Aerosol cold spraying (ACS) is modification of low-pressure cold spray technology which allows to deposit ceramic and metal-based coatings. ACS technology in vacuum possesses the formation of films from sub-micro and nanoparticles directly at room temperature. The ACS technology is still under development to cover more application and discover solutions of spraying different kind of powders on different types of material substrate and optimizing spraying conditions to obtain the best results. The main objective of the present work is to develop a new ACS cold spray technology of Hydroxyapatite (HA) and Copper powder deposition onto both the implants and ceramic substrates. The new AD spraying system with radial injection of particles to be deposited is constructed and tried. An influence of technology parameters on the coating structure and properties are presented. In addition, the combined cold spray and sintering technology technique is further investigated for additive manufacturing applications.

Understanding the complex mechanical behavior of stainless steel based composite coatings is important for engineering applications. The focus of this research was on gaining a fundamental understanding of the structure/property relationships that exist during structure formation of the coatings made by new low pressure cold spraying with propellant gas at the temperatures of 800-1000°C (warm spray). While composition is one of the key parameter in determining the final microstructure, the specific warm spray powder shock consolidation parameters (particle velocity and gas temperature) were found to have significant effects on the development of composite structure formation and mechanical properties. Microstructural examination and modeling results revealed that the strain localization mechanism differs from that of adiabatic shear band formation that results in large differences in the ensuing microstructure of the composite coating and its properties.

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.

Due to the demand for improved fuel economy as well as increased safety features, weight reduction is one of the major aims in the automotive industry. Future lightweight automotive components for the next car generation will probably use lots of magnesium alloy. These will form galvanic couples with other materials and may induce phenomena accelerating the corrosion rate of automotive components. The materials used were magnesium alloy AZ31B and several types of cold sprayed coating. The relative performance of each cold sprayed corrosion preventive compounds (CPC) was assessed in combination with the materials under several different electrochemical and accelerated corrosion tests. Baseline data for AZ31B with no CPC applied was also collected. CPC characteristics and properties are also included and discussed. The studies on bare Mg/Steel couples validated accelerated corrosion but found that CPC cold sprayed coatings mitigate corrosion rates. Thus Mg/Fe interfaces with defect-free cold sprayed coatings CPC can prevent buildup of corrosion products and reduce galvanic corrosion of automotive components.

To fully understand particle interactions with both substrate and neighboring particles in cold spray, ultrasound wave generation and ultrasonic monitoring of particle impacts were studied. The multi–channel ultrasonic system works in pulse– echo and passive modes. In pauses between pulse–echo data acquisition frames the system is in the passive mode receiving the signals generated by the particle impacts. The particles being deposited generate the ultrasonic signals in a very wideband frequency range at more than 40 dB signal-to-noise ratio. The particle impact signals are considered as a sum of the background wideband noise and the sparse strong pulses observed when the nozzle passes over the location of the transducer. It was shown that these components of the particle impact signal can be separated by threshold processing. The results of the passive monitoring are confirmed by the ultrasonic pulse–echo and direct measurements of a deposited coating geometry.

Deposition of Metal Matrix Composites (MMC) has been the subject of extensive research in the recent years. The desired functional properties of a composite coating can be achieved by analyzing and controlling the major structural processes taking place during deposition. The latter are reactions at the particle-particle and particle-substrate interfaces which can be controlled by applying advanced spraying technologies. Cold Spray (CS) and Computer Controlled Detonation Spraying (CCDS) are well-proven reliable methods for deposition of composite coating. The energy (thermal and kinetic) imparted to the particles-in-flight by CS and CCDS allows initiating interface reactions that will define distinct properties of the deposited composite layers. The applied spraying technologies are characterized by different ratio of thermal-to-kinetic energy that results in different conditions of the compounds interaction. The objective of the present study is to define the effect of CS and CCDS technologies on structure and properties of Al-Ti-based composite coatings by analyzing intermetallic reactions occurring during the process. It is shown that both CS and CCDS composites present differently sized zones of interfacial reactions.

The study of corrosion protection of magnesium and aluminum becomes increasingly important as the use of these alloys increases rapidly in the automotive and aerospace industries due to their advantages of light-weight, adequate mechanical properties and moderate cost. Corrosion, however, limits the application of magnesium and aluminum alloys. Fasteners, spot welds of dissimilar materials and their galvanic corrosion is of major concern in automotive applications. The paper presents first results of Low Pressure Cold Spray (LPCS) of Al based coatings for corrosion protection. The corrosion protection provided by these coatings was evaluated by electrochemical measurements in 1M NaCl electrolyte. The microstructures and electrochemical behavior of the coated joints were investigated. The electrochemical corrosion mechanisms of the coatings and microstructure were discussed.

