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In this work, the tribocorrosion performance of hydrogenated and hydrogen-free diamond-like carbon (DLC) coated thermal sprayed WC-based cermet/carbide were investigated comparatively. The results showed that, regardless of hydrogen containing, both coatings demonstrated the improvement of anti-tribocorrosion capability of WC-based cermet in 3.5 wt% NaCl solution, by suppressing the corrosion of Ni-based binder phases. Particularly, the hydrogenated DLC coating presented the better tribocorrosion resistance under low load due to the high hardness and excellent corrosion resistance, but it suffered from the catastrophic delamination and protective degradation at heavy load arisen from the high brittleness and large residual stress. In contrast, the hydrogen-free DLC duplex coating exhibited a low COF of ∼0.06 under higher load (10 N) with long time friction (12 h), because of its gradually shearing characteristic. This work provides theoretical basis and design principles for DLC combinations with remarkable corrosion inhibition used in harsh marines. [Display omitted] • Amorphous carbon coating with and without hydrogen were deposited on WC-based cermet for tribocorrosion comparison. • a-C:H duplex coating presented the excellent tribocorrosion inhibition properties at lower load. • Poor toughness of a-C:H duplex coating caused the catastrophic delamination at higher load in chloride solution. • a-C coated WC cermet behaved the long-term tribocorrosion resistance under heavy friction due to graphitic shearing. [ABSTRACT FROM AUTHOR]

Los materiales compuestos de matriz metálica reforzados con carburos, son conocidos por su elevada resistencia a todos los tipos de desgaste, debido a la combinación de las partículas duras en una matriz metálica tenaz. Diferentes tipos de estos materiales, se han empleado en el desarrollo de nuevas herramientas de corte de altas prestaciones. La técnica de láser cladding (LC), permite obtener recubrimientos libres de defectos sobre zonas muy concretas, con un aporte de calor muy localizado. Pero en el caso de carburos de wolframio (WC), debido a la enorme absorción de energía y la diferencia de propiedades entre el metal base y la cerámica, puede producir una gran cantidad de defectos tales como grietas, poros, gran dilución de carburos, falta de adherencia, etc. El objetivo de este trabajo, es estudiar las transformaciones metalúrgicas que aparecen durante el procesado por láser de recubrimientos tipo cermet de WC10Ni, sobre acero de herramienta para trabajo en frío (EN 12379). Además se ha relacionado los parámetros de proceso con la generación de defectos. Para ello, se analiza su microestructura, composición y se obtienen perfiles de dureza en el recubrimiento y en el acero afectado por el calor. Los resultados muestran, que aunque el control de los parámetros del proceso reduce la generación de defectos, al depositar recubrimientos por solape de cordones, se produce gran cantidad de transformaciones debido a la disolución masiva de las partículas de WC y la difusión de elementos de aleación, desde el sustrato hacia el recubrimiento.

In this study, durability and tribological properties of thermally sprayed WC-Cr-Ni cermet coatings were investigated experimentally under lubricated pure rolling or rolling with sliding contact conditions. Coatings were deposited by the high velocity oxy-fuel flame spraying (HVOF) process onto the carburized hardened steel substrate. The WC cermet coated steel roller was mated with the noncoated carburized hardened steel roller under a contact pressure of PH=1.2 or 1.4 GPa in line contact condition. It was found that durability or life of the cermet coating is significantly influenced depending on the contact pressure, slip ratio and coating thickness. Durability or life of the coating was also compared with the durability when the substrate material was an induction hardened steel or a thermally refined steel. Furthermore, it was observed that tribological properties such as coefficient of friction and surface temperature were much affected by the slip ratio and slightly affected by the contact pressure. In addition, after the running-in process it was found that surface roughness of the coated surface was remarkably influenced by the slip ratio and it was less influenced by the contact pressure. [ABSTRACT FROM AUTHOR]

Abstract: In this study, using a two-roller testing machine, the authors examined the surface durability of thermally sprayed WC-Cr-Ni cermet coating in lubricated rolling with sliding contact conditions. The coating was formed onto the axially ground, blasted and circumferentially ground roller specimens made of a thermally refined carbon steel or an induction hardened carbon steel by means of the high energy type flame spraying (Hi-HVOF) method. The WC cermet coated roller finished to a mirror-like condition was mated with the carburized steel roller without coating having a surface roughness of Ry=3.0∼5.0μm. In the experiments, a maximum Hertzian stress of P H=0.6 or 0.8GPa was applied for the thermally refined carbon steel roller and P H=1.4GPa was applied for the induction hardened carbon steel roller in line contact condition. As a result, it was found that in the case of induction hardened steel substrate, the coated roller generally exhibits a long life without any serious damage and the surface durability is hardly affected by the substrate surface finish, while in the case of thermally refined steel substrate, the durability of coated roller is lowered and the life to flaking is very short particularly when the substrate surface is circumferentially ground and the mating surface is rough. The surface durability of coated roller was also compared with the durability of steel roller without coating. Finally, in order to discuss the durability of coated roller, the elastic-plastic behavior of the subsurface layer under repeated rolling with sliding contact was analyzed using a finite element method (FEM). [Copyright &y& Elsevier]