Remelting treatment of the non-conductive oxide coatings by means of the modified GTAW method

The primary objective of the study was to adapt the GTAW (Gas Tungsten Arc Welding) technique for the purposes of the surface remelting processing of non-conductive plasma sprayed coatings. Modification concerned the surface layer of complex oxide compositions based on ZrO2 and Al2O3, which had been applied onto a steel substrate using the plasma spraying technique. In the course of research it was demonstrated that the process of surface remelting of non-conductive oxide coatings may be successfully conducted using welding sources of heat provided that the standard welding station is previously redesigned and additionally equipped. The methodological and apparatus-related work undertaken led to the development and construction of a welding set with a free independent arc, in which the active participation of the oxide coating in the creation of the electric arc and its stabilisation has been eliminated. The effects of the remelting treatment on the structure of the plasma sprayed coatings have been investigated. The microstructures of both the as-deposited and the remelted coatings were observed by optical microscope and scanning electron microscope (SEM). Observation of the remelted coating structure allowed to distinguish areas with characteristic structural and morphological effects and changes in the structure thereof. On the basis of regularities noted and observations made, a zonal model of the remelted coating structure was put forward and elaborated. ► The remelting of the oxide coatings may be conducted using modified GTAW method. ► The GTAW method is a competitive solution with respect to the laser technologies. ► The presence of the distinctly formed zones is observed in the remelted coatings.