Tribological Properties of Solid Solution Strengthened Laser Cladded NiCrBSi/WC-12Co Metal Matrix Composite Coatings

NiCrBSi, WC-12Co and NiCrBSi with 30, 40 and 50 wt.% WC-12Co coatings were produced on low carbon steel by laser cladding with an Nd:YAG laser with a multi-jet coaxial cladding-nozzle. The microstructure properties after WC-12Co alloying were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and Vickers hardness tests. The resulting microstructures consisted of a γ-Ni and Ni3B matrix, strengthened with Co and W, Ni3Si, CrB, Cr7C3, Cr23C6, WC/W2C phases. In coatings with 30, 40 and 50 wt.% WC-12Co, a solid solution, strengthened multi-matrix NiCrWCo phase formed, which yielded a higher matrix hardness. Wear tests that monitored the friction coefficients were performed with a tribometer that contained a ball-on-disc configuration, Al2O3 counter-body and reciprocal sliding mode at room temperature. The major wear mode on the NiCrBSi coatings without the WC-12Co was adhesive with a high wear rate and visible material loss by flaking, delamination and micro-ploughing. The addition of WC-12Co to the NiCrBSi coating significantly increased the wear resistance and changed the major wear mechanism from adhesion to three-body abrasion and fatigue wear.

Investigation of the friction behavior of plasma spray Mo/NiCrBSi coated brake discs

This paper presents the findings of comparative research conducted to find out the braking performance of a Mo/NiCrBSi coated automobile brake disc. The friction and wear behavior of the Mo/NiCrBSi coating (CD) used for the disc material was evaluated using a laboratory scale disc-pad dynamometer and compared with a reference disc (RD). The coating was deposited by means of the atmospheric plasma spray process on a grey cast iron substrate. Braking tests were performed according to the SAE-J2430 test standard. Disc microstructures were characterized by SEM and XRD. It was found that the bonding strength was good with an infinite rating between the accumulated coating layer and the substrate. The results show that the coated brake disc has a comparable coefficient of friction and that the amount of wear is lower than that of the reference disc. The addition of ductile phases to the disc coating was beneficial in reducing the coefficient of friction to an acceptable degree and also effectively improving wear resistance.

THE INFLUENCE OF BORON CARBIDE ADDITIVE ON THE STRUCTURE AND HARDNESS OF A NICKEL-BASED COATING

Laser cladding is increasingly frequently used in various branches of mechanical engineering since it has such advantages over traditional methods of depositing coatings as high heating and cooling rates and minimal mixing of base and melting materials. Laser-clad coatings are usually characterized by a fine-grained structure and a minimal heat-affected zone. Coatings formed from the Ni–Cr–B–Si powders are also very common in industrial applications, as they have good resistance to wear, corrosion, erosion, etc. Various strengthening particles can be added to this group of powders to improve the properties of the deposited coating. Boron carbides can act as such particles since they have high hardness, thermodynamic stability, and wear resistance. In this regard, the paper investigated the influence of the 7 wt. % of boron carbide B4C addition on the structure and hardness of the NiCrBSi coating formed by laser cladding of PG-SR2 powder on the surface of 30HRA steel. Using the scanning electron microscope, the authors carried out microscopic studies of the structure of NiCrBSi and NiCrBSi–B4C coatings and presented the results of X-ray spectral microanalysis. The study shows that the structures of both coatings in the deposited state are characterized by uniformity and fine-grain structure. The investigation revealed that the samples with NiCrBSi and NiCrBSi–B4C coatings have a narrow transition zone from the deposit to the base metal. The paper presents the results of measuring the microhardness of coatings indicating a decrease in the microhardness of laser-clad nickel-based coatings with the boron carbide addition.

Phase Transformation-Induced Improvement in Hardness and High-Temperature Wear Resistance of Plasma-Sprayed and Remelted NiCrBSi/WC Coatings

The remelting method is introduced to improve the properties of the as-sprayed NiCrBSi coatings. In this work, tungsten carbide (WC) was selected as reinforcement and the as-sprayed and remelted NiCrBSi/WC composite coatings were investigated by X-ray diffraction, scanning electron microscopy, hardness test and tribology test. After spraying, WC particles are evenly distributed in the coating. The remelting process induced the decarburizing reaction of WC, resulting in the formation of dispersed W2C. The dispersed W2C particles play an important role in the dispersion strengthening. Meanwhile, the pores and lamellar structures are eliminated in the remelted NiCrBSi/WC composite coating. Due to these two advantages, the hardness and the high-temperature wear resistance of the remelted NiCrBSi/WC composite coating are significantly improved compared with those with an as-sprayed NiCrBSi coating; the as-sprayed NiCrBSi coating, as-sprayed NiCrBSi/WC composite coating and remelted NiCrBSi/WC composite coating have average hardness of 673.82, 785.14, 1061.23 HV, and their friction coefficients are 0.3418, 0.3261, 0.2431, respectively. The wear volume of the remelted NiCrBSi/WC composite coating is only one-third of that of the as-sprayed NiCrBSi coating.