Cold Spray Process Research Articles

Experimental investigation of WC-12Co cold sprayed: Substrate hardness, bonding mechanism, powder type

Effects of substrate hardness and particle type on a single WC-12Co (Tungsten carbide cobalt) particle's deposition behavior during the cold spray process was investigated in this study. SEM was used to analyze the surface and cross-sections of the deposited particles to determine their morphology. It was discovered that the deposition behavior of WC-12Co particles changed with increasing substrate hardness, going from fully embedding into soft substrate to partially flattening and even rebounding from the hard substrate. Spherical microstructured WC-12Co particles sustained more severe deformation than other types of powder because of the smaller WC size. The porosity value of WC-12Co coatings is lower, at 1.18 %. WC-12Co particles bulk properties remained unchanged since there were no microstructural changes, decarburization, or the formation of fragile phases.

A critical analysis of collision dynamics pertaining to aluminum micro particles on aluminium 6061 alloy substrate in cold spray additive manufacturing process

Cold spray (CS) is a form of additive manufacturing process, involving the accumulation of ductile metal micro particles to create new surface coatings or free-standing structures. Metallic particles are accelerated through a gas stream, experience a high-strain-rate microscopic ballistic collisions against a target substrate. It yields tremendous amounts of kinetic energy from extreme plastic deformation of the particles and substrate. In this paper, the dynamic behavior of aluminium micro-particles during the collision is analysed using micro-ballistic method. Aluminum 6061 alloy particles, approximately 20 μm in diameter, impact and rebound off aluminum 6061 alloy substrate target surface over a broad range of surrounding temperatures and impact velocities. This, in turn, can provide insight into the underlying material science behind the cold spray process.

A Preliminary Study on the Sustainability of Metallization of Polymer Matrix Composites through Cold Spray

The cold spray (CS) process is the latest solid-state deposition method that has gained significant awareness for the metallization of polymer matrix composites (PMCs) materials to modify their surface properties, including electrical or thermal conductivity and electromagnetic shielding. In comparison with other coating processes, CS allows for the production of metallic coatings without the necessity to reach the melting temperature of the sprayed particles and provides a way to deposit resistant materials with improved properties onto various components to minimize wear, erosion and corrosion. For the first time in the literature, this work has the innovative goal of applying the life cycle assessment methodology to the case study of the CS production process in order to ascertain whether CS could be framed in the realm of green technologies offering interesting opportunities to improve manufacturing sustainability. In particular, the environmental impact of CS associated with the metallization process of PMCs was considered in terms of energy consumption and CO2, NOx and SO2 emissions, which are used as indicators in the life cycle assessment. When compared to different coating processes, the results suggest that CS has a large potential to reduce the environmental effects connected with the products in terms of the amount of CO2 and hazardous emissions created throughout the process.

The Effect of Fe/Al Ratio and Substrate Hardness on Microstructure and Deposition Behavior of Cold-Sprayed Fe/Al Coatings.

Fe/Al composite coatings with compositions of Fe-25 wt.% Al, Fe-50 wt.% Al and Fe-75 wt.% Al were deposited on pure Al and P91 steel plates by a cold spray, respectively. The microstructure of the cross-section of the fabricated coatings was characterized by SEM and EDX. The bonding strength between the coatings and substrates was measured and analyzed. The effects of the Fe/Al ratios and substrate hardness on the deposition behavior were investigated. It was interesting to find fragmented zones in all fabricated coatings, which were composed of large integrated Al particles and small fragmented Al particles. Meanwhile, the fraction of fragmented zones varied with the fraction of the actual Fe/Al ratio. An Fe/Al ratio of 50/50 appeared to be an optimized ratio for the higher bonding strength of coatings. The in situ hammer effect caused by larger and harder Fe particles played an important role in the cold spray process. The substrate with the higher hardness strengthened the in situ hammer effect and further improved the bonding strength.

