Sand blasting and high-velocity thermal spray processes can produce residual stresses in superalloy substrates that can significantly influence microstructure development. To investigate this effect, single-crystal superalloy substrates were sand blasted using different levels of force (zero, light, and heavy) and then coated with a MCrAlY layer by HVOF spraying. Cross-sectional analysis of an as-sprayed sample revealed a subsurface depletion zone with a composition rich in Mo nano precipitates. Cross-sectional examinations after vacuum heat treating and at various points during oxidation testing showed that elemental interdiffusion occurred between the coating and substrate and that sand blasting intensity has a major influence on the depth of the interdiffusion zones.

In this study, aluminum coatings were cold sprayed, with and without laser assistance, on laser-textured aluminum 6060 and Fe52 steel substrates. The results indicate that laser texturing makes for a cleaner coating interface than grit blasting and that the benefits are greatest when spraying on harder substrate materials. For the steel substrate, the optimized topography achieved through laser texturing assisted in particle deformation, leading to the formation of a much tighter coating structure. Laser-assisted cold spraying, in turn, improved deposition efficiency as well as coating density and adhesion. Separately or together, the two processes have proven to be beneficial for cold spraying.

A new process called in-mold metal spraying (IMMS) shows good potential for producing metallized plastic parts quickly and inexpensively. A zinc layer is deposited on mold cavity inserts using wire arc spraying and subsequently transferred to a plastic carrier via injection molding. Finely adjusted bonding strength between the carrier body and coating is essential for successful coating transfer. To that end, this study evaluates the influence of carrier body surface pretreatments on the transferability and bonding strength of zinc coating. Carrier bodies made of different types of steel pretreated by glass bead blasting and EDM were tested and their surface topography examined. In the initial experiments, the hardness and surface topography of carrier bodies were identified as factors that can influence coating transferability. Further experiments focusing on the adhesion strength of zinc on hardened and annealed carrier bodies were conducted to verify the influence of hardness on bonding strength.

Although research has been reported on pre and post processes for cold spraying, quantitative results are lacking. This study aims to quantify the effect of pre-coat grit blasting and post-spray stress relief and annealing treatments on cold-spray coating microhardness, bond strength, and microstructure. It was found that stress relief treatments reduce hardness, but have little effect on adhesion. Annealing also reduces hardness, but is shown to significantly improve adhesive bond strength. Grit blasting, on the other hand, was found to have a detrimental effect on tensile adhesion strength with little impact on coating microhardness.

In this work, steel columns are metallurgical bonded to tempered glass with the aid of atmospheric plasma spraying and low-temperature soldering. Glass surfaces were sandblasted using different grain sizes, then multilayer (Al 2 O 3 -Cu) coatings were applied at various power levels and spraying distances. Sn-Ag-Cu solder paste was then painted on the metallized glass and steel structures were set in place and soldered in a reflow oven. The interfacial bond strength of the alumina layer was measured along with the strength of the solder joint. The results are presented and correlated with sandblasting grain size and spraying heat input.

Suspension Plasma Spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings. This technique enables the production of a variety of structures from highly dense, highly porous, segmented or columnar coatings. In this work a comparative study is performed on six different suspension plasma sprayed thermal barrier coatings which were produced using axial injection and different process parameters. The influence of coating morphology and porosity on thermal properties was of specific interest. Tests carried out include microstructural analysis with SEM, phase analysis using XRD, porosity calculation using Archimedes experimental setup, pore distribution analysis using mercury infiltration technique and thermal diffusivity/conductivity measurements using laser flash analysis. The results showed that columnar and cauliflower type coatings were produced by axial suspension plasma spraying process. Better performance coatings were produced with relatively higher overall energy input given during spraying. Coatings with higher energy input, lower thickness and wider range of submicron and nanometer sized pores distribution showed lower thermal diffusivity and hence lower thermal conductivity. Also, in-situ heat treatment did not show dramatic increase in thermal properties.

