In the cold spray additive manufacturing (CSAM) process, layer-by-layer stacking is a good method to achieve coating AM. Different from AM processes such as selective laser cladding, which can quickly realize trajectory planning based on commercial software, the spraying trajectory of the CSAM process cannot be created easily due to the “one-stroke” character. The spray path cannot be intersected and the coating deposition cannot be interrupted during the spraying process. What’s more, the spray gun or the workpiece held by the robot usually needs to be deflected by a certain angle to compensate the coating edges. An accurate and efficient spraying trajectory for a given workpiece is the most basic and important part in CSAM process. This article proposes a novel parametric layered slicing algorithm for STL files and an optimized rapidly exploring random tree (RRT) algorithm, so as to generate spraying trajectory accurately and quickly, especially for a part with multiple features. The simulation results revealed that the algorithms can efficiently generate the corresponding spraying trajectory for CSAM.

Applications in thermal and kinetic spraying increasingly aim for coating of parts with complex geometries. So far, respective robot programming for the required path during deposition is usually adjusted individually in time-consuming procedures. Thus, it is essential to develop methods that allow a fast adaptation to part geometries and production conditions as well as possible quality control. To tackle these problems, this work addresses novel strategies for robot programming and post-spray analyses. The design of the method and workflow follows routes of smart manufacturing and should enable fast and accurate implementation into spray procedures. Here, the developed application can handle complex parts of arbitrary geometry in the form of CAD files. Supported features include (i) cutting the objects according to the object boundary, (ii) creating self-intersecting curves, (iii) generating a set of index-sequence-based spatial discrete points and (iv) reordering the discrete points to generate adaptive paths. Robot offline programming allows for process simulation, analysis and optimization of the robot kinematics. By optical scanning profilometry, the layer-by-layer deposit build-up could be monitored for quality control, as well as for the determination of the final overall coating thickness. The entire procedure was tested by cold spraying onto a complex workpiece, validating the capability of the proposed strategy. Based on the universal layout of the applied methods, the strategies can also be applied for thermal spraying in general, considering individual boundary conditions. With respect to cold spraying, the implementation framework of this study provides a good basis for part repair and additive manufacturing.

Cold Spray is a solid-state Additive Manufacturing process of 3D near-net-shape parts which requires the implementation of a good spraying strategy and the choice of the right operating parameters. This paper is the result of empirical studies on the determination of the optimal processing conditions (spraying and kinematics) for the Cold Spray Additive Manufacturing (CSAM) of pure aluminum powder using a stable layers building strategy. Vertical 3D deposits (thick walls) with a height and thickness of 13-100 mm and 5-11 mm, respectively, were obtained through a series of tests that consider an effect of some kinematic parameters. The visual analysis of the deposits shows that the nozzle traverse speed as well as middle/edge pass number ratio constitute the two most influential parameters on the final shape of the deposits (flatness and straightness). All these results prove the potential of the Cold Spray Additive Manufacturing (CSAM) process as fast 3D additive method using micron sized powders, and particularly for Al powder.

In this work, a novel HVOAF process fueled with ethanol was employed to prepare NiCoCrAlYTa coatings on AISI 304 stainless steel substrate. To be able to add compressed air into the torch, it was designed to add a second-stage combustion chamber. Thereafter, investigations were carried out to determine the influence of different compressed air flow rates on the evolution of the microstructure and properties of the resulting NiCoCrAlYTa coatings. The phase composition, microstructure, porosity, microhardness, bond strength and wear resistance of the as-sprayed coatings have been studied in detail. The results reveal that the compressed air flow rate has a substantial effect on the coating's microstructure. The addition of compressed air also contributes to reduce the degree of oxidation of the coating, which could be attributable to a decrease in the temperature of the flying particles and an increase in their velocity. Although the use of compressed air diminishes the coating's bonding strength, it still has some elevated strength. Furthermore, the injection of compressed air improves the coating's sliding wear resistance dramatically. SEM and EDS were used to investigate the sliding wear mechanism of the coating. Detailed correlation between the compressed air flow rates and the coating properties are elaborated to identify the coatings exhibiting optimum performances.

Cold spray process was chosen as a good candidate for dimensional restoration and protection of components. Commercially pure aluminum, aluminum-alloy or titanium were recommended for different applications. This paper investigates laser surface texturing association to enhance durability of sprayed coatings. Laser is easy automated, localized and reliable process. It was applied for prior-surface treatment. Textured surfaces were produced and compared to conventional treatments, such as grit-blasting, in terms of deposition efficiency and adhesion bond strength. Patterns promoted direct particle embedment. Particle-substrate interface exhibited significant temperature rate and strain in cavities. Intimate contacts and particle compressive states were assumed responsible for improvement. The particle deformation and bonding behaviors were evaluated and discussed for the different configurations. Thus, window of deposition was increased with laser surface texturing. Anchoring mechanisms increased two fold the adhesion strength compared to conventional pre-treatments. In one case, the interface was stronger than the coating cohesive strength.

