Cold atmospheric plasma spraying is used to produce thin coatings of copper and tin between 20-80 μm thickness for use in diffusion soldering. This study presents an alternative process to apply composite solders directly onto power electronic bare dies. The formation of intermetallic phases may be promoted by the homogeneous distribution of the Cu and Sn particles as they are presented not in a layered structure but as a pseudo alloy within the coating. The Cu and Sn powder is mixed in situ using two powder conveyors, enabling adjustable mix ratios. The presented approach has been shown to produce a homogeneous particle distribution within the coating. Furthermore, preliminary experiments indicate the feasibility of the technology for applications in diffusion soldering.

In Laser Cladding, a differentiation must be made between cladding by brazing and cladding by welding regarding process parameters and the resulting material properties. Results of investigations of bronze cladding on steel parts produced by Laser Deposition Brazing will be presented. This means that a strong metallurgical bond is realized by diffusion processes by Laser Deposition Brazing, but the steel base material is not molten. The coatings were characterized by hardness distribution measurements from the bronze cladding to the steel substrate, by measuring the size of the heat-affected zone and by porosity measurements. This combination of a steel substrate and a local bronze coating is used industrially in many tribological applications, such as plain bearings or hydraulic pumps etc. The bronze offers excellent tribological properties. In some cases, the bronze is used as a complete solid part. However, applying the bronze locally to a steel base body instead of using a complete solid bronze component, offers the advantage of the higher modulus of elasticity of the steel, which provides greater stability of shape with regard to possible elastic deformations as these coated parts are exposed to high mechanical loads, it is essential that a high coating quality is achieved by laser cladding and that the properties are extensively and purposefully characterized. The production technology, the characterization and the industrial applications of such bronze coated steel parts are presented and explained in this contribution.

Atmospheric plasma sprayed (APS) CuNiIn coatings have been widely used for fretting wear protection in many important areas such as aircraft engines for decades. The oxides in CuNiIn coating prepared by APS hinder splat bonding formation and thus degrade the coating fretting performance. In this study, CuNiIn powders of different boron contents were designed to realize the self-oxide-cleaning effect for in-flight molten droplets and thus deposit the dense CuNiIn coating with high fretting performance. Scanning electron microscope was used to characterize the microstructure. The oxygen content in the coating was measured by the inert gas fusion technique. Fretting test was performed for three coatings under different loadings. The results show that CuNiIn2B and CuNiIn4B coatings presented the oxide content of 0.40wt% and 0.38wt%, which are lower than 1.6wt% of the CuNiIn coating. The oxygen content in the CuNiIn4B coating decreased with the increase of spray distance while the oxygen content in CuNiIn coating increased with the increase of the spray distance. Such results clearly reveal the boron in-situ deoxidizing effect of inflight molten droplets. As a result, the dense CuNiIn2B and CuNiIn4B coatings were deposited with oxide-free molten droplets. The test results showed that the fretting wear performance of B-alloyed CuNiIn coatings were increased by a factor over three comparing with conventional CuNiIn coating.

In the current work, typical thermal-sprayed copper-based alloys are investigated to reduce the spread of pathogenic germs in broiler farming. Compressed air and nitrogen are used as process gas, while the coating torches and the alloys were varied. The results demonstrate a significant reduction in pathogenic load due to the coatings. This accounts especially for the bacterial strain E.ceocurm, which is the predominant bacteria in broiler farming. Further investigations regarded the microstructure and the electrical conductivity of the coatings.

Mechanical and fatigue properties of cold sprayed (CS) Cu 20 Sn bell metal were tested in order to assess the potential applicability of the technology to repair impact areas of church bells. The CS bell metal was compared to its traditional cast counterparts, a fine-grained Cu 22 Sn bell metal seen in small bells, and a coarse-grained Cu 20 Sn seen in large bells. Similar to other CS metals, it was shown that both the strength as well as the fatigue crack growth rates at low loading are similar to the cast materials. The fracture toughness of the CS material was comparable with the finegrained Cu 22 Sn bell metal, while both were significantly lower than the coarse-grained Cu 20 Sn bell metal. The impact damage rate of the CS material determined by a periodic impact test was significantly higher than the (finegrained) cast material. Both materials showed a stabilized, very slow damage rate after the relatively fast initial crater formation. The results presented in this paper identify CS as a feasible restoration technology for church bells, and the introduced methodology presents a characterization method for quantitative description of bell metal impact damage.