Effect of the substrate surface and coating powder hardness on the formation of a cold sprayed composite layer

Abstract In this study, the powder hardness and substrate surface hardness on the coating formation in the cold spray process was investigated. The AA6082 aluminum alloy hardened by the shot-peening process was used as the base material. Two different metallic powders and a ceramic particle powder were used as powder materials with different hardness. Thus, the powder particles from different materials were sprayed onto the surface under the same spraying process conditions. In order to obtain a workpiece surface with different hardness values, shot-peening treatment was applied to the substrate material at different treatment times. According to the microstructural examination, the harder metallic coating powder has accumulated more and the lower hardness metallic coating powder has accumulated less when the substrate material hardness increases. Al2O3 particles in the layer formed were distributed close to homogeneous. Furthermore, the size of Al2O3 particles near the contact surface has become much finer especially in the long-term shot peened samples due to their higher hardness. From the indentation experiments, the elastic behavior and recovery amount of the composite coating layer increased due to the increase of the substrate surface hardness, and the stress distributions were performed less after the load was removed.

Supersonic cold-sprayed Si composite alloy as anode for Li-ion batteries

The increasing demand for lithium-ion batteries (LIBs) continuously stimulates the research community to seek advanced fabrication of anodes with improved performance and lifespan. Silicon (Si), as one of the most promising anode materials, has been the main focus of both research and industry. In this paper, we report a type of Si alloy anode for LIBs manufactured by the supersonic cold spray technique. The microscopic analysis revealed the uniform morphologies of the anodes, indicating that Si and other metal particles were well bonded. Specific discharge capacities were obtained for the cold-sprayed anodes by half-coin cell tests, with the highest value of 1047 mAh g−1 at a current rate of 0.05 C. Most importantly, the energy-dispersive x-ray spectroscopy results demonstrated none oxidation of the powders after the cold spray process. The results strongly indicate that the concept of using cold spray technique to fabricate Si alloy anode is feasible. Compared to the conventional methods of fabricating Si anodes, the cold spray approach is simple, convenient, and scalable. This method may revolutionarily change the LIBs industries.

Breaking the trade off between corrosion resistance and fatigue lifetime of the coated Mg alloy through cold spraying submicron-grain Al alloy coatings

Although magnesium (Mg) alloys are the lightest among structural metals, their inadequate corrosion resistance makes them difficult to be used in energy-saving lightweight structures. Moreover, the improvement in corrosion resistance by the conventional surface treatments is always achieved at the expense of sacrificing the fatigue lifetime. In this study, high purity aluminum (Al) and AlMgSi alloy coatings were deposited on Mg alloys via an in-situ micro-forging (MF) assisted cold spray (MFCS) process for simultaneous higher corrosion resistance and longer fatigue lifetime. Besides contributing to a highly dense microstructure, the in-situ MF also greatly refines the grain of the deposited Al alloy coating to the sub-micrometer range due to the enhanced dynamic recrystallization and also generates notable compressive residual stress up to 210 MPa within the AlMgSi coating. The absence of secondary phases in the AlMgSi alloy coatings enable the coated Mg alloy with corrosion resistance, which is even better than its bulk AlMgSi counterparts. The unique combination of refined microstructure and the prominent compressive residual stress within the AlMgSi coatings, effectively delayed the crack initiation upon repeated dynamic loading, thereby leading to ∼10 times increase in the fatigue lifetime of the Mg Alloy. However, although residual stress is also generated in the submmicro-sized grained pure Al coating, the low intrinsic strength of the coating layer leads to a lower fatigue lifetime than the uncoated Mg alloy substrate. The present work is aimed to provide a facile approach to break the trade-off between corrosion resistance improvement and fatigue lifetime of the coated Mg alloys.

