In a typical sintered multi-component Sm_(2)Co_(17)-type magnet with strong fiber texture,we show that the distributions of grain boundary precipitates(GBPs)are heavily dependent on the grain boundary(GB)geometry with...In a typical sintered multi-component Sm_(2)Co_(17)-type magnet with strong fiber texture,we show that the distributions of grain boundary precipitates(GBPs)are heavily dependent on the grain boundary(GB)geometry with respect to the texture direction,which has significant effects on domain wall pinning.Re-sults demonstrate that the continuous GBPs turn into discrete upon the angle between{0001}planes and GB increases from 0°to 90°,meanwhile the GBPs thickness and precipitation free zones(PFZs)width both increase linearly by a factor of 2.5-4.Transmission electron microscopy(TEM)reveals that the GBPs are alternatively stacked Cu-rich SmCo_(5)and Zr-rich Sm_(n+1)Co_(5n-1)(n=2,3,4)compounds,while the PFZs are composed of 2:17R and intermediate 2:17R’phases.Atomic-level elemental mappings and first-principles calculations indicate that Cu exists at the Co-2c site in the SmCo_(5)forming SmCo_(3)Cu_(2)and Zr locates at the dumbbell Sm-6c sites in the Sm_(n+1)Co_(5n-1).The symbiotic GBPs have orientation relationships of[0001]GBPs//[0001]2:17R and[1010]GBPs//[2110]2:17R.The formation of anisotropic GBPs is owing to the strong fiber texture,i.e.,the larger angle between{0001}planes and GBs,the more{0001}diffusion channels for atoms to GBs,resulting in discrete and thick GBPs.In-situ Lorentz TEM shows that the domain walls interrupted by GBPs migrate easily under applied magnetic fields.Possible approaches to enhance the magnetic hardness via tuning the GBs are proposed.展开更多
The good combination of mechanical and tribological properties for self-lubricating materials is crucial. In this work, novel self-lubricating Fe-16.4 Mn-4.8 Ni-9.9 Al-xC(wt%) steels containing graphite phase were fab...The good combination of mechanical and tribological properties for self-lubricating materials is crucial. In this work, novel self-lubricating Fe-16.4 Mn-4.8 Ni-9.9 Al-xC(wt%) steels containing graphite phase were fabricated using mechanical alloying and spark plasma sintering. The compositions of the steels were designed by using thermodynamic calculation, and the effect of carbon addition on the microstructure was further investigated. The steel possesses high hardness of 621 HV, high yield strength of 1437 MPa and good fracture toughness at room temperature. The yield strengths are still above 600 MPa at 600?C.The tribological behavior and mechanical properties from room temperature to 800?C were studied, and the wear mechanisms at elevated temperatures were discussed. The steel has a stable friction coefficient of 0.4 and wear rate in a magnitude of 10^(-6) mm^3/N·m below 600?C. The good tribological properties of the steels were mainly attributed to the high hardness, lubrication of graphite and stable surface oxide layer.展开更多
基金the financial support by the National Nat-ural Science Foundation of China(No.52201032)the Science and Technology Innovation Program of Hunan Province(No.2023RC1013)+2 种基金supported by the Advanced Research Center(for FIB and Talos F200X usages)the State Key Laboratory of Powder Metallurgy(for Spectra 300 usage)the High Performance Computing Center(for supercomputing usage)of Central South University.
文摘In a typical sintered multi-component Sm_(2)Co_(17)-type magnet with strong fiber texture,we show that the distributions of grain boundary precipitates(GBPs)are heavily dependent on the grain boundary(GB)geometry with respect to the texture direction,which has significant effects on domain wall pinning.Re-sults demonstrate that the continuous GBPs turn into discrete upon the angle between{0001}planes and GB increases from 0°to 90°,meanwhile the GBPs thickness and precipitation free zones(PFZs)width both increase linearly by a factor of 2.5-4.Transmission electron microscopy(TEM)reveals that the GBPs are alternatively stacked Cu-rich SmCo_(5)and Zr-rich Sm_(n+1)Co_(5n-1)(n=2,3,4)compounds,while the PFZs are composed of 2:17R and intermediate 2:17R’phases.Atomic-level elemental mappings and first-principles calculations indicate that Cu exists at the Co-2c site in the SmCo_(5)forming SmCo_(3)Cu_(2)and Zr locates at the dumbbell Sm-6c sites in the Sm_(n+1)Co_(5n-1).The symbiotic GBPs have orientation relationships of[0001]GBPs//[0001]2:17R and[1010]GBPs//[2110]2:17R.The formation of anisotropic GBPs is owing to the strong fiber texture,i.e.,the larger angle between{0001}planes and GBs,the more{0001}diffusion channels for atoms to GBs,resulting in discrete and thick GBPs.In-situ Lorentz TEM shows that the domain walls interrupted by GBPs migrate easily under applied magnetic fields.Possible approaches to enhance the magnetic hardness via tuning the GBs are proposed.
基金the financial support from the National Science Fund for Distinguished Young Scholars (No.51625404)the State Key Lab of Powder Metallurgythe Natural Science Foundation of Hunan Province of China (No.2017JJ3089)
文摘The good combination of mechanical and tribological properties for self-lubricating materials is crucial. In this work, novel self-lubricating Fe-16.4 Mn-4.8 Ni-9.9 Al-xC(wt%) steels containing graphite phase were fabricated using mechanical alloying and spark plasma sintering. The compositions of the steels were designed by using thermodynamic calculation, and the effect of carbon addition on the microstructure was further investigated. The steel possesses high hardness of 621 HV, high yield strength of 1437 MPa and good fracture toughness at room temperature. The yield strengths are still above 600 MPa at 600?C.The tribological behavior and mechanical properties from room temperature to 800?C were studied, and the wear mechanisms at elevated temperatures were discussed. The steel has a stable friction coefficient of 0.4 and wear rate in a magnitude of 10^(-6) mm^3/N·m below 600?C. The good tribological properties of the steels were mainly attributed to the high hardness, lubrication of graphite and stable surface oxide layer.
