Use of Aluminium Phosphate for Sealingthe Electric Arc Thermal Spray Nickel ChromiumAlloy Coating

The NiCr20 alloy coating on a carbon steel substrate was penetrated by aluminium phosphate sealant at room temperature and under normal pressure for 12 h. Thereafter, the impregnated coatings were heat-treated at 100°C for 2 h, followed by 200°C for 2 h, and at the final curing temperature of 400°C for 4 h. The aluminium phosphate sealant was synthetized with a molar ratio P/Al = 2.3. The analysis on the cross-sectional microstructure by mean of the SEM-EDX revealed that the sealant penetrated into the coating to a depth of 700 μm. After the sealing treatment, about 85% of the pores inside the coating were filled. The XRD phase analysis on the coating surface showed an absence of crystalline compounds between NiCr20 alloy and aluminium phosphate, that meant that there was no reaction between the alloy coating and the sealant. In comparison with the unsealed coating, the application of the sealant improved the coating’s wear resistance by 12 times and the microhardness about 25%.