Cold Spray Technology Research Articles

High speed impact induced dehydrogenation of titanium hydride and formation of cellular structure via cold spray

In this study, it is revealed for the first time that ultra-high-speed impact can trigger in-situ dehydrogenation at the impact interface of titanium hydride (TiH). This phenomenon leads to a phase transformation from brittle TiH to ductile Ti, causing a shift in the ductile-to-brittle transition from the impact interface to the particle interior. Inspired by this unique behavior, and considering the mechanical interactions between particles during the spray process, TiH powders were used as feedstock to successfully produce a large-scale random cellular structure through cold spray. A systematic investigation of the deposition process revealed that unbroken TiH particles interact with dehydrogenated ones, resulting in only the ductile portion of the TiH particle being deposited, while the brittle interior is spalled off, consequently forming the “walls” of the cellular structures. This work highlights the potential of TiH powders to advance cold spray technology, particularly in the creation of complex cellular structures.

Influences of Ti3AlC2 content on tribological behavior of cold-sprayed Ni-Ti3AlC2 composite coatings

As a type of lightweight and high-strength materials, aluminum alloys have been widely applied in such fields as aerospace and automobile manufacturing, which, however, easily wear out in harsh and complex environments due to their defects like poor wear resistance, low hardness, and easy deformation. For this reason, it is necessary to prepare a coating on the surface of aluminum alloys to enhance their wear resistance. In this work, Ni-Ti3AlC2 composite coatings were prepared on the aluminum alloy surface through cold spraying technology, and the influences of Ti3AlC2 content on the microstructure, mechanical properties, and tribological behavior of the Ni-Ti3AlC2 composite coatings were explored. It turned out that the mechanical properties and tribological behavior of the composite coatings were significantly improved with the increase of Ti3AlC2 content. Therein, the Ni-50%Ti3AlC2 composite coating exhibited a porosity of 0.384 %, a hardness of 310 HV0.2, and a bonding strength of 51.6 MPa, while its wear rate significantly declined to 1.87 × 10−5 mm3/N∙m. Because of the increase of Ti3AlC2 ceramic content, the compaction effect and shot peening effect of the ceramic hard phase were gradually enhanced, which further aggravated the deformation degree of Ni metal, thus improving the density, hardness, bonding strength, and wear resistance of composite coatings.

Multi-layer formation by oxidation and solid-state crystallization of cold sprayed amorphous coatings during dry sliding wear

Amorphous alloy coatings, known for the exceptional wear resistance, have emerged as a key solution for enhancing the wear performance of magnesium alloys under harsh environments. In this study, Fe-based amorphous alloy coatings were deposited on magnesium alloy by cold spraying technology, and the influence of microstructural evolution on the wear performance of coatings under dry sliding wear conditions was discussed. The results showed that a dense adherent oxide layer with a thickness of ∼700 nm comprising nanograins of less than 8 nm was formed at the outmost surface, which played a role of self-lubricating. Underneath, a 1 μm thick nanocrystalline-amorphous layer with nanograins of ∼20 nm dispersed in the amorphous alloy matrix was formed through in-situ crystallization induced by flash temperature. This composite structure prevented the formation of shear bands in amorphous alloys and enhanced the durability. Therefore, the transition from abrasive wear to adhesive wear was a consequence of the microstructural evolution from a dual-phase composite layer to a self-lubricating oxide layer.

