Numerical simulation of the effects of the impact velocity on the particle deposition characteristics in cold gas dynamic spraying

In this study, the effects of the impact velocity on the particle deposition characteristics in cold gas dynamic spraying （CGDS） of 304 stainless steel （SS） on an interstitial free （IF） steel substrate are numerical simulated by means of a finite element analysis （FEA）. The results have illustrated that when the particle impact velocity exceeds a critical value at which adiabatic shear instability of the particle starts to occur. Meanwhile, the fatten ratio and impact crater depth （or the effective contacting area ） increase rapidly. The particle-substrate bonding and deposition mechanism can be attributed to such an adiabatic shear deformation induced by both the compressive force and the slide friction force of particle. The critical velocity can be predicted by numerical simulation, which is useful to optimize the CGDS processing parameters for various materials.

Mitigative Effects of Foliage Spraying and Root Irrigation of ALA on Banana Plantlets Exposed to Cold Stress

[Objective] This study aimed to investigate the effect of ALA applied by foliage spraying and root irrigation on banana plantlets exposed to cold stress. [Method] After applied by foliage spraying and root irrigation with 5-aminolevulinic acid （ALA） at four different concentrations, ＂Brazil banana＂ plantlets were placed in artificial climate boxes at 7 ℃ to imitate low-temperature stress. [Result] The results showed that ALA application by both foliage spraying and root application can significantly increase SOD and POD activities, and reduce O2- generation rate, MDA content and relative conductivity in leaves of banana plantlets, as well as raising proline content, soluble protein content and relative water content, and maintaining the stability of chlorophyll. Foliage application of ALA within concentration range of 0.505.00 mg/L had best effect, which increased the chlorophyll content and reduced the relative conductivity and MDA content significantly compared to root irrigation at the same concentration, and raised SOD and POD activities by 64.5% and 12.3% respectively at 5 mg/L compared to their counterparts by root irrigation. [Conclusion] Foliage spraying of ALA can better mitigate the injuries to banana plantlets caused by low-temperature stress.

Optimization of spray conditions in cold spraying based on numerical analysis of particle velocity

The effects of the parameters involved in cold spray on the acceleration of particles are systematically investigated by a CFD code in order to reveal the main factors influencing significantly particle velocity. The parameters involved include nozzle geometry parameters, processing parameters and properties of spray particles. It is found that driving gas type, operating pressure and temperature are main processing parameters which influence particle velocity. As for nozzle geometry, the expansion ratio and divergent section length of spray gun nozzle show significant effects. Moreover, the density, size and morphology of powder also have significant effects on particle velocity. The effects of those main parameters are summarized in a comprehensive equation obtained through nonlinear regression of the simulated results for the estimation of particle velocity. The interactions of the parameters on particle acceleration can be examined through the equation. Moreover, the optimization of the dimensions of spray gun nozzle and spray parameters can be realized based on the obtained results.

Influence of TiCl_4 treatment on performance of dye-sensitized solar cell assembled with nano-TiO_2 coating deposited by vacuum cold spraying

Titanium tetrachloride (TiCl4) treatment was employed to TiO2 coating deposited on fluoride-doped tin oxide (FTO) conducting glass and indium oxide doped tin oxide (ITO) conducting glass, respectively. The nano-crystalline TiO2 coating was deposited using a composite powder composed of polyethylene glycol (PEG) and 25 nm TiO2 particles by vacuum cold spraying (VCS) process. A commercial N-719 dye was used to adsorb on the surface of TiO2 coating to prepare TiO2 electrode, which was applied to assemble dye-sensitized solar cell (DSC). The cell performance was measured under simulated solar light at an intensity of 100 mW·cm-2. Results show that with an FTO substrate the DSC composed of a VCS TiO2 electrode untreated by TiCl4 gives a short-circuit current density of 13.1 mA·cm-2 and an open circuit voltage of 0.60 V corresponding to an overall conversion efficiency of 4.4%. It is found that after TiCl4 treatment to the VCS TiO2 electrode with an FTO substrate, the short circuit current density of the cell increases by 31%, the open-circuit voltage increases by 60 mV and a higher conversion yield of 6.5% was obtained. However, when an ITO substrate is used to deposit TiO2 coating by VCS, after TiCl4 treatment, the conversion efficiency of the assembled cell reduces slightly due to corrosion of the conducting layer on the ITO glass by TiCl4.