In thermal spraying uncoated substrates usually require roughening. As the most common roughening method, grit blasting increases the surface area and produces undercuts, which facilitate mechanical interlocking and thus promote the bonding between the substrate and coating. The effects of grit blasting parameters, i.e. the particle size, the blasting angle, the stand-off distance and the pressure, on the resulting surface topography are investigated. Furthermore the efficiency and wear behavior of the blasting media are analyzed. Influences of three different blasting media, corundum, alumina zirconia and steel shot, on the surface roughening are compared.

The bond strength between a thermal spray coating and substrate is critical for many applications and is dependent on good substrate surface preparation and optimised spray parameters. While spray parameters are usually carefully monitored and controlled, most surface preparation is carried out by manual grit blasting, with little or no calibration of blast parameters. Blasting is currently highly dependent on operator skill and often surface finish is only assessed visually, meaning a consistent, reproducible surface profile cannot be guaranteed. Mechanised blasting offers the promise of more tightly controlled surface preparation and presents an opportunity to improve coating adhesion. This paper presents investigations on the effect of blast parameters (including blast pressure, standoff distance, media feed rate, blast angle, traverse speed and media size) on surface profile for a range of metallic substrates using a mechanised, robotic blasting system. Substrates were characterised using contact profilometry and non-contact focus variation microscopy.

The paper discusses a possibility of metallization of polymers using low pressure cold spray (Dymet 413). The bonding mechanism of the coating is discussed as well as the influence of the number of spraying passes on coating microstructure. Two commercial powder were used (i) tin; and (ii) aluminum to obtain coatings on PA6 polymer substrate. The substrate topography was modified with sandblasting. The adhesion strength, residual stresses, electrical resistivity, and microstructure were determined and characterized. Finally the comparison with other metallization methods was made and the application of cold spray for producing local conductive paths was assessed.

This study evaluates the effect of laser texturing on the bonding strength of cylinder bore coatings deposited by plasma transferred wire arc (PTWA) spraying. Experiments were carried out on an AlSi 9 Cu 3 engine block sectioned along a plane through the length of the bores. Cylinder surfaces were laser textured on one side and degreased and grit blasted on the other. Laser power, beam angle, and pulse count were varied to determine their effect on hole morphology and coating adhesion. After surface treatment, the engine block sections were rejoined and the cylinder bores were PTWA sprayed with high carbon steel. Coating samples were examined by SEM and cross-sectional analysis and adhesion tests were conducted. The bonding strength of the coatings on the laser textured portion of the cylinder bore was significantly higher than that of the coatings on grit-blasted surfaces and is shown to vary with laser power, beam angle, and total pulses or impacts per hole.

Residual stresses arising during high-velocity oxyfuel (HVOF) spraying usually impose a limit on coating thickness. In this work, dry-ice blasting is used in combination with HVOF spraying to produce thick WC-Co coatings characterized by compact microstructure, crystal refinement, high hardness, and excellent sliding wear resistance.

In this work, alumina coatings are produced by atmospheric plasma spraying using dry-ice blasting to prepare substrate surfaces. Feedstock powder and coating microstructure are examined and dielectric strength and ac-dc breakdown voltages are measured. The results show that dry-ice blasting improves the dielectric properties of alumina coatings produced by atmospheric plasma spraying.

This study assesses the effects of dry ice blasting on the lifetime and durability of thermal barrier coatings (TBCs). Three sets of TBCs consisting of a CoNiCrAlY bond coat and YSZ topcoat were deposited by air plasma spraying, each set with a different dry ice blasting treatment. Different microstructures were obtained in both the bond coat and topcoat depending on blasting conditions. Bond coat oxidation and thermal shock lifetime of the TBC are also shown to vary with the blasting treatment. TBCs where both the bond coat and topcoat are dry-ice blasted proved to be the most durable with the biggest improvement in lifetime. They also exhibited the most regular surface roughness.

This study analyzes the mechanical properties of aluminum alloy substrates, in particular, changes in flexural behavior of laser-textured surfaces. Bending tests are conducted on samples treated by laser texturing and by conventional methods such as chemical degreasing and sandblasting. A comparison of flexural strengths caused by the different surface pre-treatments method is presented.

