Cold spray: effect of mixing powders

冷喷涂是一种看似简单的方法，通过使用载气（通常为氮气）将粒径约为20至40微米的金属粉末加速至超音速，将金属涂层涂覆到金属、陶瓷和聚合物表面。 在与待涂覆的基材撞击时，颗粒严重塑性变形并瞬间结合到基材上并彼此结合。 基材的涂覆在室温下在空气中进行。 粘结粉末颗粒的常用方法在非常高的温度下进行，在熔点的约80%之间，甚至高达熔点，并且需要非常长的时间，至少几个小时。 显然，短时间和在空气中完成涂层的事实显然是有利的;室温处理意味着避免了热损伤，也意味着可能实现不太可能的材料配对，例如嵌入金属基质中的聚合物。 此外，可以制作非常厚的3D涂层，从而将该过程提升为增材制造之一。通常，仅喷涂一种金属粉末，但该建议涉及当冷喷涂粉末混合物时会发生什么。 如上所述，可以通过冷喷涂制造有趣的“复合材料”，并且该工作的一部分涉及制造用于各种应用的复合材料：用于可生物降解支架的金属-金属复合材料、用于由碳纤维增强聚合物复合材料制成的飞机结构的雷击保护的金属涂层以及用于耐磨涂层的金属基质-碳化钨复合材料。 然而，科学的目的是了解当喷涂混合粉末时，冷喷涂过程会发生什么。 在这方面，我们主要关注的是混合物的冷喷涂性，或者这些粉末粘合到基材上以形成厚涂层的容易程度。 冷喷涂性通常通过沉积效率来判断，即有多少喷涂粉末粘附，以及涂层中的孔隙率水平，一般来说，孔隙率越低，涂层越好。 我们团队以前的工作表明，混合可以显着影响冷喷涂性，但以非常不可预测的方式，掩盖了冷喷涂概念的简单性。 这项工作的目的是了解与粉末混合相关的冷喷涂机制，并利用它来开发冷喷涂性能的准确预测。 * 冷喷涂正在迅速成为一种关键的“修复”方法，因此，增加了技术的可持续性能力。 如上所述，它是增材制造技术之一，因此对汽车和航空航天工业很感兴趣。 这个计划在科学上是有趣的，是伟大的当代工程的重要性。 这是一个很好的培训机会，可以在先进制造业中培养高素质的人才，这对加拿大经济至关重要。

Cold spray is a seemingly simple method to apply metal coatings to metal, ceramic and polymer surfaces by accelerating metal powders of about 20 to 40 micron particle diameter to supersonic speeds using a carrier gas, usually nitrogen. On impact with the substrate to be coated, the particles severely plastically deform and instantaneously bond to the substrate and each other. The coating of the substrate takes place in air at room temperature. The usual methods to bond powder particles are performed at very high temperatures, between about 80% of the melting point and even upto the melting point, and require very long times, at least a few hours. Clearly the short times and the fact that coatings are done in air are obviously advantageous; room temperature processing means that heat damage is avoided and also means that unlikely materials pairings are possible, such as polymers embedded in a metal matrix. Moreover, very thick 3D coatings can be made, thus elevating the process to one of additive manufacturing.***Usually, only one metal powder is sprayed, but this proposal is concerned with what happens when a mixture of powders is cold sprayed. As noted above, interesting ‘composites' can be made by cold spray and part of this work concerns making composites for various applications: metal – metal composites for biodegradable stents, metal coatings for lightning strike protection for aircraft structures made of carbon fibre reinforced polymer composites and metal matrix-tungsten carbide composites for wear resistant coatings. The scientific objective, however, is to understand what happens to the cold spray process when mixed powders are sprayed. In this respect we are mainly concerned with the cold sprayability of the mixtures, or how easy it is for these powders to bond onto the substrate to form a thick coating. Cold sprayability is usually judged by the deposition efficiency, i.e. how much of the sprayed powder sticks, and the level of porosity in the coating, the lower the porosity, the better the coating as a general rule. Previous work by our team has shown that the mixing can significantly affect cold sprayability, but in a very unpredictable manner, belying the simplicity of the cold spray concept. This work aims to understand the cold spray mechanisms associated with powder mixing, and use this to develop accurate predictions of cold sprayability. ***Cold spray is rapidly becoming a key ‘repair' method and, as such, adds to the capacity of technologies for sustainability. As mentioned above, it is one of the additive manufacturing technologies and is therefore of interest to the automotive and aerospace industries. This program is scientifically intriguing and is of great contemporary engineering importance. It represents an excellent training opportunity to generate high quality personnel in the advanced manufacturing sector – a vital contributor to the Canadian economy.