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5257 |
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Thursday, June 08, 2017, Hall 12 5:00 PM Aviation & Power Generation Industry IV |
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Microstructural evolution of NiCoCrAlHfYSi and NiCoCrAlTaY coatings deposited by activated combustion high velocity air fuel spray |
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Yujun Han* / Shanghai University, P.R. China Hongfei Chen/ Shanghai University, China Guang Yang/ Shanghai University, China Jinkai Fan/ Nanjing Institute of Technoloy, China Bin Liu/ Shanghai University, China Yanfeng Gao/ Shanghai University, China |
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The NiCoCrAlHfYSi and NiCoCrAlTaY coatings were successfully produced by means of AC-HVAF and APS processes respectively. The larger in-flight particles with relatively lower velocity appeared to embed in the smaller melted or semi-melted particles with higher velocity when deposit coatings by HVAF process. The lower content of oxides in TGO of HVAF coatings was obtained. The ²-(Ni,Co)Al precipitate phase of the original feedstock powder tended to dissolve into the ³-matrix lattices when deposited coatings by APS process, but the precipitate phase still remained in HVAF manufactured coatings especially the HVAF386 coating. Meanwhile, the peak broadening of ³-matrix phase was mainly attributed to the refinement grains and the local generation of stress. Furthermore, the TGO growth rate as well as the non-protective oxides in TGO, when preparing coatings by HVAF process, could be suppressed significantly. For HVAF386 coating after isothermal oxidation, the growths of both TGO scale and the alumina scale in TGO were relatively rapid. Doping Hf and Si elements could significantly retard the ¸-Al2O3?±-Al2O3 phase transformation in HVAF386 coating, and thus the acicular ¸-Al2O3 and equiaxed ±-Al2O3 could be observed obviously. For HVAF997 coating, with the prolongation of iosthermal oxidation, the initially larger grains with lower deformation storage energy in convex region of coating surface could merely undergo grain-growth stage, and the recrystallization could not occur due to without driving force. Conversely, the dramatically deformed grains in the flat regions appeared to undergo a longer stage of recrystallization prior to grain-growth stage because of larger driving force originating from formation of large amount of sub-grain boundaries, and thus the diffusion passages for aluminum atom could be reduced considerably due to significant growth-grain of ±-Al2O3. The ¸-Al2O3?±-Al2O3 phase transformation might be suppressed and finally retain numerous amount of transient polymorphs of alumina. |