Cold Spray Coating Deposition Mechanism on the Thermoplastic and Thermosetting Polymer Substrates

Cold spraying is a successful and promising coating technique for many engineering applications due to its high-rate and high-dense coating development abilities. Nevertheless, their practical use in polymer substrate is still in the fledgling phase. There are very few articles about the cold spray coating on polymers; however, the interaction of metallic particle with the polymer substrate is poorly understood, and thus a thick coating has not successfully been developed on the polymer substrate. In order to rationalize as full as possible the entire behavior of the high velocity particle with the polymer substrate, we used thermoplastic and thermosetting polymer materials as substrates. The particle behaviors with the substrate were observed under various gas pressure and temperature, and with various particles feed rate. The result showed that the particle behaviors were unique with respect to the substrate. Also it was clearly understood that the metal particles not experienced any plastic deformation due to the soft nature of the polymer substrates. The particles attached to the thermoplastic substrate either through adhesive bonding and/or mechanical inter locking, whereas only pure localized fracture observed on the thermosetting substrate and thus no particles attached firmly on the substrate.     

Metallization of Thin Al2O3 Layers in Power Electronics Using Cold Gas Spraying

A successful combination of insulating substrates with conducting metal coatings produced by cold spraying could open new industrial application areas like the fabrication of power electronic components. For minimizing the number of industrial process steps, insulating ceramic layers should ideally be processed by thermal spray techniques. Thus, this study investigates the impact behavior and coating formation of ductile metallic feedstock powders onto brittle ceramic coatings. With respect to high electrical conductivity of the metallic lines and good electrical insulation of the ceramic interlayer, copper was cold gas sprayed on previously thermally sprayed Al₂O₃ coatings. Successful cold coating formation requires different strategies for the activation of the ceramic layer to increase adhesion and to avoid brittle failure. These both can be achieved either by applying a bondcoat on the ceramic layer or using heated substrates during the cold spray process.     

冷喷涂技术在生物医学领域中的应用及展望

冷喷涂技术(cold spray technology)是一类赋予材料表面特殊性能的重要手段。概述了冷喷涂技术在制备温度敏感生物材料加工领域的优势,并重点综述了利用冷喷涂技术制备的典型生物材料。目前,冷喷涂沉积永久性植入金属材料,如Ti合金、Fe基合金、Co-Cr合金和可降解金属材料Mg合金等技术相对成熟。近年来随着冷喷涂技术的发展,有效解决和拓展了用于医疗器械表面改性的涂层材料体系,如冷喷涂制备高分子材料超高分子量聚乙烯(UHMWPE)涂层,以及高密度聚乙烯(HDPE)和聚醚醚酮(PEEK)表面冷喷涂制备生物涂层。最值得关注的冷喷涂或真空冷喷涂技术制备陶瓷涂层,如羟基磷灰石(HA)、羟基磷灰石-石墨烯(HA-graphene)以及二氧化钛(Ti O2),在生物医学领域应用具有突破性进展。同时归纳了冷喷涂技术在生物医学领域的研究现状和问题,虽然在针对冷喷涂生物涂层的微观结构、力学行为、腐蚀抗力等方面取得了一定成果,在组织工程、抗菌材料等领域也取得了尝试性突破,但尚缺乏系统的冷喷涂涂层生物学性能表征,涂层与细胞/组织相互作用机理还不明确,相关的临床研究欠缺。最后,在此基础上,展望了未来生物材料朝功能化和个性化医疗方向的发展方向。冷喷涂技术在功能化载药涂层的低温制备和个性化医疗器械增材制造等领域将有更大的应用空间,并给新型生物材料的表面改性带来更多机遇和可能。     

Antibacterial Property of Cold-Sprayed HA-Ag/PEEK Coating

The antibacterial behavior of HA-Ag (silver-doped hydroxyapatite) nanopowder and their composite coatings were investigated against Escherichia coli (DH5α). HA-Ag nanopowder and PEEK (poly-ether-ether-ketone)-based HA-Ag composite powders were synthesized using in-house powder processing techniques. Bacteria culture assay of HA-Ag nanopowder and their composite powders displayed excellent bacteriostatic activity against E. coli. The antibacterial activity increased with increasing concentration of HA-Ag nanoparticle in these composite powders. These nanocomposite powders were subsequently used as feedstock to generate antibacterial coatings via cold spray technology. The ratios of HA-Ag to PEEK in their composite powders were 80:20, 60:40, 40:60, and 20:80 (wt.%). Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out using FESEM/EDX and XRD. Antibacterial nanocomposite HA-Ag/PEEK coatings were successfully deposited using cold spraying parameters of 11-12 bars at preheated air temperature between 150 and 160 °C. These as-sprayed coatings of HA-Ag/PEEK composite powders comprising varying HA-Ag and PEEK ratios retained their inherent antibacterial property as verified from bacterial assay. The results indicated that the antibacterial activity increased with increasing HA-Ag nanopowder concentration in the composite powder feedstock and cold-sprayed coating.     