To fully understand particle interactions with both substrate and neighboring particles in Cold Spray (CS), ultrasonic monitoring and acoustic emission of particle agglomerate impact were studied. The results obtained show the influence of particle agglomeration density on stress and strain distribution in the particles and at the particle interfaces. The results are compared with metallographic structures of real coatings. The development of monitoring procedure is made using acoustic methods, specifically testing during the actual spray process itself. It is shown that the final thickness as well as the dynamics of buildup can be evaluated. Cross sections of the coating thickness are also easy to obtain and show true profiles of the coating. Comparisons of real thickness and acoustically estimated thickness show a close linear relationship.

The cold gas dynamic spray process offers a unique advantage to form composite coatings by applying powder mixtures. The powder mixture constituents are supposed to interact with each other during impact. In this study, Al and Cu-based powder mixtures are used with the aim to define specific features of the coating formation. Composite coatings with different Al 2 O 3 , SiC, and Ti content are sprayed. Impact behavior of various powder mixtures is analyzed based on scanning electron microscopy images. The Al 2 O 3 and SiC phases of the initial powder are found to be fractured on impact and preserved in the coatings. Another advantage of the kinetic spray process is the ability to mix materials which would normally react with each other and form a composite coating. Some experimental data of such reactions are discussed. Within the composite coating, each constituent changes the initial properties of the sprayed powder material: for example, the soft matrix is strengthened, and hard particles are fractured. The fracture and deformation behavior of the particles and their reactions induced by the impact are determined by micromechanical tests and EDX analysis. Morphology, physical and mechanical properties of the sprayed coatings are discussed.

To fully understand particle interactions with both substrate and neighboring particles, Finite Element Analysis (FEM) of particle agglomeration impact onto substrate was developed. To investigate particle/particle bonding mechanism, two dimensional models for various initial densities of deposited stainless steel particles has been built. In the model the stainless steel powder was deposited onto copper substrate. The results obtained from simulations show the influence of particle agglomeration density on stress and strain state. Both plastic strains, stresses and dynamics of the process has been investigated. The model was verified and compared with metallographic structures of real coatings.

This work assesses the potential of using an ultrasonic probe attached to the back of the substrate to monitor the cold spraying process. While this is only a preliminary study, focusing more on presenting the results than analyzing them, a few conclusions may be drawn. With acoustic sensing, not only can the final value of thickness be estimated, it is also possible to see the dynamics of how the buildup takes place in real time. As shown in the data plots, the buildup process for aluminum-alumina composites is fairly universal across the spray with slower buildup at the outer edges of the coating. More importantly, it is shown that nozzle speed, spray diameter, and thickness estimates fit well with measured values.

In this study, low-pressure cold spraying was used to deposit Al and Al-Al 2 O 3 composite powders on different substrate materials, including steel, aluminum, and magnesium alloy. Corrosion performance was evaluated by electrochemical testing in 1M NaCl electrolyte and microstructure was examined by means of SEM analysis. The results show that the corrosion potential of Al-Al 2 O 3 coatings depends on the content of alumina and that its presence does not appear to accelerate dissolution and failure of passivation oxide films. The investigation also revealed that pure aluminum coatings on aluminum alloy substrates can act as sacrificial anodes, thus providing corrosion protection.

Hydroxyapatite Composite (HAC) Coatings made by Low Pressure Gas Dynamic Spray (LPGDS) on the grit blasted Ti alloy substrate were studied. The powder feedstock for the HAC coating by LPGDS was prepared by mixing HA powder with Phosphate Glass particles in polyvinyl alcohol, drying and stirring. As-sprayed HAC films on the substrate were heat-treated by two steps (400-500°C and 600-900°C) and their physical characteristics were investigated by scanning electronic microscopy (SEM), X-ray diffractometer (XRD). During sintering-heat treatment, HA particles were consolidated and melted to form a dense and homogeneous coating layer which exhibits the grain structure. Application of HA-glass feedstock is found to be effective for Cold Spray HA based coatings.

