Microstructural investigation on bond coats in molybdenum and steel coatings for the renovation of mechanical pieces

Thermal spraying has been used in industry for many years to improve the properties of the surface of a workpiece, such as its mechanical and electrical properties and its wear resistance. Fabricating these high-quality coatings requires good cohesion of the deposited material and high adherence to the substrate. To improve adhesion of the coating to the substrate, the Company SNC ATRA (Algeria) uses molybdenum as the intermediate adhesion layer to restore the brace and bit. The purpose of this paper is to study the microstructure and morphology of the bond coat and coating using a flame-spray technique. Coatings have been characterized by scanning electron microscopy combined with traditional procedures of metallographic preparation. The results show that the substrate is thermally damaged when molybdenum is deposited as a bond coat, and that the bond coat is delaminated in its middle layer.