This paper presents a comparative analysis of three coating types—W 2 C/WC12Co (Metco71NS), Cr 2 O 3 -4SiO 2 -3TiO (Metco136F), and Co25.5Cr10.5Ni7.5W0.5C (Metco45C-NS)—applied to disc harrow components, focusing on their microstructural and tribological properties.

Plasma Transferred Wire Arc (PTWA) is a well-established thermal spray process that is used in high-volume production by multiple automotive OEMs. Benefits of these PTWA thermal spray coatings include closer bore spacing, improved thermal transfer, lower bore distortion, increased resistance to corrosion and abrasion, reductions in weight and friction, enhanced durability, and product cost savings. For automobiles, this leads to increased fuel economy and lower emissions. Millions of engine cylinder bores per year are coated using the PTWA thermal spray process. To ensure optimal surface coatings, it is vital to monitor the process variables. Although some process monitoring already exists in current production, new technological advancements allow for additional variables to be monitored. Arc voltage is of particular importance as it can be viewed real-time in situ to the PTWA process to determine the curvature of the feedstock wire. Straight wire is ideal for achieving peak system performance. If the wire has excessive curvature, it can lead to out-of-tolerance conditions that detrimentally affect the quality of the surface coating. Therefore, in-situ monitoring of wire curvature is both desirable and necessary for producing the highest quality PTWA thermal spray coatings possible.

Among hardfacing processes using welding, laser cladding is nowadays one of the most efficient surface coating techniques. It is widely used to increase wear and corrosion resistance of machine parts as a result of the unique process characteristics such as low heat input (smaller heat affected zone), distortion free clad layers, lower dilution rate, finer coating microstructure as well as good metallurgical bonding at the coating/substrate interface. A wide range of new hardfacing materials and corrosion-resistant alloys are available on the market and in this study, different coatings of Ni-, Co- and Fe-based alloys as well as carbide-based metal matrix composites have been deposited by laser cladding for benchmarking purposes. Coatings were deposited onto mild steel substrates using a high-power diode laser. Coating microstructure and hardness were investigated as well as their tribological properties such as 2-body and 3-body abrasion, slurry abrasion and cavitation erosion resistance. Corrosion performance of coatings was also investigated with the salt spray test. Coatings are ranked according to their performance in the different tests and relationships between microstructure and coating properties are discussed.

Hardmetal coating compositions containing both WC and Cr 3 C 2 are less intensively studied than WC-Co(Cr) and Cr 3 C 2 -NiCr. In particular, compositions with Cr 3 C 2 as the main phase are relatively new in the market. In this contribution, two commercial agglomerated and sintered feedstock powders with similar compositions (42Cr 3 C 2 -42WC-16Ni and 45Cr 3 C 2 - 37WC-18NiCoCr) were studied. Both powders differ in their porosity and the melting behavior, as was found by DSC experiments. Coatings were deposited with a liquid-fueled HVOF process (JP 5220). Optimization of the spray conditions was evaluated with five different spray parameter sets. Coating microstructures and phase compositions, as well as microhardness HV 0.3 and abrasion wear resistance were less influenced by the spray parameter sets. At the same time, significant differences in deposition efficiency between the two compositions were observed, which might be related to the differences in the melting behavior of the compositions and the powder porosity. However, coating microhardness and abrasion wear resistance were similar for each of the spray parameter sets. Coating microstructure and phase composition were studied with a focus on the interaction between Cr 3 C 2 and WC and will be discussed in detail.

Iron-based coatings are often considered as replacement of hard chromium and WC-Co, as they pose lower health and environmental impact. In many cases the combination of mechanical and chemical properties of ferrous based alloys may be satisfactory and their relatively low cost make these coatings an interesting candidate for many applications. This study is inspired by opportunities to harden the ferrous base materials by strain hardening, solid solution strengthening, dispersion strengthening, and precipitation hardening. Already commercially available Fe-based coating materials with precipitates of mixed carbides and borides in the metastable austenitic matrix achieve a high hardness. In this study the cavitation erosion and abrasion resistance of various Fe-based coatings produced by HVAF and HVOF processes were investigated. Two experimental precipitation containing materials were prepared, and the sprayed coatings were tested for abrasive and cavitation erosion wear. In addition to precipitations, the importance of proportion of ferrite and retained austenite phases were studied by affecting the microstructure by heat treatments as the ability of different phases to affect hardening and ductility may become crucial in generating desired material properties. The properties of experimental and some commercial Fe-based alloys are compared with WC-Co and Cr 3 C 2 -NiCr coatings by property mapping.

This study shows how data-driven modeling tools aid in the development of alloys that meet specific processing, property, and performance requirements. By leveraging a “big data” approach, two new alloys were designed that outperform commonly used materials in hardfacing and wear plate overlay applications. Over one million alloy compositions were analyzed to find two with the right combination of matrix and hard phases to provide the desired level of impact and abrasion resistance. The difference between the two alloys is in their matrix phase; one being austenitic, which has higher toughness, the other being martensitic, which has higher resistance to abrasive wear.

