气体温度对冷喷涂Ni粒子结合与变形行为的影响

利用SEM对冷喷涂工艺中不同气体温度下Ni粒子碰撞Cu合金基板后的结合及变形形貌进行了表征.结果表明,随着气体温度的升高,粒子扁平率呈渐缓趋势增加,射流面积增大,粒子的结合率提高.变形粒子内存在剪切失稳薄层、强塑性变形区和低塑性变形区等3个变形程度不同的区域.粒子与基板的结合质量主要受剪切失稳薄层控制,而变形后粒子的形状主要受塑性变形区控制.证实了绝热剪切失稳是Ni粒子与Cu合金基板结合的主要机制.     

颗粒材料特性对冷喷涂撞击行为影响的模拟研究

采用有限元数值计算方法研究了冷喷涂过程中Cu,Al及Ni合金和Ti合金颗粒与Cu基板的碰撞变形行为,探讨了颗粒的材料特性对其碰撞基板后的变形行为和结合行为的影响.结果表明,与基板相比,有效塑性极限大于衬底的金属颗粒易发生绝热剪切失稳,此时,基板不发生失稳,并释放积攒的变形能,使颗粒发生回弹现象.有效塑性极限小于衬底的金属颗粒不发生绝热剪切失稳,其积攒的变形能在碰撞后期释放,促进了基板的失稳.     

冷喷涂粒子碰撞行为三维有限元热力耦合分析

冷喷涂粒子的碰撞变形行为对粒子的沉积起着重要的作用.采用ABAQUS/Explicit显式有限元分析软件对冷喷涂过程中粒子碰撞行为进行了三维数值模拟.通过引入材料的失效模型,获得了与文献报道试验结果相吻合的计算结果.计算结果表明,随着粒子速度增加,粒子变形程度增加,基体坑深增加.粒子大小对其碰撞变形形貌影响不大,不同尺寸粒子的变形具有相似性.     

冷喷涂Cu涂层过程中粒子速度的影响因素分析

简要介绍了冷喷涂技术特点及工艺原理。利用粒子测速仪对各种因素下的粒子速度进行了测试；借助扫描电镜观察了涂层以及涂层与界面的形貌；具体讨论和分析了气体压力、温度、粉末以及喷涂距离等因素对颗粒速度的影响。     

冷喷涂粒子碰撞行为和临界速度预测的数值模拟研究现状

目前,冷喷涂技术受到越来越多国内外学者的关注。文中基于已公开发表的文献,详细讨论了冷喷涂过程中粒子碰撞行为的数值模拟和临界速度预测的研究现状。首先,简要介绍了冷喷涂、粒子结合机理和临界速度的概念。其次,总结了拉格朗日法、欧拉法和光滑粒子法等数值计算方法,并对数值计算获得的结果,例如:变形形貌、界面温度、能量变化及临界速度的预测进行了讨论。最后,探讨了冷喷涂粒子碰撞行为数值模拟中存在的问题和研究前景。     

喷嘴下游形状对冷喷涂粒子加速行为影响的数值模拟研究

目的 冷喷涂过程中喷嘴内流道关键尺寸是影响粒子加速的重要因素。虽然喷嘴下游长度与扩张比是喷嘴的2个最重要参量,但目前对喷嘴优化设计的研究仍有深入空间,比如喷嘴下游形状。方法 本文利用计算流体动力学的软件ANSYS/Fluent进行数值模拟研究,在与传统锥形下游相比较后,设计了钟形下游与喇叭形下游喷嘴。同时研究了喷嘴下游形状对气流与粒子加速行为的影响。结果 对于钟形下游喷嘴,其气流速度在过喉部后迅速增加到较高数值,随后变化缓慢;对于喇叭形下游喷嘴,其气流速度在过喉部后先增加缓慢,直至截面积开始快速增加时,气流速度迅速增加;喷嘴下游形状对粒子撞击基板时的速度有一定影响,且随着喷嘴下游长度和粉末粒度的变化而改变。对于Cu粉,当为下游100 mm短喷嘴时,锥形下游喷嘴对10~20 μm的粒子加速效果最好。当粉末在20 μm以上时,喇叭形下游喷嘴的加速效果最好。对于下游220 mm长喷嘴,钟形下游喷嘴对10~30 μm的粒子加速效果最好。当粉末在30 μm以上时,锥形下游喷嘴的加速效果最好。对于Al粉,当为下游220 mm长喷嘴时,钟形下游喷嘴对10~50 μm的粒子加速效果最好,喇叭形下游喷嘴加速效果最差。结论 冷喷涂喷嘴下游形状对气体与粒子加速有显著的影响。     

