Cermet double carbide coatings (WC-Cr 3 C 2 -Ni) were HVOF sprayed onto magnesium substrate. The variable parameter was spray distance (320, 360 and 400 mm). The microstructure of the coatings has been characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). Additional, porosity and residual stress have been estimated. Phase composition of WC-Cr 3 C 2 -Ni cermet coatings consists of hexagonal WC carbide, as well as the Cr 3 C 2 and Cr 7 C 3 carbides. For the longest spray distance, minor presence of WC 6 O 6 was detected, most likely as an effect of higher spraying distance, leading to partially oxidation of WC at powders particles boundaries. Comparing lattice parameters with model data it should be noted that no significant contribution of stress is present, due to minor changes in WC lattice parameters in comparison to ICDD data. It also should be noted that Cr 7 C 3 carbide in WC-Cr 3 C 2 -Ni coating has different lattice parameters than ICDD data what shows its reactive nature. In obtained results it is clearly seen, that residual stress have the lowest values for coating sprayed from the shorter distance. This tendency is visible for both, linear and shear stress. The crystallite sizes are also the smallest for the shorter spray distance. Such fine structure shows a tendency to good redistribute of the thermal stress in the sprayed coating and also on the coating-substrate interface.

Thermally sprayed WC-based hardmetal coatings offer high hardness, good sliding wear and abrasion performance and find large applications in mechanical engineering, valve construction, or offshore applications. WC-Co coatings are mainly produced by high-velocity oxy-fuel spraying (HVOF) from conventional spray feedstock powders. In our previous work, the potential of the suspension-HVOF spraying (S-HVOF) to produce dense-structured WC-12Co coatings has been shown. Significant work was devoted to the development of appropriate aqueous hardmetal suspensions starting from commercially available fine WC and Co raw powders feedstock. This contribution proposes a step forward in the development of the S-HVOF WC-12Co coatings and evaluation of their microstructural and tribological properties. Suspension spraying trials were carried out using gas-fuelled HVOF TopGun system. For comparison purposes, liquid-fuelled HVOF K2 was employed to spray WC-12Co coatings starting from commercial available spray powder. Microstructural characterization, X-Ray diffraction and microhardness of the coatings were evaluated. Oscillating sliding wear tests were conducted against sintered Al 2 O 3 and WC-6Co balls. The sliding wear performances of the WC-Co sprayed coatings were discussed in term of the microstructure, phase composition and coating-ball test couples.

This paper evaluates the cavitation erosion wear rate and failure modes of WC-10Co-4Cr coatings. These coatings are used in various industrial applications to protect against erosive, abrasive, sliding and cavitation wear in corrosive environments. Cavitation erosion tests were performed using a modified ASTM G-32 cavitation test rig. Thermally sprayed High Velocity Oxy-Fuel (HVOF) WC-Co-Cr coatings were deposited using industrially optimised coating process parameters on carbon steel and stainless-steel substrate coupons. Coatings were tested to simulate the cavitation bubbles occurring in valves, pumps, and ship propellers. Indirect cavitation was used to impact the cavitation bubbles on the test specimen at a fixed offset distance from the vibrator end. Test specimens were immersed in natural seawater. A water circulation cooling system was used to control the temperature of the water. The cumulative mass cavitation erosion and erosion rate results were evaluated. The coating microstructure was analysed using Scanning Electron Microscopy (SEM) and x-ray diffraction. Post-test evaluations included SEM observation in combination with energy dispersive x-ray analysis (EDX) to understand the failure modes. Results are discussed in terms of the factors controlling the cavitation erosion rate.

Thermally sprayed WC/CoCr coatings are established in the valve industry for wear protection. However, conventional coatings have to be cost-intensively postprocessed. Therefore, the aim of this study is to develop near net shaped (nns) WC/CoCr-coatings with a high wear resistance in order to avoid the expensive grinding postprocess. For the development of the nns coatings a parameter study is used to investigate the influence of the stand-off distance and hydrogen volume flow rate in the HVAF process. The parameter study indicates the influence of the hydrogen volume flow and the stand-off distance on the porosity, microhardness and wear resistance of the coatings. The developed coatings exhibit a low porosity and high wear resistance. Through the correlation of the coating properties with the process parameters, promising parameter ranges for a further development of HVAF-sprayed nns coatings of WC/CoCr can be identified. With these results, first benchmarks for HVAF process parameters, hydrogen flow rate and stand-off distance, could be delivered, advancing the overall goal of reducing manufacturing costs of valves.

