Thermal spray WC-NiCr coatings generally requires grinding processing to meet the surface finish requirements. The cost associated with grinding can potentially be reduced through the deposition of finer (– 30 + 5 μm) feedstock rather than the more conventional commercial (– 45 + 15 or – 53 + 20 μm) feedstock. Additionally, such a fine powder is likely to require lower energy spray parameters, resulting in less heat input to the substrate, which could be beneficial in application on heat sensitive substrates. However, the spray parameters need to be optimised to mitigate increased degradation of coatings due to unacceptable brittleness caused by decarburisation and oxidation, and to produce defect-free dense coatings. In the present work, a theoretical model to optimise spray parameters was developed, which suggested an oxygen-to-fuel ratio slightly more than 3.3 and a shorter barrel to avoid decarburisation in coatings. In total four parameter sets suggested by the theoretical model were selected to spray the fine-cut powder using a 100 mm long barrel. Scanning electron microscopy, X-ray diffraction, microhardness, and 3Dprofilometer were used to analyse the produced coatings. The coatings deposited using optimised parameters exhibited the best performance in terms of low porosity, inter-splat cracks, brittleness, and roughness. Coating deposited at lower kerosine and oxygen flow rates, with reduced stand-off distance, was denser, crack-free, and ductile. Hence, the fine-cut powder can be used to produce a finer as-sprayed finish, thereby demonstrating the potential in reducing grinding efforts. Additionally, successful deposition of coatings using low energy parameters, making this an attractive option for thermally sensitive substrates.

The metal finishing process of electrolytic hard chrome (EHC) plating has been identified as a source of environmental pollution in most industrialized countries like Australia, Europe and USA. The key driver for the technology replacement is that the EHC plating process uses hexavalent chromium, which is a known carcinogen. Our previous research has identified that cold spray nanostructured tungsten carbide cobalt (WC-Co) coatings can be a suitable alternative to provide a functional coating in wear applications. This work explores at another similar technology- Kinetic Metallization for deposition of WC-Co coatings. In this work, the objective is to characterize the residual stress profile of these WC-Co coatings that are deposited by the latest KM systems. These coating systems are used in critical applications such as landing gear pistons and axle journals, hydraulic rods, engine shaft journals, and numerous other external surfaces that operate under high cyclic loading conditions. As such, the residual stress developed during the KM coating process has a significant influence on the fatigue properties of the components. Thus, knowledge of stresses and their linkage with other properties and production parameters is essential for the quality control of these critical structures.

A study was conducted into the use of HVOF coatings on hydraulic cylinder rods in marine environments subject to both biofouling and corrosion. The study comprised a laboratory phase for candidate material selection and HVOF process optimisation. This was followed by long term field testing of the most promising candidates, which were subsequently assessed based on corrosion, adhesion, surface roughness and hydraulic sealing performance. Two candidates, nickel based WC cermet coatings, WC–10Ni5Cr and WC–18Hastelloy C, showed excellent results, and are considered as candidates for the application.

High entropy alloys (HEAs) are a new class of alloys that have multiple principal elements in an equiatomic ratio and that exhibit novel phase structures. HEAs are known for their high temperature microstructural stability, enhanced oxidation and wear resistance properties. Apart from bulk material consolidation methods such as casting and sintering, HEAs can also be deposited as a surface coating. In this work, thermal sprayed HEA coatings are investigated as an alternative bond coat material for a thermal barrier coating system. Nanostructured HEAs that were based on AlCoCrFeNi and MnCoCrFeNi were prepared by ball milling and then plasma sprayed. Splat studies were assessed to optimize the appropriate thermal spray parameters and spray deposits were prepared. Subsequently, the microstructure and mechanical properties of two HEAs coatings of different composition were characterized and compared to conventional plasma spray NiCrAlY bond coats.

This paper discusses the development of optimized processing windows for spraying high quality metal carbide-based coatings using advanced particle diagnostic technology. The cermet coatings are produced via the high velocity oxygen fuel spray process (HVOF) and are intended to be used in severe service applications such as marine hydraulics. To develop suitable coating process parameters, the traditional “trial and error” method is not technically robust, is costly and time consuming. Instead we investigated the use of real-time monitoring of parameters associated with the HVOF flame jets and particles using advanced in-flight particle diagnostics. Subsequently, coatings can be produced with knowledge concerning the molten particle size, temperature and velocity profile. The analytical results allow identification of optimized coating process windows, which translate to coatings of lower porosity and improved mechanical performance.

This investigation employs tensile adhesion tests (TAT) and tubular coating tensile (TCT) tests to measure the adhesion and cohesion bond strength of plasma sprayed YSZ coatings. Tensile adhesion testing measures the bond strength of the YSZ-bond coat system perpendicular to the spray direction, while tubular coating tensile testing measures the intersplat strength of the YSZ coating parallel to the spray direction. In both cases, the failure strength of the coatings can be approximated to a Weibull distribution, indicative of anisotropic behavior as verified by Knoop microhardness indentation tests. The average coating strength parallel to the spray direction is shown to be about 1.5 times greater than the bond strength perpendicular to the spraying direction.

The mechanical behavior of nanostructured yttria stabilized zirconia (YSZ) thermal spray deposits was examined and compared to conventional zirconia coatings. Young’s modulus was measured using indentation techniques. The anisotropy of the deposits was estimated by indenting the deposits in the perpendicular and parallel directions to the substrate. Statistical distribution of the mechanical properties was correlated with the microstructure. The effective Young’s moduli of nanostructured and standard YSZ were also modeled by means of 2D eXtended FEM; whereby actual microstructures were assessed. The simulation was based on micrographs by employing a standard meshing program combined with an in-house developed XFEM package, which incorporates the crack structure into the model. The effect of nano-scale features on the effective Young’s modulus were predicted and compared to experimental observations.