Effect of heat treatment on properties of cold sprayed nanocrystalline copper alumina coatings

Cold gas dynamic spraying appears to be the most appropriate thermal spraying technique for depositing nanocrystalline powders given its low deposition temperature. Nanocrystalline copper alumina coatings were deposited on copper substrates and the effect of heat treatment temperature on porosity, grain size, microhardness and conductivity of the coatings was studied and compared with that of cold sprayed copper. The role of alumina in inhibiting grain growth and in strengthening the copper matrix was investigated. An attempt has been made to assess the contribution of various mechanisms to the conductivity of nanocrystalline copper alumina coatings.     

Cold Spray Coating of Submicronic Ceramic Particles on Poly(vinyl alcohol) in Dry and Hydrogel States

We report an approach using cold spray technology to coat poly(vinyl alcohol) (PVA) in polymer and hydrogel states with hydroxyapatite (HA). Using porous aggregated HA powder, we hypothesized that fragmentation of the powder upon cold spray could lead to formation of a ceramic coating on the surface of the PVA substrate. However, direct spraying of this powder led to complete destruction of the swollen PVA hydrogel substrate. As an alternative, HA coatings were successfully produced by spraying onto dry PVA substrates prior to swelling in water. Dense homogeneous HA coatings composed of submicron particles were obtained using rather low-energy spraying parameters (temperature 200-250 °C, pressure 1-3 MPa). Coated PVA substrates could swell in water without removal of the ceramic layer to form HA-coated hydrogels. Microscopic observations and in situ measurements were used to explain how local heating and impact of sprayed aggregates induced surface roughening and strong binding of HA particles to the molten PVA substrate. Such an approach could lead to design of ceramic coatings whose roughness and crystallinity can be finely adjusted to improve interfacing with biological tissues.     

Production of Annealed Cold-Sprayed 316L Stainless Steel Coatings for Biomedical Applications and Their in-vitro Corrosion Response

316L powders were successfully deposited onto Al5052 aluminium substrates by cold spray method. Annealing was treated on the coated samples at 250–1000°C temperatures under Ar atmosphere. The in vitro performances of the coatings have been compared with using electrochemical corrosion test technique in the simulated body fluid (SBF) at body temperature (37°C). A scanning electron microscope (SEM-EDS) and X-ray diffraction (XRD) have been used for microstructural characterization and phases identifications of the coatings, respectively. The results were shown that there are high adhesions at particle and substrate interfaces and between the particles deposited as well. Also, the increasing annealing temperature increases corrosion resistance of the cold sprayed 316L stainless steel coatings. The corrosion susceptibility of the coating annealed at 1000°C was similar that of standard 316L stainless steel implant material in Ringer’s solution. The microstructural observations revealed that corrosion starts between the inter-splat powders and continues throughout the surface not in-depth.     

Influence of process conditions in laser-assisted low-pressure cold spraying

A laser-assisted low-pressure cold spraying (LALPCS) is a one-step coating process in which the laser irradiation interacts simultaneously with the spraying spot on the substrate or deposited coating surface in order to improve coating properties. It is expected that the LALPCS could be an effective method to improve a low-pressure cold sprayed coating deposition efficiency and denseness. The purpose of the additional energy from the laser beam is to create denser and more adherent coatings, enhance deposition efficiency and increase the variety of coating materials.In this study copper and nickel powders with additions of alumina powder were laser-assisted low-pressure cold sprayed on carbon steel. Coatings were sprayed using air as process gas. A 6 kW continuous wave high power diode laser and a low-pressure cold spraying unit were used in the experiments. The influence of laser energy on coating microstructure, density and deposition efficiency was studied. The coatings were characterized by optical microscopy and SEM. The coating denseness was tested with open cell potential measurements. Results showed that laser irradiation improved the coating denseness and also enhanced deposition efficiency.     

