Pre-Recrystallization Heat Treatment Effect on Physical and Mechanical Properties of Functional Electric Arc Composite Coatings

Abstract

In this work, the possibility of using pre-recrystallization heat treatment to improve the properties complex of composite electric arc sprayed coatings of the wire Sv-08G2S–Al₂O₃ and wire 65G-TiC systems, which are formed, using a hardening phase powder in a free form, is studied. At the first stage of research, the optimal temperature-time parameters of heat treatment were established for traditional unfilled coatings made of wire Sv-08G2S (temperature 450 °C, holding time 2 min) and 65G (temperature 400 °C, holding time 3 min), which provides an increase in Vickers hardness by 40 % and 26 % respectively. An analysis of the diffraction patterns obtained using a DRON-3 X-ray diffractometer showed a clear expansion of the diffraction peaks after heat treatment, which is associated with the refinement of the structural elements of the coating. Further determination of the size of the regions of coherent X-ray scattering using the Scherrer formula and using the harmonic analysis of heat-treated coatings showed a significant decrease in this characteristic to the level of 100 nm. It was found that the microhardness of the metal matrix of the coatings after deposition of the composition Sv-08G2S–Al₂O₃ was 1.6 GPa; 65G–TiC ― 2.6 GPa. It has been established that the optimal mode of heat treatment for coatings Sv-08G2S–Al₂O₃ is holding time 1 min at a temperature of 450 °C; for 65G–TiC coatings ― 2 min, 400 °C, while the maximum increase in the microhardness of the metal base by 54 % and 38 %, respectively, is observed. A more significant effect of increasing the hardness of composite coatings compared to unfilled coatings after processing is explained by additional work hardening of the metal matrix by high-speed hard particles of Al₂O₃ and TiC. Metallographic studies on a REMMA 102-02 scanning electron microscope-microanalyzer and ZEISS Gemini SEM 500 showed that the composite coatings are characterized by a typical lamellar structure and particles of the dispersed hardening phase (Al₂O₃, TiC) are well differentiated. After heat treatment, no structural changes are observed, porosity remains at the same level (about 8 % and 5 %, respectively). Experimental studies of bond strength using the pin method found that pre-recrystallization heat treatment provides an increase in bond strength by 15…20 % compared to coatings after spraying.