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.

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.

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, 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.

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.

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.

This work focuses on the properties of Cu-Ag alloys deposited by cold spraying. Helium was used as the carrier gas, accelerating particles to 823 m/sec, which is in the middle of the deposition window for Cu alloys. To avoid oxygen contamination, the gun was placed in a helium-filled chamber and a closed-loop circulating system was used to minimize helium loss. Deposition parameters were varied during spraying and their effect on hardness, tensile properties, residual stress, and porosity was assessed in as-sprayed and heat-treated samples. Ultimate tensile strengths of 450 MPa and yield strengths of about 420 MPa were obtained for the as-sprayed samples and it was shown that strength and ductility can be tailored by heat treating, reaching elongation values higher than 45%. An increase in deposition rate from 55 to 142 g/min was also achieved without a significant decrease in mechanical properties.

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.

The quality of thermally sprayed coatings depends on a lot of parameters (spraying power, feedstock injection, morphology of the parts, kinetics and environment). But among them, adherence between the coating and the substrate appears as the fundamental point. To favor a good interaction and also a good adherence between the coating and the substrate, it is often necessary to clean and prepare the substrate surface. Conventionally, solvents and sand-blasting are applied to remove the contaminants and increase the surface roughness for a mechanical anchorage. But according to the substrate nature (ceramic) or the substrate morphology, it can be prejudicial to apply a mechanical treatment due to a peeling of the surface or a decrease of the global properties. By this way some other treatments have to be investigated in order to obtain an appropriate preparation. From all of them (water jet, ice blasting, heating treatment, etc.), laser ablation can be an interesting technology to prepare the substrate surface. The aim of this work was to study the modifications induced by 10 ns single or cumulative pulses of a Q-switched Nd:YAG near-infrared laser and its influence on the interface adhesion. The case of an alumina coating sprayed on a Ceramic Matrix Composite (CMC) has been studied. In these conditions, the laser treatment seems favorable from the adherence point of view according to the mechanical effect (induced by a cone-like structure) and the chemical effect

Cu coatings were obtained by the VLPPS (Very Low Pressure Plasma Spray) process using a torch F4-VB. The tank pressure was varied from 1 mbar to 5 mbar: these specific conditions can allow obtaining a higher vapor condensation fraction in the coating. Different sizes of powders are used to compare the vaporization level. The other possible influencing factors for obtaining compact film-like coating are also considered such as the distance between the torch and substrate, the orientation of the vapors and also the substrate temperatures. Microstructures of coatings are analyzed and combined with the results of plasma diagnostics. Jobin-Yvon spectrometer (type TRIAX190, UK) and Plasus Specline Spectroscopy software are both used for detecting and analyzing plasma spectrum data. The value of plasma electronic excited temperature Te was calculated through choosing Hα and Hβ two atom spectra. The results showed that the plasma belongs to cold plasma in the local thermodynamic equilibrium situation in VLPPS.

A certain level of porosity is always presented in thermal spray ceramic coatings. LPPS or some specific APS processes can allow to reduce it but it is difficult to obtain coatings with a low thickness (less than 100 m) which are fully gas-tight because of cracks or interconnected pores. This gas-tight property is for example very suitable for the ceramic electrolyte of solid oxide fuel cells (SOFC). Some ZrO 2 -Y 2 O 3 coatings were obtained by the VLPPS process, a LPPS system operating at a pressure of about 100 Pa. The specific structure of these coatings is a mixture of condensed vapors and splats. The results are very satisfying because ZrO 2 -Y 2 O 3 coatings with a thickness of about 70 micrometers are tight under a hydrogen pressure of 2x105 Pa. This paper presents some ZrO 2 -Y 2 O 3 coatings obtained by different processes (APS, LPPS and VLPPS) and their properties.

The use of helium with the cold spray process is well-known to give a higher velocity to the particles and thus denser coatings than those obtained with the classical use of nitrogen. The LERMPS-UTBM laboratory has developed a unique system to use helium without losses. The spray process occurs in a LPPS tank and a specific closed circuit including the cooling and filtering of helium allows its circulation. The spray operations can be made at low helium pressure with no pollution by oxygen. The control device allows to work with different pressures and gas temperatures at the torch with the same tank pressure. Helium gas flow can reach 180 Nm 3 /h and current cold spray torches could be used. The circulation and reuse of helium in a closed circuit result in a very low consumption of helium. The first coatings of copper alloys are presented in this work.

