Cold spray (CS) is a progressive method for the deposition of metals and alloys whose principles involve considerable plastic deformation of the produced material at extreme strain rates. Positron annihilation spectroscopy (PAS) is an analytical technique capable of studying deformation on the atomic scale level, even in extremely deformed materials. In our study, the PAS method was used to characterize the deformation character at the lattice level and quantify the open-volume defects in four cold sprayed metals: Al, Cu, Ni, and Ti. As counterparts, bulk samples of these materials with ultrafine-grained structures were also produced by high-pressure torsion (HPT), a process exceeding cold spray in the total deformation, but having several orders of magnitude smaller strain rates, and by a traditional cold rolling process. The results show that the CS and HPT processes lead to the formation of similar lattice defects (dislocations and vacancy clusters), and both exhibit significantly higher dislocation densities than conventionally cold-rolled materials. Further, the vacancy clusters present in CS and HPT materials were not present in the rolled counterparts due to the lower vacancy production rate.

This study investigates the static friction properties of HVOF-sprayed Cr 3 C 2 -NiCr coatings. Measurements of the static coefficient of friction (CoF) of as-sprayed coatings show their potential for use in frictionally engaged joints. The form, orientation, and geometric characteristics of Cr 3 C 2 -NiCr friction surfaces are assessed as well and slipping curves are determined. The results show a standard deviation in the static CoF depending on nominal contact pressure, but it is not yet possible to establish a correlation with coating properties such as carbide grain size and geometrical parameters such as coating roughness.

This paper presents the results of a study on the static friction properties of (Ti,Mo)(C,N)-Ni hardmetal coatings deposited by HVOF spraying. Coating samples were sprayed on quenched and tempered CrMo steel friction rings using an experimental feedstock powder. Friction surfaces were characterized based on the geometry and distribution of prominent peaks and static coefficient of friction was measured. Test results show that the hardmetal coatings have good potential for use in frictionally engaged joints, but more work is needed to establish a correlation between coating properties and friction behavior.

Fracture strength of a WC-12Co thermal sprayed coating is investigated experimentally and analytically. In the experiments, a pair of coated butt cylindrical specimens is subjected to combined tension with torsion stresses. Stress distributions in the coating at critical loading conditions are analyzed by using FEM analysis and the fracture criterion of the coating is investigated. It is found that normal stress distributions are common to all cases of testing stress conditions and so fracture condition of the brittle coating is represented as K ≧ Kcr in the normal stress distribution even under mixed deformation mode I and III. By using the experimental method presented in this paper and the corresponding FEM analysis, an approximation for the critical bonding strength of a coating under shearing load can be estimated.

Cold spray additive manufacturing technology (CSAM) is a progressive method of 3D print of metals and alloys. Its inherent work principles allow production of the components below the material melting points, thereby avoiding several undesired material degradation processes. Among other inherently associated phenomena, the work principles of CSAM involve extreme plastic deformation of the materials, triggering formation of several types of lattice defects. Positron annihilation spectroscopy (PAS) is an analytical technique capable of studying deformation on the atomic scale level, even in extremely deformed materials. In our study, the first historical analysis of CSAM materials by PAS was carried out. For the demonstration, four different base metals were selected (Al, Cu, Ni, Ti). For these, the character of dislocations and vacancies was observed and the respective densities were quantified. The results show that the extremely high strain rate in the cold spray process prevents recovery of vacancies by diffusion to sinks. The deformation-induced vacancies agglomerate into small vacancy clusters. Hence, metals deposited using CSAM contain not only dislocations but also vacancy clusters. Both kinds of defects were detected by positron annihilation spectroscopy.

Copper particles with median diameter 15.2 micrometres were cold sprayed onto a polished aluminium 1139 substrate. Under the spray conditions used, deep embedment of the copper particles occurred. The as-sprayed copper particles were dissected using a focussed ion beam (FIB), and their microstructure investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At the crater wall an intense shear zone developed due to sliding of copper past aluminium. Evidence of melting is presented.

The application of cold spray (CS) for additive manufacturing (CSAM) of structural components using metallic materials has recently attracted much attention. However, there are limited reports on developing thick deposits or components with high entropy alloys (HEAs) via CSAM and investigating the microstructural evolution and mechanical properties after deposition and subsequent annealing heat-treatment. This work investigated the microstructure and mechanical properties of asdeposited and heat-treated thick CoCrFeNiMn HEA deposit fabricated via CSAM. The microstructure of the HEA deposit and after heat-treatment were characterised using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), and x-ray diffraction (XRD). The microstructural analysis reveals heterogeneous grain size distribution with ultrafine grains at the particle-particle interfacial regions and coarse grains at the particle interiors in the as-deposited sample. The as-deposited sample, characterised by moderate porosity, was consolidated following the heat treatment at different temperatures. Additionally, increasing the temperature increases grain sizes resulting from static recovery and recrystallisation, with annealing twin formed at higher temperatures. Most notably, phase decomposition of the deposit microstructure occurs at 600 ºC, with Cr-rich phase particles formed at regions of high dislocations and grain boundaries. Nano-and micro-hardness and tensile testing of micro-flat dogbones samples were performed on the as-deposited and heattreated samples. The effect of heat-treatment on the microstructure and mechanical properties of the cold-sprayed HEA deposit were analysed and discussed.

