Grinding wheels are usually manufactured by powder metallurgical processes, i.e. by moulding and sintering. Since this requires the production of special moulds and the sintering is typically carried out in a continuous furnace, this process is time-consuming and cost-intensive. Therefore, it is only worthwhile for medium and large batches. Another influencing factor of the powder metallurgical process route is the high thermal load during the sintering process. Due to their high thermal sensitivity, superabrasives such as diamond or cubic boron nitride are very difficult to process in this way. In this study, a novel and innovative approach is presented, in which superabrasive grinding wheels are manufactured by thermal spraying. For this purpose, flat samples as well as a grinding wheel body were coated by low-pressure (LP) cold gas spraying with a blend of a commercial Cu-Al2O3 cold gas spraying powder and nickel-coated diamonds (8-12 μm). The coatings were examined metallographically in terms of their composition. Afterwards, the grinding wheel was conditioned for the grinding application and the topography was evaluated. This novel process route offers great flexibility in the combination of binder and hard material as well as a costeffective single-part and small-batch production.

In cold spray, high adhesion of soft materials on hard substrates is commonly achieved by using helium as the propelling gas. This is the case of copper coatings on steel where adhesion may reach values as high as 60 to 80 MPa (glue failure), however, helium is a limited, expensive natural resource, and the use of more abundant nitrogen gas is preferred in an industrial setting. Unfortunately, when using nitrogen gas, little to no adhesion is obtained. In order to eliminate the use of helium gas we studied how laser assisted cold spray could lead to an improvement in adhesion of nitrogen sprayed copper coatings. In this work, several laser parameters (e.g., power and spot size) and process parameters (traverse speed, relative position laser spot vs. gas jet) were varied at a coupon level. Upon optimization, an equivalent adhesion to the coatings prepared with helium was obtained. Furthermore, the cross section of the coatings showed that the copper particles penetrated the steel, similar to what is observed when using helium gas. Optimization of these parameters for application to large diameter (~559 mm) cylinders was also performed. A discussion on the mechanisms which contribute to achieving high adhesion considering the use of helium versus laser assistance is provided.

A novel powder modification method based on the simultaneous softening and agglomeration of steel powders via heat treatment in a rotary tube furnace has been investigated as a means to improve the cold sprayability of H13 tool steel powder. By adjusting starting powder size and shape as well as heat treatment conditions (maximum temperature, cooling rate, and atmosphere), cold spray of H13 powder went from virtually no deposition to the production of thick dense deposits with a deposition efficiency of 70%. Powder agglomeration, surface state, microstructure evolution, and softening are identified as key factors determining powder deposition efficiency and resulting deposit microstructure.

A previous study showed that Cu can be cold sprayed onto carbon fiber-reinforced polymers (CFRPs) if a Cu interlayer is deposited prior to low-pressure cold spraying. In this present study, Cu was cold sprayed onto CFRP substrates that were coated with either Sn (cold spray) or Ni electroplating. Two layers of Cu powder were also cold sprayed onto a Cu-plated CFRP substrate to investigate the effect of a second particle layer on impacting particles. Test results showed that the relative hardness between the particle and substrate has a major effect on deformability, impact mode, and deposition efficiency (DE), which explains why Cu could not be cold sprayed onto Sn or Ni interlayers and why the deposition efficiency of Cu-on-Cu substrates is lower than that of one pass spraying. In summary, the results suggest that Cu can be successfully cold sprayed at low pressures onto electroplated Cu due to their similarity in hardness.

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.

Cold spray deposition is being investigated for mitigation of chloride-induced stress corrosion cracking (CISCC) in dry cask storage systems (DCSS) for spent nuclear fuel. Welded regions of austenitic stainless-steel canisters in DCSS are under tensile stress and susceptible to environmental chloride corrosion, which can potentially lead to the formation of CISCC. The low thermal input and high throughput nature of cold spraying make it a viable repair and mitigation option for managing potential CISCC. Cold spray coatings are under compressive stress and act as a barrier in Cl-rich environments. Characterization data including microstructure, hardness, and corrosion resistance are presented for cold spray coatings on stainless steel substrates.

In cold spray, particles undergo large plastic deformation upon impact in a rapid dynamic regime (up to 109 s-1) at solid state. The simulation of this impact is key to understanding the cold spray process. In this study, an approach based on laser shock and micro-compression testing was developed to characterize the mechanical behavior of powders and fit parameters of the Johnson-Cook material behavior model. In situ micro-compression particle testing was performed in a SEM equipped with a microindentation stage. From subsequent FEM simulations of the test, static coefficients of the Johnson-Cook model were identified. A laser shock powder launcher (LASHPOL) was also developed to accelerate single particles and measure their corresponding velocity using high-speed imaging. In addition, image analysis of the particles before and after impact, together with FEM simulation, were used to determine strain rate hardening coefficients for the Johnson-Cook model.