Extreme High -Speed Laser Cladding (EHLA) is a new process category of laser cladding. In this study, EH-LA layer was characterized by comparing with conventional laser cladding (LC) layer. Basic SUS316L layers, as well as WC-reinforced SUS316L layers, were formed on SUS304 substrates using both LC and EHLA processes. The macroscopic morphology, microstructure, microhardness, wear resistance, and residual stress of the four types of layers were evaluated. As a result, EHLA layers exhibited slightly higher micro-hardness and less wear loss than that of LC layers, despite the presence of more micropores. This can be due to their finer dendritic structures. Furthermore, residual stress of EHLA layer was lower than that of LC layer due to those micropores. Additionally, EHLA can add up to 45 wt.% WC into SUS316L layer without crack formation, resulting in higher wear resistance than that of LC where crack formation occurred at 25 wt.% WC. This enhanced crack resistance in EHLA is believed to be due to the less heat input during deposition.

Gas-fuel HVOF for thermal spraying of WC-CoCr powder is widely known and well described in literature. Focus are the various influencing factors like fuel-to-oxygen ratio, standoff-distance and powder feed rate on the coating characteristics like hardness and porosity. However, the total gas flow is usually not being described in this context despite its wide influence on particle characteristics and therefore on coating properties. In this study, the characteristic influence of the total gas flow on roughness, hardness and porosity is described as well as its effect on the particle characteristics. The study performed was based on technical standard values for thermally spraying WC-Co-Cr via gas-fuel HVOF (DJ2700 hybrid) and additional trials for increased and decreased total gas flow. It was possible to determine that with higher gas flow the deposition rate increases while the roughness and porosity decrease. However, these results cannot be viewed in isolation as other factors, such as the fuel-to-oxygen ratio, are affecting the particle and coating characteristics at the same time. Therefore, the total gas flow is also considered in combination with other factors.

Light alloys are being investigated as an alternative to ferrous-based engineering components. The manufacturing of such components requires a surface modification step necessary to eliminate the top surface's poor wear and corrosion response for improved functionality. Thermally sprayed cermet coatings offer improved surface resistance to wear and/or corrosion. This work presents a customized composition of WC-CoCr feedstock cut in fine and coarse powder size distribution (PSD) to fabricate different coatings on aluminium alloy and steel substrates using two high velocity spray techniques. The WC-CoCr coatings sprayed using the high velocity air-fuel (HVAF) technique at varied parameters consist of six different coatings (four thick, ~ 200 μm and two thin ones, 60-80 μm) to investigate the relationship between processing conditions, microstructure, and performance. Using scanning electron microscopy (SEM) and electro-dispersive X-ray spectroscopy (EDX) offered a comprehensive characterization of the respective coatings. Micro indentation, dry sliding wear, dry sand abrasion, and cavitation erosion tests conducted on the samples show the performance of the coatings based on the processing techniques and spray conditions. However, despite the similarities in the microstructural makeup of the coatings and the measured micro indentation hardness of the coatings (1000-1300 HV0.1), their respective specific wear rate (SWR) varied based on spray processing techniques and the substrate on which the coatings were deposited. Three of the HVAF coatings showed ~ 60 % more wear on the aluminium alloy substrate compared to the same coating deposited on a steel substrate. However, irrespective of the substrate used the HVAF coatings showed better wear resistance than the HVOF coating. The dry sand abrasion wear results of the two thick HVAF coatings show them superior to the HVOF coating in the three-body wear experiment conducted. The cavitation erosion resistance of the coatings varied based on the processing conditions and the driving mechanisms but the best two were the AF-2 and AF-6 samples.

Recently, laser deposition technologies have made significant advancements in their ability to manufacture high temperature metals and ceramics. One of these technologies, known as Direct Energy Deposition (DED), has the potential to deposit a wide range of materials from polymers to refractory materials, ceramics and functionally graded materials. This study evaluates major microstructural characteristics of WC-Co additively manufactured by DED technology. This material is commonly used for deposition of protective coatings due to its high hardness and excellent wear resistance. To this end, hardness and wear resistance of the DED processed samples were also investigated in this study. WC-Co coatings are generally deposited using various thermal spray technologies. However, it is speculated that DED deposited WC-Co could provide superior properties such as higher hardness and wear resistance. A DED manufactured WC-Co sample was examined by Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). Those studies could provide information about important microstructural features, chemical compositions and phase distribution. All the tests were also repeated on High-Velocity Oxygen Fuel (HVOF) deposited WC-Co with the same composition. Both DED and HVOF produced WC-Co coatings experience decomposition of the carbides into compound phases; however, the DED deposited sample displays unique dendritic and eutectic structures that improve the hardness and wear properties compared to the homogenous HVOF coating. In addition, DED produced samples show higher hardness and relatively better wear resistance compared to the HVOF deposited ones. The obtained results could establish a relationship between microstructural characteristics with hardness and wear properties of both samples.

