Nanostructured WC-12Co coatings were deposited by high velocity oxy-fuel (HVOF) spraying with an agglomerated powder. The effect of flame conditions on the microstructure of the nanostructured coatings was investigate...Nanostructured WC-12Co coatings were deposited by high velocity oxy-fuel (HVOF) spraying with an agglomerated powder. The effect of flame conditions on the microstructure of the nanostructured coatings was investigated. The wear properties of the coatings were characterized using a dry rubber-wheel wear test. The results show that the nanostructured WC-Co coatings consist of WC, W2C, W and an amorphous binder phase. The microstructure of the coating is significantly influenced by the ratio of oxygen flow to fuel flow. Under the lower ratio of oxygen/fuel flow, the nanostructured coating presents a relative dense microstructure and severe decarburization of WC phase occurs during spraying. With increasing ratio of oxygen/fuel flow, the bonding of WC particles in the coating becomes loose resulting from the original structure of feedstock and the decarburization of WC becomes less owing to limited heating to the powder. Both the decarburization of WC particles in spraying and the bonding among WC particles in the coatings affect the wear performance. The examination of the worn surfaces of the nanostructured coatings reveals that the dominant wear mechanisms would be spalling from the interface of WCCo splats when spray particles undergo a limited melting. While the melting state of the spray particles is improved,the dominant wear mechanisms become the plastic deformation and plowing of the matrix and spalling of WC particles from the matrix.展开更多
In this study, WC-Co powder with WC submicron grain size of 0. 7 - 0. 9μm was used as feedstock powder to deposit wear resistant coating by home-made T J-9000 HVOF system. The deposition efficiency of the feedstock p...In this study, WC-Co powder with WC submicron grain size of 0. 7 - 0. 9μm was used as feedstock powder to deposit wear resistant coating by home-made T J-9000 HVOF system. The deposition efficiency of the feedstock powder was examined. Influences of the High Velocity Oxy-Fuel （HVOF） spraying parameters on the microstructures, phase compositions, microhardness, and wear resistance of sprayed coatings were investigated. The deposition efficiency of the feedstock powder was very high, and reached to 58%. The sprayed coatings were very dense, and their porosities were lower than 1% and could be lowered than 0. 42% with optimal spraying parameters. According to the X-ray Diffraction （ XRD ） analysis, the phase compositions of the sprayed coatings consisted of WC, Co, W2 C, and Co6 W6 C. W appeared at high flame power. The average microhardness of the coating was 1 100 HVo 1 and had reversely linear relationship with the porosity of coatings. The weight loss of the counter wear ring GCrl5 was 20 times than that of the sprayed WC-Co coating. At the load of 15 kg and rotational speed of 200 r/min of GCr15 counter wear ring, the friction coefficient was 0. 68 in the dry wear conditions. It was concluded that the sprayed submicron structural WC-12Co coating had good wear resistance.展开更多
In this research, development of AI356-AI203 nanocomposite coatings has been investigated. AI356-AI203 composite powders were prepared by mechanical milling of AI356 powder and 5 vol.% micro and nanoscaled alumina par...In this research, development of AI356-AI203 nanocomposite coatings has been investigated. AI356-AI203 composite powders were prepared by mechanical milling of AI356 powder and 5 vol.% micro and nanoscaled alumina particles. The milled powders were used as feedstock to deposit composite coatings on A356-T6 aluminum alloy substrate using high velocity oxy-fuel （HVOF） process. X-ray diffractometry, optical and scanning electron microscopy, microhardness and wear tests were used to characterize the composite powders and coatings. The hardness of composite coatings containing micro and nanosized AI203 were 114.1 ± 5.9 HV and 138.4 ± 6.9 HV, respectively which were higher than those for substrate （79.2 ± 1.1 HV）. Nano and microcomposite coatings revealed low friction coefficients and wear rates, which were significantly lower than those obtained for AI356-T6 substrate. Addition of 5 vol.% micro and nanoscaled alumina particles improved the wear resistance by an average of 85% and 91%, respectively. This is mainly caused by the presence of AI203 in matrix and nanocrystalline structure of matrix. Scanning electron microscopy tests revealed different wear mechanisms on the surface of the wear test specimens.展开更多