In cold spraying, oxide-free interface is an important factor for fresh metal bonding between particles and substrate, which determines the bonding strength and final coating quality. In this study, a well-designed experiment was performed to examine the deformation behaviour of the oxide film on copper alloy particle surface after deposition. The experiment results show that partial oxide film could be disrupted during the high-speed impact. However, most of the oxide films were found to remain intact after particle deposition, which limited the exposure of oxide free interface. The presence of oxide film at the interfaces between deposited particles and substrate seriously affected the metallurgical bonding. Besides, substrate material is found to have a strong influence on the deformation behaviour and final state of the oxide film. The study also demonstrated that the bonding mode between deposited particle and substrate strongly depends on the type of substrate.

ZnO films were deposited by solution precursor plasma spray (SPPS) process with different substrate preheating temperatures and torch powers, which were used to study the effects on crystallizations and microstructures. With increasing substrate preheating temperature from 0 °C to 400 °C, ZnO films were always preferential orientation along (002) plane with much higher crystallinity. And more apparent crystallized particles appeared with higher agglomeration degree forming cauliflower-like microstructure under higher preheating temperature. For adjusting hydrogen flow rate, the moderate hydrogen flow rate was the suitable condition for obtaining oriented growth along (002). Besides, all ZnO films under different hydrogen flow rates with a constant preheating temperature as 400 °C were always combined with crystallized particles. Moreover, the increment of torch power makes microstructure becomes denser with less interspace between neighbouring particles. Moreover, it is found that crystallinity and crystallized particles is more dependent on preheating temperature and torch power plays a more important role on densification by two staggered experiments. Taking applications of metal oxides films via SPPS into consideration, choosing moderate substrate preheating temperature and hydrogen flow rate will obtain crystallized particles, unusual preferentially oriented planes and high specific surface area, which is very favourable for optical, electrical, electrochemical properties.

An innovative hybrid process which combines the two very effective solid-state techniques of cold spraying (CS) and friction stir processing (FSP), was proposed to fabricate a high-strength ultrafine-grained Cu-Zn coating. Results show that the CS coating had an elongated microstructure with 78.42% of low-angle grain boundaries. Following FSP, there appear ultrafine grains with 90.47% of high-angle grain boundaries and a composition of α, β' and γ phases while the CS coatings was mainly α. Significant mechanical properties enhancement is achieved, i.e. with the ultimate tensile strength increasing from 87.2 MPa to 257.5 MPa and fracture elongation increasing from 0.17% to 0.81%. The precipitates have a significant effect on the fracture behavior of FSP coatings.

Commercial available Ni and Ti powder were blended together and deposited on stainless steel by atmospheric plasma spray(APS). Subsequently the as-sprayed coatings were laser remelted with a Nd -YAG pulsed laser source. Cross-sections of as-sprayed and laser-remelted coatings were characterized by scanning electron microscopy (SEM). Prior to SEM observations, the laser remelted coatings were polished and etched by Kroll etchant. Meanwhile, the energy dispersive spectrometer (EDS) was employed to analyze the chemical distribution of the coating both as-sprayed and laser remelted. The results indicated that APS sprayed NiTi coatings presented a dense microstructure with Ni splats and Ti splats distributing uniformly. Oxygen partial pressure in the argon leads to the burning of Ti splats during the laser remelting process. And Ti oxides located at the bottom of the laser molten pool because of the laser stiffness and molten flow. Moreover, the top part of the molten pool mainly involved in Ni columnar grains.

NiCrBSi is a material generally used in wear-resistant coatings. In order to improve the tribological properties of atmospheric plasma-sprayed NiCrBSi coatings, Molybdenum (Mo) was incorporated into the NiCrBSi coatings to reduce the friction coefficient and wear rate under dry and oil-lubricated conditions. In this paper, Mo-NiCrBSi composite coatings with Mo content of 5, 10, 20 and 30 wt.% were deposited on stainless steel substrates respectively by atmospheric plasma spray. X-ray diffraction, optical microscopy and scanning electron microscopy equipped with energy dispersive spectroscopy were utilized to investigate the phase structure and surface morphology of the composite coatings. Reciprocating friction tests were conducted to measure the friction coefficients and 3D optical microscopy was used to depict the wear track profiles. The results showed that the 30 wt.% Mo-NiCrBSi coating exhibits the best tribological performance. In addition, MoO 2 and MoS 2 films were formed in the friction process under dry condition and oil-lubricated condition respectively.