激波对电场辅助冷喷涂纳米粒子速度的影响

通过建立二维数值分析模型,分析了不同进气温度及压力时,带电纳米粒子在激波和电场力耦合作用下的加速特性以及对粒子撞击基板速度的影响。结果表明:弓形激波气体压缩层是造成纳米粒子减速的主要因素,弓形激波气体压缩层越薄粒子撞击基板时速度越大;外加电场时,带电纳米粒子撞击基板的速度得到较大提升。     

Effect of material properties of cold-sprayed particles on its impacting behavior

采用有限元数值计算方法研究了冷喷涂过程中Cu, Al及Ni合金和Ti合金颗粒与Cu基板的碰撞变形行为, 探讨了颗粒的材料特性对其碰撞基板后的变形行为和结合行为的影响. 结果表明, 与基板相比,有效塑性极限大于衬底的金属颗粒易发生绝热剪切失稳, 此时, 基板不发生失稳, 并释放积攒的变形能,使颗粒发生回弹现象. 有效塑性极限小于衬底的金属颗粒不发生绝热剪切失稳, 其积攒的变形能在碰撞后期释放, 促进了基板的失稳.     

基于Euler法的冷喷涂粒子与基体高速冲击过程数值分析

利用非线性动力分析软件LS-DYNA,对冷喷涂中铜粒子与铜基体的碰撞过程进行了数值分析.研究冷喷涂过程中沉积粒子与被喷涂基体的变形行为.结果表明:使用Lagrange法,当粒子撞击速度过大时,网格的过度畸变会导致计算的终止,其计算结果与实验结果相比有一定差距.而采用Euler法计算得到的铜粒子与铜基体在碰撞结束后的沉积形貌与实验观察吻合很好,表明模拟结果相对于Lagrange法的计算结果更为精确.此外,Euler法能准确的模拟多粒子共同撞击基体的过程,数值计算得到的多粒子涂层内部结构与实验结果也能很好的吻合.     

SHS反应火焰喷涂粒子与基体的碰撞及其数值模拟

以Ti-B4C-C为反应喷涂体系，通过碰撞实验和ANSYS有限元分析方法，研究了反应火焰喷涂TiC-TiB2复相涂层时，喷涂粒子与基体碰撞形成摊片的温度变化情况及其对涂层与基体结合的影响。研究表明，完成自蔓延反应、处于熔融状态的喷涂粒子与基体碰撞形成的摊片各部分温差较大，温度较低，不易使基体表面熔化，难以与基体形成良好结合；自蔓延反应进行中的喷涂粒子与基体碰撞形成的摊片各部分温差较小，温度较高，能较好地实现与基体的结合。模拟结果与实验结果基本吻合。     

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.     

Measurement and numerical simulation of particle velocity in cold spraying

The velocity of cold spray particles was measured by a diagnostic system designed for thermal spray particles that is based on thermal radiation. A laser beam was used to illuminate the cold spray particles in cold spraying to obtain a sufficient radiant energy intensity for detection. The measurement was carried out for copper particles of different mean particle sizes. The particle velocity was also estimated using a two-dimensional axisymmetric model developed previously. The simulated velocity agreed well with the measured result. This fact indicates that particle velocity in cold spraying can be predicted reasonably by simulation. Therefore, it is possible to optimize the cold spray process with the aid of the simulation results. 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.     

