工艺参数变化对冷喷涂铝沉积性能的影响

在环境温度下以氦气为驱动气,在低碳钢基体上冷喷涂铝粉,采用工业纯铝粉,颗粒尺寸范围为-75 15 μm.测得涂层沉积效率达到40 %,孔隙率低于1.0 vol%,涂层的硬度由铝粉末的硬度31 kgf·mm-2提高到了53 kgf·mm-2,这主要是涂层内产生严重塑性变形的结果.研究了滞止压力、喷涂距离、送粉速率和喷枪与基板相对运动速度等工艺参数变化对沉积效率的影响.结果表明,以上每一个工艺参数的变化均对沉积效率产生显著影响.滞止压力、喷涂距离和送粉速率通过改变颗粒碰撞速度来影响沉积效率;当碰撞速率降低时沉积效率降低.然而,当颗粒速度降低时,由于参与冲击的颗粒(非沉积颗粒)比例增加,涂层的孔隙率并没有被影响.当增加喷枪与基体的相对运动速度时,沉积速率显著降低;这一结果表明沉积效率还存在某种喷射流量或剂量的影响因素,例如在沉积初期的"激活"期,喷射剂量就直接影响了沉积效率.     

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。     

基于材料性能的冷喷涂临界速度预测窗口研究取得新进展

正冷喷涂过程中,喷涂粒子被高速气流加速到较高的速度(200~1 200m/s),在固态下碰撞基体,通过粒子强烈的塑形变形沉积在基体上形成涂层。由于喷涂材料和碰撞速度不同,粒子或者从基体上反弹或者沉积于基体上,使得粒子开始沉积到基体上的速度被称为临界速度,它是冷喷涂技术的一个     

冷喷涂Al涂层性能及沉积行为的分析

利用自行研制的冷喷涂系统制备出Al涂层,对涂层的结合强度、孔隙率以及显微硬度等进行了测试,借助金相显微镜及扫描电镜对涂层与界面的组织形貌进行观察,并对Al涂层的沉积行为进行了分析.结果表明,冷喷涂铝涂层以机械镶嵌的方式结合,颗粒在与基体冲击碰撞后变成长条状,并且其变形方向与冲击方向成直角.     

冷喷涂AgSnO_2触点涂层的组织与性能

采用高能球磨方法制备AgSnO_2复合粉末,将球磨粉末冷喷涂到铜基板上,能够获得几毫米厚度的较致密的AgSnO_2触点涂层。850℃退火后涂层发生进一步致密化并且在原始粉末颗粒边界形成富银区,涂层材料硬度略为降低。电弧侵蚀和电接触试验表明,冷喷涂的AgSnO_2涂层材料具有低而稳定的接触电阻,能够满足触点的基本性能要求。     

冷喷涂过程中能量变化及沉积行为的模拟研究

采用有限元分析软件ANSYS/LS-DYNA,模拟了超音速冷喷涂过程中的颗粒碰撞过程,研究了高速颗粒与基板碰撞时的能量转化、分配以及颗粒沉积过程,分析了碰撞速度和材料特性对它们的影响.结果表明,碰撞过程中,颗粒和基板材料均发生塑性变形,使颗粒的动能被消耗,且绝大部分动能转变为材料内能.碰撞完成之后,颗粒动能被分配到颗粒和基板材料中,定义碰撞之后分配到颗粒中的与分配到基板中的能量之间的比值为能量分配系数K,K值过高或过低,均表明颗粒和基板之间变形能力相差较大,不利于颗粒与基板结合形成良好的涂层.系统初始动能以及颗粒与基板材料性能对K值都有影响.     

