Microstructure and thermal conductivity of wire-arc sprayed FeCrNbBSiC amorphous coating

For the aim of thermal barrier application in vehicle engines, a specific FeCrNbBSiC cored wire of consideration was produced to fabricate amorphous coating by wire-arc spraying. The microstructure and thermal conductivity of the as-deposited coating were characterized in detail. The results show that the FeCrNbBSiC coating (FB coating) primarily consists of amorphous phase owing to the combination of proper composition design and rapid quenching of wire-arc spraying. However, a fraction of crystalline phases coexists with the amorphous matrix, due to the both effects of partially incomplete alloying and continuous annealing. Depending on the expected amorphous structure, thermal conductivity of the developed FB coating is as low as 2.15 W/mK at room temperature, almost half of the referenced 316L stainless steel coating (SS coating, 4.20 W/mK), and displays relatively slow and limited increase with elevated temperature up to 500 °C. By means of temperature distribution analysis, an obviously higher temperature is found on the top surface of FB coating covered piston, which implies a benefit of enhancing heat energy conversion. Simultaneously, the temperature of aluminium alloy substrate could also be reduced by covered coating as the role of thermal insulation. Therefore, the wire-arc sprayed FeCrNbBSiC amorphous coating developed here with excellent thermal barrier performance and economic advantage could be a promising innovation and candidate for metal-based thermal barrier coatings applied in vehicle engines.