Abradable seal coatings are widely employed in the gas turbine of aero-engine, which not only strength enough to resist the impact of external particles and airflow, but also excellent wear resistance. In the current study, we concentrate on APS sprayed Aluminum Bronze Polyester abradable coating that can be used in turbo engines both for seals and clearance control. A composite thermal spray powder, substantially in the form of clad particles each of which has coarse polyester powders and sub-particles of Cu-Al alloy powders, was prepared using mechanically clad process. Abradable seal coating was prepared by atmospheric plasma spraying. The microstructure, hardness, bonding strength, thermal shock resistance and corrosion resistance of coatings were researched. Properties of the coating were able to meet the application requirements. The coating microstructures and phase compositions were evaluated via SEM. The corrosion mechanisms of the coating were compared by analyzing the cross-sectional and top surface microstructures of the as-sprayed and eroded coatings.

The present study compares needed prerequisites for the application of cavitation resistant bronzes by applying different coating techniques, such as cold spraying, HVOF spraying, warm spraying and arc spraying. By optimization to optimum cavitation resistance, the deposited coatings can increase the service life of ship rudders significantly and even serve as repair processes for ship propellers. The given overview aims to support the selection of processes when specifying the target properties to be set with regard to cavitation protection. By using high-pressure warm spraying and cold spraying, properties similar to those of cast nickel aluminum bronze were achieved, however at relatively high costs. In contrast, coatings produced by using HVOF and arc spraying have erosion rates that are only about four respectively three times higher as compared to cast nickel aluminum bronze, while far outperforming bulk shipbuilding steel. Hence, their properties should be sufficient for acceptable service life or docking intervals for ship rudder applications. Propeller repair might demand for better coating properties as obtained by cold spraying. With respect to costs, HVOF and arc spraying in summary might represent a good compromise to reach coating properties needed in application.

One of the main levers to reduce CO2 emissions in cars and trucks is mass and friction reduction, which is often achieved through the use of special coatings. The aim of the present work was to develop metal-ceramic-lubricant composite coatings with the best combination of wear, seizure, fatigue, and thermal resistance. Metal-based coatings incorporating hard particles and solid lubricants were cold sprayed onto steel substrates and the relationship between coating microstructure and tribology was studied. To meet the demanding tribological requirements of heavily loaded engines, the interfaces between the different components were optimized by selecting appropriate feedstock powders and assessing a wide range of process parameters. Alumina-reinforced bronze composite coatings were made from powders with different morphologies. Aggregated ceramic powders were found to be more beneficial in terms of wear than massive powders, and graphite was found to be effective for reducing seizure.

This paper provides an update on the state of cold spray corrosion mitigation and repair as it applies to equipment operated by the U.S. Navy. It also presents several application scenarios in which cold-sprayed Al 6061 and NiCr-CrC can improve preventative maintenance and dimensional restoration procedures currently used on A36 steel and CuNi structures.

Super wear-resistant aluminum-based metal matrix composite (MMC) coatings were produced using cold spraying. Cu-Ni coated diamond and pure diamond particles were used as reinforcing agents. Test results show that the metallic Cu-Ni shell served as a buffer layer, preventing the fracture of diamond particles upon impact as occurred with the uncoated diamond. The coated diamond particles were also found to have a higher deposition efficiency due to metallurgical bonding between the Cu shell and Al matrix. Under tribological testing, all coatings performed well, but those reinforced with the coated diamond showed higher wear resistance due to higher diamond content and involvement of Cu and Ni.