Microstructure and wear resistance of cold sprayed CoCrFeNi HEA coatings: Influence of powder particle size and spraying temperature

This study focuses on the successful fabrication of three distinct types of CoCrFeNi high entropy alloy (HEA) coatings through cold spray (CS) technology, with an emphasis on analyzing the impact of varying crucial CS parameters (spraying temperature and the range of powder particle size), on the coating's microstructure and tribological properties. Contrasted with conventional thermal spraying techniques, lower operational temperature in CS safeguards the materials from undergoing oxidation or phase transitions that are typically induced by high-temperature conditions. Additionally, the high-velocity impact of particles onto the substrate within CS process triggers plastic deformation, resulting in the creation of coatings that are characterized by heightened hardness, and greater density. Such coatings exhibit significantly enhanced performance and durability. The cocktail effect observed in CoCrFeNi HEA is reflected in a suite of exceptional properties that markedly surpass those exhibited by traditional alloys. Chiefly, this phenomenon is manifested through the alloy's exceptionally high hardness and dense structure, positioning CoCrFeNi HEA as a promising candidate for applications in high-wear scenarios. Experimental outcomes indicate that when smaller powder particles and higher spraying temperatures are employed, the porosity of CSed CoCrFeNi HEA coatings was observed to decrease by nearly an order of magnitude, concomitant with a 22.46% enhancement in microhardness. This improvement in microhardness translates into a significant reduction of over 72% in the wear rate, underscoring the positive correlation between enhanced microstructural integrity and wear resistance properties. By meticulously tuning spraying temperature and powder particle size, the resulting microstructure can be rendered increasingly dense and refined.

Effect of plastic deformation of particle and substrate on metallurgical bonding during cold spraying

The metallurgical bonding of cold spraying is investigated from the perspective of plastic deformation. The individual Al particle was deposited on the surface of Ni substrate by low-pressure cold spraying technology. Direct observation of the Al/Ni interface from the cross-sectional morphology shows that metallurgical bonding occurs only at the partial Al/Ni interface. The finite element simulation considering the presence of oxide layer confirms that the metallurgical bonding is located in front of the maximum plastic deformation area. In the maximum plastic deformation area, the relative displacement between Al particle and Ni substrate exists from the beginning of contact to the end of deposition, which makes the metallurgical bonding discontinuous and gradually disappear.

Effects of spraying parameters and heat treatment temperature on microstructure and properties of single-pass and single-layer cold-sprayed Cu coatings on Al alloy substrate

Exploring the deposition of single-pass and single-layer pure Cu coatings on Al alloy substrate through high-pressure cold spray technology is a crucial endeavor with significant implications for advancing the utilization of such coatings. Regrettably, research in this specific area remains scarce, highlighting the need for further investigation and understanding. This study examined the characteristics of cold-sprayed Cu coatings deposited on a 6061 T6 aluminum alloy substrate under varying gas temperatures and pressures, and explored the effects of subsequent heat treatment on the microstructure and mechanical properties of the Cu coatings. The morphology, phase composition, surface roughness, thickness, porosity, microstructure, shear strength, and microhardness of the cold-sprayed Cu coatings were systematically analyzed. The findings indicated that the spraying parameters had a substantial impact on the properties of the Cu coatings. Specifically, increased gas pressure led to rougher surfaces and lower porosity, whereas higher gas temperature produced smoother surfaces and also reduced porosity. At 800 °C and 4.0 MPa, the Cu coatings exhibited the lowest surface roughness, measuring 8.03 μm. Conversely, at 800 °C and 5.5 MPa, the Cu coatings demonstrated the lowest porosity, at 0.26 %. Moreover, the microstructure analysis showed evidence of dynamic recrystallization in the deposited Cu particles, contributing to enhanced mechanical properties. Following this, the influence of heat treatment on the microstructure and properties of the cold-sprayed Cu coatings was examined. The results demonstrated that annealing at different temperatures induced changes in the interfacial microstructure, with the formation of intermetallic compounds between the Cu coating and Al alloy substrate. This interdiffusion phenomenon led to improved bonding strength and mechanical properties of the Cu coatings, as evidenced by increased shear strength. After undergoing heat treatment at 400 °C, the Cu coatings exhibited the highest shear strength, measuring 49.89 MPa. However, excessive heat treatment temperatures resulted in the formation of cracks and a decrease in mechanical properties.

