Effects of powder and process parameters on the ductility of cold spray copper coatings for the corrosion protection of used fuel storage containers.

核废料管理组织(NWMO)成立于2002年，目的是对加拿大使用过的核燃料进行长期管理。该组织正在进行一项重大努力，为用过的核燃料开发地下深层地质库(DGR)。DGR的关键部件之一是二手燃料容器(UFC)，这是一个设计和制造的铜包钢容器，以确保数千年来燃料的密封。冷喷涂是一种新兴的热喷涂技术，该技术将金属粉末以超音速喷涂到待涂层的表面，然后在撞击时立即固化和结合，从而能够快速生产出厚重致密的涂层，同时将沉积材料的氧化和微观结构变化降至最低。这些特点是NWMO选择冷喷涂方法生产厚耐蚀铜层的主要原因。自2011年以来，NWMO一直与加拿大国家研究委员会(NRC)合作开发用于UFC应用的冷喷雾。正在开发的涂层在厚度、成分、附着力、密度、完整性和延展性方面有特定的要求。针对NWMO UFC的具体情况，已经对喷涂参数进行了优化，以最大限度地提高粉末的飞行速度，从而能够以几乎100%的沉积效率生产致密涂层。在粉末方面，为了满足使用要求，系统地研究了粒度分布对涂层附着力的影响。然而，直到最近，我们才观察到铜涂层的机械性能会因粉末原料的不同而有很大差异。例如，使用相同的喷涂参数，最近观察到延展性从0.7%到39%的变化，而粉末特性没有任何明显的变化。因此，本项目的主要目标是了解粉末原料特性和冷喷涂工艺参数对延展性的影响，以便确定粉末和工艺参数，使铜涂层具有优化和可重复的性能。

The Nuclear Waste Management Organization (NWMO) was established in 2002 for the long term management of the Canada's used nuclear fuel. The organization is undertaking a major effort to develop an underground Deep Geologic Repository (DGR) for used nuclear fuel. One of the key components of the DGR is the Used Fuel Container (UFC), which is a copper-clad steel vessel designed and fabricated to ensure the containment of the fuel for many thousands of years. Cold Spray is an emerging thermal spray technology where metal powders are sprayed at supersonic velocities onto the surface to be coated, whereupon they consolidate and bond instantly on impact, enabling the rapid production of thick and dense coating, while minimising oxidation and microstructural alteration of the deposited material. These characteristics are the main reason for the selection of cold spray method by NWMO for the production of the thick corrosion resistant copper coating. Since 2011 the NWMO has partnered with the Canadian National Research Council (NRC) for the development of cold spray for UFC application. The coating under development has specific requirements in terms of thickness, composition, adhesion, density, integrity and ductility. For the specific case of the NWMO's UFC, spray parameters have already been optimized to maximise the in-flight velocity of the powders, enabling dense coatings to be produced with a deposition efficiency of virtually 100%. On the powder side, the effect of the particle size distribution on coating adhesion has been systematically studied in order to cope with application requirements. However, it is only recently that we observed that mechanical properties of copper coating can vary significantly, from lot to lot of the powder feedstock. For instance, using the same spray parameters, a variation of ductility from 0.7 to 39 % has been recently observed, without any 'significant' change in the powder characteristics. Thus, the main goal of this project is to understand the effect of powder feedstock characteristics and cold spray process parameters on the ductility in order to define powder and process parameters to impart optimized and reproducible properties to the copper coating.