Progress in the application of cold gas dynamic spraying to repairing continuous casting molds

A new continuous casting mold repairing method--cold gas dynamic spraying （CGDS） is introduced. The study investigates the advantages of the CGDS process regarding repairing operation, such as convenient, in-situ repairation,little heat delivery, microstructural and dimensional stability and other special applications. Microstructure and mechanical properties of the copper alloy coating, nickel coating, ceramic composite coating, and their interface to the substrates ,which are usually used in repairing operation have been researched by means of optical microscopy （ OM）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and micro-hardness tests. Experimental results have demonstrated the relative density of the copper alloy coating is as high as 98.7%, and that no obvious difference can be observed between the CrZrCu substrate and the Cu alloy coating in terms of microstructures; thus the interface is quite difficult to be identified. The bonding strength and micro-hardness of the Cu alloy coating reach up to 37 MPa and 310 HV0.2 ,respectively. The interface between the copper alloy coating and the nickel coating is either zigzag or wave shaped, and the cohesion is relatively good. As-sprayed nickel coating is dominated by severely deformed particles,and the relative density is up to 98.5%. Complete recrystallization occurred after annealing at 900℃ for one hour,while its micro-hardness remains as high as 124.1 HV02. All these results have indicated that CGDS is a promising technology for repairing the continuous casting mold and that its future development is prosperous as well.

Microstructure evolution of cold-sprayed coating during deposition and through post-spraying heat treatment

The microstructural features of cold-sprayed coatings were investigated using Cu, Ti and Zn feedstocks by optical microscopy, scanning electron microscopy and transmission electron microscopy to reveal the microstructure evolution mechanisms in cold spray. Four typical effects including tamping, refinement, impact-induced fusion and annealing were examined on microstrueture. It is found that the microstructure of cold spray coating is remarkably influenced by spray materials. Ti coatings consist of evident porous layer and Cu coatings present a limited porous layer only near the surface. It is clear that the successive tamping effect and dynamic refinement of grains significantly influence the microstructure evolution of cold-sprayed coating. The tamping effect leads to the densification of porous coating layer gradually and the refinement effect leads to the formation of fine microstructure. It is considered that the large difference in the formation of porous layer is attributed to the dynamic impact pressure and hardenability of materials. It is also found that the impact-induced fusion during deposition of Zn coating can also modify the interfacial microstructure between particles in cold spray coating. Moreover, the nanocrystalline phase can be formed at the interfaces among particles resulting from the localized melting of the interfaces and tamping effect. Furthermore, the annealing treatment can modify the microstructure and property of a cold-sprayed coating.

Effect of different incidence angles on bonding performance in cold spraying

The deformation behaviour of spray particles impacting upon a substrate under the oblique impact condition in cold spraying was investigated using finite element analysis(FEA)method.The effect of incidence angle of particle on the deformation of particle and substrate was examined.It is found that the contact area between the deformed particle and substrate decreases and the crater depth in the substrate reduces with increasing the tilting angle at the same impact velocity.The normal component of impact velocity takes an important role in the impacting process and formation of bonding.

A novel approach for fabricating a CNT/AlSi composite with the self-aligned nacre-like architecture by cold spraying

A fully dense carbon nanotubes (CNTs) reinforced AlSi matrix composite with the multiscale nacre-like architecture was designed and successfully realized by flake powder metallurgy followed by cold spraying (CS). The nanolaminated and ultrafine-grained structure initially created in the CNT/AlSi flaky powder was perfectly conserved, due to the typical ‘cold’ feature of CS. As discussed based on finite element analysis and single splat observation, self-alignment behavior of the flaky powders during impact also allowed the formation of the microlaminated structure. Hence, the scalable CS technique opens a new avenue for bioinspired material design and fabrication with complex shape.

Preparation of TiAl_3-Al composite coating by cold spraying

TiAl3-Al coating was deposited on orthorhombic Ti2AlNb alloy substrate by cold spraying with the mixture of pure Al and Ti as the feedstock powder at a fixed molar ratio of 3-1 when the spraying distance,gas temperature and gas pressure for the process were 10 mm,250 ℃ and 1.8 MPa,respectively.The as-sprayed coating was then subjected to heat treatment at 630 ℃ in argon atmosphere for 5 h at a heating rate of 3 ℃/min and an argon gas flow rate of 40 mL/min.The obtained TiAl3-Al composite coating is about 212 μm with a density of 3.16 g/cm3 and a porosity of 14.69% in general.The microhardness and bonding strength for the composite coating are HV525 and 27.12 MPa.

