Cold spray: effect of mixing powders

冷喷涂是一种看似简单的方法，可以在金属、陶瓷和聚合物表面涂覆金属涂层，方法是使用载气(通常是氮气)将直径约20至40微米的金属粉末加速到超音速。当与待涂覆的基材碰撞时，颗粒会严重塑性变形，并瞬间粘合到基材上并相互粘合。基材的涂层是在室温的空气中进行的。通常的粘结粉末颗粒的方法是在非常高的温度下进行的，在大约80%的熔点之间，甚至到熔点，并且需要非常长的时间，至少几个小时。显然，短时间和涂层在空气中完成的事实显然是有利的；室温处理意味着避免了热损害，也意味着可能出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，可以制造非常厚的3D涂层，从而将该过程提升为添加剂制造之一。 通常情况下，只喷洒一种金属粉末，但这项建议关注的是当混合粉末被冷喷涂时会发生什么。如上所述，有趣的复合材料可以通过冷喷涂来制造，这项工作的一部分涉及制造各种应用的复合材料：用于生物可降解支架的金属复合材料，用于飞机结构防雷的金属涂层，由碳纤维增强聚合物复合材料制成的金属涂层，以及用于耐磨涂层的金属基碳化钨复合材料。然而，科学目标是了解当喷洒混合粉末时，冷喷涂过程会发生什么。在这方面，我们主要关心混合物的冷喷涂性能，或者这些粉末粘结到基材上形成厚涂层的难易程度。冷喷涂性能通常通过沉积效率来判断，即喷涂粉末的粘结量，以及涂层中的孔隙率，一般来说，孔隙率越低，涂层越好。我们团队之前的工作表明，混合可以显著影响冷喷涂能力，但以一种非常不可预测的方式，掩盖了冷喷涂概念的简单性。这项工作旨在了解与粉末混合相关的冷喷雾机制，并利用这一点来开发对冷喷雾性的准确预测。 冷喷涂正在迅速成为一种关键的修复方法，并因此增加了可持续发展技术的能力。如上所述，它是添加剂制造技术之一，因此引起汽车和航空航天工业的兴趣。这一计划在科学上是耐人寻味的，并具有重大的当代工程意义。这是一个极好的培训机会，可以在先进制造业中培养高素质的人才，先进制造业是加拿大经济的重要贡献者。

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.