Ni-matrix composite coating containing AI2O3 nano-particles is prepared by brush plating. The effects of the nano-particles on the microstructure, microhardness and tribological properties of the composite coating und...Ni-matrix composite coating containing AI2O3 nano-particles is prepared by brush plating. The effects of the nano-particles on the microstructure, microhardness and tribological properties of the composite coating under the lubrication of a diesel oil containing sand are investigated. The results show that the microstructure of the composite coating is finer than that of the pure nickel coating due to the codeposition of the nano-particles. When the nano-particle concentration in the electroplating bath reaches 20 g/L, the microhardness, and wear resistance of the composite coating is as much as 1.6 times and 1.3-2.5 times of those of the pure nickel coating respectively. The main hardening mechanism of the composite coating is superfine crystal grain strengthening and dispersion strengthening. The composite coating is characterized by scuffing as it slides against Si3N4 under the present test conditions.展开更多
It has been postulated that, with tensile loading conditions, micro-cracks onthin hard film act as stress concentrators enhancing plastic deformation of the substrate materialin their vicinity. Under favorable conditi...It has been postulated that, with tensile loading conditions, micro-cracks onthin hard film act as stress concentrators enhancing plastic deformation of the substrate materialin their vicinity. Under favorable conditions the localized plastic flow near the cracks may turninto macroscopic plastic strain thus affects the plasticity behaviors of the substrate. Thisphenomenon is analyzed quantitatively with finite element method with special attention focused onthe analysis and discussion of the effects of plastic work hardening rate, film thickness and crackdepth on maximum plastic strain, critical loading stress and the size of the local plasticdeformation zone. Results show that micro-cracks on thin hard film have unnegligible effects on theplasticity behaviors of the substrate material under tensile loading.展开更多
The effect of arc sprayed times, which are quantitatively described by the volume fraction of coatings, on the mechanical properties of type 316 steel, have been undertaken in the present work. Al wires were utilized ...The effect of arc sprayed times, which are quantitatively described by the volume fraction of coatings, on the mechanical properties of type 316 steel, have been undertaken in the present work. Al wires were utilized as coatings materials. Tensile tests were carried out in the temperature range of Portevin-Le Chatelier (PLC) effect It has been found that grains at edges and corners of the 316 steel specimens have been dramatically constricted by grit blasting and spraying. Grit blasting has been found to exert a shot-peening effect on the mechanical properties of 316 steel specimens. Coatings with lower values of coating volume fraction strengthen the coated specimens in the very similar way as blasting. While if the volume fraction of coating, (Vv)c, exceeds a critical value, (VV)K, softens the specimens. Specimens with low values of (Vv)c, have high values of flow stress, as well as higher values of work-hardening coefficient, Calculations based on the experimental results show that the high thickness coatings have relatively lower contribution to the mechanical properties of specimens.展开更多
Micro-properties of the oxide scale and near-surface zone of a type 316 steel annealed in air and vacuum have been systematically investigated. Microstructures of the specimens have been examined using optical microsc...Micro-properties of the oxide scale and near-surface zone of a type 316 steel annealed in air and vacuum have been systematically investigated. Microstructures of the specimens have been examined using optical microscopy and scanning and transmission electron microscopy (TEM). Chemical compositions for the oxide scale and near surface zone were also analysed. The results obtained show that the oxide scale developed in vacuum exhibits a distinct structure from that developed in air. Comparing to the vacuum-developed scale, the air-developed scale possesses a more complicated structure and relatively poor adhesion to the matrix. TEM observations reveal a difference in the dislocation density in the vicinity of the free surface, near-surface zone and the core of the specimens examined.展开更多
基金This research was financially supported by the Major Project of National Natural Science Foundation of China(No.50235030)the National 973 Planning Project(No.G1999065009)+1 种基金the Science and Technology Cooperation Project between China and Poland Governments in 2002(No.2002M3)their supports are gratefully acknowledged.
文摘Ni-matrix composite coating containing AI2O3 nano-particles is prepared by brush plating. The effects of the nano-particles on the microstructure, microhardness and tribological properties of the composite coating under the lubrication of a diesel oil containing sand are investigated. The results show that the microstructure of the composite coating is finer than that of the pure nickel coating due to the codeposition of the nano-particles. When the nano-particle concentration in the electroplating bath reaches 20 g/L, the microhardness, and wear resistance of the composite coating is as much as 1.6 times and 1.3-2.5 times of those of the pure nickel coating respectively. The main hardening mechanism of the composite coating is superfine crystal grain strengthening and dispersion strengthening. The composite coating is characterized by scuffing as it slides against Si3N4 under the present test conditions.
基金This project is supported by National Natural Science Foundation of China(No.59705009).
文摘It has been postulated that, with tensile loading conditions, micro-cracks onthin hard film act as stress concentrators enhancing plastic deformation of the substrate materialin their vicinity. Under favorable conditions the localized plastic flow near the cracks may turninto macroscopic plastic strain thus affects the plasticity behaviors of the substrate. Thisphenomenon is analyzed quantitatively with finite element method with special attention focused onthe analysis and discussion of the effects of plastic work hardening rate, film thickness and crackdepth on maximum plastic strain, critical loading stress and the size of the local plasticdeformation zone. Results show that micro-cracks on thin hard film have unnegligible effects on theplasticity behaviors of the substrate material under tensile loading.
文摘The effect of arc sprayed times, which are quantitatively described by the volume fraction of coatings, on the mechanical properties of type 316 steel, have been undertaken in the present work. Al wires were utilized as coatings materials. Tensile tests were carried out in the temperature range of Portevin-Le Chatelier (PLC) effect It has been found that grains at edges and corners of the 316 steel specimens have been dramatically constricted by grit blasting and spraying. Grit blasting has been found to exert a shot-peening effect on the mechanical properties of 316 steel specimens. Coatings with lower values of coating volume fraction strengthen the coated specimens in the very similar way as blasting. While if the volume fraction of coating, (Vv)c, exceeds a critical value, (VV)K, softens the specimens. Specimens with low values of (Vv)c, have high values of flow stress, as well as higher values of work-hardening coefficient, Calculations based on the experimental results show that the high thickness coatings have relatively lower contribution to the mechanical properties of specimens.
文摘Micro-properties of the oxide scale and near-surface zone of a type 316 steel annealed in air and vacuum have been systematically investigated. Microstructures of the specimens have been examined using optical microscopy and scanning and transmission electron microscopy (TEM). Chemical compositions for the oxide scale and near surface zone were also analysed. The results obtained show that the oxide scale developed in vacuum exhibits a distinct structure from that developed in air. Comparing to the vacuum-developed scale, the air-developed scale possesses a more complicated structure and relatively poor adhesion to the matrix. TEM observations reveal a difference in the dislocation density in the vicinity of the free surface, near-surface zone and the core of the specimens examined.
