On the one hand, cold spraying (CS) is a surface treatment that allows to produce metallic-based coatings on various materials, mainly metallic substrates. It knows a growing interest  and has a wide range of applications such as protection against corrosion, preparation of high conductivity coatings, repair of damaged metal components, metal additive manufacturing or thermal management. However this technique remains  not suitable to produce protective ceramics coatings directly on materials. On the other hand, plasma electrolytic oxidation (PEO) is an electrochemical surface treatment  which enable the formation of a relatively thick (few hundreds of micrometers) ceramic oxide layer on the top surface of lightweight metals such as aluminium and magnesium. Therefore, the combination  of  CS and PEO into a duplex surface process was proposed with the aim to elaborate new protective ceramic layers on different metal substrates. Furthermore, the versatility of the proposed duplex treatment offers the possibility to produce various oxide-based composites coatings.
 
The objective of our presentation is twofold. First, we will present the new type of microstructures that  are able to form with this duplex process and, secondly, we will show the  tribological properties of the associated duplex ceramic coatings. Secondly, we will use the opportunity to deposit different ceramics such as yttria stabilized zirconia (YSZ) or rutile TiO2 in an aluminium matrix by CS in order to make process engineering by following the behavior of these "chemical tracers" after PEO treatments. It must be said that the PEO process is not fully understood. In some conditions and after some treatment times, a particular regime, named soft regime, can be reached. The surfaces properties of materials treated in such conditions are better than the ones obtained without the occurrence of the soft regime. The physico-chemical process occurring during the soft- regime are not understood actually.   
 
In this communication, we will show that after PEO treatments, surfaces obtained by CS aluminium powder with or without the addition of ceramics, such as α-Al2O3 have different properties.
It has been shown that it is difficult to follow the transformation of the alumina particles originating for the CS process in a layer where the PEO process transform the aluminium in alumina. Using a combination of aluminium and YST or TiO2 powders allows us to better visualize the ceramic particles transformation during the PEO process. Hence, morphological transformations are observed for YSZ particles treated by PEO with soft regime, whereas morphological transformations are observed on TiO2 particles treated by the PEO process before the soft regime.
 
Concerning the mechanical behavior, the coatings obtained by the duplex process are interesting in term of wear resistance. Even if they present a high friction coefficient, the layers can undergo a high normal stress for a relative long time without presenting a high wear rate.