Due to good performance in abrasive and sliding wear and enhanced oxidation behavior, coatings based on Co-Cr-W alloys are widely used in industrial applications, where the material is exposed to high temperature. Within the scope of this study, a Co-based alloy similar to commercial Stellite 6, which additionally contains 20.6 wt.% of vanadium, was deposited by Twin Wire Arc Spraying (TWAS). Multi-criteria optimization using statistical design of experiments (DoE) have been carried out in order to produce adequate coatings. The produced coatings have been analyzed with respect to their tribological behavior at elevated temperatures. Dry sliding experiments were performed in the temperature range between 25°C and 750°C. Oxide phases were identified in the investigated temperature range by X-ray diffraction (XRD) using synchrotron radiation. The V-doped Stellite-based coating possesses a reduced coefficient of friction (COF) of about 0.37 at elevated temperatures (above 650°C), which was significant lower when compared to conventional Stellite 6 coating that serves as reference. In contrast, both produced coatings feature a similar COF under room temperature. X-ray diffraction reveals the formation of cobalt vanadate and vanadium oxides above 650°C. The formation of vanadium oxides exhibits the ability of self-lubricating behavior, thus leading to enhanced tribological properties.

This paper evaluates and compares five wear-resistant coatings produced by HVOF spraying for high-temperature use. CrC-NiCr, CrC-CoNiCrAlY, Stellite 6, NiCrBSi, and TiMoCN-Ni coatings were sprayed on grit-blasted carbon steel substrates. Abrasive, sliding, and fretting wear resistance were measured and changes in microstructure and hardness due to high-temperature exposure were recorded. CrC-NiCr coatings exhibited the best wear properties, but the oxidation of carbides at high temperatures proved to be a problem. Based on test results, alternative coatings would include CrC-CoNiCrAlY for abrasive wear, Stellite 6 for erosive wear, and NiCrBSi for sliding wear.

This study assesses the potential of kinetic-spray coatings for dealing with the effects of soldering and erosion on aluminum casting dies. In the experiments, molybdenum-boride cermet and cobalt-based alloy powders are cold sprayed onto SKD61 substrates. Coating microstructure is assessed via SEM and XRD analysis and several mechanical properties are measured. In order to evaluate soldering resistance, the coatings are immersed in a molten aluminum bath. Although cold-sprayed CoCrNiWC exhibited high coating density and low porosity, its soldering resistance was significantly lower than that of MoB-NiCr. The boride cermet coating not only exhibited superior soldering resistance, but also higher hardness, bond strength, and wear resistance. However, its deposition efficiency needs further improvement.

This paper describes microstructure control aimed for wear-resistance improvement of Co-based (Co-Cr-W-B-Si) self-fluxing alloy coating by diffusion treatment. The diffusion treatments of thermally sprayed Co-based self-fluxing alloy coating on steel substrate were carried out at 1370K to 1450K for 600s to 6000s under an Ar gas atmosphere. Microstructural variations of the coating and the interface between the substrate and the coating were investigated in detail. A proper diffusion treatment precipitates two kinds of fine compounds in Co-based matrix. XRD and EPMA analysis revealed these precipitates to be a chromium boride dissolving cobalt and a wolfram boride containing cobalt and chromium. The size of each precipitate became larger with increasing treatment temperature and time. A coating with the proper size borides showed a superior wear-resistance.

The aim of this study is to show how electron beam remelting affects the structure and properties of CoCrW coatings. As described in the paper, CoCrW powders are plasma sprayed onto nickel substrates and a modified electron beam welder is used to remelt the deposits. The effects of the treatment are assessed via SEM and XRD analysis, wear testing, and hardness measurements. In summary, electron beam remelting improves a number of coating properties including adhesion strength and fretting wear resistance. It also eliminates oxide inclusions and lamellar structures and reduces layer porosity. Paper includes a German-language abstract.