Nowadays, Cr 3 C 2 -based cermet coatings by HVOF process are widely recognized for their corrosion and erosion resistance, particularly at high temperatures. These coatings also offer the advantage of being lightweight and exhibiting superior wear, corrosion and cavitation resistance in room-temperature applications. Their lightweight nature and high temperature capability make them an attractive alternative to WC-based alloy coatings and hard Cr plating coatings. The objective of this study is to develop optimal Cr 3 C 2 -NiCr coatings by comparing different feedstock materials, including feedstock with nanocrystalline and/or submicron sized Cr 3 C 2 phases. The focus of the investigation is on understanding the impact of feedstock features such as particle size, morphology, and carbide sizes, as well as sliding abrasive wear conditions (specifically SiC grit size and working load), on the coating properties and sliding wear performance. The results of the study indicate that the sliding wear resistance of the Cr 3 C 2 -NiCr coatings is highly influenced by the features of the Cr 3 C 2 carbides. The presence of nano, submicron and few microns sized carbides in the coatings improves their density and hardness, leading to a significant reduction in wear rates under test conditions. Furthermore, the size of the abrasive SiC grit on the counter surface plays a significant role in determining the sliding wear behavior of these coatings. Based on the analysis of the test data, the mechanisms behind the performance of the Cr3C2-NiCr coatings have been investigated and used to interpret their sliding wear behaviors. A high microhardness in the coating is considered a reliable indicator of high quality, full density, and satisfactory wear resistance. This study has identified and recommended optimized materials for improved coating properties based on the key findings. These findings contribute to the understanding of the relationship between feedstock features, sliding abrasive wear conditions, and the wear rates of HVOF-sprayed Cr 3 C 2 -NiCr coatings.

Thermally sprayed wear resistant coatings have proven their effectiveness in many applications. Their benefit is unquestionable in the case of mutual sliding contact or abrasive stress caused by hard particles. However, for the case of dynamic impact loading, either single or cyclic, the lifetime of different types of coatings is rarely described, probably due to the complex influence of many parameters. The paper deals with the evaluation of resistance to dynamic impact loading of two types of HVOF-sprayed Cr3C2-rich binary hardmetal coatings (Cr3C2-42%WC-16%Ni and Cr3C2-37%WC-18%NiCoCr) with respect to the variation of their deposition parameters and compares them to a well established Cr3C2-25%NiCr coating. For each coating, a Wohler-like curve was constructed based on a failure criterion of sudden increase in impact crater volume. Besides, coatings deposition rate, residual stress, microstructure and hardness were evaluated. Differences in the coatings dynamic impact wear resistance was found, related to their residual stress. The failure mechanism and crack propagation mode are analyzed using SEM of impact surface and cross-sections. Deformation and related stress changes in coated systems during dynamic impact loading are described using FEA analyzes.

In order to overcome the problem of insufficient abradability of existing metal based coatings that cannot meet the requirements of harsh working conditions, this article designs two types of metal based abradable sealing coating materials based on the particle structure of "peeling medium", and studies the basic performance and simulated working condition service performance of the coatings. The research shows that, after undergoing a 1000 hour heat exposure test at high temperature, the two coatings still maintain good hardness, bonding strength, and abradability, indicating that under long-term high-temperature service environment, the two coatings can fracture at the location where the abradable components are exposed, thereby maintaining the abradability and good thermal stability that meet the requirements of use.