A common method to combat abrasive wear and prolong the life of a component is to hardface the exposed region by overlay welding. State of the art coatings for these applications consist of a nickel-based ductile matrix with hard tungsten carbide particles embedded in it. An alternative with low environmental impact in combination with high performance to cost ratio is to use iron-based alloys. Critical in affecting the abrasive and impact wear resistance of these alloys is the coating quality e.g. porosity, cracks, dilution from the substrate combined with chemistry, size and volume fraction of the hard phase particles formed during solidification. Selection of the process parameters is critical for producing sound clads with expected properties. This paper focuses on the properties of PTA welded and laser cladded M2, M4 and A11 high speed steel coatings. Clad quality, hardness, abrasive wear resistance and microstructure are presented and interpreted with support of thermodynamic simulations.

Erosion and abrasion are both wear processes in which a particle that strikes the surface removes material, either by impact (erosion) or contact (abrasion). These wear processes can cause damages to components, which can be protected by coatings to reduce the damage occurrence. Thermally sprayed coatings are considered candidates for a protective system against abrasion and erosion. The HVOF spray process is one of the most used thermal spray processes due to the ability of producing dense coatings, with good values of hardness and toughness. Among the materials used in thermally sprayed coatings, WC-Co based coatings are often used, as it offers a combination of high hardness, toughness and adherence, which can provide a good wear resistance. In this work, the influence of different HVOF process parameters, specifically the type of fuel used, on the residual stresses and properties of these coatings was studied. It was noted that coatings deposited by HVOF with kerosene liquid fuel, presented lower porosity, compared with coatings deposited by gas fuel. It was also observed that the coatings with lower porosity provide a better abrasion resistance, meanwhile the erosion was controlled by toughness for 30° and higher hardness for 60° of impact angle.

Highly wear resistant overlays for abrasive environments can be provided by welding technologies such as Plasma Transferred Arc Welding (PTAW) or Laser Cladding. Therefore, these overlays can contain higher amounts of hard particles with a desired homogeneous distribution through the weld overlay, all embedded in a metal matrix. Depending on the welding technology, the dissolution of the hard particles has to be considered as result of heat input and chemical reaction between hard particles and metal matrix while welding. Cast Tungsten Carbides (CTC) in self-fluxing Ni based alloys are widely used and accepted compositions and allow to target requirements such as hardness, impact toughness and/or corrosion resistance if required. This investigation compares CTC with Macroline Tungsten Carbide regarding abrasive wear resistance in Ni, Co and Fe based alloys applied by PTAW and Laser cladding and gives an outlook on potential new solutions for wear resistance in abrasive conditions. Beside the relative wear resistance, this investigation also focusses on the seam thickness as reaction zone between the carbide particles and the metal matrices. A first SEM and EDX analysis of a worn surface and precipitated phases provides an explanation regarding wear behavior in abrasive conditions.

Niobium and its alloys have been used for several industrial applications including high strength low alloy steels (HSLA) in the automotive and aerospace industries, mainly because of being highly corrosion resistant in different media. Niobium pentoxide is an excellent option to reduce costs in repairing damages caused by corrosion, protection of industrial equipment or systems for being chemically inert to corrosive agents that cause severe corrosion and are normally present in refineries and other industrial environments. Whatever the application, mechanical properties of coatings define their effective durability and performance, mainly for tribocorrosion applications. In this work, these properties are studied and correlated for Nb 2 O 5 coatings applied by Flame Spray onto steels. Salt Spray corrosion (ASTM B117), abrasive wear resistance (ASTM G65-16) and scanning electron microscopy (SEM) microstructural analysis allowed the evaluation of the coatings.

In this study abrasive wear resistance of NiCrBSi self-fluxing alloys claddings reinforced by tungsten carbide (up to 80 vol.%) and pure tungsten (up to 50 vol.%) was compared. For this purpose, metal matrix composite samples were cladded by diode laser then metallography studies and hardness measurements were provided. Finally, all specimens passed ASTM G65 abrasion test and their wear resistance was compared to alternatives claddings.

Thermally sprayed Al 2 O 3 -TiO 2 coatings were in the area of interest over the last decade because they showed improved wear properties over conventional coatings. In this study, flexicord flame spray gun was used to deposit Al 2 O 3 -TiO 2 coatings at different spray parameters. The microstructural morphology variation and phase transformation of coatings were investigated. In addition, as one of the most important properties for ceramic coatings, hardness, solid particle abrasive wear resistance of coatings were measured before and after heat treated condition. Test results show that the higher mechanical properties and wear resistance by the heat treatment at elevated temperatures.