Influence of Impact Conditions on Feedstock Deposition Behavior of Cold-Sprayed Fe-Based Metallic Glass

Cold spray is a promising method by which to deposit dense Fe-based metallic glass coatings on conventional metal substrates. Relatively low process temperatures offer the potential to prevent the crystallization of amorphous feedstock powders while still providing adequate particle softening for bonding and coating formation. In this study, Fe₄₈Mo₁₄Cr₁₅Y₂C₁₅B₆ powder was sprayed onto a mild steel substrate, using a variety of process conditions, to investigate the feasibility of forming well-bonded amorphous Fe-based coatings. Particle splat adhesion was examined relative to impact conditions, and the limiting values of temperature and velocity associated with successful softening and adhesion were empirically established. Variability of particle sizes, impact temperatures, and impact velocities resulted in splat morphologies ranging from well-adhered deformed particles to substrate craters formed by rebounded particles and a variety of particle/substrate interface conditions. Transmission electron microscopy studies revealed the presence of a thin oxide layer between well-adhered particles and the substrate, suggesting that bonding is feasible even with an increased oxygen content at the interface. Results indicate that the proper optimization of cold spray process parameters supports the formation of Fe-based metallic glass coatings that successfully retain their amorphous structure, as well as the superior corrosion and wear-resistant properties of the feedstock powder.     

冷喷涂金属基复合涂层及材料研究进展

冷喷涂是近年来一种发展十分迅速的材料固态沉积技术,其具有喷涂温度低和颗粒沉积速度高的特点,在金属基复合涂层及材料制备方面展现出了良好的应用前景。 在大量文献整理和分析的基础上,对冷喷涂金属基复合涂层及材料的最新研究进展进行了系统的介绍。 首先归纳了机械混合法、球磨法、包覆法以及造粒法等复合粉末的制备方法及其优缺点,为复合粉末的制备和选择提供了参考;其次,分类介绍了采用冷喷涂制备的铝基、镍基、铜基、钴基以及其他金属基复合涂层及材料;再次,分析了退火、激光、搅拌摩擦焊和热机械等后续处理方法对冷喷涂金属基复合涂层及材料组织结构和性能的影响,并介绍了不同后续处理方法的优缺点;最后,总结了冷喷涂金属基复合涂层及材料的潜在应用领域和存在问题。     

Tungsten carbide coatings with different binders prepared by low power plasma spray system

Thermal spraying of cermet coatings is widely used for protection of machining parts against wear and corrosion. These coatings consist of WC particles in metal binders such as Co, Cr and Ni. Three kinds of WC powders with different metal binders (Co, NiCr and CoCr) were sprayed by low power plasma spray system on Al-Si-Cu alloy substrate. Fundamental aspects of sprayed cermet coatings, including (i) the effects of binder type on the coating structure, (ii) the hardness and (iii) the microstructure, were investigated. All cermet coatings have the same phase structure such as WC and W2 C. However, the intensities of these phases are different in each coating, mainly due to the difference in solidification rate in each case. Moreover, the hardness measurements are found to be different in each coating. The results show that, binder type has a significant effect on the physical and mechanical properties of the sprayed coatings.     

医用材料聚醚醚酮等离子喷涂表面改性研究进展

聚醚醚酮材料(PEEK)具有良好的生物相容性、化学稳定性、X射线可穿透性及优异的力学性能,广泛用于创伤、脊柱和关节等生物医疗领域。然而,PEEK属于生物惰性材料,其骨整合性不足,这在一定程度上限制了该材料在骨修复与替换等领域的发展和应用。等离子喷涂技术由于工艺简单、经济,喷涂涂层的黏结强度高等特点,是解决聚醚醚酮材料骨整合能力不足的重要表面涂层改性技术。首先,简述了等离子喷涂工艺的涂层沉积机理,并分别对等离子喷涂钛以及羟基磷灰石两种常用涂层进行了介绍;其次,从不同喷涂工艺以及喷涂参数对涂层的影响出发,详细介绍了近几年对PEEK基等离子喷涂涂层的结合强度等机械性能的最新研究进展,并对等离子喷涂过程对PEEK基体的机械强度、疲劳强度、热性能和化学降解等初始性能影响进行了总结与评价,详细介绍了PEEK基等离子喷涂涂层体内外生物性能的最新研究进展;最后,展望了等离子喷涂改性PEEK基材料的临床应用前景,以期为未来设计新型PEEK基生物材料提供理论指导。     

The Effect of Surface Chemistry and Morphology on the Properties of HVAF PEEK Single Splats

