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

冷喷涂由于粉末受热较低，已发展成为一种执行高质量涂层的新技术。据报道，相对较软的金属可以通过该工艺有效地涂覆，并且与传统热喷涂涂层相比，涂层性能更优异。为了通过该工艺建立高质量的涂层，使用细颗粒可能是有效的。与普通热喷涂工艺相比，该工艺的典型特性可以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上。为了获得如此高的颗粒碰撞速度，特别是对于直径几微米左右的细颗粒，仍然需要对喷嘴设计进行优化。另一方面，在实际的冷喷涂中，已经表明，由于基材表面上的弓形冲击效应，颗粒的标称速度与净碰撞速度不同。实际上，要实现颗粒的高碰撞速度，特别是细颗粒，必须克服基材表面的弓形冲击问题。为了提高直径约5 pm的铜细颗粒在金属基材上冷喷涂过程中的沉积效率，通过数值模拟对喷嘴设计进行了优化。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达到585 m/s。在将铜颗粒喷涂到普通钢基体上时，在钢基体的界面区域附近形成了独特的层状微观结构。由于获得的颗粒速度较高，可能会显着引发加工硬化。此外，为了减少冷喷涂过程中基材表面区域的弓形冲击效应，还重新设计了专用喷嘴。使用特殊喷嘴，沉积效率、维氏硬度和涂层附着强度显着提高，尤其是在细颗粒和较高工作气体压力水平的情况下，而标称颗粒速度降低。数值模拟表明，新设计的喷嘴有效降低了基材表面的压力水平。在观察将单个颗粒喷射到基材上时，当颗粒被特殊喷嘴喷射时，在板片的外围发现了延伸的金属射流。结果表明，与传统喷嘴相比，特殊喷嘴有效抑制了弓形冲击引起的颗粒速度降低。

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