Novel braze coating materials & processes for sustainable aeroengine applications

背景反应引擎(https://www.reactionengines.co.uk))正在为氨等替代燃料开发推进系统方面的专业知识，这是以“可持续飞行”为目标的技术转变的一部分。高速、高能效飞行目标的一个核心方面是反应发动机用来冷却高速流体并回收和重新利用提取的热能的热交换器设计。其中一个关键的设计配置是管式换热器，它提供了轻便、紧凑、高效的性能。能够组装新设计的主要制造技术是真空钎焊。反应发动机在镍铬高温合金和不锈钢合金管式换热器的设计、制造和测试方面拥有丰富的经验，这些换热器是在内部使用最先进的定制真空炉进行钎焊的。多排薄壁管以紧凑的复杂阵列连接到歧管上，形状可以紧凑的模块化设计包装。随着设计在航空航天部门和其他需要高水平性能的应用中获得牵引力，反应引擎正在进一步开发真空钎焊热交换器组件。随着生产量的增加，质量保证和重复性的水平也将不得不提高。真空钎焊工艺的各个方面都必须优化。流入接头间隙的钎料的选择就是其中的一个方面。目前使用的是成熟的现成产品。通过对新的成分和格式的调查来寻求改进。除了钎焊消耗品的基本成分外，其格式也很重要(有糊、丝、箔、带可供选择)。这些不同的格式在铜耗材料局部沉积到金属衬底上的方式方面提供了不同的优势。合金耗材在铜焊温度下的熔化行为，以及合金耗材在所需位置的易用性都是反应发动机管式换热器设计需要优化的关键因素，以提高组装和铜焊生产区域的制造效率。通过涂层技术在表面上均匀地涂覆一层铜焊耗材是评估工艺效率的方法之一。项目目的这项工作将从绘制热交换器部件的反应发动机现有组装和真空钎焊路线的综合工作开始。将为代表当前管式换热器设计的钢和镍合金部件确定基准材料和制造组件。将对现有的商用钎料进行评估，以了解当前对重复性和性能的限制。将评估在所需位置将焊料施加到部件表面的方法-激光熔覆、热喷涂、冷喷涂、物理气相沉积或混合表面添加剂制造路线是感兴趣的涂层方法。目前使用的人工密集放置方法将被取代。将进行材料表征，以确定最佳工艺参数和材料性能，包括机械测试、金相和热物理性能测量。在最后阶段，将对新型涂层合金(例如，高熵合金)进行配方、制造和测试，以便与现有的商业系统进行比较。

BackgroundReaction Engines (https://www.reactionengines.co.uk) are developing expertise in propulsion systems for alternative fuels, such as ammonia, as part of the shift in technologies targeting "sustainable flight". A core aspect of the goal of high speed, energy efficient flight are the heat exchanger designs used by Reaction Engines to cool high speed fluids, and to recover and re-use the heat energy extracted. One of the key design configurations is tubular heat exchangers, which provide light-weight, compact, efficient performance. The primary manufacturing technique enabling the novel designs to be assembled is Vacuum Brazing. Reaction Engines have considerable experience in design, manufacturing, and testing of tubular heat exchangers in both nickel-chromium super alloys, and stainless-steel alloys, brazed in-house using a large state-of-the-art bespoke vacuum furnace. Multiple rows of thin-walled tubing are joined to manifolds in tightly packed complex arrays, in shapes that can be packaged in compact modular designs.Reaction Engines are developing the vacuum brazed heat exchanger assemblies further, as designs gain traction in the aerospace sectors, and other sectors demanding high levels of performance, in applications requiring certification. As production volumes increase, the level of quality assurance and repeatability will have to increase also. Various aspects of the Vacuum Brazing process must be optimised. The selection of the braze consumable alloy, which flows into the joint gaps, is one of these aspects. Well established, off-the-shelf products are currently used. Improvements are sought via the investigation of novel compositions and formats. As well as the base composition of the braze consumable alloy, the format of it is also important (paste, wire, foil, tape options exist). These different formats offer different advantages in terms of how the braze consumable is locally deposited on to the metal substrates. Both the melting behaviour of the alloy consumable at the brazing temperature, and the ease of application of the alloy consumable at the required locations are key factors to be optimised for the Reaction Engine Tubular Heat Exchanger designs, to increase efficiency of manufacturing in the Assembly and Brazing production areas. Application of uniform layers of braze consumable on to the surfaces via coating technologies are one of the methods whereby process efficiencies will be assessed.Project AimsThe work will start with the comprehensive undertaking of mapping Reaction Engines' existing assembly and vacuum brazing routes for heat exchanger parts. A baseline material and manufacturing component will be identified for both steel and nickel alloy parts, representative of current tubular heat exchanger designs. An assessment of existing commercial brazing alloys will be done to understand the current limits for repeatability, and performance. Methods for application of the brazing consumable to the component surfaces, at the required locations, will be assessed - laser cladding, thermal spray, cold spray, physical vapour deposition, or hybrid surface additive manufacturing routes are coating methods of interest. The manually intensive placement methods currently in use will be replaced. Materials characterisation will be undertaken to identify optimal process parameters and material properties, including mechanical testing, metallography and thermophysical property measurement. In a final stage novel coating alloys (e.g., high entropy alloys) will be formulated, manufactured, and tested for comparison to the existing commercial systems.