The properties of the coating depend, among other things, on the preparation of the substrate surface and the spray parameters. One of the key properties of the coating is its adhesion to the substrate. Suitable preparation of the substrate surface has a great influence on the adhesion of the thermal spray coating. This work aims to study the influence of surface preparation on roughness of substrate and the resulting surface adhesion of coating. Another aim was to compare the effect of the chosen adhesion measurement method. A series of measurements of the roughness of the samples after grit blasting was performed. The effect of using new and used corundum was also taken into account. The selected coating for testing was TWAS (twin Wire Arc Spray) sprayed Zn15Al. The substrate material was low carbon steel 1.0570. The following adhesion measurement methods were chosen for the experiment - adhesion tensile test according to ASTM C633 - 79 standard, method using a special sample holder based on the ASTM C633 - 79 standard. In addition, a series of measurements were performed using Elcometer 510 Model T.

The aim of this study is to evaluate the effect of electromechanical treatment on the structure and wear behavior of plasma-sprayed nickel coatings. The coatings were air plasma sprayed on low carbon steel substrates, then electromechanically treated using different values of current density. Erosion resistance was assessed based on volume loss and coating microstructure and phase composition were evaluated via SEM and XRD. Erosion mechanisms were compared by analyzing coating cross-section and surface microstructures and wear resistance was associated with features such as defects, porosity, and cracks.

Cold spray has been proved to be a viable method for metallization of polymers and polymer composites. It has been reported that the mechanism of cold spray on polymeric substrates is different from the conventional mechanism on metallic substrates (i.e. adiabatic shear instability). In this work, single particle impact experiments were performed on polymeric substrates as well as mild steel. The particle-substrate interactions on different substrates were analyzed. Based on the results, the mechanism of cold spray on polymeric substrates is discussed and compared to that on metallic substrates.

Previous results at McGill University have shown that metallic coatings can be successfully cold sprayed onto polymeric substrates. This paper studies the cold sprayability of various metal powders on different polymeric substrates. Five different substrates were used, including carbon fibre reinforced polymer (CFRP), acrylonitrile butadiene styrene (ABS), polyether ether ketone (PEEK), polyethylenimine (PEI); mild steel was also used as a bench mark substrate. The CFRP used in this work has a thermosetting matrix, and the ABS, PEEK, and PEI are all thermoplastic polymers, with different glass transition temperatures as well as a number of distinct mechanical properties. Three metal powders, tin, copper and iron, were cold sprayed with both a low-pressure system and a high-pressure system at various conditions. In general, cold spray on the thermoplastic polymers rendered more positive results than the thermosetting polymers, due to the local thermal softening mechanism in the thermoplastics. Thick copper coatings were successfully deposited on PEEK and PEI.

In automotive industry, thermal spray process is used to reduce engine weight by replacing cast iron liners inserted in cylinder bores. Especially, twin wire arc spray is one of widely used thermal spray processes with inexpensive cost and high deposition rate. In this study, two kinds of wire materials, low carbon steel (0.07 wt.%C) and high carbon steel (0.80 wt.%C) were deposited by twin wire arc spray process using two kinds of process gas (i.e., compressed air and nitrogen) in order to elucidate effects of carbon contents of ferrous coating and process gas type on the hardness and wear resistance of coating. In case of hardness, low carbon steel coatings had higher hardness when air was used as process gas whereas high carbon steel coatings had higher hardness when nitrogen was used, which was caused by the counter effects of carbon loss and oxide formation. The results of sliding wear test in lubricated condition indicated that coatings with higher hardness have better wear resistance and oxides improve wear resistance by playing a role as solid lubricant. The main wear mechanism was splat delamination induced by inter-splat crack, and traces of other wear behaviours such as splat tip fracture and abrasive wear were also observed.

A low-cost, low-pressure (less than 1 MPa) cold spray unit was used to deposit tungsten carbide (WC)-based metal matrix composite (MMC) coatings on low carbon steel substrates. The coatings were then friction-stir processed (FSP) by using a flat cylindrical tool. Scanning electron microscopy (SEM), image analysis, micro-hardness testing, and ASTM Standard G65 dry abrasion wear testing were conducted to study the influence of FSP on the coating properties and its wear rate. It was found that porosity increased following FSP on the coating due to insufficient flow of the metal matrix material (nickel). The hardness of the WC-based MMC coating decreased after FSP as a result of increase in porosity and possible decarburization of the WC caused by the heat of the FSP. The SEM images taken from the cross sections of the FSPed coatings confirmed the effectiveness of FSP in distributing the WC particles within the matrix to produce a coating with uniform distribution of WC particles in the matrix. As a result, the abrasion wear resistance of the coatings after FSP increased compared to that of the as-sprayed coatings. This suggested that FSP can be considered as a method to improve the wear properties of MMC coatings.