Wear leads to high material and energy losses in various industries. The manufacturing of novel nano-carbide WC/Co powder feedstock materials promises a further increase in the performance of thermally sprayed wear protection coatings. A novel experimental powder and a commercial ultra-fine carbide WC/CoCr reference are thermally sprayed onto a 1.0038 substrate by High Velocity Air Fuel (HVAF) spraying. The specimens are metallographically prepared and analyzed by means of light microscopy (LM) and scanning electron microscopy (SEM). Vickers Hardness testing is conducted by microindentation and the porosities are determined by optical image analysis. X-ray diffractometry (XRD) analysis are used to investigate the phase retention. Fine nanocrystalline WC-structures are preserved in the dense coatings. A significant effect of powder type on the porosity of the coating was found. No systematic relationships could be identified between the coating structure and the parameter settings. It was possible to influence decarburization via both the powder type and the selected parameters. The resulting experimental coatings exhibit high hardness values in the range of the commercial ultrafine carbide WC reference. The novel nano-structured coating can contribute to reduced wear and therefore improve the efficient utilization of critical raw materials like tungsten.

Surface quality lifetime and wear resistance of protective coatings can be improved by decreasing carbide grain size from submicron to nanoscale. In this study, experimental WC-CoCr powders were manufactured via novel powder manufacturing approach using water-soluble raw materials. Produced powders were sprayed with the High-Velocity Air-Fuel (HVAF) spray process to control the particle temperature and to avoid in-flight decomposition of the nanocarbides. As a result, dense and wear resistant coatings with nanosized carbides were produced. Reference coatings were sprayed using commercial sub-micron WC-CoCr powder to compare the properties of the experimental coatings to the current state-of-the-art. Phase composition and microstructural characterization of the coatings were carried out with X-ray diffraction and electron microscopy, respectively. Mechanical properties were studied by using microhardness tester, as well as rubber wheel abrasion and cavitation erosion wear tests. The wear surfaces were characterized after the abrasion and cavitation erosion tests to understand the effect of nano-carbides on degradation mechanisms. Coatings with the nanosized carbides in the structure showed excellent mechanical properties in wear testing, and even outperformed reference coatings in cavitation erosion test. Based on the obtained results, these novel nano-carbide coatings are promising alternatives for demanding applications in which better surface quality lifetime is vital.

Both as bulk material and coatings, cemented carbides currently occupy very well-established market niches and exhibit a promising future thanks to the development of compositions and manufacturing parameters. Direct comparisons of the properties of both are found only very rarely in the literature, very likely because the fields of application are complementary to each other but keep mostly separated. The current work is intended to evaluate similarities and differences in terms of microstructure and properties for two submicron WC-12 wt.%Co coatings obtained by High Velocity Air Fuel (HVAF) and Cold Gas Spray (CGS), together with a conventional sintered part. Microstructural features are discussed according to the inherent characteristics of each processing method. This covers a wide range in terms of the mechanical and thermal stresses acting on the material. While in CGS, the impacting particles do not melt, but experience extremely high plastic strain rates, the cobalt matrix is fully molten in the conventional sintering process, allowing time enough for diffusion processes. HVAF is to be placed in between, since the deposition process is characterized by a moderate heat input, leading to partial and/or full melting of cobalt, followed by rapid cooling. The microstructure and phases of the deposited coatings and bulk are characterized by using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Electron Backscattered Diffraction (EBSD) investigations enable local phase distribution of Co and WC in the samples. The hardness of the alloy processed by the three different routes is investigated as well. Additionally, electrochemical corrosion measurements in NaCl media are presented to evaluate the facility for electrolyte penetration and how the degradation of the material is affected by its inherent microstructure.

