Cold spray is continuously expanding for the repair of parts made of aluminum-based alloys. Beyond repair applications, the process is now expected to be exploited efficiently for the additive manufacturing of shaped parts. However, up to now, cold spray is limited to the achievement of rather simple shapes due to a lack of basic knowledge on coating build-up mechanisms to result in dimension-controlled deposition. The objective of this work is to fill that gap through an experimental and modeling study of the coating build-up in cold spray for this specific application. Experimentally, Al-based coatings were deposited for a large range of particle velocity due to the use of low-pressure, medium-pressure and high-pressure cold spray facilities. Particle velocity was monitored as a function of cold spray conditions. Two different types of Al 2024 (Aluminium 2024 Alloy) powders were tested. Coating porosity and microhardness were studied as a function of (both morphological and metallurgical) powder characteristics and spray conditions, primarily in the light of particle velocity. Various correlations could be exhibited. Finite element (FE) simulations of particle impacts were developed, including particle velocity from experimental measurements. These will be used as inputs in an in-house morphological model, the first stages of which could be established successfully.

This study investigates the in-flight behavior of particles during cold spraying by means of high-speed shadowgraph photography using a laser imaging system. It also characterizes the particle jet outside the nozzle for different powder sizes (<10 µm to 155 µm) and densities (copper, aluminum). Observations of the jet reveal two low-pressure cold spray flow regimes, one stable, the other unstable, the effect and control of which are discussed.

In this study, microstructural characterization is conducted on WC-17Co coatings produced via High Velocity Oxygen Fuel (HVOF), High Velocity Air Fuel (HVAF), and Cold Spraying (CS). All coatings prepared were observed to be of good quality and with relatively low porosity content. SEM study showed important microstructural features and grain morphologies of each coating. While composition of feedstock material was approximately similar, elemental composition using EDS showed higher Co content and lower WC in the CS deposited coating. XRD experiment identified formation of more complex oxides and tungsten phases in coatings deposited technologies involving melting of powders such as HVOF and HVAF. These phases consisted mainly of cobalt oxides and brittle phases such as W 3 Co 3 C or W 2 C caused by decarburization of the tungsten carbide particles. Hardness of all coating samples were examined and CS deposited coating exhibited considerably lower hardness compared to the other two coating samples instead of having significantly lower porosity content. It could be contributed to dissociation and physical loss of hard carbide phase during high velocity impact of particles in CS process. It is in good agreement with detection of higher amount of cobalt in CS deposited coating material. It is strongly believed that results obtained from this study can be used for future investigation in thermo-mechanical properties of WC-Co coatings.

In this study, MCrAlY-Al 2 O 3 composite powders were produced by ball milling and deposited by plasma, HVOF, and cold spraying. The results show that Al 2 O 3 fractions can be well controlled using composite powder due to non-preferential impact debonding of the matrix and Al 2 O 3 . The microstructure of spray powders is well retained in HVOF and cold-sprayed coatings due to the unmelted or partially molten condition of the spray particles. In the case of plasma-sprayed coatings, however, most Al 2 O 3 particles segregate at lamellar interfaces, forming a continuous oxide scale on the splat. The cold-spray coatings exhibit the highest hardness due to the work hardening effect of kinetic deposition.

In the cold spraying process, particle velocity is commonly regarded as the key factor that influences the deposition efficiency and properties of the coating. The present paper reports on a study in which the velocity of in-flight particles was measured using a DPV-2000 system. The influences of He and N 2 gas pressure and temperature and particle morphology on the particle velocity and deposition efficiency of the coating using stainless steel 316L powders were studied. The microstructure of the coating was examined using optical microscopy. The critical velocity of stainless steel 316L powders was estimated according to the particle velocity distribution and deposition efficiency of the coating. The experiment results suggested that the gas pressure has a more significant influence on the particle velocity and deposition efficiency of the coating than the gas temperature. The particle morphology also has significant influence on the particle velocity. The critical velocity of stainless steel 316L powders was in the range of 630 to 680 m/s, and it decreased slightly with the gas temperature.

The aim of this work is to characterize the performance and durability of Zn-based composite coatings produced by low-pressure cold spraying and evaluate their potential for use in repair and restoration applications. Mechanically blended Zn+Al+Al 2 O 3 , Zn+Cu+Al 2 O 3 , and Zn+Ni+Al 2 O 3 powder mixtures were deposited on grit-blasted carbon steel (Fe52), copper, aluminum, and nodular cast iron substrates using optimized feed rates. In addition, round samples were drilled and the holes were repaired by handheld spraying. Coated substrates are assessed based on microstructural analysis, laser shock adhesion testing (LASAT), and thickness and hardness measurements. Hole repairs are evaluated based on bond strength and gas permeability measurements. The procedures are described and the finding are presented and discussed.