Babbitt is used at tribology applications according to its low friction coefficient. Thermal spraying and pouring are widely used production processes of Babbitted parts. Comparative analysis of structure and wear properties of Babbitt layers produced by these technologies was done. Examples of typical arc sprayed Babbitted part's applications which were done at Mashprom are represented.

Cold gas dynamic spraying has shown to be a promising approach for fabricating titanium structures directly from powder in the absence of a controlled atmosphere. This study investigates the effect of annealing on the microstructure, hardness, and tensile properties of commercial purity titanium deposited under cold spray conditions. Equiaxed grains with ultrafine grain structure are observed in the annealed samples. A physical based model is proposed for recrystallization of cold-sprayed titanium deposits and the results are compared with conventional cold-rolled and annealed titanium products.

Babbitt surfacing is used in tribological applications because of its low friction coefficient. Thermal spray surfacing and pouring are two widely used production processes for Babbitted parts. This paper presents a comparative analysis of structures and friction properties of Sn-Sb-Cu Babbitt layers produced by these techniques. The sprayed Babbitt coatings were produced by arc spraying of 1.6 and 3 mm diameter wire.

Atmospheric Rheo-Spraying (ARS) using the HVOF process enables injection-molded structures and thick-film coatings from steels and from high-temperature Ni-based alloys with layer thicknesses down to the centimeter. The ARS process control is based on the thermal spraying of particles in the solid state at a maximum average speed of more than 600 m/s. The coating consolidation to porosity values below 1% occurs through the particle impact with high kinetic energy. Because of the low particle oxidation, the mechanical properties of the heat-treated injection-molded structures are comparable to those of forged alloys. In this paper, ARS injection molding is successfully implemented in combination with an innovative manufacturing technique in rocket engine technology to produce a model composite combustion chamber with a thermally sprayed internal pressure jacket. Paper includes a German-language abstract.

In this work, amorphous Zr-based bulk metallic glass deposit was manufactured by cold spray. The bonding mechanism of metallic glass particles was systematically investigated through studying the deformation behavior of individual particles after deposition or rebound. We revealed two collective particle bonding mechanisms that contributed to the formation of metallic glass deposit, i.e., high-velocity impact induced localized metallurgical bonding at the fringe of interface, and high gas-temperature induced partial melting of particles and resultant annular metallurgical bonding band. Moreover, the dynamic evolution mechanism of amorphous phase into nanocrystal structures at severely deformed interfacial regions during cold spray was carefully investigated. For the first time, we observed different amorphous/nanocrystal structures in cold sprayed metallic glass particles, which can represent different evolution stages in nanocrystallization process. Based on the observation, it is inferred that the nanocrystallization process can be divided into following three stages: composition segregation, the formation of ordered 1D and 2D transition structures, and 3D nanocrystals. The current study provides new insights into bonding mechanisms and the mechanistic nanocrystallization origins in cold sprayed metallic glass.

Cold spraying is a promising process for fabricating functional coatings. Because of the solid-state particle deposition, the electrical and chemical properties of the coatings are similar to those of the bulk materials. Mechanical properties, on the other hand, differ from those of bulk materials due to severe plastic deformation of the particles. Residual stress may thus be an important variable to track during cold spraying although the formation mechanism is not entirely clear. In this study, the residual stress of metallic (copper) and ceramic (titania) coatings is measured during the cold spray process. The results are presented and discussed.

Surface treatment has become an effective method to improve corrosion resistance of magnesium alloys which are the lightest commercial structural alloys with superior specific strength and stiffness. Low pressure cold spraying is used to locally deposit aluminium on AZ31 in order to enhance general and galvanic corrosion of magnesium. This study is aimed at numerical estimation of the residual stress profile due to cold spray coating using FEM. The impact of particles on the substrate is modelled in Abaqus Explicit. The challenge of AZ31 simulations is the intrinsic yield asymmetry and anisotropy which results different behaviour of the material along different direction both in tension and compression. On the other hand, there is no precise material model capable of considering the yield asymmetry and anisotropy experienced by AZ31 in Abaqus. This paper studies the effect of anisotropy of the AZ31 on residual stress induced by cold spray. The results are compared with experimental X-Ray diffraction measurements. It is suggested that an isotropic analysis in the dominant stress direction of AZ31 may result in good estimation of the residual stress profile.

