Improvements in MMC coatings - influence of powder preparation (mixture or ball milling) and powder size on the coating behavior

摘要

Metal-Matrix Composites (MMC) are composed of hard particles that exhibit exceptional wear resistance. In this way, many investigations were conducted to improve the life span of structures. Regarding surface stress, thermal spraying can be appropriate to elaborate thick composite coatings with specific behaviour. In order to improve coating mechanical properties, it is necessary to manufacture samples with more homogeneous microstructures. Thus, the chosen approach was to optimize the powder morphology through mechanical alloying. Indeed, when mechanical alloying process is used to synthesize composite powders strengthened by particle dispersion, powders tend to fracture into small segments, especially when a high content of hard particles is added. Powder microstructures are then refined which induces thinner coating morphology and reduces their porosity content. In the present work, the mechanical alloying (ball milling) method was developed to synthesize NiCrBSi-WC composite powders using HVOF. Considering different granular sizes of powders (micrometric and nanometric) after parameter optimization, composite coatings were compared with standard coatings elaborated from mixed powders. SEM observations, hardness measurements, DRX analysis were the first technologies implemented to characterize Metal Matrix Composite coatings.