This study investigates the solid particle erosion performance of cold sprayed tungsten carbide-nickel coatings using alumina particles as erodent material. After coating fabrication, specimens were annealed in an electric furnace at a temperature of 600 °C for 1 hour. The coatings were examined in terms of microhardness and microstructure in the as-sprayed (AS) and annealed (AN) conditions. Subsequently, the erosion tests were carried out using a General Full Factorial Design with two control factors and two replicates for each experimental run. The effect of the annealing on the erosion behavior of the coating was investigated at the two levels (AS and AN conditions), along with the impact angle of the erodents at three levels (30°, 60°, 90°). Finally, two regression models that relate the impact angle to the mass loss were separately obtained for the two cold spray coatings.

The demand for energy reduction increases every year. In general, reducing the weight of mechanical components is a direct and efficient way to reduce the energy consumption. Therefore, the automotive industry has been growing its use of low-density alloys, as the cases of aluminum and magnesium. High production rate and dimensional precision are need, which narrows the manufacturing techniques suitable. Among the manufacturing processes, high pressure die casting (HPDC) has shown a viable solution. Nonetheless, every process has gaps for improvement. In the case of HPDC tooling is one of the major costs, being responsible for a significant ratio of the final product price. Whereas many articles are focused on the improvement by the development of new materials and thin coatings for HPDC, there is a lack of thermal spray coatings as solution for the wear problems over HPDC. This paper has the focus on showing the use of Cr 3 C 2 25 NiCr as a coating for the components used for HPDC, mainly the ones submitted to direct contact to the metal in fluid state. The idea is to compare the coating with the substrate regarding to thermal fatigue and verify whether it is a viable solution or not.

The HVOF sprayed WC-CoCr coatings are widely spread due to their excellent resistance against wear and corrosion. These coatings are one of the most suitable alternatives for hard chromium in many applications. Within the research project, the most suitable hard chromium alternative for hydraulic devices in aircraft is being developed and tested. This application is highly demanding not only on the functional properties of applied coatings but also on the surface quality. Grinding and polishing of the coating are not sufficient, to achieve the necessary surface properties. This study aims to optimize the superfinishing process of HVOF sprayed WC-CoCr coating. The achieved surface quality is primarily measured using profilometry. With optimized surface preparation, the tested parts for aircraft hydraulic parts are treated and tested for leakage of operating fluids and high cyclic lifespan.

In recent years, laser-based post-processing of thermally sprayed coatings has gained significant attention as an alternative post-processing route; to mitigate the microstructural defects such as pores, microcracks, and splat boundaries associated with thermally sprayed coatings. Optimisation of the parameters for the laser post-processing is of paramount importance to maintain the required properties of these coatings. The current thermo-mechanical model simulates the impact of laser heat treatment on thermally sprayed Tungsten Carbide Cobalt (WC-17Co) coating and AISI 316L as substrate. A sequentially coupled transient thermal and structural analysis is performed. Transient temperature field from thermal analysis due to laser source will become input loads for the subsequent stress-strain analysis with appropriate boundary conditions. Both the coating and substrate are given temperature-dependent material properties. A gaussian heat flux distribution is used to model the laser source. The finite element analysis results underline the importance of temperature gradients and the presence of thermally induced stress-strain fields responsible for promoting coating degradation. The obtained results also revealed that heat input and dimensional characteristics play a vital role in the annealing treatment's efficacy. Three separate test cases were considered wherein the hatch spacing was varied, keeping the other parameters (scan speed, laser power, and laser spot diameter) constant. The impact of hatch spacing on the temperature and residual stress distribution across the coating was assessed by this simulation. Residual compressive stress was observed in the coating for two out of the three test cases, which further improved the durability of the coating.