This paper describes the influence of post-spray heat treatment parameters on mechanical properties of Ni-TiC composite coatings. Thin Ni-TiC composite coatings were produced by low pressure cold gas dynamic process (also referred as cold spray or kinetic spray process) on an Inconel alloy substrate. In the coating process, mechanically mixed micron-sized Ni-TiC powders (~50 µm) were injected into a de-Laval nozzle propelled by a supersonic gas stream to high velocity (>300 m/s) to impinge upon a substrate. The coatings are formed subsequently as the metallic particles are severely deformed plastically and bonded to both the substrate and to one another. However the tensile adhesion strength levels were determined to be in the range of 10-14 MPa. A subsequent post-spray heat treatment in vacuum was found to enhance the bond strength of the coated particles with the substrate due to good metallurgical bonding caused by diffusion mechanism.

The corrosion behavior of Al alloys, produced by cast and powder (Low Pressure Gas Dynamic Spray or Cold Spray) technologies, was examined in 3% sodium chloride solution from the viewpoint of localized corrosion. The susceptibility to localized corrosion is known to be strongly affected by intermetallic phases present in the alloy’s microstructure. The influence of individual cathodic and anodic intermetallic phases was investigated by using a microelectrochemical setup and by electrochemical methods. The optical and scanning electron microscopy data reveal that the cast and powdered alloys experience localized corrosion due to presence of the intermetallic phases which results in the micro-corrosion effects such as exfoliation corrosion, intergranular or crevice corrosion, and most severely pitting. Cast material has lower corrosion properties because of the higher heterogeneity of the structure as compared with powder sprayed composite.

The response of Ni-SiC powders deposited by Gas Dynamic Spraying (GDS) with various particle velocities, and their compaction behavior to the different packing densities were studied in parallel. Bulk compacts (90–99% dense), made in the form of 6 mm diameter by 3 mm thick disks, were analyzed to determine the structural changes occurring within the particles and at the particle boundaries, and to examine their mechanical properties. Optical microscopy and SEM observations revealed the presence of a lamellar morphology and a strong interparticle bonding in the composite coating. An analysis of the experimental data revealed the retention of the nanoscale structure and a localized grain refinement. Adiabatic shear band areas were observed and thought to be responsible for the grain refinement. Powder layers, which were shear compacted to the packing density (up to 90% dense), showed the best densification characteristics. Correspondingly, coatings with enhanced mechanical properties and a strong exchange coupling between hard and soft phases are obtained.

The present study was carried out to evaluate the applicability of the Gas Dynamic Spraying (GDS) of different powder compositions for depositing wear-resistant composite coatings on iron and steel castings. This process, simply known as “cold spray,” utilizes the kinetic energy of particles sprayed at supersonic velocities to produce a bonding of the particles to the substrate. Ni and Cu based coatings containing W, Zn and TiC as reinforcement were made by the low pressure GDS technique and investigated. The coatings microstructures were studied by both optical and scanning electron microscopy. Phase composition, hardness and wear resistance of the GDS coatings were analyzed. The ball-on-disc sliding wear test was used for assessing the wear resistance characteristics of the coatings using a ceramic (Si 3 N 4 ) ball. W and TiC reinforced coatings showed the best wear performance. These were further evaluated in greater detail. In addition to the obtained test results, the application prospects for such GDS coatings were discussed.

Thermal spraying processes are well known in industry for providing relatively dense components. The Gas Dynamic Spray (GDS) technologies are a growing alternative, especially after the great success of certain applications such as plasma and thermal spray formed components. One of the advantages of GDS is the possibility to obtain complex thin-walled shapes of various powder materials and composites. The optional post-spraying processes such as sintering, sizing and little machining may be applied. Using the low pressure radial injection GDS method, some new thin wall components have been formed. The process involves the automatic mechanical removal of sprayed ring components from a mould. Both the structure and properties of powdered material along with the GDS technology itself were studied. The main spraying and mould parameters were found to achieve high durability of moulds, which allowed the realization of a large scale GDS forming technology.

The Radial Injection Gas Dynamic Spray (RIGDS) technology of powder wear resistant coatings deposition is considered. A coating is created by injection of powders with variable composition into the supersonic air jet and deposited on the substrate. Functionally graded coatings with advanced mechanical and corrosion properties were produced and tested. It is shown that operational parameters of supersonic powder-gas jet have a significant influence on the coating’s microstructure, thus defining the high performance of the coating. Compaction and bonding of particles were analyzed. Shear localization features of the GDS process are also discussed.