In this work, a novel HVOAF process fueled with ethanol was employed to prepare NiCoCrAlYTa coatings on AISI 304 stainless steel substrate. To be able to add compressed air into the torch, it was designed to add a second-stage combustion chamber. Thereafter, investigations were carried out to determine the influence of different compressed air flow rates on the evolution of the microstructure and properties of the resulting NiCoCrAlYTa coatings. The phase composition, microstructure, porosity, microhardness, bond strength and wear resistance of the as-sprayed coatings have been studied in detail. The results reveal that the compressed air flow rate has a substantial effect on the coating's microstructure. The addition of compressed air also contributes to reduce the degree of oxidation of the coating, which could be attributable to a decrease in the temperature of the flying particles and an increase in their velocity. Although the use of compressed air diminishes the coating's bonding strength, it still has some elevated strength. Furthermore, the injection of compressed air improves the coating's sliding wear resistance dramatically. SEM and EDS were used to investigate the sliding wear mechanism of the coating. Detailed correlation between the compressed air flow rates and the coating properties are elaborated to identify the coatings exhibiting optimum performances.

Cold Spraying (CS) is a thermal spray process capable of producing dense and thick coatings by the spraying of powders under high velocity and relatively low temperature. The high deposition efficiency and the thickness of each pass make possible the use of CS to produce freestanding parts, as an additive manufacturing process (CSAM). Traditionally, CS is performed spraying perpendicularly to the substrate, which ensures maximum deposition efficiency among other benefits. This, however, presents two main disadvantages for CSAM. First, by keeping the spraying angle constant, there is not much control on the final geometry of the part being built, and, second, the resultant part’s properties show anisotropy depending on whether this property is measured along the spraying axe or not. In this work, we present a method (Metal Knitting) that aims to help reduce both disadvantages. Metal Knitting is based on the performance of certain spraying movements that build near squared shapes step-by-step like in a knitting process. The principle of the method and examples are presented in this work, as well as some results on the anisotropy of 316L stainless steel freeform parts obtained by CSAM, measuring the tensile stress, hardness, and evaluating the microstructure in different directions of the material. The effect of annealing on the material properties is also investigated.

Stainless austenitic steels like the 316L (1.4404) are widely applied in various applications and were also used for surface protection using thermal spraying. The reason for this is the easy processability and the high corrosion resistance. Stainless austenitic steels typically contain the following alloying elements: The formation of an austenitic microstructure is achieved by nickel (Ni). The addition of chromium (Cr) lead to good corrosion resistance due to formation of an oxide layer. For resistance against pitting corrosion, molybdenum (Mo) can be added. Also, stainless austenites usually exhibit very low carbon and nitrogen contents to prevent chromium carbides and nitrides which reduces the corrosion resistance. However, both alloying elements cannot be classified as being detrimental in stainless austenites in general. In contrast high nitrogen contents can also be used to improve the chemical properties, especially the resistance against pitting corrosion. Finally, carbon and nitrogen lead to an increase in hardness of the thermal sprayed layer. Based on this knowledge, a high-strength austenite for thermal spraying was developed. The new high strength austenite was processed by HVAF spraying with different particle distributions and parameter variations. Resulting coatings were investigated regarding the microstructure, elemental composition, hardness and corrosion properties in comparison to the standard coating material 316L.

The development of thermal spray processes usually requires an analysis of the complex coating microstructure. In order to inspect critical areas of a coating, destructive testing methods such as the preparation of cross-sections are commonly used. In this work, the suitability of largely non-destructively measured polarisation curves for the quality assessment of thermal sprayed AISI 316L coatings is investigated. Therefore, a 3.5 % NaCl gel electrolyte was developed to prevent the corrosive medium from infiltrating the porous and micro-cracked microstructure characteristic for thermal sprayed coatings. In addition, a measuring cell based on the 3-electrode arrangement was designed to simplify the setup, reduce the measurement time and enable mobile measurements directly on the component surface at a later stage of development. The effects of process-related differences in the microstructure of HVAF and APS AISI 316L coatings on the polarisation curve was investigated by determining the corrosion current density. The microstructure of the AISI 316L coatings was analysed by optical microscope, SEM and EDS, focussing on the porosity and oxide content. The results clearly show that the potentiodynamic polarisation curves of the AISI 316L coatings differ significantly depending on the spray process used and microstructure created. Even small changes in the oxide content within a coating can be detected. Therefore, electrochemical measurement methods using gel electrolyte offer an interesting opportunity to evaluate the quality of thermal sprayed AISI 316L coatings in a largely non-destructive manner.

FeMnCrSi and 316L alloy coatings were deposited on carbon steel substrates via high-pressure cold gas spraying and their microstructure, hardness, and wear resistance were obtained. Ball-on-disk testing (ASTM G99) was used to measure sliding wear behaviors. The mechanism of wear was found to be the same for both coatings, although FeMnCrSi had a higher coefficient of friction while 316L had less volume loss.