Effects of Cold Spraying Process and Diamond Addition on Microstructure and Thermal Conductivity of Copper Matrix Composites

The operation speed and integration degree of electronic components are getting higher and higher, which puts forward higher requirements for electronic packaging materials. Diamond is added to copper matrix composites to improve the thermal conductivity. The effects of cold spraying process and diamond addition on the microstructure and thermal conductivity of copper matrix composites are studied. The results show that the copper matrix composite prepared by cold spraying is a deformed strip copper layer. The change of cycle times has little effect on the microstructure, while the flattening rate of the deformed copper layer decreases as the carrier gas temperature increases. The diamond particles are uniformly distributed at the copper grain boundary after adding copper plated diamond powder, which are closely bound to the copper matrix. Increasing the temperature is conducive to increasing the thermal conductivity, while the change of cycle times has little effect on it. The addition of 20% diamond particles reduces the thermal conductivity, so the diamond content should be increased to play its role in thermal conductivity.

Titanium and Tantalum Used as Functional Gradient Interlayer to Join Tungsten and Eurofer97

For the DEMO reactor, tungsten is considered as an armor material. Eurofer97 is planned to be used as a structural material for the first wall and in the divertor region, especially for the shielding liner component. To date, several joining solutions between W and Eurofer97 have been developed (copper brazing, W and Eurofer97 functional gradient material (FGM), etc.). Each existing joining solution has its own advantages (joining material, improved manufacturing process). In the present study, the choice of the joining material is driven, among other constraints, by a desire to minimize the thermal stresses at the materials’ interface. In this regard, FGM represents a promising solution. Another constraint that is taken into account in this study concerns the manufacturing process involved, which should be an improved industrial process. The present study proposes a joining solution, based on FGM, which, additionally to the advantages of the existing solutions, could reduce the long-term activation of the joining material. The development of a joining solution via Ti and Ta as materials constituting the FGM (Ti/Ta FGM) is presented in this paper. Due to the achieved density and the composition’s accuracy, the cold spray process is shown to be adapted for the Ti/Ta FGM’s manufacturing. Based on the feedback on the experience of joining between W, W/Cu FGM and CuCrZr, the final joining between W, Ti/Ta FGM and Eurofer97 is achieved using hot isostatic pressing, followed by a thermal treatment to recover Eurofer97’s mechanical properties, resulting in good joining quality.

Measurement methods for quantifying powder flowability and velocity in cold spray systems

Four powders with varying bulk densities, Al, Al2O3, Sn, and Cu, were used to determine quantifiable relationships between powder flowability, mass flow rate, and powder velocity with particle morphology and particle distribution in a cold spray system. High particle density results in good powder flowability, specifically when the powders are spherical relative to irregular morphology. Particle velocity during cold spray, measured with a double disk rotary system, increases non-linearly with an increase of inlet pressure. The increase in mass flow rate from the hopper and the resulting mass output of the cold spray system shows a consequence of good powder flowability. Conversely, a high mass flow rate decreases the particle velocity during the cold spray process, with better flowability leading to decreases on the order of 10% in particle velocity in the cold spray system. The described methods, proposed tools, and findings can be easily made with cost-effective and on-the-spot measurements.

Microstructure and mechanical properties of cold spray additive manufactured Cu-Cr-Nb and Fe-Ni-Cr alloys

The main objective of this work was to investigate the microstructure and mechanical properties of Cu-Cr-Nb (GRCop-42) and Fe-Ni-Cr (HR-1) alloy deposits produced using a high-pressure cold spray process. GRCop-42 powder blended with varying content of HR-1 powder (0, 15, 25, 50, 75, 85, and 100 wt%) was cold spray deposited, and the microstructure and mechanical properties of the deposits were evaluated. The deposits were characterized using optical microscopy, X-ray diffraction, and scanning electron microscopy. The use of He process gas resulted in relatively lower porosity and better mechanical properties compared to the deposits produced with N2 process gas. In the as-deposited condition, all the cold spray deposits exhibited brittle behavior with no appreciable ductility. Post-deposition heat treatment significantly improved ductility and tensile strength for both GRCop-42 and HR-1 deposits. However, post-deposition heat treatment resulted in coarsening of Cr2Nb precipitates in GRCop-42, the formation of η phase in HR-1, and the formation of σ phase at the interface in GRCop-42 and HR-1 composite deposits.

