International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

In this study, the stress state of metal coating on a steel substrate under tensile straining was investigated by with finite element modelling with the aim of better understanding the mechanism of delamination for the coating. The investigations showed cracking and delamination of the coating by the application of uniaxial tensile strain to the substrate. Due to interfacial stress crack appeared in the coating-substrate interface. The stress measurements in coated substrate, using FEA, indicated interfacial shear and peeling stresses at the interface near the edges of the coating under tensile load. When tensile stress is applied externally on the coated substrate, the coating exhibits multiple cracking perpendiculars to the tensile direction, and then interfacial debonding occurs. A good agreement is found between the modelling approach and the corresponding experimental tensile tests of the coated specimens. The effect of coating thickness on the evolution of the stress distribution was also studied. The cracking and delamination of the coatings with a thickness ranging from 90 to 160 m was studied by tensile test experiments. The estimation of the stress distribution and concentration at the interface during these experiments allows the failure stress of the coating in the interface coating–substrate to be evaluated.

Technique and equipment for plasma spraying of wear-resistant and corrosion-resistant coatings with enhanced adhesive strength was developed. Ceramic powders coated metal thin films were used for plasma spraying. Optimal conditions for deposition of the metal films on the particles of alumina powder (40…63µm fraction) by PVD process were obtained. Deposition of two- layer films on the powder particles was carried out. The first layer was titanium and the second layer was aluminum or copper. The titanium as adhesively-active element capable of wet alumina is necessary for increase the adhesion strength vacuum films as well as plasma sprayed coatings.

A special plasma-spray gun with external arc working in a mode of laminar plasma argon jet generation was designed. Such regime provides melting of the refractory ceramic core, saving metal films as well as localization of thermal effects during spraying process.
The results of testing coated specimens confirmed that the developed technique improves the physical and mechanical properties of the plasma sprayed composite coatings. The sprayed composite coatings were compared with coatings sprayed using pure alumina powders in terms of adhesion, wear and corrosion properties. The shear adhesion strength increases up to about 1.9 times, the wear resistance increases about 5 to 7 times, the corrosion resistance increases about 2.5 to 5 times.

The shear adhesion strength was measured at tension of coated specimen at room temperature by developed adhesion testing technique. The substrate was flat and dog-bone-shaped. The substrate with rectangular cross-section was partially coated with plasma- sprayed coating. The specimens were tested in uniaxial tension under displacement control. The tensile specimens were loaded to adhesion delamination of the coating. Sprayed coating was detached as a result of shear interface stresses.