Dianran Yan

An investigation of the corrosion behavior of Al2O3-based ceramic composite coatings in dilute HCl solution

Abstract In this paper, the corrosion behavior of Al 2 O 3 –SiO 2 , Al 2 O 3 –TiO 2 and Al 2 O 3 –SiO 2 –TiO 2 ceramic composite coatings in boiling 1 N HCl solution is investigated. It is shown that the addition of 3% SiO 2 to the base spraying powder of Al 2 O 3 increases porosity in the coatings and causes deterioration in their corrosion resistance. Adding 13% TiO 2 to Al 2 O 3 improves the anti-corrosion property of the ceramic coating due to a reduction in porosity. The connected porosity in the Al 2 O 3 -based ceramic composite coatings rises with the open porosity and is independent of the density of the coating.

Microstructure and properties of Al2O3-13%TiO2 coatings sprayed using nanostructured powders

Abstract The microstructure and wear performance of Al2O3-13% TiO2 coatings prepared by plasma spraying of agglomerated nanoparticle powders were investigated. SEM analysis showed that the as-sprayed Al2O3-TiO2 coatings comprise of two kinds of typical region: fully melted region and unmelted/partially melted nanostructured region, which is different than the conventional coating with lamellar structure. It is shown that the microhardness of the nanostructured coatings was about 15%-30% higher than that of the conventional coating and the wear resistance is significantly improved, especially under a high wear load. The nanostructured coating sprayed at a lower power shows a lower wear resistance than the coatings produced at a higher power, because of the presence of pores and microstructural defects which are detrimental to the fracture toughness of the coatings.

Studies on composite coatings prepared by plasma spraying Fe2O3–Al self-reaction composite powders

Abstract Fe 2 O 3 –Al composite powders were prepared using ferric oxide agent powders, aluminum powders and polyvinyl alcohol. Self-reaction composite coatings containing ceramic and metal multi-phases were fabricated by plasma spraying Fe 2 O 3 –Al composite powders. This technology successfully combines self-propagating high-temperature synthesis with plasma spraying. The morphology of the composite powders was examined by scanning electron microscope (SEM). The chemical composition, microstructure, Vickers hardness, density, porosity and wear resistance of the composite coating were studied. The wear resistance of the ceramic and metal multi-phase composite coating was significantly improved under heavy load.

The corrosion behavior of plasma-sprayed Ni/Al–Al2O3 and Ni/Al–Al2O3+13 wt.% TiO2 graded ceramic coatings in 5%HCl solution

Abstract The corrosion behavior of plasma-sprayed Ni/Al–Al 2 O 3 and Ni/Al–Al 2 O 3 +13 wt.% TiO 2 graded ceramic coatings in 5%HCl solution was investigated. It was shown that the corrosion resistance of a Ni/Al–Al 2 O 3 graded coating was 130 times that of a single Al 2 O 3 coating. The corrosion resistance of Ni/Al–Al 2 O 3 +13%TiO 2 graded coatings was increased by 39.2% compared to a Ni/Al–Al 2 O 3 graded coating with the same compositional gradient. The improvement in corrosion resistance of graded ceramic coatings mainly resulted from the change of corrosion behavior due to the change in structure of the coating. The bond layer alloy particles in the transition layers were distributed isolated in the ceramic matrix. Thus, the connected pores in the working layer were actually pseudo-connected pores. As a result, the electrochemical corrosion between the bond layer and the matrix was restrained. In addition, the pseudo-connected porosity in graded coatings lay on not only the open porosity but also the structure of the graded coating.

Reactive Plasma Sprayed TiN Coating and Its Thermal Stability

TiN coating was prepared by reactive plasma spraying in the Ar and N2 containing plasma jet. The results of XRD show that the TiN coating consists of TiN and T3 O, neither T2 N nor TiO2 phases. The toughening mechanism was characterized by analyzing the SEM morphologies of the TIN coating’s indentation of microhardness and fracture surfaces. The results indicate that the coating possesses a high toughness. The adhesion strength among the TIN layers is 25.88 MPa, which is slightly lower than that of the Ni/Al bonding coating. The oxidation process of the RPS TIN coating is TiN→T3 O→TiO2.

Dry sliding wear behavior of ceramic-metal composite coatings prepared by plasma spraying of self-reacting powders

Ceramic-metal composite (CMC) coatings were deposited on the surface of Fe-0.14–0.22 wt.% C steel by plasma spraying of self-reacting Fe2O3−Al composite powders. The dry sliding friction and wear character of the CMC coatings are investigated in this paper. The wear resistance of the CMC coatings was significantly better than that of Al2O3 coatings under the same sliding wear conditions. The tough metal, which is dispersed in the ceramic matrix, obviously improved the toughness of the CMC coatings. Wear mechanisms of the CMC coatings were identified as a combination of abrasive and adhesive wear.

Corrosion behavior in boiling dilute HCI solution of different ceramic coatings fabricated by plasma spraying

An Al2O3 ceramic coating (A), a 13 wt.% TiO2-Al2O3 (13TA) composite ceramic coating, and a Ni-Al-13wt.%TiO2-Al2O3 (NA-13TA) gradient composite ceramic coating were prepared on Q235 steel by plasma spraying. The corrosion behavior of samples sprayed with these coatings in a boiling 5% HCl solution was investigated. It was shown that an A ceramic coating and a 13TA composite ceramic coating were destroyed after immersion for 17 and 23 h, respectively. The NA-13TA gradient composite ceramic coating was still sound after 14 days of immersion. The corrosion resistance of samples with the NA-13TA gradient composite ceramic coating was sharply improved due to the decreased amount of connected pores in the coating. The corrosion of the sample sprayed with the gradient ceramic coating included the partial corrosion of the surface ceramic coating and the interlayer coatings. The corrosion weight loss depended on the degree of open porosity.

TITANIUM CARBONITRIDE COATINGS PREPARED BY REACTIVE PLASMA SPRAYING Ti POWDERS

Titanium Carbonitride (TiCN), a new high hardness and wear-resistant material, has been applied widely in many fields. TiCN coating was first fabricated using reactive plasma spraying (RPS) technology in the reactive chamber that was filled with nitrogen and acetylene (N2 and C2H2) in this study. The microstructure and the phase composition of the coatings were analyzed by SEM and XRD. More chemical information of surface was analyzed by XPS. The Vickers microhardness of TiCN coating is 1659.11 HV100g, and the cross-section of the coating shows a conspicuous phenomenon of indentation size effect.