Development of fabrication technology cold spraying for innovative coating by means of collision of high velocity solid particles

冷喷涂由于其较低的粉末加热温度，已发展成为一种获得高质量涂层的新技术。该工艺有效地对相对较软的金属进行了涂层，并且与传统的热喷涂涂层相比，涂层性能更优越。通过该工艺可制得高质量的涂料，可有效地利用细小颗粒。与顺序热喷涂工艺相比，该工艺的典型相同之处可由涂层形成单元作为固体颗粒给出，该固体颗粒以相当高的速度碰撞到基材表面或先前沉积的涂层表面。要获得如此高的颗粒碰撞速度，特别是对于直径在少数PM左右的细颗粒，喷嘴设计仍需进行优化。另一方面，在实际的冷喷涂中，由于弓激波对亚…的影响，粒子的名义速度与净碰撞速度不同。更平坦的表面。为了实现颗粒的高碰撞速度，特别是在细小颗粒中，必须克服金属表面的弓形激波问题。为了提高冷喷涂过程中直径在5 pm左右的铜微粒在金属表面的沉积效率，通过数值模拟对喷嘴设计进行优化。根据模拟结果，采用自行设计的喷嘴，在最佳条件下，颗粒速度可达585m/S。在普通钢基材上喷涂铜粉时，在钢基材的界面附近形成了独特的层状组织。由于获得了较高的颗粒速度，加工硬化可能显著地被诱导。此外，为了减少冷喷涂过程中对基材表面的弓形冲击效应，还设计了特殊的喷嘴。当工作气体压力较高时，沉积效率、维氏硬度和涂层结合强度均显著提高，而名义颗粒速度随专用喷嘴的增加而降低。数值模拟表明，新设计的喷嘴有效地降低了衬底表面的压强。在对喷涂到基片上的单个颗粒的观察中，当颗粒通过特殊的喷嘴喷射时，在飞片的外围发现了延伸的金属射流。结果表明，与常规喷管相比，特殊喷管能有效地抑制由于弓形激波引起的颗粒速度下降。

Cold spraying has developed as a new technology to perform a high quality coating due to its lower heating of the powder. Relatively soft metals have been effectively coated by the process and superior coating properties compared with conventional coatings thermally sprayed have been reported. To establish the high quality coating by the process, utilization of fine particle may be effective. Typical identity of the process compared to the ordinal thermal spray process can be given by the coating formation unit as a solid particle, which collided onto the substrate surface or prior deposited coating surface at a quite higher velocity. To attain such a high collision velocity of the particle, especially for the fine particle around few pm in diameter, optimization in nozzle design still has to be performed. On the other hand, in a practical cold spraying, it has been indicated that the nominal velocity of the particle differ from net collision velocity due to bow shock effect on the sub … More strate surface. To realize a high collision velocity of the particle actually, especially in fine particle, bow shock problem onto the substrate surface has to be overcoine.To improve the deposition efficiency of copper fine particles, around 5 pm in diameter, in cold spray process onto metallic substrate, optimization in nozzle design was performed by numerical simulation. Particles velocity reached up to 585 m/s under the optimum conditions by using self-designed nozzle based on the simulation results. In the spraying of copper particle onto normal steel substrate, unique lamellar-like microstructure was formed near the interface region in the steel substrate. Work hardening may be induced significantly due to the higher velocity of the particles attained. Moreover, to reduce the bow shock effect on the substrate surface region in cold spray process, special nozzle was newly designed. The deposition efficiency, Vickers hardness and coating adhesion strength increased significantly especially in the case of both fine particle and higher pressure level of the working gas, while nominal particle velocity decreased with the special nozzle. Numerical simulation indicated that the pressure levels on the substrate surface decreased effectively in the nozzle newly designed. In the observation of sprayed individual particles onto the substrate, extended metal jet was recognized at the splat's periphery when the particle was sprayed by the special nozzle. The results indicate that the decrease of particles velocity due to bow shock was suppressed effectively in the special nozzle as compared with conventional one Less