Thermal spray of polymers has had limited investigation due to the narrow processing windows that are inherent to polymer powders, especially their low temperatures of thermal degradation. The polymer poly aryl ether ether ketone (PEEK) has a continuous use temperature of 260 °C, does not suffer significant thermal degradation below 500 °C (Lu et al., Polymer, 37(14):2999-3009, 1996), and has high resistance to alkaline and acidic attack. These properties led to PEEK being selected for investigation. To minimize thermal degradation of the particles, the high velocity air fuel technique was used. To investigate the effect of substrate pretreatment on single splat properties, single splats were collected on aluminum 5052 substrates with six different pretreatments. The single splats collected were imaged by scanning electron microscopy and image analysis was performed with ImageJ, an open source scientific graphics package. On substrates held at 323 °C, it was found that substrate pretreatment had a significant effect on the circularity and area of single splats, and also on the number of splats deposited on the substrates. Increases in splat circularity, area, and the number of splats deposited on the surface were linked to the decrease in chemisorbed water on the substrate surface and the decrease of surface roughness. This proved that surface chemistry and roughness are crucial to forming single splats with good properties, which will lead to coatings of good properties.     

Study of adhesion of different plasma-sprayed coatings to aluminium

The aim of the work was to determine the bond strength of plasma-sprayed layers to aluminium substrate. The layers of nickel alloy, iron alloy, wolfram carbides with different amounts of nickel were plasma sprayed onto AK12 and PA6 aluminium alloys. The stress affecting the separation of coatings from the substrate was taken into account as the criterion of bond strength. The influence of the substrate surface roughness, the thickness of coatings, the amount of metal binder in carbide layers as well as spraying technique on bond strength were investigated. The microscope observations and sample cross-sections showed very strong adherence of the sprayed layers to aluminium substrates. It was stated that local micro-welds could take place in the layers containing metal. Properly sprayed layers reached bond strength of at least 20 MPa. It was found out that the use of the device providing continuous cleaning of the substrate surface during plasma spraying process significantly increased bond strength and improved coatings structure.     

Substrate Effect on Microstructure and Performance of LTHVOF Sprayed Copper Coatings

The performance of copper coatings fabricated on three substrates by LTHVOF spraying process was researched.XRD shows that substrate material has little effect on phase composition of coatings,and there is no oxide in the three coatings almost.These coatings are dense,and demonstrate little difference on the microstructure of the inner part of the coatings.However,microstructure of bonding area between coating and substrate shows big difference,copper coatings bonds compacter on soft substrate aluminum than hard substrate steel.Bonding strength of coatings sprayed on the soft substrate is higher than that on the hard substrate.Microstructure analysis of fracture surface shows that strong mechanical alloying phenomena when copper particles deposited on aluminum substrate.The average bonding strength of copper coatings on 1Cr18Ni9Ti,45#steel and LY12 is relatively 18.83,17.49 and 32.14 MPa.Substrates have strong effect on microstructure and bonding strength,but little on phase composition...     

Investigation of surfacing processes using aluminium-based alloys

Summary

It has been recently reported that porous Ti-N sprayed coatings can be made fine-structured by laser irradiation. This paper describes an investigation of the effects of infiltrated metal species on the wear resistance of Ti-N remelted layers.

Non-ferrous metal powders were sprayed on SS400 steel plate substrates in an argon atmosphere. The coating thickness was around 200 μm. Pure titanium was also sprayed on the non-ferrous sprayed coatings in a nitrogen atmosphere. The coating thickness was around 400 μm. Coating specimens consisting of non-ferrous and Ti-N layers were remelted by laser in a nitrogen atmosphere. The remelted layers of the coatings had a fine microstructure with a hardness value above HV1000. The wear resistance of the Ti-N coatings was appreciably improved by remelting.     

Deposition Behavior of Copper Fine Particles onto Flat Substrate Surface in Cold Spraying

Cold spray is a promising process to fabricate high-quality metallic coatings. However, it is necessary to improve some properties, especially the adhesive strength of the coating to the substrate to clarify deposition mechanism of the solid particles onto substrate surface. In this study, deposition behavior of the cold sprayed copper fine particles was observed precisely and the adhesive strength of the coating was evaluated. The deposition behavior of the sprayed individual copper particles on mirror polished stainless steel substrate was fundamentally investigated. The interface microstructure between sprayed particle and substrate revealed that an amorphous-like band region was recognized at interface during coating fabrication at high power conditions. For the deposition mechanism of the cold sprayed particles onto substrate surface, it was indicated that the deformation of the particles initially induce the destruction of its surface oxide and an appearance of the active fresh surface of the material may enhance the bonding between particles and substrate. On the other hand, in coating fabrication at high power condition, bonding between particle and substrate may be possibly formed via oxygen-rich amorphous-like layer at interface.     