The aim of this work is to fabricate a particle-reinforced FeAl composite coating by cold spraying. Fe, Al, and WC powders were placed in a ball mill and mechanically alloyed for up to 36 h in order to obtain a nanostructured Fe(Al) solid solution reinforced with a high volume fraction of WC particles. The powder was examined and then cold sprayed on stainless steel substrates using N 2 as the accelerating gas. The as-sprayed deposits exhibited rough surface morphology and dense cross-sectional microstructure with dual-scale WC dispersoids distributed uniformly in the Fe(Al) matrix. The coatings were annealed at 650 °C and subsequently reexamined. In-situ phase transformation from the solid solution to an intermetallic compound occurred after the post-spray treatment along with an improvement in microstructure.

In this study, Al-SiC composite coatings are produced by cold spraying ball-milled Al powders with different volume fractions of SiC particles. The morphology and microstructure evolution of the powder during ball milling are evaluated along with the effect of SiC content on the microstructure and wear behavior of the coatings. The results show that dense Al-SiC coatings with different volume fractions of SiC particles can be fabricated by cold spraying and that abrasive wear resistance is improved by raising the volume fraction of SiC particles. Wear surfaces indicate that the predominant wear mechanism is gouging of the soft Al matrix in the early stages and cracking and spalling of SiC particles in the latter stages. The dispersed SiC particles serve to protect the matrix from wear products thus raising the wear resistance of the coatings.

In the present work, a coupled thermomechanical-Eulerian model was developed to calculate particle impact behavior during cold spraying. The model is based on temperature-displacement elements and is capable of nonlinear transient analysis of impact deformation and heat conduction. Simulation results show that heat conduction has a major effect on temperature distribution within the particle, but little influence on particle deformation. The FEA model is also used to calculate critical velocities of commonly sprayed materials and the results are evaluated based on the morphology of deformed particles and plastic strain analysis.

Design, manufacturing, and utilization of efficient heating systems for pipelines and closed-pressure equipment are necessary for cold regions to compensate for heat loss and prevent damages that are caused by freezing of the enclosed liquid. Given large-scale financial losses that stem from failure and bursting of the pipes, the development of novel, efficient, and affordable heaters, which can lead to improved efficiency, cost savings, and environmental benefits across various industries and applications, is of crucial importance. Heating systems have already been produced via different high-temperature thermal spraying techniques to achieve higher efficiency compared to conventional heating cables. In this study, tin, as the heating element, was deposited by using the cold spray process onto alumina coating that was fabricated by flame spraying (FS) to provide electrical insulation. Techno-economic assessment of fabrication and utilization of the coating-based heaters was conducted. It was found that cold-sprayed heater coatings exhibit improved performance compared to other thermally sprayed heater coatings and conventional heater cables. Further, their fabrication and utilization were more economically feasible. The results suggest that the new generations of coating-based heating systems may be competitive with conventional heat tracers that are widely used in industry.

This contribution gives an overview concerning basic principles of cold spraying (CS) and current trends in respective applications. As powder spray technique dealing with solid impacts, cold spraying results in coatings of high purity and unique properties, not attainable by other spray methods. Particularly within the last two decades, cold spraying developed from laboratory scale to a reliable industrial process. The presentation summarizes current models and key parameters in order to achieve and to improve bonding and coating qualities, and gives examples for applications in electronics, mechanical part repair and additive manufacturing.

This paper presents a study on Cu-Ag-Zn abradable seal coatings prepared by cold spraying. The micro-morphologies of the coatings were analyzed using scanning electron microscopy and electron dispersion scanning. The hardness of the coatings was analyzed. Thermal shock tests were conducted to evaluate the combination strength between the coating and the substrate. The friction and wear properties of the coatings were also tested. Two methods, annealing the coatings in vacuum and heating the feed powders in cold spraying, were tried to improve the combination strength and quality of the coating. The results showed that Cu-Ag-Zn coatings made by cold spraying with powder heating exhibited better combination strength and anti-friction properties compared to coatings annealed in vacuum and the original samples. The paper also proposed a combination mechanism for the Cu-Ag-Zn coatings.

This paper deals with some of the latest developments and serial production applications at OBZ innovation GMBH. With three serial production cold gas systems and one for the R&D department, obz innovation gmbh is the leading supplier of cold sprayed coatings. The development of the well-known serial production process of a sinusoidal copper coating for hybrid cars is explained. Furthermore our ferritic chromium steel induction coating and our newly developed product, an immanent temperature limiting function for safety critical reasons, will be addressed. As an example for a current field of research currently examined at obz within a public funded project will be discussed insulating ceramics for power electronics with cold sprayed circuit paths for a potential use in fields like automotive and others. Last but not least, the latest product, “obz fingerprint” and “obz sensor” coatings that can be used against plagiarism and as a sensory element are presented for the first time.

