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| Home > Publications database > Impact of Processing Conditions and Feedstock Characteristics on Thermally Sprayed MCrAlY Bondcoat Properties |
| Home > Publications database > Impact of Processing Conditions and Feedstock Characteristics on Thermally Sprayed MCrAlY Bondcoat Properties |
| Journal Article | FZJ-2016-07254 |
; ; ; ; ;
2017
Elsevier Science
Amsterdam [u.a.]
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Please use a persistent id in citations: doi:10.1016/j.surfcoat.2016.08.079
Abstract: One of the options to manufacture MCrAlY bondcoats (M = Co, Ni) for thermal barrier coating systems is High Velocity Oxy-Fuel spraying (HVOF). In this work, particle diagnostics were applied to investigate the impact of processing conditions and feedstock characteristics on the relevant bondcoat properties. The results showed that compromises must be made on the oxygen/fuel ratio, spray distance, and particle size distribution to strike a balance between low oxidation and dense microstructures.These limitations initiated the development of the High Velocity Atmospheric Plasma Spray process (HV-APS) as a further alternative process. In this work, HV-APS process parameters were developed for a three cathode torch in combination with a 5 mm diameter high speed nozzle. A one-dimensional calculation of the expansion through this nozzle to atmospheric pressure yielded supersonic conditions with a Mach number of 1.84. The calculated plasma temperatures at the nozzle exit and in the expanded jet are 8400 K and slightly above 5200 K, respectively, which is low compared to conventional APS processes.A very fine powder with a median particle size of 18 μm was identified to be most suitable. Although the spray conditions were relatively cold, reasonable deposition efficiencies up to 61% and rather dense coatings were achieved using this feedstock. The as-sprayed porosity was ≈ 2% which was reduced by the subsequent vacuum heat treatment to < 1%. The oxygen content determined by chemical analysis for a sample sprayed at a spray distance of 100 mm was 0.41 ± 0.04 wt%.Moreover, reference samples were manufactured by Low Pressure Plasma Spraying (LPPS). The oxidation behavior was compared in isothermal and cyclic oxidation tests. The oxidation rates of the HV-APS coatings were found to be significantly lower than those of LPPS coatings. The thermally grown oxide scale showed less yttrium incorporation and better adherence in case of HV-APS. The latter is suggested to be related to a unique new distribution of Y-rich nano-sized oxide precipitates. The cyclic oxidation test confirmed the better oxidation resistance of the HV-APS coatings.
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