Tungsten carbide coatings are often applied to improve surface properties such as wear, high temperature degradation, and corrosion resistance. Zirconia coatings have also been used extensively in various industries due to their excellent tribological and insulation properties combined with high stiffness. It is speculated that adding zirconia to tungsten carbide may result in a coating with combination of excellent thermal and mechanical properties of constituents. In the current study, a powder mixture of 50 wt. % WC-Ni and 50 wt. % ZrO 2 -Y 2 O 3 deposited on a low carbon steel substrate using atmospheric plasma spray technique. The microstructural evolution of deposited sample was investigated. Splat boundaries, micro cracks, pore morphology conversion, and grain growth mechanism were elucidated comprehensively. Results indicated a good adhesion between two different major components. No porosity formed due to mismatch between zirconia and tungsten carbide. This study pays special attention to the dependency of the microstructural characteristics to the phase distribution within the coating.

Thermally sprayed coatings are mechanically bonded to the substrate and present porosities and a lamellar microstructure that make them less attractive in applications requiring high coating toughness and impermeability to gas and liquids, these properties been obtained with more technically advanced overlaying processes. This paper presents the research work carried out to increase the erosion resistance of arc-sprayed coatings containing hard Fe 2 B crystals dispersed in mild and alloyed steel-based matrices. These arc-sprayed coatings were a) heat-treated in furnace up to 1000°C and b) fused with an oxy-acetylene torch. The sprayed specimens were tested in a particle erosion device at the impact angles of 25° and 90°. The evolution of microstructure was done by SEM and wear damage by Time- Domain Optical Coherence Tomography. It was shown that both the heat treatment and fusing processes considerably enhanced the erosion resistance of coatings particularly at the impact angle of 90°. This increase in erosion resistance is attributed to the disappearance of stringers between sprayed lamellae. Liquid phase sintering is the mechanism responsible for the homogenization of arc-sprayed coatings containing Fe 2 B. Grain growth observed in arc-sprayed coatings heat-treated up to 1000°C or fused with an oxyacetylene torch does not have a detrimental effect on erosion resistance.

Surface preparation is very important for reliable adhesive bonding of cold sprayed coatings to the substrate. In this work, the grit blasting of low-carbon A516 steel substrates with Al 2 O 3 particles was studied and the roughness parameters Ra and Rt of the grit blasted surfaces were then measured. The influence of alumina grit size on the roughening of the A516 steel substrate, and the resulting effect on the roughness of the Cu coating – steel interface were studied. The results showed that variations of the grit blast size had significantly affected the resultant surface roughness of the substrate. The adhesive strength of the formed copper coatings on A516 steel substrates depends on the surface roughness and hardness of the base material. The adhesive strength about 110-200MPa was achieved. The specific features of the Cu coating-A516 steel interface topography were examined and discussed.

The main purpose of this study was to form cold sprayed copper coatings on A 516 low carbon steel, which is considered a prospective material for manufacturing used nuclear fuel containers. The 3 mm-thick Cu coatings were formed using the high pressure cold spray method with N 2 as the propellant gas. To increase the adhesion strength of the deposited coatings a copper sublayer was formed first, using He as the propellant gas. The deformation of copper particles during the deposition process was studied. The obtained SEM images of the Cu layer-A 516 low carbon steel substrate cross-sections demonstrated that the Cu sublayer had a dense microstructure, and local jet-metallic mixing areas. The Cu particles were deformed considerably more severely in the sub-layer than in the following layers. The steel substrate underwent severe deformation due to the impact of Cu particles. The mutual severe deformation of Cu particles and steel substrate resulted in a considerable increase of adhesion strength up to 120MPa. The structure of coatings and coating-substrate interface was studied by OIM, SEM and EDS.

