HVOF-Deposited WCCoCr as Replacement for Hard Cr in Landing Gear Actuators

WCCoCr coatings deposited by HVOF can replace hard Cr on landing gear components. Powders with two different WC particle sizes (micro and nano-) and geometries have been employed to study the effects on the coating’s properties. Moreover, coatings produced employing two sets of parameters resulting in high and low flame temperatures have been evaluated. Minor differences in microstructure and morphology were observed for the two powders employing the same spraying parameters, but the nano-sized powder exhibited a higher spraying efficiency. However, more significant microstructural changes result when the low- and high-energy spray parameters are used. Moreover, results of various tests which include adhesion, wear, salt fog corrosion resistance, liquid immersion, and axial fatigue strength, indicate that the coatings produced with high-energy flame are similar in behavior. On the other hand, the nanostructured low-energy flame coating exhibited a significantly lower salt fog corrosion resistanc

Effect of particle and carbide grain sizes on a HVOAF WC-Co-Cr coating for the future application on internal surfaces: microstructure and wear

The use of nanoscale WC grain or finer feedstock particles are possible methods of improving the performance of WC-Co-Cr coatings. Finer powders are being pursued for the development of coating internal surfaces, as less thermal energy is required to melt the finer powder compared to coarse powders, permitting spraying at smaller stand - off distances. Three WC-0Co-4Cr coatings, with two different powder particle sizes and two different carbide grain sizes, were sprayed using a high velocity oxy-air fuel (HVOAF) thermal spray system developed by Castolin Eutectic - Monitor Coatings Ltd., UK. Powder and coating microstructures were characterised using XRD and SEM. Fracture toughness and dry sliding wear performance at three loads were investigated using a ball–on-disc tribometer with a WC–Co counter body. It was found that the finer powder produced the coating with the highest microhardness, but its fracture toughness was reduced due to increased decarburisation compared to the other powders. The sprayed nanostructured powder had the lowest microhardness and fracture toughness of all materials tested. Unlubricated sliding wear testing at the lowest load showed the nanostructured coating performed best; however at the highest load this coating showed the highest specific wear rates with the other two powders performing to a similar, better standard

Structure property relationship of suspension thermally sprayed WC-Co nanocomposite coatings.

Tribomechanical properties of nanostructured coatings deposited by suspension high velocity oxy-fuel (S-HVOF) and conventional HVOF (Jet Kote) spraying were evaluated. Nanostructured S-HVOF coatings were obtained via ball milling of the agglomerated and sintered WC-12Co feedstock powder, which were deposited via an aqueous-based suspension using modified HVOF (TopGun) process. Microstructural evaluations of these hardmetal coatings included transmission electron microscopy, x-ray diffraction, and scanning electron microscopy equipped with energy dispersive x-ray spectroscopy. The nanohardness and modulus of the coated specimens were investigated using a diamond Berkovich nanoindenter. Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that low porosity coatings with nanostructured features were obtained. High carbon loss was observed, but coatings showed a high hardness up to 1000 HV2.9N. S-HVOF coatings also showed improved sliding wear and friction behavior, which were attributed to nanosized particles reducing ball wear in three-body abrasion and support of metal matrix due to uniform distribution of nanoparticles in the coating microstructure

Microstructural and Wear Characteristics of High Velocity Oxygen Fuel (HVOF) Sprayed NiCrBSi-SiC Composite Coating on SAE 1030 Steel

In this paper, wear properties of NiCrBSi-SiC coatings were investigated using the ball-on-disk wear test. In experimental study, NiCrBSi-SiC powders were sprayed using a high-velocity oxygen fuel technique on an SAE 1030 steel substrate. Powder mixtures with different weight mixing ratios, NiCrBSi + 10 wt\% SiC, NiCrBSi + 20 wt\% SiC and NiCrBSi + 40 wt\% SiC coatings were prepared. The deposited coatings are compared in terms of their phase composition, microstructure and hardness. It is proved that the degree of mixing of the NiCrBSi and SiC components in the powder has a massive effect on the phase composition, microstructure and hardness of the coatings. Wear tests were conducted on both the uncoated and coated substrates at same normal load, speed, and wear distance. It has been determined that the coated substrates exhibit a very good tribological performance in comparison to the uncoated substrate. The increase in the adhesive wear resistance provided by the coating has been attributed to the presence of a large amount of dispersed Ni and Cr carbide and/or borides in the Ni matrix