Conceptual Design and Analysis of Cold Mass Support of the CS3U Feeder for the ITER

In the International Thermonuclear Experimental Reactor（ITER） project,the feeders are one of the most important and critical systems.To convey the power supply and the coolant for the central solenoid（CS） magnet,6 sets of CS feeders are employed,which consist mainly of an in-cryostat feeder（ICF）,a cryostat feed-through（CFT）,an S-bend box（SBB）,and a coil terminal box（CTB）.To compensate the displacements of the internal components of the CS feeders during operation,sliding cold mass supports consisting of a sled plate,a cylindrical support,a thermal shield,and an external ring are developed.To check the strength of the developed cold mass supports of the CS3U feeder,electromagnetic analysis of the two superconducting busbars is performed by using the CATIA V5 and ANSYS codes based on parametric technology.Furthermore, the thermal-structural coupling analysis is performed based on the obtained results,except for the stress concentration,and the max.stress intensity is lower than the allowable stress of the selected material.It is found that the conceptual design of the cold mass support can satisfy the required functions under the worst case of normal working conditions.All these performed activities will provide a firm technical basis for the engineering design and development of cold mass supports.

Microstructure and micro-hardness of the Inconel 718 superalloy coating prepared by cold gas dynamic spraying

Inconel 718 superalloy coating was prepared on a martensitic steel substrate by cold gas dynamic spraying （ CGDS ）. Microstructure and micro-hardness of the coating were characterized by means of scanning electronic microscope （SEM） ,energy dispersive spectrometer （EDS）, and micro-hardness and nano-indentation tests. The results have indicated that the coating＇ s thickness can reach more than 300 um, and there exists a good interfacial cohesion between the coating and the substrate. The quantity and size of the defects at the bottom, middle and top areas increase gradually. There is no significant change to the original microstructure of the Inconel 718 superalloy particle after the process of CGDS ;and an obvious torsional deformation on the particle＇ s profile is produced while little deformation at the center part occurs. The micro-hardness of the coating at the bottom, middle and top areas decreases in turn. Compared with the bottom area, the micro-hardness of the middle and top areas decreases by about 10% and 21%, respectively. The nano-hardness of the coating is much lower than the original particle,which decreases by about 13.5% at the bottom area and 28% at the top area,respectively. The distribution of micro-defects is an important factor to the micro-hardness of the coating.

Study on the 316L stainless steel coatings and their properties by cold gas dynamic spraying

316L stainless steel coatings were prepared by cold gas dynamic spraying （CGDS） on a carbon steel. A new heater of sprayed powders was added to the traditional facility. The results show that the coating quality is obviously improved, due to better interface bonding and reduced porosity.

Numerical simulation of particle tracks in the cold gas dynamic spraying process

In this study,the distribution behavior of the particle flow field in cold gas dynamic spraying （CGDS） was simulated through the Computational fluid dynamics （CFD） method. Traces of the particles with different diameters in the gas flow field were analyzed, and effects of fiat and sphere substrates on the particle tracks were also compared .Simulation results indicate that different escaping directions of particles flow with the two substrates. These investigations. gave instructions on how to design the powder recovery and dusting machines in a CGDS system.

Influence of the preheated substrate temperature on the microstructure deposition behavior of the 304 stainless steel coatings deposited by cold gas dynamic spraying

The effects of the substrate temperature on the deposition and microstructure of the 304 stainless steel （SS） cold gas dynamic spraying （CGDS） coatings were investigated. It was found that the higher substrate temperature could increase the deposition rate of the 304 SS particles,even the oxide films existed at the interface. There was a critical oxide film with a thickness of 3 -4 um which could be destroyed by the impacted particles. The micro-hardness and microstructure of the 304 SS coatings under different substrate preheating temperatures were almost the same.

Effects of standoff distance on the supersonic flow fields in cold gas dynamic spraying

In this study,the effects of standoff distance （SOD） on the supersonic flow fields （including gas and particle flow fields） during cold gas dynamic spraying （ CGDS ） are investigated by means of computational fluid dynamics （CFD）. The variation of velocity,temperature,pressure and density with different SoD is elucidated through the analysis of the distribution properties of the flow fields. It is found that the shock waves in front of the substrate remarkably influence the gas and particle flow fields. The wave system of expansion waves and pressure waves come into being continuously. The velocity of gas reaches the super.,;onic speed at the position of the Mach disc, while it decreases sharply when the gas flow crosses the Mach disc. The optirnal SoDs are 40 mm for 1 um particles and 50 mm for both 5 um and 22 um particles.