Printability of low-cost pre-heat-treated ball milled Al7075 powders using compressed air assisted cold spray additive manufacturing

• Cold spray printing using low-cost ball-milled powders was successfully demonstrated. • As-received powders were irregular in shape and size, significantly work-hardened, and consisted of very fine precipitates in its microstructure that affected its printability. • Annealing the powders resulted in significant reduction in hardness and coarsening of precipitates, thereby facilitating cold spray printability. • A deposition efficiency of 59% was realized with pre-treated powders using compressed air as propulsive gas, which is higher than the deposition efficiencies reported in published literature. A successful attempt at the cold spray additive manufacturing (CSAM) of low-cost ball milled Al7075 powders using air as the carrier gas is demonstrated. The irregular shape and hardness of the as-received powders are identified as a primary obstacle to the successful printability which demonstrated 0% deposition efficiency. Thus, different annealing procedures are suggested as an optimization technique to facilitate printing. These annealing procedures are compared and contrasted using differential scanning calorimetry (DSC) and the hardness/printability of the annealed powders are correlated exactly to the enthalpies in the low temperature i.e., <300 °C region. The annealing procedure of 300 °C for 4h (referred to as the C4 powder) is found to be the most optimal based on the combination of hardness, deposition efficiency, porosity and enthalpy values. On printing, the C4 powder also shows the best combination of good quality edge spraying, highest deposition efficiency of 59% and low porosity of 1.80%. Finally, while the microstructure of the C4 powder particles is retained in the microstructure of the printed part, the hardness of the printed part is higher than that of the C4 powder. This is attributed to a combination of deformation strain induced within the interparticle boundaries during the cold spray process and excellent interparticle interlocking.

Bulk-like ductility of cold spray additively manufactured copper in the as-sprayed state

• As-sprayed CSAM Cu can exhibit a simultaneous high ductility and strength. • This is triggered by a specific topology of bimodal grain size. • The deposits have a high thermal conductivity comparable to bulk. • They are perfectly gas-tight with He leakage rate of less than 1 × 10 −7 mbar•l/s. • All these were achieved with 99% efficiency using inexpensive nitrogen. In recent years, cold spray process is increasingly used for additive manufacturing of metallic components, referred to as cold spray additive manufacturing (CSAM). Unlike the fusion-based AM processes, CSAM is achieved in a solid-state, bringing several advantages such as the absence of severe oxidation or phase composition changes. At the moment, the main limitation of CSAM is the generally low ductility of the as-sprayed deposits. In this paper, using Cu as a model material, we demonstrate a way to overcome this limitation. Importantly, a high ductility of the deposits in their as-sprayed state is achieved without a trade-off in mechanical strength. Furthermore, we show that without any post-heat treatment, the properties of CSAM Cu are comparable to bulk, non-AM Cu.

Friction surfacing and cold spray deposition for surface crack repair in austenitic stainless steels

Two technologies, friction surfacing (FS) and cold spray deposition (CSD), have been investigated for field repair of cracks in 304 L austenitic stainless steel. Both technologies are low-heat-input, solid-state technologies that do not introduce the detrimental effects of solidification, such as compositionally segregated microstructures and shrinkage stresses. Friction surfacing was performed using a 304 L stainless steel rod over the substrate of the same material. The process was performed at a high spindle speed of 20,000 RPM allowing for process forces below 500 N to be used effectively. Spherical gas-atomized 304 L stainless steel powder, in size range of 25 µm - 44 µm, was used as feedstock powder for the cold spray process for deposition on 304 L substrates. Both technologies showed leak-tight crack repair capabilities on ~ 30-50 µm wide simulated through-crack specimens based on helium leak tests.

