Cold gas dynamic spraying of iron-base amorphous alloy

This paper describes recent efforts to synthesize iron-base amorphous alloys coatings using cold gas dynamic spraying. Characterization of the gas-atomized iron-base (Fe-Cr-Mo-W-C-Mn-Si-Zr-B) powder shows that the powder is fully amorphous when the particle diameter is below 20 μm. The coatings produced were composed of the same microstructure as the one observed in the feedstock powder. The overall deformation suggests the occurrence of a localized deformation process at the particle/particle boundary and a possible adiabatic deformation softening inside the powder particles during splat formation. The synthesis of fully amorphous, porous-free coatings using cold gas dynamic spraying was demonstrated in this work. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Cold-Spray processing of a nanocrystalline Al−Cu−Mg−Fe−Ni alloy with Sc

This work describes recent progress in cold-spray processing of conventional and nanocrystalline 2618 (Al−Cu−Mg−Fe−Ni) aluminum alloy containing scandium (Sc). As-atomized and cryomilled 2618+Sc aluminum powder were sprayed onto aluminum substrates. The mechanical behavior of the powders and the coatings were studied using micro-and nanoindentation techniques, and the microstructure was analyzed using scanning and transmission electron microscopy (SEM and TEM). The influence of powder microstructure, morphology, and behavior during deposition on the coating properties was analyzed. This work shows that Al−Cu−Mg−Fe−Ni−Sc coatings with a nanocrystalline grain structure can be successfully produced by the cold-spray process. Inspection of the scientific literature suggests that this is the first time a hardness value of 181 HV has been reported for this specific alloy. The original version of this paper was published in the CD ROM Thermal Spray Connects: Explore Its Surfacing Potential, International Thermal Spray Conference, sponsored by DVS, ASM International, and IIW International Institute of Welding, Basel, Switzerland, May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany.     

Laser Shock Flier Impact Simulation of Particle-Substrate Interactions in Cold Spray

Coating-substrate adhesion in cold spray is a paramount property, the mechanisms of which are not yet well elucidated. To go into these mechanisms, due to the intrinsic characteristics of the cold spray process (particle low-temperature and high velocity) direct observation and control of inflight particles and related phenomena cannot be done easily. For this reason, an experimental simulation of the particle-substrate reactions at the particle impingement was developed. This simulation is based on original flier impact experiments from laser shock acceleration. Relevant interaction phenomena were featured and studied as a function of shearing, plastic deformation, phase transformation primarily. These phenomena were shown to be similar to those involved in cold spray. This was ascertained by the study of the Cu-Al metallurgically reactive system using SEM, TEM, EPMA, and energy balance and diffusion calculations. This simulation could also be used to feed finite element modeling of cold spray and laser shock flier impact.     

Review on Cold Spray Process and Technology: Part I—Intellectual Property

The number of research papers as well as of patents and patent applications on cold spray and cold spray related technologies has grown exponentially in the current decade. This rapid growth of activity brought a tremendous amount of information on this technology in a short period of time. The main motivation for this review is to summarize the rapidly expanding common knowledge on cold spray to help researchers and engineers already or soon to be involved for their future endeavors with this new technology. Cold spray is one of the various names for describing an all-solid-state coating process that uses a high-speed gas jet to accelerate powder particles toward a substrate where they plastically deform and consolidate upon impact. Cold gas dynamic spray, cold spray, kinetic spray, supersonic particle deposition, dynamic metallization or kinetic metallization are all terminologies found in the literature that designate the above-defined coating process. This review on cold spray technology is divided into two parts. In this article, Part I, patents and patent applications related to this process are reviewed, starting from the first few mentions of the idea at the beginning of the 20th century to its practical discovery in Russia in the 1980s and its subsequent occidental development and commercialization. The patent review encompasses Russian and USA patents and patent applications. Part II will review the scientific literature giving a general perspective of the current understanding and capability of this process.     