Thermal spraying is a widely used technology in a range of industrial applications to provide coatings improving the surface characteristics. According to the thermal and kinetic specificities of processes (APS, VPS, flame, electric arc), any kind of material can be sprayed. Among materials, ceramic coatings present several interesting aspects for wear resistance, corrosion protection as well as for thermal or electrical insulation; particularly alumina coatings which appear as the most commonly used. Many techniques can be used to spray such kind of materials. From all of them, atmospheric plasma spraying (APS) is a rather well-established process but some other processes can also be used with a lower economical impact as the flame technology. The aim of this study was to analyse the alumina coating properties according to the technology employed such as atmospheric plasma spraying or wire flame spraying using the Rokide and the Master Jet guns. After usual micrographic analyses by SEM, physical and mechanical properties were measured considering the thermal conductivity and the hardness.

In the present paper, both CFD computations and experiments were carried out in order to quantify thermal fluxes from an impinging HVOF jet. The case of a CDS gun fed by natural gas is considered. Standoff distances ranging from 50 mm up to 300 mm were investigated. The CFD model implements a 2-layer extension to the Chen-Kim k-? turbulence model for a better quantification of thermal exchanges with the front body surface. Experiments were performed using two different methods. The first device incorporates two square calorimeters positioned side by side. It was elaborated in order to attempt defining the radial profile of the transferred thermal flux. Additionally, an infrared thermal camera was used to measure the front part surface temperature.

The knowledge of thermal fluxes transferred from impinging high temperature jets is always important. For example, during thermal spray applications, the impinging jet acts directly on the transient surface temperature of the substrate. For preheating applications, it acts on the time required to reach the required surface temperature. It is also important to estimate it for some other applications like thermal cycling tests of parts for example. In the present paper, both CFD computations and experiments were carried out in order to quantify thermal fluxes from an impinging HVOF jet. The case of a CDS gun fueled by natural gas was considered. Stand-off distances ranging from 50 mm up to 300 mm were investigated. The model incorporates a 2-layer extension to k-å models for a better estimation of thermal exchanges through the viscous layer on the front body surface. The experiments were performed using a system incorporating two square calorimeters positioned one beside the other in order to attempt defining a radial profile. Abstract only; no full-text paper available.

The aim of this study was to investigate potential weight savings using multi-layer blade containment systems for turboengines. The association of an external ductile layer with an internal hard layer could provide a good ductility of the armor with the capability to withstand the perforation of high kinetic projectiles. Comparisons between several thick deposits obtained by the vacuum plasma spray process were performed using a Charpy impact testing machine. Mechanical and structural characterisations of these two-layer structures were performed and compared to the behavior of monolithic ones. Heat treatment effects were also considered.

The aim of this work was to determine the behavior of multi-layered structures under high heat fluxes. A direct simulation by the implicit finite difference method was used to predict the transient temperature distribution in each layer of the multimaterial. The influence of the thickness of layers was also studied. Experimentally, high heat fluxes were produced using a HVOF gun operated with a methane-oxygen mixture and internally cooled samples. Multi-layered deposits were vacuum plasma sprayed onto a copper block containing coolant channels for a circulation of water. Transient and static tests were performed with heat fluxes up to 100 MW/m 2 and durations of a few minutes to several hours.

Pure copper thick deposits were vacuum plasma sprayed in such a way that several porosity levels were obtained. Mechanical compressive tests permitted to assess the mechanical behavior of these materials and to study the associated pore microstructural changes. A linear porosity level decrease was observed during the first stages of the compressive squeezing, until the stress reached a specific value corresponding to a transition between pore contraction and copper splats deformation. Stereological measurements showed that the pore squeezing was isotropic.

The integration of thermocouples into thermal spray deposits and especially into vacuum thermal spray coatings could provide temperature monitoring between the substrate and the coating or between two different coatings during the spray process and later during post treatments and service life. Thermocouples of 251µm in diameter were made using Chromel and Alumel wires. Electrical insulation was obtained using a ceramic cement. Astroloy and Copper coatings were successfully sprayed over these sensors and the temperature given by an embedded thermocouple was compared to the response of an infrared pyrometer during the spraying process.