This study evaluates the erosion-corrosion performance of thermal spray hardcoats on bronze-coated gray cast iron. In the experiments, gray cast iron plates are coated with a bronze powder by PTA welding and the coatings are characterized based on microstructure and corrosion and wear testing. The bronze coatings provide good corrosion protection, but are shown to be susceptible to cavitation and erosion wear. To compensate, thermal spray hardcoats, including atmospheric plasma sprayed Al 2 O 3 and Cr 2 O 3 and HVOF sprayed WC-Co, were applied over bronze-coated cast iron and corrosion and wear tests were performed. It is shown that the thermal spray hardcoats greatly improve wear resistance, but despite their interconnected porosities, do not affect the corrosion performance of the underlying bronze.

This study assesses the effect of laser melting on MCrAlY-coated copper substrates. CoNiCrAlY, NiCoCrAlY, and NiCrAlY powders were applied to copper alloy substrates by atmospheric plasma and HVOF spraying. Sample surfaces were then laser melted and coating properties were determined and correlated with coating composition, surface morphology, and cross-sectional microstructure. Laser melting not only caused the coatings to fuse to the substrate, but also precipitated the formation of an aluminum oxide surface layer that reduced the oxygen content in the coating. As a result of this finding, the coating samples were heat treated in order to measure their high-temperature oxidation resistance.

ASTM C633 has been an industry standard for determining thermal spray coating adhesion and cohesion strengths for nearly 40 years. The test, however, has several drawbacks that can greatly affect the results. The epoxies used cannot withstand stresses greater than 15,000psi, producing data that may suggest coatings cannot function beyond the epoxy threshold under uniaxial tensile loading, resulting in data that can only be used for general quality control or acceptance testing. Previously published data shows coatings functioning beyond C633 limits, yet there is no standardized test to show true functional stress limitations. A four-point bend test method with an instrumented strain-gage has been used to show coating adhesion well beyond the yield point of the steel substrates and beyond the C633 limits for three materials and thermal spray processes: electric arc sprayed aluminum bronze, plasma sprayed alumina, and HVOF WC/Co/Cr. A strain-gage is applied to a prepared coating surface on a bend bar and loaded under tension or compression. The MTS universal load frame force data is used to calculate the stress at the coating/substrate interface by beam theory equations, allowing for stress and strain vs displacement curves to be generated and directly compared against C633 data for coating adhesion strengths. The resulting data can indicate microscopic coating behavior (cracking, de-bonding) as a result of the test sensitivity and can ultimately be used as design data for the practicing engineer.

In state-of-the-art manufacturing of sliding bearings, brass components are soldered to respective parts, which is costly and energy-intensive. Furthermore, up to now most bearings still contain lead, which by EU regulations for new part has to be omitted due to associated health risks. Cold spraying can be employed as additive manufacturing technique and opens the perspective to deposit the requested bearings in desired leadfree layout where needed. Aside cohesion and tribological behaviour, sufficient adhesion of the coating is essential for applications. The present study aims to systematically elucidate the influence of surface roughness on adhesion. The surface roughness was adjusted by varying the grit blasting material, grit size, blast pressure, blast distance and substrate material with the aim to study influences by impact conditions, surface topography on particle deformation and bonding in cold spraying. The results show that the adhesion strength reaches a maximum for a certain roughness. The ideal surface roughness to ensure good adhesion of cold-sprayed coatings apparently depends on specific impact conditions related to the powder material strength but also on the substrate material strength and particle size distribution. By systematic tuning of blasting conditions, coating adhesion can be increased by about a factor of two, thus meeting the requirements for new lead-free bearings.

The alloys CuAl9Ni5Fe4Mn and CuMn13Al8Fe3Ni2 were arc-sprayed with a spiral-shaped pattern in this work, using both pressurized air and a mixture of nitrogen and hydrogen. Process temperatures were recorded by thermographic imaging and residual stresses were measured by modified hole-drilling method. Moreover, analyses of the cavitation erosion behavior and other properties were carried out. It was found that a change in the spray pattern can strongly reduce residual stresses and material loss by cavitation erosion.

