The crack-free Ni60 A coating was fabricated on 45 steel substrate by laser cladding and the microstructure including solidification characteristics, phases constitution and phase distribution was systematically inves...The crack-free Ni60 A coating was fabricated on 45 steel substrate by laser cladding and the microstructure including solidification characteristics, phases constitution and phase distribution was systematically investigated. The high temperature friction and wear behavior of the cladding coating and substrate sliding against GCr15 ball under different loads was systematically evaluated. It was found that the coating has homogenous and fine microstructure consisting of γ（Ni） solid solution, a considerable amount of network Ni-Ni3 B eutectics, m^23C6 with the floret-shape structure and Cr B with the dark spot-shape structure uniformly distributing in interdendritic eutectics. The microhardness of the coating is about 2.6 times as much as that of the substrate. The coating produces higher friction values than the substrate under the same load condition, but the friction process on the coating keeps relatively stable. Wear rates of the coating are about 1/6.2 of that of the substrate under the higher load（300 g）. Wear mechanism of the substrate includes adhesion wear, abrasive wear, severe plastic deformation and oxidation wear, while that of the coating is merely a combination of mild abrasive wear and moderate oxidation wear.展开更多
In order to simulate thermal strains, thermal stresses, residual stresses and microstructure of the steel during gas quenching by means of the numerical method, it is necessary to obtain an accurate boundary condition...In order to simulate thermal strains, thermal stresses, residual stresses and microstructure of the steel during gas quenching by means of the numerical method, it is necessary to obtain an accurate boundary condition of temperature field. The surface heat transfer coefficient is a key parameter. The explicit finite difference method, nonlinear estimation method and the experimental relation between temperature and time during gas quenching have been used to solve the inverse problem of heat conduction. The relationship between surface temperature and surface heat transfer coefficient of a cylinder has been given. The nonlinear surface heat transfer coefficients include the coupled effects between martensitic phase transformation and temperature.展开更多
By means of supersonic fine particles bombarding （SFPB）,a nanostructured surface layer up to 15 μm was fabricated on a 45 steel plate with ferrite and pearlite phases. To reveal the grain refinement mechanism of SF...By means of supersonic fine particles bombarding （SFPB）,a nanostructured surface layer up to 15 μm was fabricated on a 45 steel plate with ferrite and pearlite phases. To reveal the grain refinement mechanism of SFPB-treated 45 steel,microstructure features of various sections in the treated surface were systematically characterized by X-ray diffraction （XRD）,scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Grain size increases with an increase of depth from the treated surface. Plastic deformation and grain refinement processes are accompanied by an increase in strain. Plastic deformation in the proeutectoid ferrite phases has precedence over the pearlite phases. Grain refinement in the ferrite phases involves： the onset of dislocation lines （Dls）,dislocation tangles （DTs） and dense dislocation walls （DDWs） in the original grains; the formation of fine lamellar and roughly equiaxed cells separated by DDWs; by dislocation annihilation and rearrangement,the transformation of DDWS into subboundaries and boundaries and the formation of submicron grains or subgrains; the successive subdivision of grains to finer and finer scale,resulting in the formation of highly misoriented nano-grains. By contrast,eutectoid cementite phase accommodated strain in a sequence as follows： onset of elongated,bended and shear deformation under deformation stress of ferrites,short and thin cementites with a width of about 20-50 nm and discontinuous length were formed. Shorter and thinner cementites were developed into ultra-fine pieces under the action of high density dislocation and strains. At the top surface,some cementites were decomposed under severe plastic deformation. Experimental evidences and analysis indicate that surface nanocrystallization of 45 steel results from dislocation activities,high strains and high strain rate are necessary for the formation of nanocrystallites.展开更多
The cross-sectional microstructure of an ion-nitrided layer on a No.45 steel was studied by transmission electron microscopy (TEM). The results show that the columnar crystals constitute the compound layer. Most of t...The cross-sectional microstructure of an ion-nitrided layer on a No.45 steel was studied by transmission electron microscopy (TEM). The results show that the columnar crystals constitute the compound layer. Most of them have the microstructure of alternating ε-Fe2-3N and γ-Fe4N and others are single ε-Fe2-3N phase. There are abnormal strip ferrites between the columnar crystals. The transition layer mainly consists of spherical γ-Fe4N and cementite (Fe3C) particles in the pearlite are dissolved in this layer. In diffusion layer, besides the equilibrium phase γ-Fe4N, there are α -Fe16N2 and the satellite spots around main spots of α-Fe16N2 demonstrate its modulation structure. A metastable ordered cluster zone of the nitropen atoms was found in the division layer.展开更多
