Novel braze coating materials & processes for sustainable aeroengine applications

reaction Engines （https://www.reactionengines.co.uk）正在开发替代燃料（如氨）推进系统方面的专业知识，这是针对“可持续飞行”的技术转变的一部分。高速节能飞行目标的一个核心方面是反应发动机用于冷却高速流体的热交换器设计，并回收和再利用提取的热能。其中一个关键的设计配置是管式热交换器，它提供了重量轻，紧凑，高效的性能。使新设计能够组装的主要制造技术是真空钎焊。Reaction Engines在镍铬超级合金和不锈钢合金管式热交换器的设计、制造和测试方面拥有丰富的经验，并使用最先进的大型定制真空炉进行内部钎焊。多排薄壁油管以紧密排列的复杂阵列连接到歧管上，其形状可以封装在紧凑的模块化设计中。Reaction Engines正在进一步开发真空钎焊热交换器组件，因为该设计在航空航天领域以及其他要求高性能的领域获得了发展，需要认证。随着产量的增加，质量保证和可重复性的水平也必须提高。真空钎焊工艺的各个方面都必须优化。流入接头间隙的钎焊耗合金的选择就是其中一个方面。目前使用的是成熟的现成产品。改进是通过调查新颖的组成和格式寻求。除了钎焊耗材合金的基本成分外，它的形式也很重要（有粘贴、金属丝、箔、胶带等选项）。这些不同的格式提供了不同的优势，就如何钎焊消耗品局部沉积到金属基板。合金消耗品在钎焊温度下的熔化行为，以及合金消耗品在所需位置的易于应用，都是优化反应发动机管式热交换器设计的关键因素，以提高装配和钎焊生产区域的制造效率。通过涂层技术将均匀的钎焊消耗品层应用于表面是评估工艺效率的方法之一。项目目标：该工作将从综合承担反应发动机现有的热交换器部件组装和真空钎焊路线的测绘开始。将确定钢和镍合金部件的基准材料和制造部件，代表当前的管式热交换器设计。将对现有的商用钎焊合金进行评估，以了解目前的可重复性和性能限制。将评估在所需位置将钎焊消耗品应用于组件表面的方法——激光熔覆、热喷涂、冷喷涂、物理气相沉积或混合表面增材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，金相学和热物理性能测量。在最后阶段，新型涂层合金（例如，高熵合金）将被配制、制造和测试，以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.