Adhesion properties on the substrate blasted by multi-angle blasting with white alumina grit were examined. The low carbon steel substrates were blasted at two blasting angles (high and low angles) in a multi-angle blasting process. The sprayed coating of zinc alloy was evaluated by an adhesion test. The surface roughness levels after the multi-angle blasting were lower than those in the case of normal blasting. The multi-angle blasting was an effective blasting process to obtain improved adhesive properties. The low blasting angle may have contributed for removing contamination from the substrate surface. The high blasting angle may have contributed for an effective surface roughness to enhance the adhesive properties.

Iron based coatings have recently gained much attention as they have favorable mechanical, frictional, and corrosion properties. The coatings possessed a high content of iron borides are particularly valuable for satisfying engineering needs. Boron and iron form two major boride phases, FeB and Fe2B, with different mechanical and thermal properties. Orthorhombic boride FeB is considered to be viable candidate to enhance the surface hardness and wear resistance of components, since it has high hardness. Producing of such coating by cold spray method is considered to be an alternative for boronizing method which is a conventional thermochemical surface hardening process. In this work, the crushed ferroboron (FeB) powders of Fe-17.9B-0.4C-1.6Si-0.3Al (wt. %) were deposited onto low carbon steel substrate by cold spraying. However, low and high pressure cold spraying allowed depositing very thin and single layer on the substrate, due to the intrinsic brittleness of the powder. Therefore, several contents of Al, Ni and Fe metallic powder and their combinations were added to FeB powder to obtain thick coating via cold spray processes. Post heat treated coatings at a temperature of 700 °C resulted in increase of the hardness, possibly the formation of hard phases such as intermetallic compound.

Polypropylene (PP) was flame sprayed onto rough mild steel substrates at room temperature (RT) that was preheated at 70 °C, 120 °C, and 170 °C. Single solidified droplets (splats) were collected and analysed to understand how processing variables influenced the thermal spray coating characteristics. The splat morphology was characterized in detail using optical and scanning electron microscopy (SEM). The splats exhibited a disk-like shape with a large central viscous core and a fully melted wide rim with a thin edge. The splat size increased with increasing substrate temperature. A unique flat microstructure was observed on the surface of the splat deposited onto the RT substrate, whereas a flowing pattern appeared on the splat surfaces deposited onto the preheated substrates and the pattern increased by increasing the substrate temperature. The results of this study revealed improved splat-substrate adhesion by heating the substrate from RT to 170 °C. On the basis of the result, the influence of substrate parameters on splat morphologies was employed to establish a relationship between the microstructural characteristics and processing variables of flame sprayed polymeric coatings.

Thermal spray coatings are comprised of millions of heated particles that are driven at high velocity to impact against a substrate; thereby building up to form a consolidated coating. Thus, investigating single solidified droplets contributes to fundamental understanding of coating evolution and their properties. In this study, Scanning Electron Microscopy (SEM) studied the splat morphology of flame sprayed ethylene methacrylic acid (EMAA) with respect to the stand-off distance when deposited onto glass and mild steel substrates. A splat shape transition from a “splash” to a “disc shape” was observed. The morphology of EMAA droplets can be described as a ‘splash splat’ when sprayed onto mild steel at room temperature, whereas a 35 cm stand-off distance produced a disk-shaped splat when the polymer was deposited onto a glass substrate.

Al 2 O 3 -13 % wt TiO 2 thermal sprayed coatings exhibit good wear resistance under tribological conditions, thanks to their high toughness. Alumina/titania coatings with two different structures, and similar titania content, have been elaborated by atmospheric plasma spraying (APS). The aim was to compare the effect of the structure on hardness and wear resistance. As feedstocks were used Al 2 O 3 -13 wt % TiO 2 powders with two different structures: micrometer sized ones, with two size distributions (5 – 30 μm and 15 – 45 μm), and agglomerated nano-meter sized particles (grain diameters between 200 to 500 nm) with a size distribution between 10 and 45 μm. Coatings were sprayed onto low carbon steel (XC38) substrates with several spray parameters, the plasma forming gas used being mixtures of Ar and H 2 (45/15 and 53/17 SLM, respectively). Results show that, with the tribological conditions used in this study, the wear resistance of coatings principally depends of their hardness and not very much on the starting powder morphologies.

