Development of metal-ceramic-lubricant composite coatings obtained by Cold Spray for tribological applications in the automotive industry

As many transportation industries, one of the main levers of the automotive industry to reduce CO2 emissions is the friction reduction. One way of realising this objective is using efficient coatings tailored for high tribological performances, to be used in some heavily loaded engine parts. The aim of the present work was to develop metal-ceramic-lubricant composite coatings onto steel parts, which could exhibit the best compromise between several properties, primarily wear and seizure resistance, fatigue resistance and thermal resistance. For this, metal-based coatings with addition of hard particles and solid lubricants were produced using cold spray and the relations between the resulting multi-material coating microstructure and its tribological properties were studied. To meet high tribological properties, the interfaces between the different constituents were optimized by selecting carefully the starting powders and testing a large range of process parameters. Alumina-reinforced bronze based composite coatings were produced using powders with different morphologies. Aggregated ceramic powders revealed to be more beneficial for wear properties compared with monolithic powders. Graphite was also added in order to reduce seizure and different grain sizes were compared. Experimental studies were correlated with particle impact modelling which was developed using in-flight particle velocity measurements and involving particle shape.