Since cold spray is widely considered as an additive manufacturing and damage repair technology, it is crucial to understand the coating build-up process and the temperature evolution. In this work, a 3D numerical model was developed to simulate the transient coating build-up process as well as the heat transfer in cold spray. By coupling the heat transfer with the ALE (Arbitrary Lagrangian–Eulerian) moving mesh and coating thickness model, this 3D model is able to investigate the temperature evolution of a coating which simultaneously grows according to the nozzle trajectory. The nozzle trajectory that represents the heat source and mass flux of particle impact is generated and simulated in the offline programming software RobotStudio. By assigning the results of coating thickness distribution, the simultaneous build-up of coating computational domain is achieved by ALE moving mesh method. The validation of the FEA (finite element analysis) model was carried out by measuring the coating surface temperature via an infrared imaging camera. With the proposed model, it is able to study the actual coating build-up process as well as the heat transfer phenomena, which may provide more insights for the application in additive manufacturing and damage repair.

In this study, YSZ coatings were deposited on different substrate materials (stainless steel and aluminum) using suspension plasma spray (SPS) technique. The effects of substrate properties (material, surface topology, temperature, and thickness) on the formation of coatings were investigated. The results showed that, with the identical spray parameters, the porosity is higher for the coatings deposited on aluminum than that on stainless steel due to the high thermal transfer ability of the former substrate material. The SEM results revealed that the microstructure of as-prepared coatings could be tailored from the vertical cracked structure to the columnar structure by increasing the substrate surface roughness and their formation mechanisms were discussed. The substrate preheating temperature has an influence on the microstructure of the coatings, especially in the interfacial region and increasing the substrate temperature is an effective means for reducing the interface defects in the coatings. With the increase of the substrate thickness, the quantity of the vertical cracks in the coatings is reduced and their width becomes narrower.

In this study, a numerical model is developed to simulate cold-spray coating profiles based on spray angle, nozzle traverse speed, and scan step. An extension of the model was also developed that predicts coating thickness distributions based on kinematics data obtained using robot trajectory monitoring equipment. Experimental studies were also conducted to validate the numerical models and assess the simulated results.

In this study, cold sprayed Ni is deposited on Al substrates using different gas pressures. Spherical Ni powder was sprayed on cylindrical substrates using argon as the powder carrier and compressed air as the propellant. Coating and splat surfaces and cross-sections were examined, adhesion strength was measured, and particle velocity and temperature were determined through CFD simulations. The results show that denser, more well adhered coatings were obtained under higher propellant pressure. Higher gas pressure increases particle velocity, which intensifies material deformation and the disruption of surface oxides in the impact area, resulting in greater metallurgical bonding between the splats and the substrate. The formation of Ni-Al intermetallic phase at the interface region due to heat treatment was confirmed and its effect on bonding strength is discussed.

Cold Spray is a material deposition process where the effects of substrate roughness on cratering phenomenon are often observed. In order to understand and explain crater formation on cold sprayed coatings, the laser surface texturing technique is used. This innovative process allows to control the substrate surface roughness and to create a controlled topography. In this study, five hole sizes from 20 to 100 μm diameters with an angle of 45° were drilled to obtain different working craters. Subsequent, build up of the coating was investigated. Aluminum powder and nitrogen were used for this study. The main gas temperature and pressure were respectively 500°C and 3MPa. The morphology and the microstructure of aluminum coatings were characterized by optical microscopy and scanning electron microscopy. Surface improperly filled crater affects bond strength. The objective is to determine the effect of surface morphology on craterisation weakening the bond strength. The erosion velocity creates locally a hydrodynamic penetration leading to strong erosion.

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.

ZnO nanostructured coatings have been prepared on Al 2 O 3 substrates fitted with Au electrodes on one side and a Pt heater on the other, forming a solid-state gas sensor. The coatings were deposited by solution precursor plasma spraying (SPPS) using aqueous zinc acetate as the precursor solution. FE-SEM images show that the coatings are nanostructured with grain sizes of 50-100 nm. Surface morphology and grain size were found to be influenced by the flow rate of H 2 in the plasma forming gas. The gas sensing function was characterized by measuring the electrical resistance of the coating in the presence of NO 2 gas, showing good sensitivity down to the sub-ppm range.

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.

To improve the mechanical properties of aluminum coatings, ceramic reinforcement may be added resulting in an aluminum matrix composite. Two processing routes were investigated to manufacture aluminum matrix composite powders for thermal spraying: ball milling and mixing. Three sizes of SiC reinforcement particles were used: 2, 15, and 25 µm. For the ball-milled powders, morphology and microstructure were investigated as a function of SiC grain size and milling time. It is shown that the hardness of the composite and the efficiency of the spray process depend on the size of the hard particles as well as the preparation method. Friction tests were also carried out and the results are shown to correlate with coating microstructure.

In this investigation, high carbon steel wire is deposited on aluminum cylinder bores with different surface profiles by plasma transferred wire arc (PTWA) spraying. The first part of the study deals with feedstock materials, process parameters, droplet formation, and splat morphology. The second part deals with bead profiles, build rates, and the influence of substrate composition, temperature, and surface profile on coating characteristics including microstructure, morphology, composition, and bond strength.