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Huang X.,Carleton University | Puetz P.,Carleton University | Yang Q.,NRC Institute for Aerospace Research | Tang Z.,Northwest Mettech Corporation
Surface Engineering | Year: 2011

To better understand transient oxide formation on the surface of standalone NiCrAlY in a vacuum, plasma sprayed NiCrAlY samples were subjected to a series of heat treatments at temperatures ranging from 1000 to 1100°C and for two different holding times. The morphology, composition and type of transient oxide(s) formed after heat treatment were characterised using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction (XRD). All samples exhibited the formation of a top layer of discrete or island like Ni rich oxide in cellular shaped alumina. The alumina layer, although difficult to be detected in cross-section, was very dense and covered most of the coating surface. The transisent oxide formation on the heat treated surfaces was further analysed using XRD and α-Al2O3 was detected on all heat treated samples in addition to NiO and possible spinel. Cr 2O3 seemed to be present on the samples heat treated at 1000 and 1050°C but not on the sample heat treated at 1100°C. Increased Al surface content, in comparison to the as sprayed sample, was found on all heat treated samples. High Al content, corresponding to the extent of alumina formation on heat treated samples, was observed for samples heat treated for a longer time as more oxygen diffusion took place. The coating surface Al content increased with heat treatment from 1000 to 1050°C and reduced from 1050 to 1100°C. © 2011 Institute of Materials, Minerals and Mining. Source


Puetz P.,Carleton University | Huang X.,Carleton University | Yang Q.,NRC Institute for Aerospace Research | Tang Z.,Northwest Mettech Corporation
Journal of Thermal Spray Technology | Year: 2011

In this study, the transient surface oxide formation on APS NiCrAlY samples was examined after oxidation heat treatment at temperatures between 1000 and 1100 °C. The surface oxides observed on the NiCrAlY surface included a sporadic top layer of NiO and a continuous layer of alumina immediately adjacent to the NiCrAlY coating. Cr-rich oxide in smaller quantities than alumina was also found surrounding the NiO and dispersed within alumina. The alumina assumed whisker-shaped morphology when being observed from the surface but formed continuous film along the NiCrAlY surface. Although the formation of alumina has been observed on all the samples examined in this study, the NiCrAlY sample heat treated at 1050 °C for 5 h generated more continuous α-alumina layer and also contained less surface NiO and Cr-rich oxide. Based on the results, it is believed that NiO developed first upon exposure to an oxidizing environment at high temperature, and stable alumina began to form with the increase in heat treatment temperature and time. © 2010 ASM International. Source


Curry N.,University College West | Tang Z.,Northwest Mettech Corporation | Markocsan N.,University College West | Nylen P.,University College West
Surface and Coatings Technology | Year: 2015

Suspension plasma spraying has become a very promising candidate for the production of strain tolerant coatings for the gas turbine industry. Under certain process conditions suspension plasma spraying (SPS) generates column-like structures in the produced coatings. While a mechanism for column formation has been suggested previously based on columns forming on surface asperities, the effect of modification of surface structures on SPS coating properties has not been investigated. In this study, the surface topography of bond coats within a TBC system were modified by the combination of polishing and surface grit blasting. Yttria stabilized zirconia coatings were deposited using an axial feed suspension plasma spray gun. The surface topography of the resultant coatings was characterized using striped light projection. Samples were tested for thermo-cyclic fatigue lifetime at 1100. °C during 1. hour cycles. Thermal shock performance was evaluated using the burner rig test and thermal conductivity evaluated using the laser flash analysis. The results indicate that columnar SPS coating microstructure is strongly influenced by surface topography. Test results suggest that control of surface topography may be an important factor to improve the performance of SPS coatings. © 2014 Elsevier B.V. Source


Patent
NORTHWEST METTECH Corporation | Date: 2012-08-31

A liquid-in-gas injector tube in which the diameter of the inner liquid-bearing tube within the gas-transmitting tube is reduced adjacent the outlet end of the injector. Clogging may be further reduced by adding vanes to the outer surface of the inner liquid-bearing tube within the gas-transmitting tube to impart swirling or otherwise focus the flow of gas at the exit of the injector tube.


Kitamura J.,Fujimi Incorporated | Tang Z.,Northwest Mettech Corporation | Mizuno H.,Fujimi Incorporated | Sato K.,Fujimi Incorporated | Burgess A.,Northwest Mettech Corporation
Journal of Thermal Spray Technology | Year: 2011

Yttrium oxide (Y 2O 3) coatings have been prepared by axial suspension plasma spraying with fine powders. It is clarified that the coatings have high hardness, low porosity, high erosion resistance against CF 4 -containing plasma and retention of smooth eroded surface. This suggests that the axial suspension plasma spraying of Y 2O 3 is applicable to fabricating equipment for electronic devices, such as dry etching. Surface morphologies of the slurry coatings with splats are similar to conventional plasma-sprayed Y 2O 3 coatings, identified from microstructural analysis. Dense coating structures with no lamellar boundaries have been seen, which is apparently different from the conventional coatings. It has also been found that crystal structure of the suspension coatings mainly composed of metastable monoclinic phase, whereas the powders and the conventional plasma spray coatings have stable cubic phase. Mechanism of coating formation by plasma spraying with fine powder slurries is discussed based on the results. © 2010 ASM International. Source

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