冷喷涂技术及其在增材制造中的应用专题研讨会(襄阳)通知

冷喷涂技术是利用加热的高压气体通过拉瓦尔喷嘴产生超音速气流,将送入气流的粉末颗粒加速到300~1500m/s后使其碰撞基体产生剧烈的塑性变形并与基体形成固相连接、进而实现涂层沉积的方法。因其具有涂层厚度不受限制、加工效率高等特点,目前已逐渐发展成为一种快速增材制造技术,备受业界关注。与传统热喷涂方法不同,其加工温度低,金属材料在喷涂过程中氧化程度低,材料受到的热影响较小,通过工艺控制制备的沉积体孔隙率极低,部分材料沉积体性能可与相应块材媲美。随着冷喷涂技术的研究与发展,其实际应用范围正在不断扩大。冷喷涂技术作为材料加工技术的新生一员,已进入实际应用阶段,将成为具有潜力的现代涂层制造以及快速增材制造技术之一。     

超音速激光沉积Ti-6Al-4V合金结合界面特征数值模拟及试验验证

目的探究超音速激光沉积(SLD)过程中激光辐照温度和颗粒撞击速度对Ti-6Al-4V合金结合界面特征的影响规律,并通过试验对数值模拟结果进行验证。方法基于Johnson-cook材料模型,利用ABAQUS2017软件并采用欧拉-拉格朗日耦合CEL(CoupledEuler-Lagrange)计算模型和Lagrange计算模型,进行Ti-6Al-4V单颗粒和多颗粒的撞击行为数值模拟,并结合超音速激光沉积试验验证模拟结果。采用扫描电镜(SEM)和光镜(OM)对涂层的界面结合特征进行观察和分析。结果单颗粒撞击温度场模拟结果表明,当激光辐照温度为1073K时,随着撞击速度的增加,颗粒界面结合温度不断升高。当撞击速度为800m/s和900 m/s时,颗粒与基体局部最高温度分别为1876.7 K和1874.8 K,界面发生微熔。800 m/s时,颗粒压缩率为34.3%,扁平率为1.27,有效塑性应变为2.6,基体的凹坑深度为7.88μm,该参数下的超音速激光沉积涂层界面结合良好。多颗粒撞击温度场模拟结果表明,当撞击速度为800 m/s时,随着激光辐照温度的升高,孔隙逐渐减少。激光辐照温度为1073 K时,颗粒撞击界面的温度高达3463.7 K,但颗粒内部的温度还未达到熔点并保留在1073～1676.8 K。随着激光功率的升高,钛合金涂层的孔隙率降低为0.67%(SLD 700W),约为同条件下CS涂层孔隙率(8.31%)的1/12。结论激光辐照的热能使颗粒与基体以及颗粒间界面处的温度达到了材料熔点,实现颗粒表面微熔形成冶金结合。冷喷涂Ti-6Al-4V涂层中,颗粒与基体以及颗粒间均存在明显的孔隙,超音速激光沉积Ti-6Al-4V涂层颗粒与基体以及颗粒间的界面结合良好,试验结果与数值模拟结果大致吻合。     

等离子喷涂参数对TiB2可湿润阴极涂层沉积效率的影响

采用大气等离子喷涂（APS）在石墨质碳阴极材料上沉积TiB2可湿润性阴极涂层。研究了喷涂工艺参数对涂层沉积效率的影响。结果表明,涂层沉积效率随喷涂距离的增加而增加,随主气流量、喂料速率和喷涂功率增加呈现出先增加后减少的趋势,随粉末尺寸的减少而增加。最佳工艺参数为：喷涂距离80 mm,主气流量1900 L/h,送粉气流量（Ar）120 L/h,喂料速率27.34 g/min,喷涂功率35.8 kW,颗粒直径(d50) ≤37.4 μm,该条件下涂层沉积效率为67.26%。该TiB2涂层在220 kA铝电解槽上应用,槽稳定后铝液中Ti含量为0.0021%（质量分数）。     

团聚粉末制备工艺对冷喷涂Ti2AlC沉积的影响

以热压烧结后球磨粉碎的Ti_2AlC亚微米粉末为原料,通过水热处理使其团聚成微米级粉末,并运用冷喷涂技术在Zr-4合金基体上沉积Ti_2AlC涂层。采用扫描电子显微镜、金相显微镜、XRD衍射仪、激光粒度分析仪等对Ti_2AlC颗粒和涂层微观结构进行表征;采用显微硬度仪和拉伸测试系统对Ti_2AlC涂层的基本力学性能进行测试;采用N2吸附法测涂层孔隙,采用电化学工作站测涂层的贯通孔隙。结果表明:对平均粒径0.3μm的Ti_2AlC粉末进行水热处理时,添加硫酸铵能够促进亚微米颗粒的团聚,团聚粉末的平均粒度可达到6μm。此粉末的冷喷涂特性最好,沉积的Ti_2AlC涂层厚度达到100μm,涂层中有微孔和介孔但没有贯通孔隙,涂层和基体结合强度达到了44MPa。     

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.     