This paper presents an investigation of the influence of the spray angle on thermally sprayed coatings. Spray beads were manufactured with different spray angles between 90° and 20° by means of atmospheric plasma spraying (APS) on heat-treated mild steel (1.0503). WC-12Co and Cr 3 C 2 -10(Ni20Cr) powders were employed as feedstock materials. The spray beads were characterized by a Gaussian fit. This opens the opportunity to analyse the influence of the spray angle on coating properties. Furthermore, metallographic studies of the surface roughness, the porosity, the hardness and the morphology were carried out and the deposition efficiency as well as the tensile strength were measured. The thermally sprayed coatings show a clear dependence on the spray angle. A decrease in spray angle changes the thickness, the width and the form of the spray beads. The coatings become rougher and their quality decreases. In addition, the spray process becomes inefficient as the deposition efficiency declines. Especially, below 30° for Cr 3 C 2 -10(Ni20Cr) and below 50° for WC-12Co a significant change in microstructure was observed.

Welding of dissimilar materials in particular ceramics to metals is a technical challenge with attractive economical consequences. In this study a ceramic coating was processed by plasma transferred arc (PTA). ZrO 2 –7wt.%Y 2 O 3 powders were deposited on low carbon steel plates and on Ni based alloys layers previously welded on a steel plate. Coatings were evaluated regarding the soundness and features of the metal/ceramic bond. Results showed that the pair ZrO 2 –7wt.%Y 2 O 3 /metallic alloy played a major role on the quality of the processed surfaces determining the effectiveness of the bonding. The presence of Al in the Ni based intermediate layer was detrimental to the adhesion of the ceramic coating. Deposition of ZrO 2 –7wt.%Y 2 O 3 on NiCrFe intermediate layers allowed for a metal/ceramic bond resulting on 3,0mm thickness coatings. Ceramic deposits exhibited cracks, whose features were altered after a stress relief treatment of the substrate (AISI 1020+NiCrFe layer) prior to the deposition of ZrO 2 –7wt.%Y 2 O 3 . Transverse section analysis revealed the presence of second phase particles in the ceramic coating and the diffusion of elements from the intermediate Ni based layer into the ceramic deposit.

The properties of pure Cu, Ni and Ti cold spray coatings on mild steel substrates were examined. Samples were prepared using CGTTM Kinetics 3000 system varying gun temperatures from 200 to 600 °C and gun pressures from 10 to 30 bars with N 2 as propelling gas. For these conditions, deposition efficiencies and critical velocities were characterized. In addition, the microstructural and mechanical properties of coatings were examined.

In this study, three kinds of engineering metals, which are aluminum (1100-H12), commercially pure titanium and mild steel were combined as particle/substrate and classified into four cases, i.e., soft/soft, hard/hard, hard/soft and soft/hard, according to their physical and mechanical properties respectively. Based on finite element modeling, impacting interface elements of four cases were analyzed and impact behaviors were numerically characterized. For soft/soft and hard/hard cases, the maximum temperature at the substrate side, which approached melting point, is higher than that of particle side when the shear instabilities occur. In particular, the different size of thermal boost-up zone was numerically estimated and theoretically discussed for these two cases. Meanwhile, for soft/hard and hard/soft cases, the specific aspect of shear instability, which has very high heat-up rate, was always observed at the relatively soft impact counterpart, and a thin molten layer was expected as well. Thus, the successful bonding of the above mentioned four cases can be predicted as a result of the synergistic effect of localized shear instability with interfacial melting.

The significant erosion of the boiler tube at high temperature becomes an important problem for the safe operation of circulating fluidized bed boiler. This paper investigated the erosion behavior of the HVOF sprayed Cr 3 C 2 -NiCr coating at high temperature comparing with the typical mild steel for boiler tube. Results showed that the erosion rate of the mild steel increased with the increase of temperature. The erosion rate of the mild steel at 800°C was 4 times that at 300°C at an erosion angle of 30°. However, the erosion rate of the HVOF sprayed Cr 3 C 2 -NiCr coating was not influenced by the temperature in the range of 300 to 800°C. It is found that the erosion resistance of HVOF sprayed Cr 3 C 2 -NiCr coating was more than 3 time higher than that of the mild steel at 700 to 800°C. In addition to the ploughing on the surface of the worn coating, the cracking along splats interfaces in the coating was clearly observed on the cross-sectional microstructure of the coating. The results indicate that the erosion performance of the HVOF sprayed Cr 3 C 2 -NiCr coating is controlled by the cohesion between splats in the coating and can be further enhanced by improving splat cohesion.