In this study, NbC coatings, 250 µm thick, were deposited by low-velocity flame spraying on stainless steel substrates and were laser remelted in a controlled argon atmosphere. Isolated passes transverse of the coatings were performed at different focal lengths at speeds of 10, 15, and 20 mm/min. Using the selected laser parameters, layers were recast with eight passes at 10% superposition. Erosion-corrosion tests were performed and coating surfaces and cross-sections were characterized via SEM, EDS, and XRD analysis. Modified surfaces of dense, 800-µm thick coatings with no defects and excellent metallurgical bonding with the substrate were obtained. It was found that dilution of the coating with the substrate formed a gradient of chemical composition and mechanical properties and that erosive-corrosive wear resistance was highest for an erodent impact angle of 90°.

In this study, WC-Co coatings were deposited on additively manufactured 316L stainless steel substrates by HVOF spraying. Prior to spraying, the SLM parts were exposed to various mechanical pretreatments, before and after which their surface topography and residual stress state were assessed. After spraying, Vickers indentation tests were conducted to assess interfacial bond strength between the coating and substrate. To differentiate between topographical effects and residual stress related phenomena, stress-relief heat treatments were conducted at various points in the investigation.

Cold spraying of automotive engine blocks requires a gun adaptation for inner diameter spraying with a very short nozzle. In this work, 316L coatings are sprayed with such a gun and the behavior of particles impacting aluminum and stainless steel surfaces is studied in order to understand the factors that affect coating adhesion and cohesion. Correlations between spraying parameters and coating properties were investigated via design of experiments and the effect of process parameters on deposition efficiency and coating thickness was optimized for mass production. Post-process honing was also employed as part of the study and smooth coatings with small pores were obtained.

In this investigation, thermally sprayed cylindrical specimens are machined by turning with different cutting speeds. To ensure that process-induced shearing loads do not cause delamination, a fine helical dovetail structure is cut into the substrate before it is coated with FeCrNi alloy by air plasma spraying. Dovetail structures with different geometries were produced and their effectiveness is compared. The finish-machined surfaces of the FeCrNi coatings were examined and characterized with respect to feed marks, cracks, open pores, pull outs, and residual stresses. It is shown that surface roughness and the number of pull outs decrease with increasing cutting speed while residual stresses remain relatively unchanged, except for the orientation of the first principal stress.

In this study, 316 stainless was deposited by low-pressure plasma spraying under various conditions to obtain different coating structures and by cold gas dynamic spraying for comparison. The coatings were characterized by cross-sectional metallography to assess porosity, oxidation, particle flattening, and elemental composition. The samples were also subjected to flyer plate impact testing in a gas gun to determine their shock propagation and porosity compaction properties. Comparing the results with that of the reference sample shows the effect of deposition conditions on the dynamic behavior of the coatings.

In this work, a novel additive manufacturing process was proposed and employed in the production of stainless steel components. The underlying concept is to use selective laser melting (SLM) to fabricate a core structure onto which basic features are added by cold spraying (CS), followed by heat treatment and finish machining. The microstructure and mechanical properties of as-fabricated and heat-treated parts were studied, and interfacial bonding between the SLM core and a typical CS feature was assessed. In the as-fabricated state, it is observed that the CS material has a dendritic structure similar to the feedstock, while the SLM core is characterized by cellular subgrains confined in coarse grain structures. Following heat treatment, interparticle boundaries are less well defined, equiaxed coarse grains and twinning appear, and the extremely fine subgrains in the SLM material are enlarged. Heat treatment is also shown to improve tensile strength in the CS material and interfacial bond strength between the CS features and SLM core.

This paper describes a method for producing textured surface layers on vacuum chamber components that act as particle traps. The novel textures consist of a stainless steel core produced by direct energy deposit laser cladding covered with a twin-wire arc sprayed aluminum film. The process has been qualified for 20 nm and older IC architectures and is now implemented in production equipment. It has been proven to significantly increase preventive maintenance intervals, reduce particle levels, and enhance yield.

Coating characteristics are very dependent on the substrate preparation and spray parameters. That’s why the surface must be adapted mechanically and physico-chemically to favor coating/substrate adhesion. Conventional surface preparation method as Grit-Blasting is limited by surface embrittlement and produces large plastic deformations throughout the surface resulting compressive stresses. Among all, Laser Surface Patterning is suitable to prepare the surface of sensitive material. It leads to several benefits such as surface free of Grit-Particle inclusions and improves directly the quality of coating bond strength so life-span. Finally, Laser Surface Patterning adapts impacted surface creating a large anchoring area. The essential idea here is to compare adhesion for two surface preparation methods Grit-Blasting and Laser Surface Patterning for two couples of materials used in aeronautic: Ni- Al and YSZ powder sprayed on 2017 aluminum alloy and AISI 304L stainless steel respectively. Optimized surface topographies can then be designed according to the materials as well as their applications.

