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
目的提高F92耐热钢基体在600、630℃下的高温耐磨性能。方法采用超音速火焰喷涂方法(High velocity oxy-fuel,HVOF)在F92表面制备CoCrWSi、Stellite-6两种涂层,利用扫描电子显微镜(Scanning electron microscope,SEM)和X射线衍射仪(X-ra...目的提高F92耐热钢基体在600、630℃下的高温耐磨性能。方法采用超音速火焰喷涂方法(High velocity oxy-fuel,HVOF)在F92表面制备CoCrWSi、Stellite-6两种涂层,利用扫描电子显微镜(Scanning electron microscope,SEM)和X射线衍射仪(X-ray diffraction,XRD)分析涂层的表面、截面形貌和物相组成,通过显微维氏硬度计(HV-1000STA)、高温摩擦磨损试验机(UMT-TRIBOLAB)、二维轮廓仪(TencorD-100)测定其显微硬度、高温摩擦学性能和磨痕体积。结果采用超音速火焰喷涂技术制备的CoCrWSi、Stellite-6两种涂层表面较平整,与基体结合紧密,内部组织均匀无裂纹,涂层的厚度约为200μm。XRD分析表明,CoCrWSi、Stellite-6涂层在室温下的物相都由γ(Co)、Cr_(7)C_(3)、CrSi_(2)组成。硬度及耐磨性能测试显示,CoCrWSi、Stellite-6涂层的维氏硬度相较于F92基体分别提高了3.12、2.68倍,F92耐热钢在600、630℃时的平均摩擦因数分别为0.87、0.86,体积磨损率分别为0.49×10^(-4)、1.11×10^(-4)mm^(3)/(N·m),其磨损机理主要为疲劳磨损、黏着磨损、氧化磨损。相较于基体,CoCrWSi涂层在2种温度下的平均摩擦因数分别降低了68%、71%,约为0.28、0.25,体积磨损率分别降低了约95%、97%,为0.20×10^(-5)、0.30×10^(-5)mm^(3)/(N·m),这主要归功于内部的Cr2O3、γ(Co)、Co_(3)O_(4)相在高温摩擦过程中具有良好的润滑效果。Stellite-6涂层也能在一定程度上改善基体的高温耐磨性能,其平均摩擦因数为0.85、0.71,体积磨损率为0.32×10^(-4)、0.57×10^(-4)mm^(3)/(N·m)。2种涂层的主要磨损机理均为磨粒磨损和黏着磨损。结论采用超音速火焰喷涂制备的CoCrWSi、Stellite-6涂层可以改善F92耐热钢在600、630℃下的耐高温滑动磨损性能,且CoCrWSi涂层的防护效果更佳。展开更多
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.