Strengthening Ti3SiC2/Cu brazed joint assisted with cold spray additive manufacturing: Lower brazing temperature through interdiffusion and graded reinforcement for stress relaxation

Graded composite fillers exhibit unique advantages in alleviating residual stress in ceramic/metal brazed joints. However, traditional methods for preparing graded composite fillers are often complex and may deplete their strengthening phases. In this study, cold spray additive manufacturing was employed to fabricate yttria-stabilized zirconia (YSZ)-Ti25Zr25Ni25Cu25-Ag graded composite coatings on Cu substrates to serve as fillers. The graded composite coatings and the resultant Ti3SiC2/Cu brazed joints were systematically characterized to elucidate the deposition mechanism of the coatings and its residual stress-relaxed mechanism. The bondings between particles in the coatings, based on their plastic deformation ability, were classified into noncrystalline weak bonds and homogeneous strong bonds. Both bondings facilitated the elemental interdiffusion between filler and Cu substrate during the heating process, which contributed to the formation of Ag-Cu eutectic. This significantly reduced the required brazing temperature and its induced residual stress. Furthermore, the solid phase transformation of graded-distributed YSZ within the brazing seam from tetragonal to monoclinic achieved a smooth thermal transition and releasing residual stress at the same time. Consequently, the shear strength of the brazed joint reached to the highest value of 110.23 ± 3.45 MPa, which was Much higher than the previously reported values. This study introduces a novel method for residual stress relaxation assisted with cold spray technology and broadens its application in the brazing field.

Bonding mechanism and fracture behavior of cold-sprayed Fe-based amorphous alloy on 6061 Al alloy

Using cold spray technology to prepare amorphous alloy coatings can effectively prevent crystallization, thereby preserving the excellent properties of amorphous alloys. However, interfacial bonding significantly affects performance, such as weak bonding impacting the durability and stability of the coating. Therefore, in-depth study of the interfacial bonding mechanism is crucial for a comprehensive understanding of coating properties. This paper uses cold spray technology to prepare Fe-based amorphous alloy coating on 6061 aluminum alloy substrates. The bonding mechanisms at the particle/substrate, particle/particle, and coating/substrate interfaces are studied, and the fracture behavior in the tensile bond strength test is analyzed. The results show that the heat accumulation and the increase in strain rate generated by the particles impacting the substrate cause the viscosity of the amorphous alloy to suddenly decrease from 1.2×103 g·cm−1 s−1 to 8.4×10−1 g·cm−1 s−1. Increased fluidity and micro-friction accelerate the mixing of elements and form a metallurgical bond at the particle/substrate interface. Meanwhile, the oxides at the particle/particle interface are extruded, and the exposed fresh metal is subjected to a huge shear rate to promote atomic fusion. Tamping of the subsequent particles leads to further deformation of the deposited particles, forming a stronger metallurgical bond and mechanical anchoring at the particle/particle interface. In addition, the continuous impact of particles triggers dynamic recrystallization of the substrate, and the average grain size decreases from 14.28 μm to 1.39 μm. This fine-grained structure strengthens the mechanical anchoring of the coating/substrate interface. Furthermore, the bonding strength measured by the tensile test is determined to be 18.51 MPa. The main reasons for the final fracture occurring in the coating are the coating pores, cracks formed by shear bands accumulated in free volume, and the low adhesion oxide layer at the particle interface.

Duplex surface engineering of cold spray Ti coatings and physical vapor-deposited TiN and AlTiN thin films