The development of materials and alloys for coatings has been increasingly important for reducing costs in different manufacturing processes. The Inconel alloy is widely used due to its chemical inertness and high resistance to high temperatures, but it does not present adequate resistance to erosive wear. In this context, the resistance to wear from cavitation erosion and slurry erosion was evaluated of samples with depositions obtained by laser cladding (Laser directed energy deposition - L-DED) of Inconel 718 and Inconel 718+10%NiNb. The cavitation erosion wear tests were carried out following the ASTM G32 standard (2016), and the ASTM G73-10 standard (2017) was used to evaluate the resistance to slurry erosion wear. The scanning electron microscopy technique (SEM-EDS), and X-ray diffraction (XRD) were used to characterize the cross-section and the surface after wear. The wear mechanism was checked and identified. Microhardness profiles of the cladding cross-section were carried out. The mass loss and wear rate due to cavitation and slurry jet erosion of Inconel 718 and Inconel 718+ 10% NiNb coatings were determined. It was proven that the addition of 10% NiNb in the formation of the cladding caused a 45% increase in average microhardness in the cross-section of the Inconel 718 cladding. The addition of 10% NiNb to the Inconel 718 cladding caused a decrease in mass loss due to slurry erosion from 38.9 mg to 21.9 mg (33%) when the erodent impact angle was 60°.

A variety of process parameters affect the properties of the deposited coatings in the High Velocity Oxygen Fuel (HVOF) spraying process. In fact, the quality of coatings can be improved without changing feedstock or deposition technology by the application of optimized spraying process parameters. In this study, a large set of data “Big Data” is used to create a variety of machine learning models for prediction of porosity content and hardness values of HVOF deposited coatings. A set of process parameters was selected as validation run and actual HVOF coating was deposited using those parameters. The porosity level and hardness were measured and compared to those predicted by models. The models differ based on the number of neurons utilized in each layer for the calculations. A model with six neurons could predict closest porosity level and the one with three was the best in prediction of hardness. The final model could be obtained by running data through both models. Through this study, a robust machine learning model for the optimization of HVOF process parameters will be developed that could be used for other coatings and thermal spraying techniques.

Cold spray (CS) is a solid-state process for depositing metal powder, accelerated by a high-velocity gas such that it bonds to the substrate metal through kinetic impact energy. Although the technology is finding applications in non-load bearing repair and coating applications, work is needed in the quality control procedures for CS for its use in load bearing structural applications. in this study, the viability of electrical conductivity and through thickness ultrasound wave velocity measurement methods are studied to serve as a means for nondestructive quantitative measurement methods for quality control in CS and potentially other additive manufacturing (AM) methods. Eddy current, ultrasound, porosity, hardness, and uniaxial tensile strength tests were conducted on copper and aluminum samples that were manufactured using CS. Ultrasound measurements of longitudinal wave velocity and eddy current electrical conductivity measurements showed good correlation with process conditions that were varied to control particle velocity to intentionally produce samples with varying deposition quality. Influence of process conditions on particle velocity was confirmed via particle image velocimetry. Porosity, hardness, and tensile test results were further correlated to ultrasound wave velocity and electrical conductivity measurements. The results of this work show that nondestructive testing methods can be effectively used to quantitatively assess the cold spray products for quality control purposes.

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.

In this study, microstructural characterization is conducted on WC-17Co coatings produced via High Velocity Oxygen Fuel (HVOF), High Velocity Air Fuel (HVAF), and Cold Spraying (CS). All coatings prepared were observed to be of good quality and with relatively low porosity content. SEM study showed important microstructural features and grain morphologies of each coating. While composition of feedstock material was approximately similar, elemental composition using EDS showed higher Co content and lower WC in the CS deposited coating. XRD experiment identified formation of more complex oxides and tungsten phases in coatings deposited technologies involving melting of powders such as HVOF and HVAF. These phases consisted mainly of cobalt oxides and brittle phases such as W 3 Co 3 C or W 2 C caused by decarburization of the tungsten carbide particles. Hardness of all coating samples were examined and CS deposited coating exhibited considerably lower hardness compared to the other two coating samples instead of having significantly lower porosity content. It could be contributed to dissociation and physical loss of hard carbide phase during high velocity impact of particles in CS process. It is in good agreement with detection of higher amount of cobalt in CS deposited coating material. It is strongly believed that results obtained from this study can be used for future investigation in thermo-mechanical properties of WC-Co coatings.