Cold spray-based rapid and scalable production of printed flexible electronics

Flexible electronics (FE) is attracting great attention from both scientific and industrial communities, and plays a crucial role in smart device applications. Despite great promise, traditional printing approaches ( e.g. , screen printing, ink-jet printing, etc.) often need a high-temperature post-sintering process to produce FE with desired electrical conductivity and adhesion strength. The post-sintering processes, however, often lead to fast oxidation of the functional coating while limiting the use of low-thermal budget substrates. Exponential advance of FE in a large-scale and energy-efficient manner relies on rationally eliminating the post-sintering processes. To this end, with the aim of uncovering process-structure-properties relationships, we employ the emerging cold spray (CS) technique for rapid and scalable production of FE without a need for high-temperature post-sintering. In this regard, micron-scale Tin (Sn) particles are directly written on a flexible polymer substrate (PET) by cold spraying under ambient conditions. The effect of CS process parameters on the resultant coatings is comprehensively characterized in terms of microstructure, film thickness, electrical conductivity, linewidth, and adhesion strength. The resulting electrodes show excellent electrical conductivity (6.98×10 5 S.m -1 ), adhesion strength, long-term stability, and flexibility without significant conductivity loss after 1,000 bending cycles. By leveraging the CS operational settings, a resistive macro-heater (12×15 cm 2 ) and an LED circuit (2.5 cm×18 cm) are fabricated to demonstrate the applicability of the CS in printed FE. Moreover, to address the low-spatial resolution of CS writing, a case study on sequential CS and femtosecond laser machining is performed, which further led to ultra-high resolution ( i.e. , 30 µm linewidth) custom-designed flexible electrodes. Thus, the present study reveals the immense potential of the CS technique for rapid and scalable production of FE without the need for post-sintering. • Cold spray deposition is employed in printed flexible electronics (FE). • Tin (Sn) particles are directly written on a flexible substrate (PET) at ambient conditions. • Flexible electrodes with excellent electrical conductivity (6.98×10 5 S.m -1 ) are achieved. • The resultant electrodes are constructed into FE applications such as a resistive heater. • Cold spray is found to be promising for rapid and scalable production of printed FE.

Mechanical and Tribological Study on Aluminum Coatings with High-Pressure and Low-Pressure Cold-Spray Processes

Cold spray is a promising approach to repair all damages and defects in aluminum (Al) constituent elements. The study aims to investigate the mechanical and tribological properties of Al coatings deposited using high-pressure cold-spray (HPCS) and low-pressure cold-spray (LPCS) techniques. Al powder was sprayed on a cold-rolled plate of aluminum 1100, which was used as the substrate. The results showed that the micro-hardness of the LPCS Al coating reached up to 196.6 HV before the wear test compared to that of HPCS (174.3 HV). Moreover, more low friction coefficients obtained by LPCS (0.798) than HPCS (0.807) indicated good tribological properties with a high amount of oxide composition. Meanwhile, the wear studies reveal that the specific wear rate of the Al coating of LPCS (0.008) was lower than the HPCS (0.009) as the load increased from 3 N to 5 N, thus providing excellent wear resistance. Therefore, the results exhibited greater mechanical and tribological characteristics for Al coatings produced by the LPCS process than by the HPCS process.

Accelerated corrosion testing of cold spray coatings on 304L in chloride environments

Cold spray is an advanced metal manufacturing technique applied across many fields for a wide range of functions. Low heat input and compressive stresses induced into the substrate by the cold spray process makes it a promising choice for protective corrosion resistant coatings. One potential application for cold spray is as a protective coating against corrosion for spent nuclear fuel (SNF) interim dry storage canisters. As these canisters are currently stored at interim storage locations longer than originally intended, chloride induced stress corrosion cracking has been identified as a high priority knowledge gap, specifically with respect to prolonging or extending canister lifetimes (Teague et al., 2019). The high deployability of cold spray, for which nozzles have been developed for application in constrained spaces, in conjunction with beneficial properties inherent to cold spray makes this a good candidate for a corrosion protection coating on SNF canisters. This work explores a pathway to rapidly down-select cold spray coatings for canisters by focusing on the corrosion properties. Specifically, this study examines the corrosion protection abilities of nickel and nickel-based alloy cold spray coatings on 304 L stainless steel in chloride rich environments through electrochemical scans and ferric chloride pitting tests (ASTM G48 Method A). It was shown that the porosity of the coating, the processing gas, material selection, and deformation in the substrate all impact the corrosion behavior of cold spray coatings and are areas where optimization could reduce potential materials degradation, enabling enhanced coatings development.