Investigation of Deposition Behavior of Cold-Sprayed Magnesium Coating

Two types of magnesium powders with different particle size distributions were deposited by cold spraying at different main gas temperatures. The effects of gas temperature and particle size distribution on the deposition efficiency of particles were studied. The microstructure of coatings was observed, and the porosity of coatings was evaluated. The deposition efficiency of particles increased, and the porosity of coatings decreased with the increase of gas temperature. The deposition efficiency of particles increased when using the powder with a smaller particle size distribution. Stainless steel and aluminum plates were used as substrates. The bonding strength and mechanism between the coating and substrate were studied. The commercial finite element software ABAQUS was used to help us better understand the deformation behavior of particles and substrates. The mean bonding strength slightly increased when aluminum plates were used as substrates. The bonding mechanism of Mg coatings on stainless steel and aluminum substrates was discussed.     

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...     

The Effects of Successive Impacts and Cold Welds on the Deposition Onset of Cold Spray Coatings

In this study, the impact and deposition behavior of nickel particles onto relatively soft 6061-T6 aluminum alloy and copper substrates in a kinetic spray process was investigated by comparing individual particle impact with full coating deposition. The results indicated that the deposition onset of nickel coatings on the two substrates follows different deposition mechanisms depending on corresponding deformability of the impact couples (substrate and particle). Nickel particles were hardly attached onto the relatively soft 6061-T6 substrate in case of individual impact, but the deposition onset of full coating took place depending on embedding, tamping of successive impact and metallurgical “cold welds” of viscous metal at impact interface when the impinging particles’ velocity was relatively low. In case of Ni-Cu impact, the bonding formed at the peripheral impact interface dominated the deposition onset of nickel coating due to the comparable deformability of the impact couples (Ni and Cu).     

Analysis of Bonding Features between the Particles and the Substrate during Cold Spraying

Cold spraying is a new coating process and manufacturing technology. The coating quality is upgraded with dense layers, higher bonding force and lower oxidation comparing with thermal spraying. Bonding of particles onto substrate is a result of extensive plastic deformation and related phenomena at the interface. The cold-sprayed copper and aluminum deposits on aluminum and steel substrates were prepared, and the features of interface were observed by using scanning electron microscope (SEM). Then the particle/substrate impact process was modeling through finite-element methods (ANSYS/LS-DYNA software). Numerical results show that the high plastic strain at the interface can result in an adiabatic shear instability at the interface. Due to these extremely high pressure and strain rate, it may be more appropriate to treat the material adjacent to the particle/substrate interface as a viscous ‘fluid-like’ material, various fluid-based phenomena, such as interfacial instabilities and roll-ups and vortices, can lead to interface material mixing. In numerical simulation, adiabatic shear instability both in the particle and the substrate at contact interface is regarded as a criterion for predicting the optimal process parameters and the bonding feature.     

Electrodeposition of Copper on Mild Steel: Peculiarities of the Process

The process of electrodeposition of copper coatings on a mild steel substrate was analyzed. The reasons for poor adhesion of the coatings from acid and alkaline cyanideless electrolytes were determined. It was shown that the problem of the direct copper coatings’ electrochemical plating on a steel substrate from cyanideless electrolytes results from the presence of the adjoint process of contact exchange in a copper ions–iron system. Good adhesion coatings can be developed only on termination of the contact exchange at the initial stage until the steel substrate under the sediment pores is not subjected to significant etching. In acid electrolytes, the adhesion is poor because of a large value of the contact exchange current. In alkaline cyanideless electrolytes iron is passivated, and adhesion of the coating is insufficient because of the presence of a separating passive film at the substrate–coating interface. In neutral electrolytes, it is possible to obtain a coating with a good adhesion to the substrate, but the results are not stable due to a low buffer capacity of the solution. During the deposition of a copper coating from acid electrolytes using a prenickel-plating, a thin nickel sublayer has pores through which the process of the contact exchange occurs. It is shown that, in order to develop coatings with a good adhesion, the minimum thickness of the nickel sublayer must be 3–5 μm.     