冷喷涂TC4涂层临界沉积速度计算及制备涂层性能研究

目的研究冷喷涂TC4涂层的临界沉积速度及粒子温度对临界沉积速度的影响规律,并研究气体压强对沉积涂层性能的影响规律。方法理论研究上,采用有限元LS-DYNA软件中的Johnson-Cook塑性模型,选取3D164计算单元建立模型,研究粒子在不同温度和不同速度下碰撞基体后的形貌特征,确定粒子沉积临界速度。试验研究上,采用N_2作为冷喷涂驱动气体,在TC4合金上制备TC4涂层,然后采用SEM、Image J图像分析软件、硬度计等分析已沉积涂层的孔隙率和硬度等性能。结果 25、400、500、600℃温度下,计算表明10μm的TC4合金粒子在TC4基板上的临界沉积速度分别为730、465、392、361 m/s,即随粒子温度升高,粒子临界沉积速度降低,粒子沉积成涂层更容易。采用冷喷涂工艺在TC4基板上沉积TC4涂层,在N_2温度600℃、气体压力3 MPa的条件下,制备的TC4涂层厚度约1000μm,与TC4钛合金基体结合紧密,涂层孔隙率约为6.46%。结论气体温度升高,粒子临界沉积速度降低;气体压强变大,制备的涂层厚度就大且更加致密。     

气体温度对冷喷涂7075铝合金涂层性能的影响

目的研究气体温度对冷喷涂7075铝合金涂层性能的影响,以期为制备高性能涂层提供重要参考。方法利用冷喷涂技术,在较高的工作气体压力(5 MPa)下,通过改变工作气体温度(450、500、550、600℃),采用氮气在纯铝基体上制备了大厚度7075铝合金涂层。采用光学显微镜(OM)、扫描电子显微镜(SEM)对涂层组织结构及孔隙率进行了分析测定,用维氏显微硬度法测定涂层硬度,通过拉伸实验测定涂层结合强度,研究了冷喷涂工作气体温度对7075铝合金涂层组织及沉积特性的影响。结果工作气体温度在450～550℃范围时,对涂层组织及力学性能影响有限。当工作气体温度为450℃时,涂层孔隙率为0.14%,显微硬度为117.8HV0.1,结合强度超过55.3 MPa。但过高的工作气体温度并不利于冷喷涂7075铝合金涂层的制备,当喷涂气体温度达到600℃时,涂层孔隙率升高到4.2%。结论仅采用廉价的氮气即可制备高致密度和高结合强度的冷喷涂7075涂层,当主气温度在450～550℃区间时,涂层微观组织和性能随气体温度变化不大,而过高的工作气体温度(600℃)并不利于冷喷涂7075涂层相关性能的提升。     

Manufacturing Process of Nanostructured Alumina Coatings by Suspension Plasma Spraying

This paper describes the formation process of nanostructured alumina coatings and the injection system obtained by suspension plasma spraying (SPS), an alternative to the atmospheric plasma spraying technique in which the material feedstock is a suspension of the nanopowder to be sprayed. The nanoscale alumina powders (d ≈ 20 nm) were dispersed in distilled water or ethanol and injected by a peristaltic pump into plasma under atmospheric conditions. Optical microscopy (OM), scanning electron microscopy (SEM), and x-ray diffraction (XRD) analyses were performed to study the microstructure of the nanostructured alumina coatings. The results showed that the nanoscale alumina powders in suspension were very easily adsorbed at the inner surface of injection, which caused the needle to jam. The rotation of the pump had a great effect on the suspension injection in the plasma. The very small resistance of the thin plasma boundary layer near the substrate can drastically decrease the impacting velocity of nanosize droplets. The concentration of suspension also has a significant influence on the distribution of the size of the droplet, the enthalpy needed for spraying suspension, and the roughness of the coating surface. The phase structures of alumina suspension coatings strongly depend on the plasma spraying distance. A significant nanostructured fine alumina coating was obtained in some areas when ethanol was used as a solvent. The microstructures of the coating were observed as a function of the solvent and the spraying parameters.     

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.     