Cermets are composite materials consisting of a ceramic reinforcement and a metal matrix. Conventional tungsten carbide cermet parts containing a cobalt matrix phase are mainly produced by powder sintering. Laser Powder Bed Fusion (L-PBF) is an additive manufacturing technology widely applied for direct fabrication of metal functional parts with complex geometry. The present paper deals with the feasibility study of additive manufacturing of cermet parts by L-PBF using WC-17Co powder. The results showed that parametric optimisation of the L-PBF process allowed the production of solid WC-17Co part. Structural analysis revealed the presence of significant porosity (1.41%) and small-scale cracks in the as-built samples. Post-processing, such as HIP (Hot Isostatic Pressure) significantly improved the structure of manufactured parts. The porosity after HIP was very low (0.01%) and phase analysis revealed that the samples after HIP did not contain the fragile W 2 C phase. Abrasive wear tests showed that the wear resistance performance of additively manufactured parts was comparable to a reference produced by powder sintering. High values of hardness (around 1100 HV 30 ) were observed for the as-built and HIP samples. The study successfully demonstrated the possibility of manufacturing wear-resistant cermet parts by L-PBF.

In this work, a novel liquid fuel HVOF process fueled with ethanol was used to prepare 75wt%Cr 3 C 2 –25wt%NiCr coatings on AISI304 stainless steel substrate. Taguchi method was employed to optimize the spray parameters (ethanol flow rate, oxygen flow rate, powder feed rate and standoff distance) to achieve better erosion resistance at 90° impact angle. The results indicated that ethanol flow rate and oxygen flow rate were identified as the highly contributing parameters on the erosion wear loss. The important sequence of the spray parameter is ethanol flow rate > oxygen flow rate > standoff distance > powder feed rate. The optimal spray parameter (OSP) for minimum erosion wear loss was obtained under ethanol flow rate of 28slph, oxygen flow rate of 420slpm, powder feed rate of 76.7 g/min and standoff distance of 300mm. The phase composition, microstructure, hardness, porosities, and the erosion wear behaviors of the coatings have been studied in detail. Besides, erosion wear testing of the optimized coating was conducted at 30°, 60° and 90° impact angle using air jet erosion testing machine. The SEM images of the erodent samples were taken to analyze the erosion mechanism.

Manufacturing of steel components is often done at high temperatures (HT) posing a serious challenge to components such as forming tools. Thermal spray coatings provide a cost-effective solution for surface protection under HT, corrosive environments and severe wear conditions. Thermally sprayed coatings based on cubic hard materials such as TiC and TiCN can provide an alternative to widely used Cr3C2-NiCr. While the latter possess a superb oxidation resistance and wear resistance at HT, they are prone to degradation in the presence of Mn, an element commonly alloyed in many modern steel grades such as TWIP (twinning-induced plasticity steel). In this study, a (Ti,Mo)(C,N)-29% Ni hardmetal feedstock powder was prepared by agglomeration and sintering. Coatings were deposited using a high velocity air-fuel (HVAF) spray process. The coating was benchmarked against a standard Cr3C2-NiCr coating obtained with the same spray process. Our work comprises analyses of the feedstock powder along with the resulting coating microstructure after deposition and heat treatment. Further, the HT sliding behavior against TWIP steel using a HT pin-on-disc tribometer at 700°C was investigated. The results showed a clear benefit of the TiCN-based coating, with almost no wear detected, while the Cr3C2-coating showed a significant wear loss. Based on these results, the TiCN-based coating is regarded as potential solution for prospective forming applications of modern high Mn steels, such as TWIP.

Internal diameter (ID) coating by means of thermal spraying for the wear and corrosion protection of components is currently experiencing growing interest in science and industry. While high-kinetic spray processes (such as HVOF, HVAF or warm spraying) in combination with cermet materials (e.g. WC-Co or Cr3C2-NiCr) are well established for this purpose in traditional coating of external OD (outer diameter) surfaces, they have hardly been used in the ID (internal diameter) area so far. Even though a few special ID spray guns with compact design and low combustion energy are by now available on the market, only little is known about the effects and interactions of the spray parameters on the particle behavior and the coating properties. Due to the mentioned gun specifications and the usually required short spray distances for ID coating, fine spray powders < 15 μm must be used to ensure sufficient melting and acceleration of the particles. In this study warm spraying of fine WC-12Co powders (-10 + 2 μm) using a novel spray gun “ID RED” (Thermico, Germany) was investigated. Statistical design of experiments (DoE) was employed to analyze and to model the influence of varying spray parameter settings on the in-flight particle behavior and the corresponding coating properties.

