Tribological And Corrosion Properties Of Plasma Spraying Al₂O₃/Al₂O₃-TiO₂Reinforced Aluminum And Nickel-based Coatings

Particles reinforced metal matrix composite coatings have the comprehensiveperformance of both metal and ceramic, they have a better application than a singlemetal or ceramic coatings. This paper made Al₂O₃and Al₂O₃-13wt.%TiO₂reinforced aluminum and nickel based composite coatings by air plasma spraying,which takes advantage of both good corrosion resistance and thermal shockresistance of aluminum and nickel-based metal and high hardness and excellentwear resistance of Al₂O₃and Al₂O₃-13wt.%TiO₂. Then this paper analysis themorphology of the spraying feeding, microstructure and hardness and bondingstrength mechanical properties of the coating. The research was mainly focused onthe frictional wear, erosion wear and scratch tribological performance of thecomposite coatings. And this paper studied thermal shock resistance and corrosionbehavior in3.5%NaCl solution of the composite coatings.The surface of the coatings were piled up waves of uneven topography by SEMobservation, and reinforcing particles was observed in the surface of particlesreinforced coatings. Reinforcing particles were found distributed uniformly in thecoatings. There were no obvious layered structure and large pores by looking at thecross section of aluminum coatings. Nickel-based coatings were layer structure andwith a porosity of about1%. XRD analysis found that the aluminum coatings weremainly consist of Al, α-Al₂O₃and a little TiO₂, while the nickel-based coatings weremainly consist of Ni, NiO, α-Al₂O₃and a little TiO₂. Reinforcing particles greatlyincreased the hardness of the coatings. The bond strength of aluminum coatings wasslightly reduced, and that of the nickel-based coatings was basically remainedunchanged.Sliding friction and wear tests showed that it can reduce the friction coefficient,quality and volume loss of the composite coatings while adding reinforcingparticles. Reinforcing particles improve the wear resistance of the compositecoatings. Erosion wear tests showed that erosion wear of aluminum coatingsdropped substantially, and reinforcing particles improved the wear resistance morethan15times. For Nickel-based coatings, the amount of erosion wear ofNi-20%Al₂O₃coating increased from85mg of pure Ni coating to122mg, andNi-20%Al₂O₃TiO₂coating was reduced to64mg. Scratch tests showed that,, thecritical load of the coatings that adding reinforcing particles increased. The fri ctioncoefficient of aluminum coatings was constant substantially, and that ofnickel-based coatings reduced.There were no cracks and damage found in the surface of the aluminum coatings after thermal shock230times at550. The aluminum coatings haveexcellent thermal shock resistance. Compared with thermal shock cycles of30timesof pure Ni coating at1000, the thermal shock cycles of nickel-based coatingswhich adding Al₂O₃and Al₂O₃-TiO₂decreased by48%and39%respectively.Potentiodynamic polarization tests showed that the corrosion tendency ofaluminum coatings was weakened and that of nickel-based coatings wasexacerbated after adding the reinforcement.3.5%NaCl solution immersion testsshowed that reinforcement made long-term corrosion resistance of the coating’sdeclined. The the main corrosion mechanism of aluminum coatings were that therewere a large number of pores in the surface which formed a closed cell andproduced pitting. And the accumulation of corrosion products lead to generalcorrosion. The corrosion products were Al（OH）₃mainly. The same to the corrosionmechanism of nickel-based coatings, but the extent of corrosion declined. Thecorrosion products were NiO and Ni（OH）₂mainly.