In the formation of plasma sprayed splats, the spreading behaviour of molten droplet is essential for forming desirable lamella with good adhesion to substrate. To understand the effect of active element chromium on droplet spreading, pure Ni and Ni-20Cr alloyed powders with the size of 45~63μm were plasma sprayed on mirror polished 304 stainless steel heated to different temperatures (below 200°C) through electrical resistance heaters. The substrate heating resulted in very little change in the surface roughness. However, there was a measureable change in the surface chemistry of the outermost few nanometers, which became increasingly enriched in Fe at higher temperatures. The splat morphologies were characterised and the transition temperatures were estimated. The results show that the transition from splashed to disk splats was not solely dependent on the temperature of the substrate. In some cases, splashing still occurred to a measureable extent even at relatively high substrate temperatures, even above temperatures at which adsorbates (water) were totally removed from the surface. The splashing behaviour could be correlated to a combination of the change in the surface chemistry of the substrate and the presence of active elements in the coating materials.

The main goal of the combined Cold Spray – Sintering technology development is to obtain high density ductile Fe- Al intermetallics based thermal barrier coatings as an alternative to conventional ZrO2 coatings widely applied in industry. The task of this paper is to examine the structural changes of cold sprayed Al-AISI 316L composite coatings due to synthesis of Fe-Al intermetallics during annealing and find the conditions of high density composite formation. A dense Fe/Al intermetallic-Al composite coating is obtained. Three factors are found to play the main role in the structure formation of dense Fe-Al intermetallic composite coating: i) layered structure, ii) particle size and thickness of Fe and Al layers, iii) annealing temperature.

One of the most widely accepted and versatile materials used with many coating deposition methods is austenitic stainless steel 316L. This is due to the combination of good corrosion and mechanical properties that are suitable for numerous varying applications. As a result of our familiarity with 316L we assume the properties achieved will be within the expected frame as described in the literature. Deposition techniques and component size and shape have an impact on the heating and cooling variations which will then affect the microstructure of the final coating. This in turn will result in variations in the properties achieved. Some of these numerous factors such as: deposition technique, component geometry and size, impurities in the substrate and chemistry of the substrate will be considered. The influence of these factors on the microstructure and the definitive properties of 316L will be presented.

This paper aims at improving the adhesive strength of SS 316L coating by substrate preheating (400, 600 and 700°C). The relationships between the adhesive strength of coating/substrate interface and the substrate preheating temperature are discussed. It was found that stronger adhesion is able to occur despite the presence of a thick oxide film on the substrate surface. The preheated substrate surface undergoes a stronger plastic deformation that disrupts the oxide films for obtaining an intimate contact between particle and substrate material. In addition, the oxide films on the substrate surface can prevent the generation of material jet of the substrate. The effects of substrate preheating on the microstructure and hardness were also investigated.

The equiaxed microstructure of 316L stainless steel coating was successfully deposited by low pressure plasma spraying (LPPS), which was different from the lamellar microstructure prepared by other thermal spraying technologies. In this article, the effect of substrate temperature during deposition process and post annealing treatment on the lamellar – equiaxed microstructural transition were investigated. The results indicated that the homogeneous equiaxed grains without lamellar boundaries coatings were observed when the deposition temperature was about 900 °C. Completely lamellar microstructural coatings were deposited at the substrate temperature of about 300 °C, and the lamellar microstructure can transform to equiaxed microstructure after annealing treatment. The hardness of equiaxed coating was lower than lamellar coating.

In this study, bioactive glass powders were synthesized from four different types of oxides (SiO2, P2O5, CaO and MgO). These oxides were mixed, melted, milled and sieved to produce powders with two chemical compositions of the 31SiO2-11P2O5-(58-x)CaO-xMgO system. The powders were plasma sprayed onto AISI 316L stainless steel and Ti6Al4V titanium alloy substrates using a F4MB Sulzer Metco gun. The physical and mechanical properties of coatings, as well as their bioactivity were evaluated. The bioactivity tests were carried out exposing the surface of coatings to simulated body fluid (SBF) during 1, 9 and 15 days. The thickness and hardness of apatite layer produced on the surface of each coating during bioactivity tests were evaluated. The results indicate that the thickness of apatite layer formed during 15 days in SBF is between 31 and 51 µm and its hardness is between 1.5 and 1.9 GPa according to the chemical composition of feed stock powder used to manufacture the coatings. Additionally, the harness of bioglass coatings decreased around 26% after to expose them to SBF.

In the current investigation plasma spray technique was used for depositing hydroxyapatite (HA) and hydroxyapatite – silicon oxide (SiO2) coatings on 316L SS substrate. In HA-SiO2 coating, 20 wt% SiO2 was mixed with HA. The feedstock and coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) / energy-dispersive X-ray spectroscopy (EDX) analyses. The corrosion resistance of the uncoated, HA coated and HA + 20 wt% SiO2 coated 316L SS was investigated by electrochemical corrosion testing in simulated human body fluid (Ringer’s solution). After the corrosion testing, the samples were analyzed by XRD and SEM / EDX analyses. The addition of SiO2 reduces the crystallinity of the coating. The corrosion resistance of the 316L SS was found to increase after the deposition of the HA + 20 wt% SiO2 and HA coatings.