This study was focused on the biocidal efficacy on spores of copper alloy sheet and copper alloy coating at two different surface topographies. Endospores can remain viable in a dormant state for centuries. Our work compares the effectiveness of copper alloy coating and copper sheet metal in killing endospores. A twin-wire arc spray system was used for coating of stainless steel coupons. The feedstock was CuNiZn wire, the coating thickness was 400 µm. The copper alloy sheet metal had the same composition and is registered as antimicrobial by Environmental Protection Agency (US). Uncoated stainless steel coupons were used as controls in all experiments. The surface was polished to two roughness levels: Ra=3.5 µm and Ra=0.1 µm. The surface topography was analyzed by a stylus profilometer and 3D image analysis. EDS and FIB were used to characterize the elemental composition and structure of flower-like nanostructures and endospores. The results obtained in this study indicated that changes in Ra values of 0.1 and 3.5 µm had no significant impact on the biocidal activity of sheet metal and the coating on E. coli , S. epidermidis and B. subtilis . The coating was as effective as the EPA-certified sheet metal in the destruction of vegetative cells within 5 minutes. This study indicates that degradation of B. subtilis endospore begins within 2 hours after exposure to the coating. By day seven, only extensively degraded endospores and nanostructures were visible on both surfaces. Our results show that thermal spray copper alloy coatings were as effective as certified antimicrobial sheet metal in the destruction of endospores within hours; however, the coating was more effective in killing the endospores after one week of exposure.

In cold spraying, oxide-free interface is an important factor for fresh metal bonding between particles and substrate, which determines the bonding strength and final coating quality. In this study, a well-designed experiment was performed to examine the deformation behaviour of the oxide film on copper alloy particle surface after deposition. The experiment results show that partial oxide film could be disrupted during the high-speed impact. However, most of the oxide films were found to remain intact after particle deposition, which limited the exposure of oxide free interface. The presence of oxide film at the interfaces between deposited particles and substrate seriously affected the metallurgical bonding. Besides, substrate material is found to have a strong influence on the deformation behaviour and final state of the oxide film. The study also demonstrated that the bonding mode between deposited particle and substrate strongly depends on the type of substrate.

The highly cavitation erosion resistant propeller alloys CuAl9Ni5Fe4Mn and CuMn13Al8Fe3Ni2 were arc sprayed with different traverse speeds by using a mixture of nitrogen and 2 % of hydrogen as atomising gas. Residual stresses were measured by the modified hole-drilling method using ESPI. Microstructural, chemical and mechanical analyses were realised to examine adhesive and cohesive properties. Additionally, the cavitation erosion behaviour was investigated. In comparison to coatings sprayed with pressurised air, the results of the study show superior coating qualities with regard to microstructure, cavitation erosion resistance and residual stresses.

In current process techniques to manufacture sliding bearings, bronze components are soldered to the respective parts, which is cost and energy intensive. Apart from that, so far most bearing materials still contain lead, which in new applications is omitted by EU law to avoid associated health risks. The present study aims to offer solutions for both by using cold gas spraying as additive manufacturing technique for processing bearings directly onto steel parts and by applying that to new lead-free bronze alloys. A lead-free bronze alloy was processed as powders by gas atomization and classified to optimum sizes for cold spraying. During cold spraying, the process gas pressures and temperatures as well as the substrate temperature were varied with the aim to study influences by impact conditions and effective surface temperature on particle deformation and bonding. Respective coatings show low porosity, high hardness and high electrical conductivities. With properties similar to that of bulk cast material respectively manufactured parts should meet the requirements for new bearing applications.

An innovative hybrid process which combines the two very effective solid-state techniques of cold spraying (CS) and friction stir processing (FSP), was proposed to fabricate a high-strength ultrafine-grained Cu-Zn coating. Results show that the CS coating had an elongated microstructure with 78.42% of low-angle grain boundaries. Following FSP, there appear ultrafine grains with 90.47% of high-angle grain boundaries and a composition of α, β' and γ phases while the CS coatings was mainly α. Significant mechanical properties enhancement is achieved, i.e. with the ultimate tensile strength increasing from 87.2 MPa to 257.5 MPa and fracture elongation increasing from 0.17% to 0.81%. The precipitates have a significant effect on the fracture behavior of FSP coatings.