Numerical Studies of the Application of Shock Tube Technology for Cold Gas Dynamic Spray Process

A new method for a combustion-free spraying is studied fundamentally by modeling and simulation in comparison with first experiments. The article focuses on the numerical simulation of the gas-particle nozzle flow, which is generated by the shock reflection at the end wall section of a shock tube. To study the physical fundamentals of this process, at present only a single shot operation is considered. The particles are injected downstream of the nozzle throat into a supersonic nozzle flow. The measurements of the particle velocity made by a laser Doppler anemometry (LDA) set up show that the maximum velocity amounts to 1220 m/s for stainless steel particles of 15 μm diameter. The CFD-Code (Fluent) is first verified by a comparison with available numerical and experimental data for gas and gas-particle flow fields in a long Laval-nozzle. The good agreement implied the great potential of the new dynamic process concept for cold-gas coating applications. Then the flow fields in the short Laval nozzle designed and realized by the Shock Wave Laboratory (SWL) are investigated. The gas flow for experimentally obtained stagnation conditions is simulated. The gas-particle flow without and with the influence of the particles on the gas flow is calculated by the Surface Engineering Institute (IOT) and compared with experiments. The influence of the injection parameters on the particle velocities is investigated, as well. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Application of Suspension Plasma Spraying (SPS) for Manufacture of Ceramic Coatings

Conventional thermal spray processes as atmospheric plasma spraying (APS) have to use easily flowable powders with a size up to 100 μm. This leads to certain limitations in the achievable microstructural features. Suspension plasma spraying (SPS) is a new promising processing method which employs suspensions of sub-micrometer particles as feedstock. Therefore much finer grain and pore sizes as well as dense and also thin ceramic coatings can be achieved. Highly porous coatings with fine pore sizes are needed as electrodes in solid-oxide fuel cells. Cathodes made of LaSrMn perovskites have been produced by the SPS process. Their microstructural and electrochemical properties will be presented. Another interesting application is thermal barrier coating (TBC). SPS allows the manufacture of high-segmented TBCs with still relatively high porosity levels. In addition to these specific applications also the manufactures of new microstructures like nano-multilayers and columnar structures are presented.     

Cold gas dynamic spraying of aluminum: The role of substrate characteristics in deposit formation

Aluminum powder of 99.7 wt.% purity and in the nominal particle size range of −75+15 μm has been sprayed onto a range of substrates by cold gas dynamic spraying (cold spraying) with helium, at room temperature, as the accelerating gas. The substrates examined include metals with a range of hardness, polymers, and ceramics. The substrate surfaces had low roughness (R _a < 0.1 μm) before deposition of aluminum in an attempt to separate effects of mechanical bonding from other forms of bonding, such as chemical or metallurgical bonding. The cross-sectional area of a single track of aluminum sprayed onto the substrate was taken as a measure of the ease of initiation of deposition, assuming that once a coating had begun to deposit onto a substrate, its growth would occur at a constant rate regardless of substrate type. It has been shown that initiation of deposition depends critically upon substrate type. For metals where initiation was not easy, small aluminum particles were deposited preferentially to large ones (due to their higher impact velocities); these may have acted as an interlayer to promote further building of the coating. A number of phenomena have been observed following spraying onto various substrates, such as substrate melting, substrate and particle deformation, and evidence for the formation of a metal-jet (akin to that seen in explosive welding). Such phenomena have been related to the processes occurring during impact of the particles on the substrate. Generally, initiation of aluminum deposition was poor for nonmetallic materials (where no metallic bonding between the particle and substrate was possible) and for very soft metals (in the case of tin, melting of the substrate was observed). Metallic substrates harder than the aluminum particles generally promoted deposition, although deposition onto aluminum alloy was difficult due to the presence of a tenacious oxide layer. Initiation was seen to be rapid on hard metallic substrates, even when deformation of the substrate was not visible. The original version of this article was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Sciences and Applying the Technology, International Thermal Spray Conference (Orlando, FL), May 5–8, 2003, Basil R. Marple and Christian Moreau, Ed., ASM International, 2003.     