The feasibility of a duplex coating based on cold spray technology and magnetron sputtering was evaluated for repair applications requiring a ‘thin-on-thick’ layered structure. Commercially pure angular-shaped Ti grade 4 particles are fed to a cold spray gun and accelerated toward a Ti alloy substrate to deposit thick coatings (∼4.5 mm). TiN and AlTiN thin films are deposited on polished cold spray coatings using a four-source closed-field unbalanced magnetron sputtering (CFUBMS) system. Microstructure was characterized using focused ion beam (FIB) lift-out, scanning electron microscopy (SEM), and electron channeling contrast imaging (ECCI). The nanoindentation technique was used to evaluate the mechanical properties of coatings. The H/E ratios and H3/E2 ratios for TiN films were found to be 0.098 and 0.26 GPa, respectively, while those for AlTiN films were measured at 0.066 and 0.052 GPa, respectively, suggesting higher capacity of TiN films to withstand both elastic and plastic deformation. Using scratch testing, the adhesion of TiN and AlTiN thin films to cold spray Ti was investigated, with TiN-Ti duplex coatings exhibiting better performance compared to AlTiN-Ti coatings. Tribological testing was performed on duplex coatings using a reciprocating tribometer equipped with an alumina ball counterface. The wear rate for AlTiN-Ti coatings after 2000 sliding cycles was found to be (1.0 × 10−3 ± 0.1 × 10−3 mm3/Nm), three orders of magnitudes higher than that for TiN-Ti (8 × 10−6 ± 2 × 10−6 mm3/Nm. SEM was used to reveal worn surface morphologies and cross-sectional analysis of the wear track. Subsurface microstructural changes due to wear were examined using focused ion beam cross-sectioning, revealing bending cracks and tribofilm formation.

Repairing Al7075 surface using cold spray technology with different metal/ceramic powders

Cold spray process is essentially a coating technique as well as used in repair applications. This method is a low-temperature solid-state process. In this study, the damaged surface of Al7075 was repaired by low pressure cold spray method with Ni-Zn-Al2O3, Al-Zn-Al2O3, Al-Al2O3, Ni-Al2O3, and Zn-Al2O3 metal/ceramic feedstock powders. Microstructure examination, microhardness measurements, tribological experiments, and tensile tests were conducted on the repaired samples and compared with Al7075. The repaired regions exhibited a composite microstructure characterized by the presence of Al2O3 ceramic particles with high hardness dispersed within a metal matrix composed of Al, Ni, Zn, Ni-Zn, and Al-Zn. This composite structure was attributed to the interlocking mechanism of cold spray. The highest hardness value was measured in the repaired area using Ni-Al2O3, which is approximately 1.28 times higher than that of Al7075 alloy. According to the dry sliding test, the wear performance of all repaired specimens was superior to that of Al7075. The wear resistance of samples repaired with Ni-Al2O3 and Ni-Zn-Al2O3 increased approximately 7.1 and 5.8 times, respectively, compared to Al7075. The specimens repaired with Ni-Zn-Al2O3 feedstock powder showed the most similar results in tensile and yield strength values to Al7075 to the tensile test.

Cold Spray Technology and Its Application in the Manufacturing of Metal Matrix Composite Materials with Carbon-Based Reinforcements

Cold spray technology, as an emerging surface engineering technique, effectively prepares hard coatings by high-speed projection of powder materials onto substrates at relatively low temperatures. The principal advantage of this technology lies in its ability to rapidly deposit coatings without significantly altering the properties of the substrate or powder materials. Carbon-based materials, especially carbides and diamond, etc., are renowned for their exceptional hardness and thermal stability, which make them indispensable in industrial applications requiring materials with high wear resistance and durability at elevated temperatures. This review elucidates the fundamental principles of cold spray technology, the key components of the equipment, and the properties and applications of hard coatings. The equipment involved primarily includes spray guns, powder feeders, and gas heaters, while the properties of the coatings, such as mechanical strength, corrosion resistance, and tribological performance, are discussed in detail. Moreover, the application of this technology in preparing metal matrix composite (MMC) materials with carbon-based reinforcements, including tungsten carbide, boron carbide, titanium carbide, and diamond, are particularly emphasized, showcasing its potential to enhance the performance of tools and components. Finally, this article outlines the challenges and prospects faced by cold spray technology, highlighting the importance of material innovation and process optimization. This review provides researchers in the fields of materials science and engineering with a comprehensive perspective on the application of cold spray technology in MMC materials with carbon-based reinforcements to drive significant improvements in coating performance and broaden the scope of its industrial applications.

