at the interface of steel/Mg laminated composites,resulting in the inability to achieve high-strength metallurgical bonding.In this paper,20#steel/Mg laminated composites were prepared by large deformation rolling and subse-quent diffusion heat treatment process.The interfacial bonding strength was improved by constructing high-density crystal defects at the interface to promote element diffusion.The mechanisms of interface morphology evolution and element diffusion were analyzed by finite element simulation and theoretical calculation.The results show after diffusion heat treatment,the bond strength of the large deformation rolled interface was increased from 14 to 30 MPa.Fe-Mg transition layer with about 80 nm thickness as well as high-density vacancies,dislocations and grain boundaries were formed in the large deforma-tion rolled interface region.During diffusion heat treatment,Mg elements diffused into grain interior and grain boundary regions of 20#steel under the effect of heat-force coupling,and the thickness of Fe-Mg transition layer increased to 150 nm,forming an Fe-based supersaturated solid solution.The in-terface with high-density defects constituted a non-equilibrium interface.The 20#steel internal energy in the non-equilibrium interface is able to overcome positive mixing heat of immiscible Fe-Mg system and provide the driving force for Mg elements diffusion.Promoting elemental diffusion by constructing high-density defects can be a new concept to achieve metallurgical bonding at the interface of immiscible metal laminated composites.
文摘Garnet is an essential phase in a wide range of metamorphic grades. Ratios of Fe and Mg concentrations in garnet have been widely used as a geothermometer for the crystallization, cooling rate and tectonic uplift rate because garnets in natural rocks always show a variety of Fe-Mg compositional partition. Normally, Fe-Mg concentrations of natural garnets vary widely and the Fe-Mg exchange reactions usually occur in a complex chemical system. Effect of pressure and temperature on Fe-Mg compositions of garnet in natural pelitic system was studied experimentally at temperatures of 700 to 780 ℃ and pressures from 21 to 29.4 kbar. The concentrations of FeO and MgO of garnet in the run products showed a linear relation with experimental temperatures. The result provided experimental evidence of Fe-Mg partition trend with temperature in a complex natural rock and therefore improved our understanding in the determinations of metamorphic temperature calculated by garnet geothermometer. Although the accurate geological application of our results requires the knowledge of the effects of other components upon [D(Mg)] and [D(Fe)] which is largely unknown currently, the data provided in this study are useful to build the relation between FeO-MgO contents and temperature, which is useful in the metamorphic temperatures determine of rocks with pelitic composition.
基金supported by the National Science Fund for Distinguished Young Scholars(Grant No.42325203)the National Science and Technology Major Project(Grant No.2025ZD1005200)。
文摘The kinetics of Fe-Mg interdiffusion in nominally dry polycrystalline olivine was investigated at 6 GPa and 1373-1673 K using diffusion couples of forsterite(Fo_(100))and olivine(Fo_(90))aggregates.Diffusion profiles were measured by electron microprobe,and diffusion data were analyzed by the Boltzmann-Matano method.Our results show that the Fe-Mg interdiffusion coefficient(D_(Fe-Mg))depends on the iron content(with X_(Fe)ranging from 0 to 0.1).The temperature dependence of D Fe-Mg in olivine can be described by the Arrhenius relation.By combining the present data and a simple model,it is found that the length scale over which the chemical heterogeneities are homogenized by Fe-Mg interdiffusion in the upper mantle is very limited at the geological time scale,only through solid-state diffusion.
