This study evaluates the erosion-corrosion performance of thermal spray hardcoats on bronze-coated gray cast iron. In the experiments, gray cast iron plates are coated with a bronze powder by PTA welding and the coatings are characterized based on microstructure and corrosion and wear testing. The bronze coatings provide good corrosion protection, but are shown to be susceptible to cavitation and erosion wear. To compensate, thermal spray hardcoats, including atmospheric plasma sprayed Al 2 O 3 and Cr 2 O 3 and HVOF sprayed WC-Co, were applied over bronze-coated cast iron and corrosion and wear tests were performed. It is shown that the thermal spray hardcoats greatly improve wear resistance, but despite their interconnected porosities, do not affect the corrosion performance of the underlying bronze.

In this study, finite element models are used to simulate the impact of porous WC-Co and Al particles cold sprayed onto substrates of the same materials. Effects of high strain rate, heat generation due to plasticity, interfacial friction, heat transfer, and material damage and failure are taken into account as are differences in the initial kinetic energy and strength of the materials. It was found that the influence of porosity increases with impact velocity and that the pores channel stress waves in unique ways not observed for solid particles. The results suggest that using porous particles for solid-state consolidation, as in cold spraying, could have advantages in terms of energy dissipation, although further investigation is required.

In this study, WC-Co coatings with nano-sized TiC additions were deposited on steel substrates by high velocity air fuel (HVAF) spraying and their microstructure and phase composition was analyzed using different electron microscopy techniques. Tungsten-reinforced cobalt phases detected in the vicinity of WC grains were identified as Co 0.9 W 0.1 by selected area diffraction. No titanium phases other than TiC were found, which suggests that nano-TiC may increase the stability of metallic matrix microstructure in WC-based coatings.

This study investigates the influence of substrate preheating on the microstructure, hardness, and adhesion of detonation sprayed WC-CoCr coatings. Using commercially available powders, coating samples are deposited on low carbon steel substrates, some at room temperature and some having been preheated to 300°C. Test results show that the coatings deposited on preheated substrates are harder, more crack resistant, and better adhered, with no significant differences in microstructure. After tensile testing, fracture surfaces and interfaces were investigated, showing how fracture behavior, along with hardness and bonding strength, correlate with phase composition and particle impact conditions.

A nanostructured WC-CoCr coating was fabricated by HVOF spraying using a new type of WC-CoCr powder in which the CoCr exists in the form of a metallic compound. The CoCr powder constituent was prepared by induction melting and mechanical milling. It was then combined with a WC-Co composite nanopowder and the mixture was agglomerated by spray drying and heat treating. The powders and coatings produced were characterized by means of XRD, EDS, and BSE analysis, nanoindentation testing, and potentiodynamic polarization studies. The results show that the presence of the intermetallic CoCr compound makes nanostructured WC-CoCr coatings harder and much more corrosion resistant than conventional WC-Co-Cr coatings in which Cr exists as an unalloyed metal.

In this study, Vickers indentation testing is used to determine the fracture toughness of hard flame spray coatings produced from cored-wire feedstocks, including WC-10Co4Cr, 75CrCo-25NiCr, and WC-12Co. Average measured values are compared with fracture toughness values calculated from seven different equations found in the literature in order to validate the experimental results and to better understand the relationship between fracture toughness and coating hardness for each of the tested materials.

This study assesses the microstructure and mechanical properties of tungsten boride (WB) powder and cemented carbide coatings with WB additions. HVOF-sprayed layers produced from 60WC-30WB-10Co composite powders are compared with conventional 88WC-22Co and 86WC-10Co-4Cr coatings based on phase composition, hardness, wear resistance, and wear surface structure. The results indicate that Co reacts with WB during spraying, forming ternary phases (WCoB, W 2 CoB 2 ) that increase hardness as well as sliding wear resistance.

With appropriate process control, near-net-shape coatings can be successfully applied to parts with complex geometries using HVOF spraying and fine cermet powders. This study assesses the influence of critical process parameters on the deposition rate and properties of HVOF coatings produced using fine agglomerated WC-12Co powder (2-10 µm) with nanosized WC particles. Spray angle, standoff distance, gun velocity, track pitch, and backside air cooling pressure were varied during the experiments in order to determine their effect on coating hardness, roughness, and porosity as well as deposition efficiency. Variations in spray parameters were found to have a significant effect on deposition rate and coating properties.

Low-temperature HVOF spraying finds its potential applications in the preparation of high-performance metallic coatings with low oxygen content and porosity. In this study, the spraying method is used to deposit fine WC-10Co4Cr powders on stainless steel substrates at different spraying distances and the effects on microstructure, microhardness, fracture toughness, splat morphology, and surface roughness are investigated and discussed.

