Dense Fe-Al-Cr coatings with approximately 50 μm in thickness are successfully prepared on the 1045 carbon steel substrates via a laser cladding process. Proper Cr content(5 at% Cr) will lead to decrease in the melti...Dense Fe-Al-Cr coatings with approximately 50 μm in thickness are successfully prepared on the 1045 carbon steel substrates via a laser cladding process. Proper Cr content(5 at% Cr) will lead to decrease in the melting point, and improves the viscosity of the liquid and the nucleation rate of the molten pool, leading to refining grains of the solidification structure. As a result, the Fe-29 Al-5 Cr laser cladding layer exhibits the best hardness, plasticity properties, and wear resistance at 400 °C. Excessive Cr for the Fe-29 Al-7.5 Cr coating leads to the formation of Cr2 Al in the grain boundaries and thermal vacancies during the solidification process, resulting in inferior mechanical properties and poor tribological behavior.展开更多
Double glow plasma surface metallurgy technique was used to fabricate a Fe?Al?Cr?Nb alloyed layer onto the surface of the 45 steel. The microstructures and composition of th?eA Fl?eCr?Nb alloyed layer were analyzed by...Double glow plasma surface metallurgy technique was used to fabricate a Fe?Al?Cr?Nb alloyed layer onto the surface of the 45 steel. The microstructures and composition of th?eA Fl?eCr?Nb alloyed layer were analyzed by scanning electronic microscopy, X-ray diffraction and energy dispersive spectroscopy. The results indicate thatthe 20 μm alloyed layer is homogeneous and compact. The alloyed elements exhibit a gradient distribution along the cross section. Microhardness and nanoindentation tests imply that the surface hardness of the alloyed layer reaches HV 580, which is almost 2.8 times that of the substrate. Compared with the substrate, the alloyed layer has a much smaller displacement and a larger elastic modulus. According to the friction and wear tests at room temperature, the? FeAl?Cr?Nb alloyed layer has lower friction coefficient and less wear mass, implying that the Fe?Al?Cr?Nb alloyed layer can effectively improve the surface hardness and wear resistance of the substrate.展开更多
To obtain the stable temperature field required for growing sapphire crystals, the influence of relative positions between RF coil and crucible on the performances of sapphires produced by edge-defined film-fed growth...To obtain the stable temperature field required for growing sapphire crystals, the influence of relative positions between RF coil and crucible on the performances of sapphires produced by edge-defined film-fed growth（EFG） technique was investigated. For comparison, the crucible was located at the top（case A） and the middle（case B） of the RF coil, respectively. Furthermore, the lattice integrities were studied by the double-crystal X-ray diffraction, and the dislocations were observed under the optical microscope and atomic force microscope after corroding in molten KOH at 390 ℃. The crystals in case B exhibit better lattice integrity with smaller full width at half maximum of 29.13 rad·s, while the value in case A is 45.17 rad·s. The morphologies of dislocation etch pits in both cases show typical triangular symmetry with smooth surfaces. However, the dislocation density of 2.8×104 cm-2 in case B is only half of that in case A, and the distribution is more uniform, compared to the U-shaper in case A.展开更多
基金Funded by National Natural Science Foundation of China(No.51371097)Six Talent Peaks(2015)Project of Jiangsu Province(No.YPC16005-PT)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Dense Fe-Al-Cr coatings with approximately 50 μm in thickness are successfully prepared on the 1045 carbon steel substrates via a laser cladding process. Proper Cr content(5 at% Cr) will lead to decrease in the melting point, and improves the viscosity of the liquid and the nucleation rate of the molten pool, leading to refining grains of the solidification structure. As a result, the Fe-29 Al-5 Cr laser cladding layer exhibits the best hardness, plasticity properties, and wear resistance at 400 °C. Excessive Cr for the Fe-29 Al-7.5 Cr coating leads to the formation of Cr2 Al in the grain boundaries and thermal vacancies during the solidification process, resulting in inferior mechanical properties and poor tribological behavior.
基金Project(51371097)supported by the National Natural Science Foundation of ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions,China
文摘Double glow plasma surface metallurgy technique was used to fabricate a Fe?Al?Cr?Nb alloyed layer onto the surface of the 45 steel. The microstructures and composition of th?eA Fl?eCr?Nb alloyed layer were analyzed by scanning electronic microscopy, X-ray diffraction and energy dispersive spectroscopy. The results indicate thatthe 20 μm alloyed layer is homogeneous and compact. The alloyed elements exhibit a gradient distribution along the cross section. Microhardness and nanoindentation tests imply that the surface hardness of the alloyed layer reaches HV 580, which is almost 2.8 times that of the substrate. Compared with the substrate, the alloyed layer has a much smaller displacement and a larger elastic modulus. According to the friction and wear tests at room temperature, the? FeAl?Cr?Nb alloyed layer has lower friction coefficient and less wear mass, implying that the Fe?Al?Cr?Nb alloyed layer can effectively improve the surface hardness and wear resistance of the substrate.
基金Project(BA2012049)supported by the Special Fund of Jiangsu Province for the Transformation of Scientific and Technological Achievements,China
文摘To obtain the stable temperature field required for growing sapphire crystals, the influence of relative positions between RF coil and crucible on the performances of sapphires produced by edge-defined film-fed growth（EFG） technique was investigated. For comparison, the crucible was located at the top（case A） and the middle（case B） of the RF coil, respectively. Furthermore, the lattice integrities were studied by the double-crystal X-ray diffraction, and the dislocations were observed under the optical microscope and atomic force microscope after corroding in molten KOH at 390 ℃. The crystals in case B exhibit better lattice integrity with smaller full width at half maximum of 29.13 rad·s, while the value in case A is 45.17 rad·s. The morphologies of dislocation etch pits in both cases show typical triangular symmetry with smooth surfaces. However, the dislocation density of 2.8×104 cm-2 in case B is only half of that in case A, and the distribution is more uniform, compared to the U-shaper in case A.