Direct Writing of Mesoscale Circuits using Subsonic Cold Spray

Abstract This article reports on work at the Center for Thermal Spray Research over the past 25 years to develop and commercialize a new technology for digital printing of mesoscale circuits directly from a CAD file onto plates, cylinders, and complex 3D components and structures. With the evolution of cold spray technology and new powder materials, as well as advancements in control and robotics, innovative thermal spray applications are on the horizon.

Synthesis and tribological characterization of cold-sprayed Ni-based composite coatings containing Ag, MoS2 and h-BN

The tribo components often fail to perform in a desired way due to absence of adequate lubrication in severe conditions and may cause loss of material. Even under room temperature (RT), it is desirable to maintain the proper lubrication for efficient functioning. In recent years, many efforts have been made to develop a coating material which can facilitate low friction and wear properties in diverse working conditions. The proper use of the solid lubricants can deliver utmost lubricity and, therefore, minimize the loss of materials. Solid lubricating coatings have found various industrial applications in harsh environmental conditions, such as in internal combustion engine, gas turbine and aircraft. As far as development of coating is concerned, cold spray (CS) technology has been observed to develop the coatings at relatively low temperature (avoids decomposition) as compared to conventional thermal spray technologies (plasma spray & high velocity oxy fuel). In the current investigation, synergistic response of the participating solid lubricants viz. silver (Ag), molybdenum disulfide (MoS2) and hexagonal boron nitride (h-BN) on the tribological properties of the developed coatings were studied in various working regime of loads. The tribological characteristics of different composite coatings, such as NiAl-MoS2-Ag (NB0), NiAl-MoS2-Ag-5 wt. % hBN (NB5), NiAl-MoS2-Ag-7.5 wt % hBN (NB7.5) and NiAl-MoS2-Ag-10 wt % hBN (NB10) against alumina ball were explored at various loads (6, 11, 16 and 21 N) and at a fixed speed of 0.3 m/s under room temperature (RT). The fixed concentration of Ag and MoS2 with varying weight percentage of h-BN (0, 5, 7.5 and 10 wt %) were introduced as solid lubricants for evaluating the lubricating potential of h-BN. During the tests, coefficient of friction (COF) and wear rate were observed to lessen as the load increased from 6 to 16 N. However, increased COF and wear rate were noticed for all the participating coatings at higher load (21 N). The ideal content of hBN in the deposited coatings was ascertained in order to get the utmost favourable lubricating conditions. It was observed that NB7.5 coating exhibited the enhanced tribological characteristics under the aforesaid operating conditions. Coating NB7.5 shows the best friction and wear characteristics during each testing load and reached a COF (0.19) and wear rate (2.1 × 10−5 mm3/Nm) at 16 N load. The observed wear mechanisms were analysed on the basis of the synergy shown by Ag, MoS2, and hBN as well as the optimal hBN level in the coating (NB7.5) which helped in attaining the improved tribological properties.

Recover the tensile strength of hard aluminum alloy through laser assisted cold spray

In the present study, Al6061/Al2O3 composite coating was produced to repair the notched Al7075 substrate by cold spraying (CS) and laser assisted cold spray (LACS) technology. The preparation process and parameter selection of high-performance coating were discussed by combining simulation and experiment. Results showed that the LACS experiment guided by simulation results achieved high-quality bonding of single particle with the substrate. In addition, the tensile strength of samples repaired by LACS recovered to the level of original substrate, and the ductility was significantly higher than that of CS process. This is attributed to the introduction of laser irradiation heating, which improves the plastic deformation ability of particles and produces atomic-level metallurgical bonding between the particles. This study provides a possibility for the repair and remanufacture research of high-quality components, and has great development potential in future research.