Fabrication of Metal/Graphene Composites via Cold Spray Process: State-of-the-Art and the Way Forward

Cold spray (CS)-fabricated metal–graphene composites have applications in several fields ranging from tribology and corrosion protection to antibacterial applications. However, it is critical from a process perspective to create a viable feedstock, and to this end, there are two widely reported techniques: ball milling and in situ reduction. In this paper, the CS feedstocks prepared via these two methods are compared and contrasted with other miscellaneous techniques in the literature based on their efficacies and the end properties of the fabricated coatings. CS metal–graphene composite coatings are found to display self-healing behaviour and excellent corrosion/wear resistance and mechanical properties, but at this juncture, there is a gap in the literature as far as the CS fabrication of self-standing metal–graphene composite parts is concerned. Several future research avenues are discussed to fully comprehend the printability and functionality of metal/GNP composite cold-sprayed structures.

Behavior of melt flow and porosity formation in laser welding of steel to aluminum with cold-sprayed steel interlayer

A multimaterial car body design, using light materials in combination with steel, has become widespread in recent years in order to reduce a vehicle's weight. The joining of dissimilar materials is one of the most critical issues in this area. In our previous research, we reported on a new dissimilar laser lap joining method, using a cold-spray process. In that procedure, a steel coating was first sprayed onto an aluminum surface, after which a steel sheet, together with the coating, was laser welded. However, it was found that porosity occurred in the weld metal due to melting of the coating. In this study, we investigated the effects of welding parameters on porosity formation in this joining process as well as the behavior patterns of the flow and bubbles in a molten pool. The porosity increased as the laser input energy decreased. It was also discovered that the porosity could be reduced drastically by the melting of the aluminum substrate, together with the steel sheet and coating, even at lower input energy. Electron probe microanalyzer results showed that both the solidification rate, related to the input energy, and aluminum's melting were strongly associated with the generation of flow from the bottom to the surface of the molten pool. This was captured by means of an x-ray in situ observation, using tungsten tracers, behind the keyhole. The bubbles, moving upward and reaching the surface of the pool, were also observed there in the welding conditions, where only a little porosity occurred. These results demonstrated that this flow helped the bubbles move up and go outside the molten pool and, hence, prevented porosity formation.

SPH modeling and investigation of cold spray additive manufacturing with multi-layer multi-track powders

Cold spray (CS), as a new solid-state additive manufacturing technique, involves complex phenomena like high-speed impacting of micro-powders, large material deformations, phase change and jet generation. The CS process is difficult to be accurately simulated, and the underlying coating mechanisms, especially for multi-powders CS, have not been well understood. As a Lagrangian and particle method, the smoothed particle hydrodynamics (SPH) method has natural advantages in treating large deformations and capturing moving interfaces. In this work, we present an improved SPH approach to implement three-dimensional particle modeling and study of the multi-layer multi-track CS problem. The kernel gradient correction (KGC), adaptive smoothing length and the constitutive model are integrated in the improved SPH. The contour profile and width thickness ratio of the deformed powder obtained by the present simulation are very close to the experimental results. The bonding behaviors in a single powder CS with different materials are first explained where the critical velocities for different materials are obtained. Furthermore, coating behaviors in CS with different layers and tracks of powders are comprehensively analyzed. Some typical deformation parameters of the powders track with regard to an increasing impacting velocity are attained. With the present numerical model, a larger scale multi-layer multi-track CS is promising to be reproduced with some parameter windows predicted, which is greatly helpful to CS operations.