Effect of vacuum heat treatment on microstructure and corrosion behavior of HVOF sprayed AlCoCrFeNiCu high entropy alloy coatings

To improve the corrosion resistance of coalbed methane drilling equipment, an AlCoCrFeNiCu high entropy alloy coating was prepared on the AISI 4135 (35CrMo) steel substrate by high velocity oxygen fuel (HVOF) technology, and the coating was subjected to vacuum heat treatment (VHT) at different temperatures (500, 700, 900 and 1100 °C). The corrosion test of the substrate and the coatings after VHT in coalbed methane drilling fluid was carried out. The results show that the HVOF sprayed AlCoCrFeNiCu high entropy alloy (HEA) coating has a good bonding with the substrate, and the porosity of the coating is about 2.4%. There is partial segregation in the coating, and the coating mainly consists of body-centered cubic phase. The coating has good thermal stability, and the phase structure and microstructure of the coatings have changed after VHT at different temperatures. Compared with the substrate, the as-sprayed coating has better uniform corrosion resistance, and the corrosion resistance of the coating after VHT is further improved. After VHT at 500 °C, the HVOF-sprayed AlCoCrFeNiCu HEA coating has the best corrosion resistance.