In the present paper,a method for reliable estimation of defect profile in CK45 steel structures is presented using an eddy current testing based measurement system and post-processing system based on deep learning te...In the present paper,a method for reliable estimation of defect profile in CK45 steel structures is presented using an eddy current testing based measurement system and post-processing system based on deep learning technique.So a deep learning method is used to determine the defect characteristics in metallic structures by magnetic field C-scan images obtained by an anisotropic magneto-resistive sensor.Having designed and adjusting the deep convolution neural network and applied it to C-scan images obtained from the measurement system,the performance of deep learning method proposed is compared with conventional artificial neural network methods such as multilayer perceptron and radial basis function on a number of metallic specimens with different defects.The results confirm the superiority of the proposed method for characterizing defects compared to other classical training-oriented methods。展开更多
A binary Fe-Al alloyed layer was synthesized on 45 steel by means of double glow plasma surface alloying technique. The corrosion-resisting layer prepared is composed of a sedimentary layer and a diffusion layer, with...A binary Fe-Al alloyed layer was synthesized on 45 steel by means of double glow plasma surface alloying technique. The corrosion-resisting layer prepared is composed of a sedimentary layer and a diffusion layer, with a total thickness of about 180 μm. The aluminum content of the alloyed layer shows gradual change from surface to the inside of substrate. The ideal profile is beneficial to the metallurgical bonding of the surface alloying layer with substrate materials. The microstructure of both layers consists of the Fe-Al intermetallic compound, which is FeAl with B2 structure in the sedimentary layer and Fe3Al with incompletely ordered DO3 structure in the diffusion layer. The protective film exhibits high micro-hardness. In comparison with the substrate of 45 steel, the corrosion resistance of the aluminized sample is much higher in 2.0% Na2S and 0.05 mol/L Na2SO4 + 0.5 mol/L NaCl mixed solutions.展开更多
基金Project(2012AA040210)supported by the National High-Tech Research and Development Program of ChinaProject(510-C10293)supported by the Central Finance Special Fund to Support the Local University,ChinaProject(2010A090200048)supported by the Key Project of Industry,Education,Research of Guangdong Province and Ministry of Education,China
文摘The crack-free Ni60 A coating was fabricated on 45 steel substrate by laser cladding and the microstructure including solidification characteristics, phases constitution and phase distribution was systematically investigated. The high temperature friction and wear behavior of the cladding coating and substrate sliding against GCr15 ball under different loads was systematically evaluated. It was found that the coating has homogenous and fine microstructure consisting of γ（Ni） solid solution, a considerable amount of network Ni-Ni3 B eutectics, m^23C6 with the floret-shape structure and Cr B with the dark spot-shape structure uniformly distributing in interdendritic eutectics. The microhardness of the coating is about 2.6 times as much as that of the substrate. The coating produces higher friction values than the substrate under the same load condition, but the friction process on the coating keeps relatively stable. Wear rates of the coating are about 1/6.2 of that of the substrate under the higher load（300 g）. Wear mechanism of the substrate includes adhesion wear, abrasive wear, severe plastic deformation and oxidation wear, while that of the coating is merely a combination of mild abrasive wear and moderate oxidation wear.
基金This work has been supported by the National Natural Science Foundation of China (10162002) and Foundation for University Key Teacher by the Ministry of Education and The Yunnan Foundation of Natural Science (1999A0023M).
文摘In order to simulate thermal strains, thermal stresses, residual stresses and microstructure of the steel during gas quenching by means of the numerical method, it is necessary to obtain an accurate boundary condition of temperature field. The surface heat transfer coefficient is a key parameter. The explicit finite difference method, nonlinear estimation method and the experimental relation between temperature and time during gas quenching have been used to solve the inverse problem of heat conduction. The relationship between surface temperature and surface heat transfer coefficient of a cylinder has been given. The nonlinear surface heat transfer coefficients include the coupled effects between martensitic phase transformation and temperature.
