Studying the Erosion Corrosion Behavior of NiCrAlY Coating Layer Applied on AISI 446 Stainless Steel Using Thermal Spray Technique

Erosion-Corrosion behavior of NiCrAlY coatings deposited on 446 stainless steel samples by flame thermal spraying was performed in this research. The hardness of uncoated and coated sample is measured, using HVS-1000 Digital Micro hardness Tester. The results of hardness show that the coated samples have higher hardness than uncoated samples. Microstructure and phase analysis of the coating layer was observed by using optical microscope, X-ray diffraction (XRD), and SEM respectively. Erosion –Corrosion test was performed in different period of time (6, 12, and 18 hr.) using the erosion-corrosion system. The result shows that because of uniform distribution and homogeneous of coating layer, weight loss was very low and approximately equal in all period of testing time.

Tribocorrosion Properties of NiCrAlY Coating in Different Corrosive Environments

Atmospheric plasma spraying (APS) was taken to fabricate the NiCrAlY coating. The corrosion-wear properties of NiCrAlY coating was measured respectively under deionized water, artificial seawater, NaOH solution and HCl solution. Experimental results presented that the as-sprayed NiCrAlY coating consisted of Ni3Al, nickel-based solid solution, NiAl and Y2O3. In deionized water, the coating with the lowest corrosion current density (icorr) of 7.865 × 10−8 A/cm2 was hard to erode. Meanwhile, it presented a lower friction coefficient and the lowest wear rate. In HCl solution, NiCrAlY coating gave the highest corrosion current density (icorr) of 3.356 × 10−6 A/cm2 and a higher wear rate of 6.36 × 10−6 mm3/Nm. Meanwhile, the emergence of Al(OH)3 on the coating surface could reduce the direct contact between the counter ball and sample effectively, which was conducive to the lowest friction coefficient of 0.24.

Tribological Performance of a Ni-Based Composite Coating in Artificial Seawater

NiCrAlY and NiCrAlY-Mo coatings were fabricated by atmospheric plasma spraying (APS). The corrosion-wear performance of the coatings was investigated in artificial seawater and the synergistic mechanism between wear and corrosion were evaluated in detail. Results showed that the diffraction peaks of Ni3Al shifted to the right and the microhardness of the coating was improved from 329.8 HV to 342.5 HV with adding the Mo element. Meanwhile, the NiCrAlY-Mo coating had a lower friction coefficient, with a wear rate of 0.26 and 3.69 × 10−6 mm3/Nm, compared to the NiCrAlY coating with a wear rate of 0.37 and 4.67 × 10−6 mm3/Nm. The NiCrAlY coating had severe corrosion and the corrosion mainly occurred in grain boundary. Adding the Mo element, the Mo element was distributed in the grain boundary and the coating had a lower corrosion rate and visibly slighter corrosion. The NiCrAlY-Mo coating had excellent corrosion-wear properties in artificial seawater.