Abstract
Oxidation barrier coatings on the base of a perhydropolysilazane precursor with different amounts of Si, B, SiB6 and Mo5SiB2 (T2) fillers for the oxidation protection of Mo-Si-B alloys were developed. The influence of different filler compositions as well as the influence of pyrolysis conditions (temperature and atmosphere) was studied. The coating slurries were examined with respect to their rheological behavior, which allows optimization of the coating slurry. Dilatometry studies show that the coefficient of thermal expansion of the composites can be matched to refractory, especially molybdenum alloy based, substrates by varying the content and the composition of the filler. The pyrolyzed coating systems offer a low porosity, which is one of the key parameters to a high oxidation protection capability.
Highlights
A process–cost–effective alternative to various coating techniques such as pack cementation coating, magnetron sputtering and plasma spraying is offered by coating processes with preceramic polymers under ambient conditions [1]
The oxidation protection mechanism of polymer–to–ceramic converted, homogeneously filled coating layers consists in the formation of a high temperature stable SiO2 /SiNO matrix, which, in a combination with glass-forming filler particles, protects the alloy surface at the initial stage of oxidation [4,5,6]
Further essential parameters for coatings were investigated on bulk samples of coating systems
Summary
A process–cost–effective alternative to various coating techniques such as pack cementation coating, magnetron sputtering and plasma spraying is offered by coating processes with preceramic polymers (ceramic precursors) under ambient conditions [1] After their thermal conversion (pyrolysis) into polymer-derived ceramics, they may serve as protective and functional layers for metallic materials [2,3]. Oxidation barrier coatings were developed using a perhydropolysilazane precursor and homogeneously distributed in it Mo5 SiB2 , SiB6 , Si and B powder fillers [4,5] These coating systems are intended to protect Mo-base alloys, in particular Mo-Si-B, Mo-Hf-B and Mo-Zr-B alloys, against high temperature oxidation above 1100 ◦ C. The oxidation protection mechanism of polymer–to–ceramic converted, homogeneously filled coating layers consists in the formation of a high temperature stable SiO2 /SiNO matrix, which, in a combination with glass-forming filler particles, protects the alloy surface at the initial stage of oxidation [4,5,6]
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