Microstructure Characteristics of SiC Particle-Reinforced Aluminum Matrix Composites Coatings by Cold Spraying

A dense Al/SiCp composite coating with high volume fraction(60%)of nano SiCp reinforcement was fabricated by cold spraying of ball-milled Al-60SiCp composite powder.The morphologies evolution of the Al-60SiCp composite powder during ball milling and the microstructure and microhardness of the cold-sprayed Al-60SiCp composite coating were investigated.The results show that Al particles undergone fracture deformation and nano SiC particles are uniformly distributed in soft Al matrix after ball milling.A dense Al-60SiCp composite coating can be fabricated by cold spraying of ball milled composite powder.Nano SiC particles in the cold-sprayed Al-60SiCp composites coating exhibit a reasonably uniform distribution.The Hv0.5 microhardness of the Al-60SiCp composite coating is reached up to(5.30±0.53)GPa due to the enhancement of SiC particles,compared to(0.34±0.03)GPa for the pure Al bulk.     

Air gas dynamic spraying of powder mixtures: Theory and application

The radial injection gas dynamic spray (RIGDS) technology of powder coatings deposition was considered for this work. A coating was created by injecting powders with variable compositions into a supersonic air jet and depositing powder on the substrate. This study describes the preliminary analysis of an air gas dynamic spray method realized by a portable RIGDS apparatus with a radial injection of powder. Attention was given to shock compaction processes during the coating structure formation and examples of powder mixtures utilization in RIGDS. It was shown that the operational parameters of supersonic powder-gas jet have a significant influence on the coating's microstructure, thus defining the high performance of the coating. Compaction and bonding of particles were analyzed. The original version of this paper was published in the CD ROM Thermal Spray Connects: Explore Its Surfacing Potential, International Thermal Spray Conference, sponsored by DVS, ASM International, and HW International Institute of Welding, Basel, Switzerland, May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany.     

冷喷涂制备多孔Ta涂层及生物相容性

目的 提高生物医用钛合金的生物相容性。方法 采用冷喷涂技术在其表面制备了内部多孔且表面粗糙的钽涂层,并对涂层的微观组织、弹性模量、表面粗糙度、孔隙率、相组成等进行表征;通过溶血率实验、动态凝血时间实验、血小板黏附实验和细胞增殖实验等评价其血液相容性。结果 涂层表面粗糙度为24.9μm,孔隙率为12.6%,弹性模量为147 GPa。喷涂后涂层相组成为Ta,涂层与基体的结合强度为24 MPa。TC4钛合金基体和钽涂层2种材料均具有优异的红细胞相容性且2种材料表面的动态凝血程度相似,表明在TC4钛合金表面制备钽涂层后,钽涂层不会影响凝血因子的活性。钽涂层具有更好的防止血小板黏附与变形的性能。在细胞增殖实验中,细胞在钽涂层表面的增殖能力略高于TC4钛合金。结论 多孔钽涂层的弹性模量相对钽块降低了22%。其生物活性高于TC4钛合金基体。     

300M钢表面冷喷涂锌镍复合涂层性能研究

目的 研究300M高强钢表面的冷喷涂锌镍复合涂层的涂层性能.方法 采用机械混合的方式将锌粉和镍粉进行混合,利用低温气动喷涂技术在300M高强钢表面制备锌镍复合涂层,采用扫描电子显微镜、能量色散谱和显微硬度测试仪研究涂层的微观组织结构.采用普通中性盐雾加速实验、涂层破损盐雾加速试验及户外暴晒试验,对冷喷涂锌镍涂层的抗腐蚀性能进行综合评价.考核冷喷涂对300M钢基材疲劳性能的影响.结果 根据SEM的表面及截面图片分析,冷啧涂锌镍复合涂层十分致密,且无孔隙及裂纹,涂层的孔隙率平均为0.4％,结合强度40 MPa左右.根据EDS结果分析,锌镍复合涂层中锌的质量分数为85％左右,镍的质量分数为15％左右.锌镍复合涂层的显微硬度为70.8HV0.49.锌镍复合涂层中镍粒子的强化作用,提高了涂层的硬度.冷喷涂锌镍复合涂层具有非常好的抗腐蚀性能,盐雾实验超过770h,即使涂层破损也可以达到600h.户外暴晒实验12个月表面无明显腐蚀,并且冷喷涂对300M钢基材的疲劳性能没有影响.结论 冷喷涂锌镍复合涂层作为抗腐蚀涂层,可以对300M高强钢提供保护.     

