Active oxidation protection coatings for Mo-Si-B high temperature materials

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Due to an increase in efficiency, the high-temperature stabile material Mo-Si-B is intensely investigated as a substitute material in combustion turbines. A problem not solved yet in this material system is its oxidation behavior: the Mo component shows pesting in form of Mo(IV) oxid formation. The intrinsic material protection mechanism– the oxidation of near-surface Si and B and its reaction to form an oxygen diffusion limiting glass layer – is insufficient. Aim of this work is to develop a novel-type, active multi-layer environmental barrier coating with an initial protective glass layer formation at low temperatures (500 °C to 800 °C), and a high oxygen-trapping capacity and oxygen diffusion inhibition layer under service conditions (1100 °C to 1200 °C). These layers are based on a perhydropolysilazane filled with particulate Si-, B-, Ti and/or Al-containing components of variable particle size and volume fraction, and it will be applied by dip coating of Mo-Si-B substrate materials followed by heat treatment for the conversion into an active ceramic material (layer conditioning) and heat treatment under service-like conditions. Standard methods will be carried out for solid-state sample characterization after conditioning and treatment under service-like conditions. XPS investigations will give a deeper insight into protective-layer formation mechanisms and nanoindentation experiments allow to characterize and to understand the layers´ mechanical properties. The results will be used for models development to understand the physicochemical layer formation and their function under service conditions. This will help to transfer the development of protective layers for other than Mo-Si-B refractory based alloys.