Fast streaming fluid media causes cavitation-erosion in pumps, ship-propellers and rudders. To avoid severe damage, materials with high resistance against plastic deformation and a high fatigue strength should be used. Bronzes fulfill these criteria, but as-cast bulk parts are rather costly. A promising alternative is cold-spray deposition of dense and oxide-free coatings onto exposed surfaces. To achieve high quality bronze coatings by cold-spraying, parameter optimization has to tackle the high hardness of the feedstock powder materials. Additionally, practical limits due to nozzle clogging have to be considered, which may occur at gas temperatures above 700 °C. The present study investigates possible solutions by systematic process parameter and feedstock material optimization, including variation of bronze compositions. Thus, dense coating microstructures and - in consequence - high hardness and good cavitation resistance were obtained. Cold-spray coatings reach up to 8 times better cavitation resistance as compared to conventional ship-building steel (GL-A).

In the last years, results of many studies have been published contributing to enhance the understanding of the fundamental mechanisms of cold spray coating generation and bonding, as well as coating characteristics. From the point of view of a job shop in thermal spraying and a user of cold spraying equipment, the procedure in development of new applications is presented. Besides the technical requirements, some general factors determining the success of industrial use of cold spraying are shown. Examples of cold sprayed coatings are described to show on one hand the possibility of a fast integration of this new technique in established coating jobs and on the other hand the exploration and use of the new possibilities of cold spraying and the development of applications, which still have not been in the focus of thermal spraying. Suggestions to further research and development activities are made on the base of practical cold spray experience.

The critical velocity of copper powder for particle deposition in cold spraying was estimated both experimentally and theoretically. The dependency of the critical velocity on particle temperature was examined. The theoretical relationship between deposition efficiency and critical velocity at different spray angles was utilized to estimate the critical velocity experimentally. The numerical simulation of particle impact deformation was utilized to estimate the critical velocity theoretically. The estimation was performed for Cu particle under different particle temperatures. The experimental deposition was conducted using Cu particles of different temperatures under different spray angles to reveal the evidence of the dependency of the critical velocity on particle temperature. The theoretical estimation was based on the critical velocity corresponds to the particle velocity at which the impact begins to cause the adiabatic shear instability. It is found that the critical velocity is significantly influenced by particle temperature besides the type of material. The critical velocity of particle decreased with the increase in particle temperature, which is attributed to the thermal softening effect at elevated temperatures.

In Cold Spraying, bonding occurs when the impact velocities of particles exceed a critical value. This critical velocity depends not only on the type of spray material, but also on the powder quality, particle size and the particle impact temperature. For metallic materials, the critical velocity is in the range of 200 – 1200 m/s. In analogy with explosive welding, bonding in Cold Spraying is associated with adiabatic shear instabilities caused by high strain rate deformation during impact. Numerical and experimental methods are developed to investigate the influence of impact conditions and related phenomena on the coating quality. For a deeper understanding of impact phenomena and coating formation, the particle impact was modelled by using the finite element software ABAQUS/Explicit. The numerical analyses indicate shear instabilities localized to the particle surfaces, and thus provide a basis for the calculation of critical velocity in terms of materials properties and process parameters. In addition, modelling is used to obtain information about the effect of process parameters on the bonding quality. For most materials, high-strain-rate data are not available. For a quantitative analysis, therefore, the respective materials behaviour was investigated through individual spraying experiments, which were complemented by additional relevant experiments such as impact tests or explosive powder compaction. In this way, impact dynamics, bonding mechanism and critical velocities could be linked. This type of analysis was proved as a powerful tool to reduce the number of experiments for the optimisation of coating quality in Cold Spraying and also to provide a broader overview of the process.

Various metals such as aluminum, copper, zinc, steel, nickel, titanium, and niobium have been deposited on a wide range of substrate materials via cold spraying. This paper provides a detailed overview of the cold spray process and the coatings typically produced. It discusses the powders and gases used, the dynamics of gas-particle flow in spray nozzles, the effect of temperature and pressure, and the concept of critical velocity. It also presents examples of the properties and microstructures recently achieved in cold sprayed aluminum, zinc, NiCr, MCrAlY, and Cu-Al coatings. Paper includes a German-language abstract.

This paper provides an overview of the equipment used in cold gas spraying. It discusses the general design and operation of key components, including the nozzle, the control system, the gas heater, and powder feeder. It also describes a typical gas supply system, the recycling of helium, and the provisions for health and safety that are necessary in a spray booth. Paper includes a German-language abstract.

A number of studies have been conducted over the past few years with the aim of modeling high-speed particle-substrate interactions during cold spraying. This paper summarizes the work conducted and some of the more important findings. Based on experimental measurements and dynamic deformation modeling, it is shown a radial jet of metal forms at the contact zone during cold spraying. The effect is similar to that observed in explosive welding and it leads to corona-shaped ejection of metal at the periphery of the contact zone. Paper includes a German-language abstract.