Enhancing the piezoelectric coefficient of SrTiO3 nanocubes and PVDF film deposited by supersonic spraying for energy-harvesting nanogenerators

Many perovskites and their piezoelectric composites have been investigated for harvesting ambient mechanical energy over the past two decades; however, the prospects for their commercialization appear remote because of several practical challenges. Therefore, highly scalable supersonic cold-spraying technology was used to fabricate flexible piezoelectric films of poly(vinylidene fluoride) (PVDF) and a novel perovskite SrTiO3 (ST). Substantial shear stress was exerted on PVDF during cold spraying owing to the hydrothermally synthesized SrTiO3 nanocubes and supersonic velocity, and the resulting film delivered an effective piezoelectric coefficient (69.6 pm·V−1) as confirmed by piezo-response force microscopy. As a result, the piezoelectric nanogenerator yields a maximum power of 130 µW at a load resistance of 0.9 MΩ. The composite film exhibited durability for 21,000 tapping cycles with 20 N applied force and 7 Hz frequency. The flexibility endurance was confirmed from 3000 bending cycles. PENG attached to knee delivered 1 and 2.3 V on bending to 45 and 90°, respectively. After electrical poling, the PENG was subjected to a 20 N tapping force that yielded a piezopotential of 31 V. To the best of our knowledge, this is the first time piezoelectricity was obtained using an ST/PVDF composite via mechanical energy harvesting. The flexible PENG film deposited by cold-spraying shows good potential for wearable self-powered devices.

Application of cold spray technology in design and manufacturing of complex geometries

Application of cold spray technology in design and manufacturing of complex geometries

Painting with Metal: When History and Art Meet Thermal Spray

Abstract Cold spray technology provides a multidisciplinary approach to additive manufacturing at the intersection of science and art. This article describes the novel use of cold dynamic spray technology to create a large and complex 3D artwork that incorporates six different metals.

The evolution and future of polymer cold spray technology

The evolution and future of polymer cold spray technology

A Comparative Study on Wear Resistance of Cold-Sprayed Aluminum/Quasicrystal Composite Coatings

Cold spray (CS) technology has proven a great potential in the production of composite coatings, enabling the production of materials with superior qualities such as enhanced tribological behavior. This study aims to investigate the tribological properties of CS Al-based composite coatings reinforced by quasicrystalline (QC) particles. Two different Al alloys were used as the matrix, AA 6061 and AA 2024, and mixed with Al-based QC particles (Al-Cr-Fe-Cu) at different Al/QC ratios. A room-temperature ball-on-disc test was then used to evaluate the wear resistance of the composite CS coatings in air and compared to those of the non-reinforced Al alloy CS coatings as well as a cast counterpart (AA 6061-T6). We have demonstrated that CS could be employed to produce thick and dense Al-QC composites that can retain up to about 50 wt.% QC reinforcement in the structure. The incorporation of the QC particles increased the wear resistance by a factor of 7.

Cold spraying of Al-5Si/Al2O3 composite coatings on AZ31 Mg alloy: Microstructure, adhesion strength, and tribological properties

To improve the wear resistance of commercial AZ31 Mg alloy, two types of dense and thick composite coatings were prepared on AZ31 Mg alloy by means of cold-spray technology. For this purpose, Al2O3 particles with different morphology (round and irregular) were separately added to the Al5Si feedstock. The morphological effects of Al2O3 on the microstructure, adhesion strength, hardness, and tribological properties of the coatings were comprehensively studied. Microstructural features of the coatings were examined by means of optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD). The analysis reveals that most of the grains in both coatings are ultrafine, and approximately half of the total grain boundary length is composed of low-angle grain boundaries. Wear, hardness, and pull-off tests showed that both types of Al2O3 particles have a positive impact on porosity, adhesion, hardness, and wear resistance of the composite coatings. Compared to round Al2O3, irregular Al2O3 particles exhibit better retention in the coating, thereby resulting in a higher hardness and wear resistance.