激光复合冷喷涂技术研究进展

冷喷涂是一种基于材料高速撞击产生剧烈塑性变形实现结合的沉积方法,具备加工温度低、沉积效率高、热影响小等优势,已在增材制造、工业关键零部件的修复再制造等领域展现出巨大潜力。冷喷涂复合制造技术是一种新兴技术,其中激光复合冷喷涂是一个重要的方向,近年来得到了越来越多的关注。对激光复合冷喷涂技术研究进展进行回顾和总结,对激光预处理、激光同步复合和激光后处理3种复合方式进行重点阐释。针对每种复合方式,分别从复合原理、复合优势及复合效果3个方面进行总结,对比激光复合冷喷涂技术与单一技术在沉积层微观组织以及性能等方面的差异。通过对激光复合冷喷涂技术最新进展的全面总结和归纳,将为进一步推动激光复合冷喷涂技术的研究和应用提供指导和参考。

基于替代电镀硬铬的WC增强金属复合涂层疲劳性能的研究现状

传统电镀硬铬涂层存在网纹裂纹缺陷、抗疲劳性能不足以及环境污染严重等问题,针对新一代航空工业急需新技术替代传统电镀硬铬这一迫切需求,研发新型的耐磨耐蚀涂层体系及其先进环保的再制造技术迫在眉睫。根据先进涂层技术的发展情况,研发出了基于高温熔化-凝固技术的物理气相沉积、超音速火焰喷涂以及激光熔覆技术,这在绿色制备航空工业用耐磨耐蚀涂层上表现出了一定的应用前景,并表现出了比传统电镀硬铬更长的疲劳寿命,但其仍存在内应力过高而开裂、粉末氧化或相变导致疲劳性能下降等一系列关键问题。近年来,冷喷涂涂层技术作为先进环保的新技术,凭借其低温固态沉积特性在制备金属基复合涂层上展现出了显著的冶金优势,其中冷喷涂涂层的残余压应力有助于提高零件的疲劳性能。此外,从起落架防护涂层沉积到其修复再制造环节,冷喷涂技术均可参与其中。因此,作为固态沉积工艺的冷喷涂,其在替代传统电镀铬的新型涂层制备工艺方面具有显著的应用潜力,未来的研究将集中于优化冷喷涂涂层材料和工艺上,以进一步提高其力学性能和疲劳性能。

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。

Ni,Co元素对FeCrAlCu系高熵合金涂层组织和耐磨性能的影响

为了解决金属零件表面的防护问题,采用冷喷涂辅助感应重熔合成高熵合金涂层的方法,在45#钢基体表面制备FeCrAlCu,FeCrAlCuNi,FeCrAlCuCo,FeCrAlCuNiCo高熵合金涂层,通过XRD,SEM,EDS,TEM,磨擦磨损试验机等,研究Ni,Co元素添加对FeCrAlCu系高熵合金涂层的相结构、显微组织以及耐磨性能的影响。结果表明:FeCrAlCu系高熵合金涂层均为FCC+BCC相构成,其中Ni元素添加可以促进FCC相形成,Co元素添加促进B2相(AlCo)生成。FeCrAlCu系高熵合金涂层组织均为树枝晶,随着Ni,Co元素的同时添加,涂层中的枝晶数目增加,并明显粗化。Ni,Co元素同时添加时,FeCrAlCuNiCo高熵合金涂层的摩擦性能最佳,涂层的硬度为565.5HV,摩擦因数为0.349,磨损率为3.97×10^(-5)mm^(3)·N^(-1)·m^(-1)。

基于冷喷涂工艺的Mg-Zn-Al-Sn-Mn合金防腐Al涂层制备

采用冷喷涂技术在Mg-Zn-Al-Sn-Mn合金表面制备Al涂层,以提高其耐腐蚀性能。研究工作气体温度和压力对Al涂层显微组织和腐蚀行为的影响。结果表明,随着气体温度和压力的升高,Al涂层的致密度和厚度均明显增加。高的气体温度能降低颗粒沉积的临界速度,并提高沉积效率。高的气体压力不仅提升机械结合质量,而且对沉积的涂层具有较强的夯实作用。由于孔隙的减少,Al涂层的耐蚀性随着气体温度和压力的升高而提高。Al(OH)_(3)和Al_(2)O_(3)等腐蚀产物可以堵塞涂层中的孔隙,并作为阻碍腐蚀的物理屏障,从而有效保护Mg合金免受腐蚀。