In this study, detonation spraying was used to deposit commercially available Ni-20Cr and WC-Co powders on SA213-T22 boiler steel. Coated and uncoated specimens were subjected to 50 thermal cycles in a molten salt boiler environment 900 °C in order to evaluate their hot corrosion behavior. Mass change measurements were made at the end of each cycle to assess corrosion kinetics and XRD and SEM/EDS were used to characterize corrosion products. An analysis of the reaction kinetics and the formation of oxide scales is provided in the paper.

In this study, WC-CoWC coatings were produced by HVOF spraying using bimodal-structured WC-Co powder with both micro- and nano-sized WC particles. Due to the melting characteristics of the powder during spraying, the microsized particles are retained in the deposit, but the nanosized particles dissolve into the Co matrix, forming a Co-W-C ternary phase. Compared to coatings sprayed from conventional WC-CoWC powder, the bimodal coatings are more resistant to corrosion and wear and are comparable in microhardness.

Residual stresses arising during high-velocity oxyfuel (HVOF) spraying usually impose a limit on coating thickness. In this work, dry-ice blasting is used in combination with HVOF spraying to produce thick WC-Co coatings characterized by compact microstructure, crystal refinement, high hardness, and excellent sliding wear resistance.

In this investigation, particle image velocimetry (PIV) and direct imaging are used to measure particle velocities during cold spraying. Four feedstock powders were sprayed, including Ni, WC-Co, carbonyl Fe, and Cr steel. Multiple exposures at 500 ns intervals were used to measure in-flight particle velocities via direct imaging with a high shutter speed camera. Velocimetry measurements were made with a double-pulse laser and a high-resolution camera. With the minimum frame straddling time set to 100 ns, a maximum particle velocity of 1052 m/s was measured.

This study investigates the effects of operating environment and temperature on the friction behavior of self-mated WC-CoCr coatings in sliding contact. Nickel superalloy substrates were coated with 86WC-10Co-4Cr powder using a warm spray gun. Coating cross-sections and surfaces were examined by SEM, XRD, EDX, and x-ray photoelectron spectroscopy (XPS). Tribological tests were conducted on a high-load tribometer at various temperatures in air, nitrogen gas, and distilled water. Test samples were examined by SEM and XPS, revealing wear patterns and elemental compositions while providing insights on oxide formation.

A special pin-on-disc test setup designed for vacuum environments was used to conduct wear tests in a large chamber scanning electron microscope. Arc-sprayed NiCrBSi and HVOF-sprayed WC-12Co coatings were tested using a pin with an Al 2 O 3 ceramic ball as the wear counterpart. During testing, different wear mechanisms were identified and the processes were recorded in short video streams.

In this study, cold spraying is used to develop WC-Co coatings with a WC-10Co core as reinforcement and a Co-rich WC-Co matrix as the binder. Core-shell structured powders were prepared by mechanical milling and coating samples were deposited by cold spraying. Post-spray annealing was carried out to further modify the coating microstructure. WC-Co coating microstructure and mechanical properties were investigated along with various structure-property relationships. It was found that a WC-Co layer with a porosity of only 0.7 % was realized by cold spraying the mechanically milled powder and that annealing at 900 °C for 2 h resulted in a remarkable improvement in fracture toughness with no evident change in hardness.

In this study, a path strategy for robot-based HVOF spraying is developed via deposition simulations. The simulations include the analysis of the spray plume footprint and the consideration of robot dynamics in the path planning strategy. A fine WC-Co powder was used as the feedstock material.

This study shows that the quality of detonation sprayed coatings can be improved by adding propane or butane to the high-energy acetylene fuel. WC-Co coatings sprayed with binary fuel were found to have very low porosity (< 0.5%), low abrasion wear rates (< 1 mm 3 /1000 rev), high hardness (~1500Hv300g), and good bonding strength (150 MPa). These values were achieved over a range of stand-off distances (150-350 mm) and at a substrate inclination of up to 30°.

WC-Co cermet powders were deposited on aluminum substrates by cold gas spraying. XRD tests were run on the powder and coatings to reveal possible phase changes during spraying. Bonding strength, abrasive wear resistance, and corrosion resistance were also measured and are compared with values obtained from HVOF sprayed WC-Co coatings.

This study investigates the sliding wear behavior of HVOF sprayed coatings derived from conventional, fine, and nanostructured WC-Co powders. The results show that WC-Co coatings produced from fine and nanostructured feedstocks have significantly higher wear resistance and lower friction coefficients than coatings derived from conventional sized powder. This is attributed to scaling effects in the microstructure and phase evolution of the coating material as explained in the paper.