High-Performance Smart Ceramic Coatings on Light Alloys

为了最大限度地延长运输用轻合金的使用寿命，采用表面处理是一种常见做法。然而，传统的被动涂层只起到了对环境的物理屏障的作用，一旦损坏，就不再提供保护。从这一局限中，智能涂层的概念诞生了，智能涂层的定义是能够通过选择性地对某些触发因素做出反应来与环境相互作用的材料，如机械断裂、时间、温度或pH变化。根据所包含的功能，可以实现不同的性能，例如特定的腐蚀抑制、自我修复或损坏指示。智能涂料的发展主要是有机材料的一个领域，因为聚合物的高化学反应活性促进了新功能的加入。然而，此类材料的适用范围仅限于温和环境和中等载荷。该项目提出的科学问题是，在极端腐蚀性和磨损性环境中具有优异性能的陶瓷基涂层中提供智能功能是否可行。由于与有机材料相比，无机基质的刚性和惰性，陶瓷涂层的活性功能化是相当具有挑战性的。该项目提出的实现陶瓷涂层主动功能化以解决腐蚀损害的科学方法，是基于加入装有缓蚀剂的对pH敏感的纳米容器。当检测到与腐蚀启动相关的电化学活动引起的pH变化时，这些元素被释放到介质中。缓蚀剂将起到局部抑制腐蚀扩展的作用，而陶瓷基质将同时提供磨损和磨损保护。本项目的重点是材料的主动和动态行为，而不是涂层的被动性能。两种沉积技术被用于制备陶瓷涂层，即等离子体电解氧化法(PEO)和气溶胶沉积(AD)法。聚氧化乙烯是一种源于阳极氧化的电解表面改性技术。对这项技术的兴趣源于当前需要取代欧盟(REACH)限制的阳极氧化中使用的致癌电解液。聚氧化乙烯对环境友好，所得涂层在耐腐蚀性和耐磨性方面明显优于传统的电解技术。然而，PEO需要很高的能耗，这限制了其对具有优异性能的利基组件的适用性。因此，为了扩大本研究的适用范围，增加本研究的潜在行业影响，还提出了一种更具成本效益和易用性的技术：AD方法-一种非常通用的室温喷涂技术。AD中采用的沉积原理是基于使用来自前驱体的亚微米粉末颗粒产生气溶胶，并向衬底高速喷射。为了实现陶瓷涂层的主动功能化，提出了两种制备工艺。事实证明，单步处理过程将更具挑战性，但另一方面，它将节省处理时间，从而降低经济成本。此外，单步工艺有望在整个涂层厚度范围内产生统一的功能化，这将改善主动保护性能。两步法需要更长的时间，但更容易获得。成功的结果将延长运输行业中使用的铝和镁部件的寿命，这将直接影响能源效率，并将有助于资源的可持续消耗。

The application of surface treatments is a common practice to maximize the working life of light alloys used in transport. However, traditional passive coatings only act as a physical barrier against the environment and, once damaged, no longer provide protection. From this limitation, the concept of smart coatings was born, which are defined as materials capable of interacting with the environment by responding selectively to certain triggers, such as mechanical fracture, time, temperature or pH variations. Depending on the incorporated functionality, different properties can be achieved, e.g. specific corrosion inhibition, self-healing or damage indication. The development of smart coatings is primarily a domain of organic-based materials since the high chemical reactivity of polymers promotes the incorporation of new functionalities. However, the applicability of such materials is limited to mild environments and medium loads. The scientific question proposed in this project is whether providing smart functionalities is feasible in ceramic-based coatings that have excellent performance in extremely corrosive and abrasive environments. The active functionalisation of ceramic coatings is quite challenging given the rigid and inert nature of inorganic matrices compared to organic materials. The scientific approach proposed in this project to achieve the active functionalisation of ceramic coatings to tackle corrosion damage, is based on the incorporation of pH-sensitive nanocontainers loaded with corrosion inhibitors. These are released into the media when detecting pH changes arisen from electrochemical activity associated with corrosion initiation. The corrosion inhibitors will act locally inhibiting corrosion propagation, while the ceramic matrix will provide wear and abrasion protection simultaneously. This project focuses on the active and dynamic behaviour of the materials rather than in the passive properties of the coatings.Two deposition techniques are used to manufacture the ceramic coatings, namely Plasma Electrolytic Oxidation (PEO) and Aerosol Deposition (AD) method. PEO is an electrolytic surface modification technique that derives from anodising. The interest for this technique arises from the current need to replace carcinogenic electrolytes used in anodising restricted by the EU (REACH). PEO is environmentally friendly and the resulting coatings are considerably superior in terms of corrosion and wear resistance to those obtained by conventional electrolytic techniques. However, PEO requires a high-energy consumption and this limits its applicability to niche components with excellent performance. Therefore, in order expand the range of applicability and increase the potential industry impact of this research, a more cost-effective and readily available technique is also proposed: the AD method-an extremely versatile room temperature spray coating technology. The deposition principle employed in AD is based on the generation of an aerosol using submicron powder particles from the precursor, which are sprayed at high velocity towards the substrate. It results in coatings with excellent high temperature and abrasion-resistant properties.To achieve the active functionalisation of the ceramic coatings, two manufacturing processes are proposed. The single-step process will prove more challenging, but on the other hand, it would save processing times leading to reduced economical costs. Moreover, the single-step process is expected to produce a uniform functionalisation throughout the entire thickness of the coating, which would improve the active protection properties. The double-step process requires longer times, but it is more accessible.Successful results would increase the lifetime of Al and Mg-based components used in the transport industry that would have a direct impact on energy efficiency and would contribute to the sustainable consumption of resources.