Cermet Coating by APS : Influence of the Ceramic Phase and the Particle Size Range on the Mechanical Properties

The cermet coatings constituted by a metallic phase mixed with a ceramic one allows obtaining coating properties with a wide range of variations. This is particularly interesting for graded coatings produced by APS technique with two different injection ports devoted to each kind of powder. By monitoring the powder feed rates independently it is relatively easy to obtain the requested composition and also the gradient as a function of the coating thickness. In the present work 600 ìm graded coatings were produced with 5 or 6 layers, each one with a specific composition. The hardness properties of the whole coating were evaluated by the Knoop technique. Also each layer was produced separately and characterized as well. These coatings were devoted to thermo-mechanical applications. In this work the metallic phase is always NiCr 80/20 wt% and the ceramic phase is zirconia doped with yttria or ceria as well as Al₂TiO₅. The powders used as a standard have a size range included between 40 and 10 µm. Smaller size ranges were evaluated to produce NiCr / ZrO₂, Y₂O₃ graded coatings and were compared to those obtained with the standard powder. In this last part a post heat treatment of the coating was evaluated against the mechanical properties.