The performance of two distinct coating materials under alumina particle impingement was tested in this study. CrMnFeCoNi and WC-Ni coatings were applied to 2205 duplex stainless steel substrates using cold spray method with nitrogen as the process gas. In between the substrate and the high entropy alloy coating, an interlayer coating of 316 stainless steel was used. The presence of WC particles in the WC-Ni composite coatings was confirmed by SEM cross sectional inspection. Following deposition, the coatings were heat treated in an air furnace. The influence of heat treatment holding time on the WC-Ni coatings was studied using chemical analysis by X-ray diffraction. Heat treatments peak temperatures for the WC/Ni- Ni and high entropy alloy coatings were 600°C and 550°C, respectively. Coatings microhardness and porosity volume fraction were measured for all the samples. The HEA coating outperformed the WC/Ni-Ni hardness but exhibited a higher level of porosity. The coatings were then subjected to erosion experiments using alumina particles with variable impact angles (30°, 60°, and 90°). To compare the different materials, an average erosion value was calculated for each target specimen. The WC/Ni-Ni as-sprayed coating was the most effective against a 60° impingement angle. The HEA coating, on the other hand, demonstrated greater resistance to impact angles of 30° and 90°. SEM was utilized to examine the eroded areas and determine the main mechanisms of erosion.

Cold spraying (CS) of high strength materials, e.g., Inconel 625 is still challenging due to the limited material deformability and thus high critical velocities. Further fine tuning and optimization of cold spray process parameters is required, to reach higher particle impact velocities as well as temperatures, while avoiding nozzle clogging. Only then, sufficiently high amounts of well-bonded particle-substrate and particle-particle interfaces can be achieved, assuring high cohesive strength and minimum amounts of porosities. In this study, Inconel 625 powder was cold sprayed on carbon steel substrates using N 2 as propellant gas under different refined spray parameter sets and powder sizes for a systematic evaluation. Coating microstructure, porosity, electrical conductivity, hardness, cohesive strength and residual stress were characterized in as-sprayed condition. Increasing the process gas temperature or pressure leads to low coating porosity of less than 1 % and higher electrical conductivity. The as-sprayed coatings show microstructures with highly deformed particles and well bonded internal boundaries. X-ray diffraction reveals that powder and deposits are present as γ- solid-solution phase without any precipitations. By work hardening and peening effects, the deposits show high microhardness and compressive residual stresses. With close to bulk material properties, the optimized deposits should fulfill criteria for industrial applications.

Successful cold spray of tool steels and other hard steels would unlock several opportunities, including the repair of molds as well as ships and heavy industry components. However, the high hardness of typical atomized steel powders strongly limits their cold sprayability. It has been recently demonstrated that heat treatment in a rotating furnace can significantly improve H13 cold sprayability via softening and agglomeration. In this work, this powder modification method is extended to a range of transformation hardenable steels: 4340, SS420, A588, 1040 and P20. The results show that powder heat treatment improves the powder deposition efficiency and the quality of the final cold sprayed coating, probably as the result of the decreased powder micro-hardness. The effects of the powder heat treatment atmosphere, a key parameter, will also be presented and discussed.

The application of thermally sprayed coatings on CFRPs has gained great interest to enhance thermal and tribological properties and several processes have been optimized. However, for the coating of internal surfaces of tubes there is no sufficient technical solution. This paper introduces a novel and unique process technique for coating the internal surfaces of CFRP tubes using the transplantation of thermally sprayed coatings. A negative shape tube with defined surface and material properties was used as a mandrel and coated using atmospheric plasma spraying (APS). The CFRP was then produced using filament winding onto the coating, and after curing, the specimen was separated from the mandrel. With this process innovation, CFRP tubes with internal ceramic or metallic coatings can be produced without any thermal degradation of the polymeric matrix or damage to the carbon fibers. Compared to conventional coating methods, this novel process technique has several advantages. It allows for the production of internal coatings with low roughness of R z = 10 μm as sprayed without post-processing. The specimens also have a significantly lower tendency to corrode compared to conventional coated CFRPs. A high adhesion strength of the coatings of 15.9 MPa was achieved and the hardness of the internal ceramic coating is 918 HV0.1

In the current work, a NiCrAlY and Fe-based alloy are HVOF-sprayed due to the combination of high coating density and customizable coating properties. The oxygen to fuel gas ratio was varied to modify coating defects in a targeted manner. The results demonstrate material dependent defect mechanisms. Further investigations regarded residual stresses, hardness, and electrical conductivity. In particular, the thermal diffusivity proved to be very promising. Moreover, the coatings were compared with previous work on arc-sprayed coatings of similar chemical composition regarding insulation capability.