Examination of the critical velocity for deposition of particles in cold spraying

The critical velocity of copper (Cu) particles for deposition in cold spraying was estimated both experimentally and theoretically. An experimental method is proposed to measure the critical velocity based on the theoretical relationship between deposition efficiency and critical velocity at different spray angles. A numerical simulation of particle impact deformation is used to estmate the critical velocity. The theoretical estimation is based on the critical velocity corresponding to the particle velocity at which impact begins to cause adiabatic shear instability. The experimental deposition was conducted using Cu particles of different particle sizes, velocities, oxygen contents, and temperatures. The dependency of the critical velocity on particle temperature was examined. Results show that the critical velocity can be reasonably measured by the proposed test method, which detects the change of critical velocity with particle temperature and oxygen content. The Cu particles of oxygen content 0.01 wt.% yielded a critical velocity of about 327 m/s. Experiments show that the oxygen content of powder significantly influences the critical velocity. Variations in oxygen content can explain the large discrepancies in critical velocity that have been reported by different investigators. Critical velocity is also found to be influenced by particle temperature as well as types of materials. High particle temperature causes a decrease in critical velocity. This effect is attributed to the thermal softening at elevated temperatures. 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.     

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.     

几种金属基板上冷喷涂铜涂层的试验与模拟

采用自主研制的冷喷涂设备在三种典型基板上进行喷涂试验,相同的工艺参数下,在铜和铝基板上得到良好的铜涂层,而在钢基板上则没有沉积.实验结果表明:涂层与基板界面、涂层内部颗粒界面结合良好,铜涂层组织致密,显微硬度高达150HV0.1;从涂层表面形貌扫描电镜(SEM)照片中可以观察到射流状的金属,说明颗粒发生了巨大变形,经计算知颗粒在碰撞中压缩率达69%;粉末和涂层的X射线衍射(XRD)结果表明铜粉末在冷喷涂过程中没有发生氧化.同时,数值模拟了铜颗粒与三种基板的碰撞过程,讨论了形成有效结合的判断准则,根据该准则,计算出铜颗粒在铜、铝、钢基板上的临界沉积速度分别为600m/s,500m/s,800m/s,从而解释了铜颗粒在三种基板上不同的沉积行为.     

Electrochemical corrosion behavior of arc sprayed Zn-Al coatings

Cored wires and high velocity arc spraying (HVAS) technique were applied to produce high Al content Zn-Al alloy coatings on low carbon steel substrates. The electrochemical corrosion behaviors of Zn, Al and Zn-Al coatings were studied with potentiodynamic measurement in 5 % NaCl solution. Compared with pure Zn, pure Al and Zn-15Al coatings, Zn-26Al coatings show a higher corrosion resistance in salt solution. The potentiodynamic polarization tests show that the corrosion resistance of Zn-Al coatings increases as Al content is raised. Pure Al coating exhibits different electrochemical behaviors with other coatings. The corrosion initiated at the micro-pores of the coating and the underlying corrosion mechanism is very similar to that of the pitting corrosion.     

高速电弧喷涂雾化熔滴传热过程数值分析Ⅱ.工艺参数对熔滴传热过程的影响

在高速电弧喷涂雾化熔滴传热过程数学模型的基础上，用Fe-Al合金进行了数值计算，分析了工艺参数对熔滴传热过程的影响。结果表明，熔滴尺寸越小，在一定喷涂距离上的对流换热系数则越大、熔滴温度越高、固相分数越小、冷却速度越大；雾化气流压力和喷涂电流越大，在一定的喷涂距离上熔滴温度也就越高，熔滴中的固相分数越低，且其凝固过程也越长；熔滴的冷却速度对熔滴尺寸和喷涂距离的变化十分敏感，而对雾化气流压力和喷涂电流的变化不太敏感；Fe-Al合金熔滴的液态冷却速度达10^5～10^7K／s数量级，预示涂层将具有快速凝固组织特征。     

热加工对冷喷涂铝合金块材性能的影响

为了提高冷喷涂增材制造铝基块材性能，对低压冷喷涂法沉积的7075铝合金块材进行了后续退火和热轧加工。采用光学显微镜和扫描电镜观察试样的组织结构特征，并通过拉伸试验和电化学测试表征了块材的应力-应变曲线和耐蚀性。结果表明，低压冷喷涂法沉积的铝合金块材结构上存在大量的颗粒界面和少量微孔等缺陷，拉伸时发生脆性断裂，塑性很差，耐点蚀性能差；经过400℃退火4 h后，结构缺陷显著减少；再经过30%压下量的热轧加工后，结构更加致密，强度和韧性均提高，耐蚀性也随着结构缺陷的减少而提高。