Enhancement of the corrosion properties of cold sprayed Ti–6Al–4V coatings on mild steel via silica sealer

The pore formation associated with the cold spray process requires the development of an economical sealer to enhance the corrosion resistance of Ti–6Al–4V coatings on a mild steel substrate. Herein, a sound method is developed to seal pores in the cold sprayed Ti–6Al–4V coatings with silica sealer. Potentiodynamic polarization tests in 3.5 wt% sodium chloride electrolyte were employed to investigate the corrosion resistance of cold sprayed Ti–6Al–4V coatings fabricated at two standoff distances (30 and 70 mm) before and after the sealing process. The polarization resistance of cold sprayed Ti–6Al–4V coatings significantly increased by >80% after the sealing process. The electrochemical responses of cold sprayed Ti–6Al–4V were dependant on sealing the pores with agglomerated silica nanoparticles as observed by scanning electron microscopy and energy-dispersive X-ray analysis. The increase in polarization resistance makes the sealer an effective treatment for cold sprayed Ti–6Al–4V coatings used in marine environments and other engineering applications. This sophisticated sealing process can reduce the deposition cost by reducing the thickness of Ti–6Al–4V coatings and increasing their lifetime on metal components.     

喷涂工艺对超音速火焰喷涂Al-Cu-Fe-Si准晶合金涂层性能的影响

目的使用活性燃烧高速燃气喷涂(AC-HVAF)方法制备高质量的Al-Cu-Fe-Si准晶涂层,研究喷涂工艺对涂层性能的影响。方法采用气雾化Al-Cu-Fe-Si准晶合金粉末,利用AK02T型AC-HVAF喷涂系统制备Al-Cu-Fe-Si准晶涂层材料。通过X射线衍射及扫描电镜观察分析准晶合金粉末和涂层的组织与结构,通过电化学工作站、显微硬度计和接触角测试仪等手段分析准晶合金涂层的耐蚀性、显微硬度及抗粘性能。结果对气雾化准晶Al-Cu-Fe-Si合金粉末的研究发现,冷却速率显著影响准晶合金粉末的组织,在冷却速率较快的粉末中形成胞状晶组织,准晶I相含量较高。对准晶合金涂层进行热处理,高温退火显著提高了涂层的硬度,950℃退火12 h后,硬度值达到(724±153)HV0.1。分别对准晶合金涂层和基体45~#钢的接触角进行测量,准晶合金涂层的接触角最大为95°,而45~#钢的仅为79°。通过电化学工作站测试比较涂层的耐蚀性,发现在3.5%(质量分数)的Na Cl溶液中,喷涂在45~#钢和5052铝合金基体上的涂层腐蚀电流密度J_(corr)分别为6.8×10~(-6),2.0×10~(-7)A/cm~2。结论不同粒径的气雾化准晶合金粉末的相组成不同,选择合适的粒径是保证铝基准晶合金涂层质量的前提。对涂层进行合适的热处理可以有效地提高涂层的显微硬度,铝基准晶合金涂层的接触角较45~#钢的高,提高了基体的抗粘性。不同基体上制备的准晶合金涂层的耐蚀性有很大差异,5052铝合金基体上的准晶涂层耐蚀性优于喷涂在45~#钢基体上的涂层。     

Cold Sprayability of Mixed Commercial Purity Ti Plus Ti6Al4V Metal Powders

In the present work, metallic composite coatings of commercial purity Ti plus Ti6Al4V were produced by cold spraying to explore the effect of mixing on porosity and mechanical properties of the coatings. The coatings were deposited using N₂ gas at 800 °C and 4 MPa pressure on 1020 steel substrate. Coating characteristics were studied by examining porosity percentages and Vickers’s hardness. The microstructure was examined using optical and electron microscopy techniques. It was observed that mixing metal powders can lead to improvements in cold sprayability, specifically decreases in the porosity of the ‘matrix’ powder. It is shown that a critical addition can significantly influence porosity, but above this critical level, there is a little change in porosity. Hardness differences between the two powders are considered to be the first-order influence, but differences in particle sizes and morphology may also be contributing factors.