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
The properties of two different types of thermal barrier coatings （TBCs） were compared to improve the surface characteristics on high temperature components. These TBCs consisted of a duplex TBC and a five-layered f...The properties of two different types of thermal barrier coatings （TBCs） were compared to improve the surface characteristics on high temperature components. These TBCs consisted of a duplex TBC and a five-layered functionally graded TBC. NiCrAIY bond coats were deposited on a number of Inconel-738LC specimens using high velocity oxy-fuel spraying （HVOF） technique. For duplex coating, a group of these specimens were coated with yttria stabilized zirconia （YSZ） using plasma spray technique. Functionally graded NiCrAIY/YSZ coatings were fabricated by plasma spray using co-injection of the two different powders in a single plasma torch. The amount of zirconia in functionally graded coatings were gradually increased from 30 to 100 vol. pct. Microstructural changes, thermally grown oxide （TGO） layer growth and damage initiation of the coatings were investigated as a function of isothermal oxidation test at 970℃. As a complementary test, the performance of the fabricated coatings by the optimum processing conditions was evaluated as a function of intense thermal cycling test at 1100℃. Also the strength of the adhesive coatings of the substrate was also measured. Microstructural characterization was analyzed by scanning electron microscopy （SEM） and optical microscopy whereas phase analysis and chemical composition changes of the coatings and oxides formed during the tests were studied by XRD （X-ray diffraction） and EDS （energy dispersive spectrometer）. The results showed that microstructure and compositions gradually varied in the functionally graded coatings. By comparison of duplex and functionally graded TBCs oxidation behavior （duplex failure after 1700 h and funcitionally graded TECs failure after 2000 h）, thermal shock test and adhesion strength of the coatings, the functionally graded TBC had better performance and more durability.展开更多
基金supported by the National 863 projects by the Department of Science and Technology of China (No. 2002AA331080)the Program of Beijing Significant Science and Technology Project (No.020420050021)
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.
文摘The properties of two different types of thermal barrier coatings （TBCs） were compared to improve the surface characteristics on high temperature components. These TBCs consisted of a duplex TBC and a five-layered functionally graded TBC. NiCrAIY bond coats were deposited on a number of Inconel-738LC specimens using high velocity oxy-fuel spraying （HVOF） technique. For duplex coating, a group of these specimens were coated with yttria stabilized zirconia （YSZ） using plasma spray technique. Functionally graded NiCrAIY/YSZ coatings were fabricated by plasma spray using co-injection of the two different powders in a single plasma torch. The amount of zirconia in functionally graded coatings were gradually increased from 30 to 100 vol. pct. Microstructural changes, thermally grown oxide （TGO） layer growth and damage initiation of the coatings were investigated as a function of isothermal oxidation test at 970℃. As a complementary test, the performance of the fabricated coatings by the optimum processing conditions was evaluated as a function of intense thermal cycling test at 1100℃. Also the strength of the adhesive coatings of the substrate was also measured. Microstructural characterization was analyzed by scanning electron microscopy （SEM） and optical microscopy whereas phase analysis and chemical composition changes of the coatings and oxides formed during the tests were studied by XRD （X-ray diffraction） and EDS （energy dispersive spectrometer）. The results showed that microstructure and compositions gradually varied in the functionally graded coatings. By comparison of duplex and functionally graded TBCs oxidation behavior （duplex failure after 1700 h and funcitionally graded TECs failure after 2000 h）, thermal shock test and adhesion strength of the coatings, the functionally graded TBC had better performance and more durability.