In particular, eutectic HEAs (EHEAs) are of interest for coating technology. The microstructure of these multiphase systems is determined by the cooling conditions during solidification and the heat treatment condition. High cooling rates can suppress segregation and allow the formation of a supersaturated solid solution microstructure. Therefore, the property profile differs from that of the equilibrium state. The effect of cooling conditions on the functional properties of EHEA coatings has not been investigated so far. In the current study, the microstructure formation and wear resistance of the metastable EHEA Al 0.3 CoCrFeNiMo 0.75 was investigated. Laser metal deposition (LMD) of the inert gas atomized powder forms a directional vertically solidified lamellar structure. A supersaturated solid solution and a metastable BCC and HCP phase was formed. The microstructure resembles a Widmanstätten structure. By spark plasma sintering (SPS), a statistically distributed orientation of the fine lamellae was produced. The highest microhardness and oscillating wear resistance were detected for the ultrafine LMD coating. By increase of the microstructure domain size, the hardness and oscillating wear resistance decrease. This study reveals the great potential of supersaturated solid solutions of ultrafine EHEAs obtained by LMD processing with high cooling rates.

Hybrid aerosol deposition (HAD) has been proposed recently as a new coating regime to deposit homogeneous ceramic coatings via the utilization of mesoplasma and solid particle deposition. This study will discuss the implementation of HAD for the deposition of alumina (Al 2 O 3 ) coatings on 304 stainless steel and aluminum substrates, and evaluation of the hardness and Young’s modulus using a nanoindentation method to clarify the through-thickness properties. Dense and uniform coatings with a nanocrystalline structure were fabricated on both substrate materials. The fabricated HAD coatings consisted of α-Al 2 O 3 phase. The hardness and Young’s modulus distributions along the through-thickness direction showed a significant difference across the coating-substrate interface and tended to show a slight decrease by 10-15% as the measured position went close the surface. Increasing the hardness and Young’s modulus on the substrate side near the interface is presumably related to the peeing effect of the substrate as well as the increase of interface roughness during the room temperature impact consolidation (RTIC) and deformation of the hard ceramic particles on the substrate. The decrease in the coating’s mechanical properties along the through-thickness direction is considered to be related to the particle deformation tendency during the coating build-up. At the beginning stage of the deposition, initial particles are impacting on a metallic substrate which is ductile enough to facile plastic deformation and the deposited layer can have an enough hammering effect by the subsequent impacting particles. The hardness and Young’s modulus in this location are 15.6 GPa and 246 GPa, respectively, and the highest through the thickness in case of the stainless steel substrate. However, the later particles are impacting on a hard ceramic surface (initially formed HAD Al 2 O 3 layers), which hardly undergo plastic deformation or led to less particle deformation. In addition, through-thickness measurements revealed that the deposited coatings on the stainless steel substrate showed higher hardness than deposited coatings on aluminum substrates. Thus, the stainless steel enhances the degree of deformation of the deposited particles, and the resulted smaller crystallite size and strain lead to increased hardness and modulus.

A micro-plasma system was investigated for its capability in additive manufacturing (AM). Micro-plasma AM system has the advantage of lower cost and higher deposition rate over the laser-based AM systems, and generates leaner and cleaner weld deposit than other arc-based AM systems. However, the microplasma system is complex and involves a large number of process variables. In this study, the effects of two arc and wire feed modes on dimensional consistency and hardness were firstly examined. Subsequently, one set of the specimens was further subjected to oxidation tests and the results were compared to that from conventional wrought Inconel 718. It was found that all four processes could produce crack free samples without measurable distortion. Some surface discoloration was observed, ranging from light straw to a purple tint. After heat treatment, the hardness of the samples varies from 403 to 440 HV, with the transverse surface showing slightly lower hardness values. The oxidation tests at 900 °C yielded similar weight change for AM Inconel 718 and its counterpart wrought alloy; however, the rate constant for wrought alloy was slightly higher. Microstructural analysis with SEM and EDS revealed a dendritic structure in the AM Inconel 718 and the presence of Nb-rich compounds in the interdendritic region. The polycrystal grain structure was not delineated in AM material as that in wrought 718. With the increase of exposure time, the oxide layer continues to increase at a higher rate, along with a sublayer of Ni 3 Nb above the metal substrate. In addition, after 200 hours, the wrought alloy developed porous chromia, while AM material exhibited uneven oxide thickness. In consideration of all aspects of the evaluation carried out thus far, it is concluded that the AM material produced by micro-plasma process is equivalent to wrought material in mechanical properties and oxidation performance.