As an emerging additive manufacturing method, cold spray additive manufacturing (CSAM) has attracted more and more researchers’ attention due to its unique advantages. However, only a few researchers have studied the fabrication of complex structural components. Therefore, it is important to develop a general CSAM framework that is suitable for the fabrication of different shapes of workpieces. In particular, the choice for the optimal kinematic spraying parameters, the prediction of deposit evolution and the planning of spraying trajectory are the most basic and crucial. Different sub-modules are integrated in the proposed framework to solve these problems. In detail, the modeling methodology is used to obtain the optimal kinematic spraying parameters and to predict the deposit evolution in the simulation. Based on the feasible parameters, the trajectory planification methodology is used to generate the spraying trajectory for the workpiece being manufactured, especially the workpiece with complex structure. Finally, the simulation and experimental results of a fabrication for a workpiece with complex structure provide the developed system is reliable and effective. The framework developed in this paper can considered as a general tool for additive manufacturing of with complex structural workpieces in the CSAM.

In order to utilize the blasting process for preparing surfaces of precision products, the factors affecting the work piece distortion and the degree of the distortion were investigated. The long and flat shaped specimens of the different materials and the thickness were blasted, and the phenomena induced by the blasting were investigated. In the result, almost the linear relationship between the surface roughness and the maximum deflection existed. In addition, the equivalent load was applied to the simple model of the distortion, and the correlative expression among the maximum deflection, the specimen's size, and the equivalent load was deduced. The results made it possible to select and design beforehand the products, and to optimize the blasting condition.

Cyclic, mechanical fatigue testing of coated materials has increased with the wider use of thermal spray coatings on components experiencing fatigue loading. Fatigue testing of coated specimens presents all of the difficulties associated with fatigue testing of uncoated specimens and several difficulties that do not arise when testing uncoated specimens. A summary of fatigue test methods and test specimen geometries for both coated and uncoated specimens is presented. Issues of specimen standardization, geometry, substrate preparation, and post-spray surface finishing are discussed. Several specimen configurations are described.

cBN/NiCrAl nanocomposite coating was deposited by cold spraying using mechanically alloyed composite powders. To examine the thermal stability of coating microstructure, the nanocomposite coating was annealed at different temperatures from 750 to 1000°C. The microstructure of composite coatings was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the nanostructure was retained in the coating when the annealing temperature was lower than 825°C which is 0.7 times of the melting point of NiCrAl matrix. The dislocation density significantly reduced when annealing temperature was higher than 750°C. The cBN particle growth became significant when the annealing temperature was higher than 825°C. The effects of crystal grain refinement and work-hardening strengthening mechanisms were quantitatively estimated as the function of annealing temperature. The effect of annealing temperature on the contribution of different strengthening mechanisms to coating hardness was discussed.

The wear resistance of thermal spray coatings mainly depends on coating properties such as the microstructure, hardness, and porosity, as well as on the residual stress in the coating. The residual stress is induced by a variety of influences e.g. temperature gradients, difference of the thermal expansion coefficient of the coating / substrate materials, and the geometry of the components. To investigate the residual stress, the Impulse Excitation Technique was employed to measure the Young’s and shear moduli. The residual stress was determined by using the hole-drilling method and X-ray diffraction. Pin-on-Disc and Pin-on-Tube tests were used to investigate the wear behavior. After the wear tests, the wear volume was measured by means of a 3D-profilometer. The results show that the value of the residual stress can be modified by varying the coating thickness and the substrate geometry. The compressive stress in the HVOF-sprayed WC-Co coatings has a significant positive influence on the wear resistance whereas the tensile stress has a negative effect.

As applications of thermal spray processes are expanding, the importance of computer-aided design systems and computer-aided engineering systems for these processes has been growing. The principal objective of this study is to propose a new analytic method for the prediction of coating thickness and deposition efficiency. This method is called the particle tracing method and is based on the Monte Carlo simulation method. In order to evaluate the validity of this model, several tests were carried out. The same stainless steel 316L layers coated by the HP/HVOF process (TAFA JP-5000) were used throughout each test. First, spray patterns were observed which had formed on flat-plate specimens from various spray gun angles. Coating thickness distributions on several curved planes were consequently investigated. Finally, the coating process for a blade of a compressor in a gas turbine was simulated. In the right of the results of these experiments, it is summarized that the calculated values of the coating thickness obtained by our method are in good agreement with experimental values. The accuracy is within 10% of the maximum thickness value in each specimen, except for at the edge of the work-piece. In conclusion, the particle-tracing method can be applied to the fundamental analytic model in the CAD or CAE system for thermal spray processes.