Effects of pulse frequency on the microstructure and properties of AlCoCrFeNiMo(TiC) high-entropy alloy coatings prepared by laser cladding

Abstract

The effects of pulse frequency (0.5, 5, 50, 500, and 5000 Hz) on the microstructure and properties of AlCoCrFeNiMo(TiC) high-entropy alloy coatings were investigated. The microstructure of the coatings was analysed by performing X-ray diffraction, backscattered electron image, electron backscattered diffraction, and energy dispersive spectroscopy. The wear resistance, corrosion resistance, and high-temperature oxidation resistance of the coatings were also tested by carrying out wear, electrochemical, and high-temperature oxidation tests. Both the BCC phases and TiC particles were present in all coatings. In addition, the Mo-rich phases, which were FCC (NiCrCoMo) and σ phases, appeared within the pulsed wave coatings. The average TiC particle size and the percentage of the Mo-rich phase increased by increasing the applied pulse frequency. The effect of frequency on wear resistance, corrosion resistance, and high-temperature oxidation resistance was reflected by performing fitting using mathematical equations. As the pulse frequency decreased, the microhardness, wear resistance, corrosion resistance, and high-temperature oxidation resistance of the coatings gradually increased, while the best performance was achieved when the pulse frequency was 0.5 Hz. The main reason for this effect is that as the pulse frequency decreased, the mechanical properties of the coatings improved mainly because the TiC particle refinement enhanced the dispersion strengthening. Moreover, the corrosion resistance and high-temperature oxidation resistance were improved because the TiC particle refinement and the reduced Mo-rich phase content synergistically reduced the electrocoupling corrosion of the alloying elements during corrosion and the alloy diffusion rate during oxidation.