文摘Nanostructured WC-12Co coatings were deposited by high velocity oxy-fuel (HVOF) spraying with an agglomerated powder. The effect of flame conditions on the microstructure of the nanostructured coatings was investigated. The wear properties of the coatings were characterized using a dry rubber-wheel wear test. The results show that the nanostructured WC-Co coatings consist of WC, W2C, W and an amorphous binder phase. The microstructure of the coating is significantly influenced by the ratio of oxygen flow to fuel flow. Under the lower ratio of oxygen/fuel flow, the nanostructured coating presents a relative dense microstructure and severe decarburization of WC phase occurs during spraying. With increasing ratio of oxygen/fuel flow, the bonding of WC particles in the coating becomes loose resulting from the original structure of feedstock and the decarburization of WC becomes less owing to limited heating to the powder. Both the decarburization of WC particles in spraying and the bonding among WC particles in the coatings affect the wear performance. The examination of the worn surfaces of the nanostructured coatings reveals that the dominant wear mechanisms would be spalling from the interface of WCCo splats when spray particles undergo a limited melting. While the melting state of the spray particles is improved,the dominant wear mechanisms become the plastic deformation and plowing of the matrix and spalling of WC particles from the matrix.
文摘In this study, WC-Co powder with WC submicron grain size of 0. 7 - 0. 9μm was used as feedstock powder to deposit wear resistant coating by home-made T J-9000 HVOF system. The deposition efficiency of the feedstock powder was examined. Influences of the High Velocity Oxy-Fuel （HVOF） spraying parameters on the microstructures, phase compositions, microhardness, and wear resistance of sprayed coatings were investigated. The deposition efficiency of the feedstock powder was very high, and reached to 58%. The sprayed coatings were very dense, and their porosities were lower than 1% and could be lowered than 0. 42% with optimal spraying parameters. According to the X-ray Diffraction （ XRD ） analysis, the phase compositions of the sprayed coatings consisted of WC, Co, W2 C, and Co6 W6 C. W appeared at high flame power. The average microhardness of the coating was 1 100 HVo 1 and had reversely linear relationship with the porosity of coatings. The weight loss of the counter wear ring GCrl5 was 20 times than that of the sprayed WC-Co coating. At the load of 15 kg and rotational speed of 200 r/min of GCr15 counter wear ring, the friction coefficient was 0. 68 in the dry wear conditions. It was concluded that the sprayed submicron structural WC-12Co coating had good wear resistance.
文摘In this research, development of AI356-AI203 nanocomposite coatings has been investigated. AI356-AI203 composite powders were prepared by mechanical milling of AI356 powder and 5 vol.% micro and nanoscaled alumina particles. The milled powders were used as feedstock to deposit composite coatings on A356-T6 aluminum alloy substrate using high velocity oxy-fuel （HVOF） process. X-ray diffractometry, optical and scanning electron microscopy, microhardness and wear tests were used to characterize the composite powders and coatings. The hardness of composite coatings containing micro and nanosized AI203 were 114.1 ± 5.9 HV and 138.4 ± 6.9 HV, respectively which were higher than those for substrate （79.2 ± 1.1 HV）. Nano and microcomposite coatings revealed low friction coefficients and wear rates, which were significantly lower than those obtained for AI356-T6 substrate. Addition of 5 vol.% micro and nanoscaled alumina particles improved the wear resistance by an average of 85% and 91%, respectively. This is mainly caused by the presence of AI203 in matrix and nanocrystalline structure of matrix. Scanning electron microscopy tests revealed different wear mechanisms on the surface of the wear test specimens.