Microstructural Studies of Cold Sprayed Copper,Nickel, and Nickel-30% Copper Coatings

Cold spraying enables to produce metallic coatings with low porosity level and low oxygen content. Several material properties such as electrical conductivity and corrosion resistance rely on these properties. Aim of this study was to characterize microstructural properties of cold sprayed copper, nickel, and nickel-30%copper coatings. Microstructures, denseness, and deformation of particles were investigated. SEM analysis and corrosion tests were done to get information of through-porosity. Open porosity has an important role on protectiveness of anodically protective coatings, such coating materials like copper and nickel. In this study, cold-sprayed Cu coating was fully dense. However, cold-sprayed Ni and Ni-30%Cu coatings seemed to be microstructurally dense but some porosity in some areas of the coatings especially in some parts of particle boundaries was noticed after corrosion tests. Furthermore, effect of annealing to microstructure and corrosion test behavior was studied. Cold sprayed Ni coating became denser during heat treatment.     

Q345R板材表面冷喷涂Al-Zn涂层的组织及性能研究

目的 研究添加元素Zn含量的变化对涂层的显微组织、孔隙率、硬度及涂层-基体间界面结合强度等的影响规律.方法 采用冷喷涂技术在Q345R板材表面制备性能优良的纯Al和Al-Zn复合涂层,通过扫描电子显微镜对涂层的形貌进行分析,通过维氏显微硬度计对涂层的力学性能进行表征,并揭示涂层与基体间的界面结合机理.结果 冷喷涂纯Al...     

Effect of Cathode Microstructure on Arc Velocity and Erosion Rate of Cold-Sprayed Copper Cathodes in a Magnetically Rotated Atmospheric Pressure Arc

Atmospheric pressure arc velocity and erosion measurements were performed on cold-sprayed cathodes in a continuously running arc system. Ultrahigh purity (99.99% pure) argon was used as plasma forming gas. An external magnetic field of 0.10 T was used to rotate the arc, which was operated at a constant power of 6 kW (40 V). Cathodes having microstructures with mean grain sizes, ranging from 1.12 to 3.06 μm, were produced using cold spraying (CS) and annealing methods. CS cathodes were tested in their as-sprayed state and annealed state. Annealed CS coatings with near equi-axed grains of 2.29 μm average size gave 60% higher steady-state arc velocities and up to 50% lower erosion rates than massive copper cathodes having 20-23 μm average grain size. An effect of cathode microstructure on arc velocity and on arc erosion rates was observed.     

冷喷涂单颗粒铜在铝基体上的显微结构研究

采用冷喷涂法在铝(Al)基体上沉积单颗粒铜(Cu),利用聚焦离子束/电子束(FIB/SEM)系统精确定位并原位制备了完整单个颗粒Cu沉积在Al基体上的透射样品,分析其显微结构及形成原因。实验结果表明,撞击过程中温度与应力分布不均匀,导致沉积Cu颗粒不均匀形变。Cu/Al界面受影响较大:颗粒动能转化为形变能和热能,打破了界面处氧化膜,使界面附近温度迅速升高,发生动态再结晶,生成金属间化合物Cu_9Al_4;Cu颗粒内距界面越远的区域,受温度和应力的影响越小,其变形主要是通过晶体内位错增殖和移动;沉积颗粒顶部,远离Cu/Al界面,几乎不受应力和温度影响,保持原始显微结构。     

Kinetic sprayed rare earth iron alloy composite coatings

One unique advantage of the kinetic spray process is its ability to mix constituents that would normally react with each other to form coatings. This attribute was used to produce composite coatings with different rare earth iron alloys (REFe₂) and several ductile matrices. Composite coatings of Terfenol-D [(Tb_0.3Dy_0.7)Fe_1.9] and SmFe₂ were combined with ductile matrices of aluminum, copper, iron, and molybdenum. Evidence of an induced magnetic coercivity was measured for the REFe₂-Mo and Fe composite coatings. Coatings were produced on flat substrates and shafts. Coating morphology as well as the physical, magnetostrictive, and magnetic properties of these coatings are discussed. This article was originally published inBuilding on 100 Years of Success: Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.