Cold spraying is a promising candidate for the metallization of carbon fiber reinforced polymer (CFRP) composites, but it requires the use of a protective interlayer deposited by either flame or plasma spray. This study evaluates the effect of different surface treatments on interlayer adhesion strength. CFRP samples were treated mechanically, chemically, and thermally and then a copper layer was deposited by atmospheric plasma spraying. Adhesion strength was measured by pullout testing and the results are compared with surface roughness measurements, SEM fracture surface images, FIB bisections of single Cu splats, and XPS analysis of the chemical affinity between the polymer and copper.

This study investigates the effect of dry-ice blasting distance on the deposition of CoNiCrAlY coatings obtained by plasma spraying. Dry-ice blasting was used before, during, and after spraying and its effect on coating quality was measured. The results show how blasting distance influences the deposition efficiency as well as the microstructure, porosity, adhesion strength, hardness, and oxide content of plasma-sprayed coatings. The optimal dry-ice blasting distance was proposed as 25 mm.

In previous work, a thermal spray multilayer system consisting of ZrO 2 and an MCrAlY top coat showed promising results regarding oxidation behavior of the γ-TiAl substrates tested, which encouraged further research activities. Diffusion of substrate material was successfully inhibited by a ceramic ZrO 2 coating. A building up of a dense and stable oxide layer could be achieved by additional application of an MCrAlY top coat, leading to improved oxidation resistance and thus showing feasibility. In this work the main focus for development was put on enhancing adhesion and lowering residual stresses of the coatings in order to allow long term and cyclic testing without delamination taking place. Being a very brittle material, Gamma Titanium Aluminides require special surface treatment to enable roughening which is crucial for a strong mechanical bond between substrate and coating. Alternatives to conventional grit blasting as a standard preparation method were investigated. These were micro-abrasive blasting and blasting at elevated temperature (≈300-550 °C) to allow a more ductile behavior. The paper will highlight the implications by means of these measures and will also show the present development status of the multilayer system.

A carbon steel was blasted by white alumina, and removability of residual grit was investigated. Blasting parameters such as grit particle size were varied. Residual grit was removed from substrate surface by dissolving the substrate in mixed acid solution, and the amount of residual grit was measured. Removal of residual grit was carried out by ultrasonic cleaning. The amount of residual grit was 7-17 g/m 2 , and penetration depth of embedded grit of most residual grit was 25-40 µm. The amount of residual grit increased with decreasing the grit size. However, the minimum amount of the substrate dissolution required for the grit removal increased with increasing the grit size.

Thermal sprayed coatings often need to be removed for maintenance, repair or recycling and are accomplished by various conventional methods such as grinding, abrasive blasting and chemical removal processes. The coating removal for repair is typically done for expensive and/or very complex parts. Parts of turbines, equipped with functional coatings, are stripped for inspection and repair as well as old coatings are renewed. When removing a thermal sprayed coating, damage to the part or ablation of the substrate must be avoided. A new process of dry ice blasting alone as well as in combination with a laser beam in a hybrid process has been approved for the removal of thermal sprayed coatings in a project aided by the Federal Ministry of Economic Affairs and Employment via the Federation of Industrial Research Associations (AIF). The aim of the project is to obtain the properties for the comparison and benchmarking of coating removal processes. Comparative studies have been made with the water jet and the abrasive water jet process at the Institute of Materials Science of the University of Hanover.

The morphology of sprayed splat raises the coatings adhesion and the properties which are determined by the spraying parameters. A lot of studies in this field show that the substrate surface temperature is a very relevant factor for the splat shape: the hypotheses of substrate surface wetability and contamination or absorption layer on the surfaces are supported by the fact that the near disk-shaped splat can be obtained in increasing the substrate temperature. In the PROTAL process, a short duration pulse laser is used to ablate the substrate just before powder spraying. This ablation is powerful enough to eliminate the contaminations on the substrate surface and to improve the adhesion. In this study the analyses of NiAl splat morphology on polished TA6V substrate were carried out using PROTAL process with different substrate temperatures and different heating modes: the flame and another laser. Results show that the temperature at which the disk shaped splat can be obtained was decreased dramatically by PROTAL process and PROTAL process combined with another laser has increased the adhesion strength of the coatings.