超音速火焰喷涂镍基涂层颗粒沉积特性的数值模拟

目的 考虑后续不同粒径颗粒随机冲击的影响,探索热喷涂涂层颗粒的沉积特性。方法 利用ABAQUS建立颗粒与基底冲击模型,通过颗粒冲击的凹坑深度和应力分布进行网格收敛性研究。通过实验验证模型的可行性。随后,应用验证模型研究颗粒以不同入射角和速度冲击基底时的沉积特性,以及4个颗粒重叠冲击基底及多颗粒随机冲击基底表面时的沉积特性。结果 在颗粒入射角从15°增至60°时,颗粒更好地附着于基底表面;当颗粒速度从350 m/s增至500 m/s时发生了溅射现象,可能造成绝热剪切失稳现象,形成有效结合;在4个颗粒冲击基底时,第2个颗粒对第1个颗粒及基底的影响都最明显;当多颗粒随机冲击基底时,在后续颗粒的冲击和沉积作用下,填充颗粒的形状不规则,同时第1层颗粒可能与基底形成机械咬合。结论 在超音速火焰喷涂时应当倾斜一定角度,同时提升颗粒速度,这对制备涂层更有利;在颗粒重叠冲击时,后续颗粒增大了第1个颗粒的压缩效果,且更深入地嵌入不锈钢基底,这有利于颗粒与颗粒之间的后续黏结;当多颗粒随机冲击基底时,在第1层沉积颗粒与基底之间,以及涂层内相邻颗粒之间均观察到高塑性应变,表明涂层出现黏结,同时后期沉积的颗粒未完整压缩变形。     

Nanopowder deposition by supersonic rectangular jet impingement

With a view toward developing the next generation of coatings using nanopowders, a cold gas dynamic spray (CGDS) technique has been investigated. In this method, a powder feeder is used to inject nanopowder agglomerates into a supersonic rectangular jet, with a design Mach number of 3.2. The powder particles gain speeds of up to 700 m/s through momentum transfer from the jet and bond to the substrate surface due to kinetic energy dissipation. Coatings of copper and nano-WC/10% Co on steel and aluminum substrates (3 to 5 μm in thickness) have been produced. The benefit of this process is that the material does not undergo any chemical changes during coating formation. To improve the quality of the coatings produced, the flapping motions produced by supersonic jet impingement were studied. Powder particle velocities and the jet impingement flow field were quantified using particle image velocimetry (PIV).     

Microstructural Development and Deposition Behavior of Titanium Powder Particles in Warm Spraying Process: From Single Splat to Coating

Warm spraying has been developed by NIMS, in which powder particles are accelerated and simultaneously heated, and deposited onto a suitable substrate in thermally softened solid state. In this study, commercially available titanium powder was sprayed onto steel substrate by the spraying process. Microstructural developments and deposition behaviors from a deposited single particle to a thick coating layer were observed by high resolution electron microscopes. A single titanium particle sprayed onto the substrate was severely deformed and grain-refined mainly along the interfacial boundary of particle/substrate by the impact of the sprayed particle. A successive impact by another particle further deformed the previously deposited particle and induced additional grain refinement of the remaining part. In a thick coating layer, the severe deformation and grain refinement were also observed. The results have demonstrated the complex deposition behavior of sprayed particles in the warm spraying using thermally softened metallic powder particles.     

Fe粒子参数对低温超音速火焰喷涂层构建的影响

应用LS-DYNA大应变有限元耦合算法,研究了低温超音速火焰喷涂Fe粒子参数对喷涂层构建的影响.结果表明,随着粒子温度或者速度的升高,粒子所含内能的增加,使得涂层界面温度不断升高,粒子的沉积塑性应变发生变化.粒子在不同基体上的沉积特征表明基体硬度将影响沉积粒子与基体界面的结合状态.随着涂层的构成,后续粒子对已沉积粒子的高速撞击使得先沉积的粒子产生二次塑性变形,并引发温变.先沉积的粒子塑性变形引起的粗化作用将降低后续粒子沉积的临界速度.这些将导致涂层在拉应力作用下发生脆性断裂.