In general, similar MAX-Phase coatings are considered as oxidation protection layer for preventing disastrous reactions of the Zircaloy fuel rods during a cooling water failure in a nuclear power plant. For the present study on Aerosol Deposition, Ti3SiC2 was selected as MAX-phase model system due to the availability of property data and commercial powder. The as-received powder was milled to different nominal sizes. For revealing details on coating formation and possible bonding mechanisms, Aerosol Deposition experiments were performed for different particle size batches and process gas pressures. Microstructural analyses reveal that coating formation preferably occurs for particle sizes smaller than two microns. Using such small particle sizes, crack-free, dense layers can be obtained. The individual deposition efficiencies for the different particle sizes, particularly the critical size below which deposition gets prominent, vary with process gas flows and associated pressures. Detailed microstructural analyses of coatings by high resolution scanning electron microscopy reveal plastic deformation and fracture, both attributing to shape adaption to previous spray layers and probably bonding. In correlation to coating thickness or deposition efficiencies, respective results give indications for possible bonding mechanisms and a tentative window of Aerosol Deposition for Ti3SiC2 MAX-phases as spray material.

Thermally sprayed WC-Co coatings provide excellent wear resistance and corrosion protection under heavy loads, but their application usually involves additional grinding and polishing steps, which can be 3-4 times costlier than the spraying process itself. There is thus the motivation to develop a process that produces smooth, near-net-shape carbide coatings. This contribution is an investigation of WC-12Co coatings obtained by suspension HVOF spraying. Significant work was devoted to the development and characterization of water-based hardmetal suspensions synthesized from commercially available WC and Co powders. The suspensions produced were sprayed using the HVOF process, and the resulting coatings were evaluated based on microstructure, hardness, and phase composition.

Hydroelectric turbines are strongly affected by cavitation and the damage it can cause to critical part surfaces and profiles. The study of thermal spray processes and materials is thus relevant to improving turbine performance. The main objective of this work is to evaluate the influence of fuel-oxygen ratio on tungsten- and chromium-carbide cermet coatings deposited by HVOF. Particle velocity and temperature were measured as were coating hardness, porosity, and cavitation resistance. Higher particle velocities were obtained at higher fuel ratios, producing harder, denser coatings with better cavitation resistance. Based on test results, the wear mechanism starts with the nucleation of the cavitation that occurs in the pores, resulting in the formation of craters and the eventual detachment of lamellae as indicated by the smoothness of the surface.

Two kinds of cermet powders, WC-10Co4Cr and WC-20CrC-7Ni, were deposited on 1040 steel via high velocity air fuel (HVAF) spraying to evaluate resistance in cavitation erosion conditions with additional electrochemical effects. Coating microstructure, phase composition, and microhardness were examined along with the topography of eroded surface layers. The cavitation resistance of the WC-20CrC-7Ni coating was found to be approximately 1.3 times greater than that of the other coating, which can be attributed to its finer grain structure, lower pore density, and the presence of high Cr and Ni content in the feedstock powder which serves to strengthen the matrix.

High-velocity oxyfuel (HVOF) sprayed coatings of Cr3C2-NiCr containing solid lubricants such as nickel cladded graphite and hexagonal boron nitride were successfully developed and characterised with the aim of optimizing their friction and wear behaviour. HVOF technology was used for the integration of solid lubricants to achieve strong cohesion between particles while minimizing thermal decomposition. Coating microstructure and composition were measured and correlated to the results of tribological and corrosion tests. The integration of the solid lubricant greatly reduced friction and wear volume at room temperature, but the lubricating effect was highly dependent on atmosphere and temperature. Cr3C2-NiCr with hBN, however, tends to exhibit more stable wear resistance over a wider temperature range and can be used at temperatures beyond 450 °C.