文摘By means of supersonic fine particles bombarding （SFPB）,a nanostructured surface layer up to 15 μm was fabricated on a 45 steel plate with ferrite and pearlite phases. To reveal the grain refinement mechanism of SFPB-treated 45 steel,microstructure features of various sections in the treated surface were systematically characterized by X-ray diffraction （XRD）,scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Grain size increases with an increase of depth from the treated surface. Plastic deformation and grain refinement processes are accompanied by an increase in strain. Plastic deformation in the proeutectoid ferrite phases has precedence over the pearlite phases. Grain refinement in the ferrite phases involves： the onset of dislocation lines （Dls）,dislocation tangles （DTs） and dense dislocation walls （DDWs） in the original grains; the formation of fine lamellar and roughly equiaxed cells separated by DDWs; by dislocation annihilation and rearrangement,the transformation of DDWS into subboundaries and boundaries and the formation of submicron grains or subgrains; the successive subdivision of grains to finer and finer scale,resulting in the formation of highly misoriented nano-grains. By contrast,eutectoid cementite phase accommodated strain in a sequence as follows： onset of elongated,bended and shear deformation under deformation stress of ferrites,short and thin cementites with a width of about 20-50 nm and discontinuous length were formed. Shorter and thinner cementites were developed into ultra-fine pieces under the action of high density dislocation and strains. At the top surface,some cementites were decomposed under severe plastic deformation. Experimental evidences and analysis indicate that surface nanocrystallization of 45 steel results from dislocation activities,high strains and high strain rate are necessary for the formation of nanocrystallites.
文摘The cross-sectional microstructure of an ion-nitrided layer on a No.45 steel was studied by transmission electron microscopy (TEM). The results show that the columnar crystals constitute the compound layer. Most of them have the microstructure of alternating ε-Fe2-3N and γ-Fe4N and others are single ε-Fe2-3N phase. There are abnormal strip ferrites between the columnar crystals. The transition layer mainly consists of spherical γ-Fe4N and cementite (Fe3C) particles in the pearlite are dissolved in this layer. In diffusion layer, besides the equilibrium phase γ-Fe4N, there are α -Fe16N2 and the satellite spots around main spots of α-Fe16N2 demonstrate its modulation structure. A metastable ordered cluster zone of the nitropen atoms was found in the division layer.
文摘In the present paper,a method for reliable estimation of defect profile in CK45 steel structures is presented using an eddy current testing based measurement system and post-processing system based on deep learning technique.So a deep learning method is used to determine the defect characteristics in metallic structures by magnetic field C-scan images obtained by an anisotropic magneto-resistive sensor.Having designed and adjusting the deep convolution neural network and applied it to C-scan images obtained from the measurement system,the performance of deep learning method proposed is compared with conventional artificial neural network methods such as multilayer perceptron and radial basis function on a number of metallic specimens with different defects.The results confirm the superiority of the proposed method for characterizing defects compared to other classical training-oriented methods。
基金Project(BK2005128) supported by the Natural Science Foundation of Jiangsu Province, China
文摘A binary Fe-Al alloyed layer was synthesized on 45 steel by means of double glow plasma surface alloying technique. The corrosion-resisting layer prepared is composed of a sedimentary layer and a diffusion layer, with a total thickness of about 180 μm. The aluminum content of the alloyed layer shows gradual change from surface to the inside of substrate. The ideal profile is beneficial to the metallurgical bonding of the surface alloying layer with substrate materials. The microstructure of both layers consists of the Fe-Al intermetallic compound, which is FeAl with B2 structure in the sedimentary layer and Fe3Al with incompletely ordered DO3 structure in the diffusion layer. The protective film exhibits high micro-hardness. In comparison with the substrate of 45 steel, the corrosion resistance of the aluminized sample is much higher in 2.0% Na2S and 0.05 mol/L Na2SO4 + 0.5 mol/L NaCl mixed solutions.