Adhesive-corrosion resistance is an important issue for the application life of solid lubricant coatings. With abundant metal droplets deposited on the surface of a solid self-lubricating coating, the coefficient of friction of the coating changes and results in adhesive wear. In this paper, a new method for evaluating the adhesive resistance for solid self-lubricating Ni-WSe2-BaF2·CaF2-Y-Ag-hBN coatings was reported. The microstructures and anti-adhesive characteristics under different angles of aluminum metal droplets obtained with an arc supersonic nozzle were investigated for high temperature solid self-lubricating coatings produced by plasma spray. The results demonstrate that the friction coefficient of Ni-WSe2-BaF2·CaF2-Y-Ag-hBN solid self-lubricant coatings is distributed between 0.086 and 0.299 at 25-800℃. The effect of molten metal drops on the coating adhesive-corrosion rate increases with the deposition angle. At 90°, the deposition rate of metal droplets on the coating and substrate surface is maximized, and the hexagonal boron nitride (hBN) self-lubricating coating deposition rate is only 58 mg/(cm2·s). This work demonstrates that hBN can effectively decrease the adhesive layer of the coating by the rate of the polishing and stripping.

This paper presents the results of research, testing, and comparison of polyamide (nylon) 11 coatings made by flame spraying and electrostatic spraying followed by oven or induction heating. It discusses the advantages and disadvantages of each process and the coating properties that can be achieved.

This study assesses the effect of machine hammer peening (MHP) and carbide grain size fraction on the friction and wear behavior of arc-sprayed WC-W 2 C FeCMnSi coatings. SEM examination shows that post-treatment by MHP compresses the coating, reducing both thickness and porosity, particularly in coatings with ultrafine carbides. The treatments also cause cracking, however, especially in carbide phases. Ball-on-disk tests were carried out on as-sprayed and treated samples to determine sliding wear and friction properties, and dry sand rubber wheel tests were used to evaluate abrasion resistance. SEM and EDX analyses before and after wear testing show how coating microstructure and grain size correlate with the friction and wear test results obtained and the given surface treatments.

In this work, a design-of-experiments approach is used to map the main parameters of a high-velocity airfuel (HVAF) spraying process. Chromium carbide based material with a NiFeCrSi matrix was sprayed with varying gas flows and nozzle designs while monitoring their effect on particle temperature, velocity, and coating build-up. It was found that sufficient heating is critical to abrasive wear resistance and that particle temperatures are primarily controlled by fuel flow rates. Nozzle geometry, on the other hand, had the biggest effect on particle velocity, which was found to increase nearly 100 m/s by switching from a cylindrical to a convergent-divergent design.

Nano-sized, micro-sized, and bimodal Cr 3 C 2 -25NiCr feedstock powders were prepared using a spray drying and agglomeration sintering process and deposited by HVOF spraying. The microstructure and phase composition of the three powders and corresponding coatings were assessed along with coating hardness, toughness, and abrasive wear resistance. All three powders were nearly spherical in shape, but the bimodal powder had the best sphericity, the most uniform composition distribution, and the highest deposition efficiency. All three coatings were primarily composed of Cr 3 C 2 and NiCr phases, although a small amount of Cr 2 O 3 was detected in the nano- and micro-coatings due to oxidation. Compared with the micro-coating, the nano-coating has higher toughness but lower microhardness and abrasive resistance. The bimodal coating, however, integrates the advantages of the other coatings, has low porosity and a dense microstructure, and is tightly adhered to the substrate, thus displaying the best comprehensive performance.

In nuclear plants, the replacement of hardfacing Stellite, a cobalt-base alloy, on parts of the piping system in connection with the reactor has been investigated since the late 60’s. Various Fe-base or Ni-base alloys, Co-free or with a low content of Co, have been developed but their mechanical properties are generally lower than that of Stellites. The 4th generation nuclear plants impose additional or more stringent requirements for hardfacing materials. Plasma transferred arc (PTA) coatings of cobalt-free nickel-base alloys with the addition of sub-micrometric or micrometric alumina particles are thought to be a potential solution for tribological applications in the primary system of sodium-cooled fast reactors. In this study, PTA coatings of nickel-base alloys reinforced with alumina particles were deposited on 316L stainless steel substrates. The examination of coatings revealed a refinement of the microstructure. Under the conditions of the study, the addition of alumina particles did not improve the micro-hardness of coatings but improve their resistance to abrasive wear.

In this study, TiB 2 -40Ni and TiB 2 -50Ni powders are deposited on mild steel substrates by HVOF spraying in order to investigate the influence of Ni on coating hardness and corrosion, wear, and thermal shock resistance. The surface morphology and cross-sectional microstructure of the ball-milled powders and composite coatings are examined, and various tests are conducted to measure properties of interest. The findings are presented and discussed in the paper.

This study evaluates the effect of annealing on the microstructure, hardness, and wear resistance of FeAl-WC coatings obtained by cold spraying. As-sprayed deposits exhibited a dense microstructure with uniformly dispersed WC particles in the iron matrix. The Fe(Al) solid solution was transformed to an FeAl intermetallic compound at around 650 °C. Further increases in temperature were found to improve the composite microstructure with a slight decrease in microhardness. Wear resistance peaked at 750 °C, and at 950 °C, a diffusion layer appeared at the bottom of the coating close to the substrate.