COLD SPRAY: FUNDAMENTAL STUDIES

冷喷涂是一个看似简单的概念，其中塑性变形粉末“仅仅”通过在远离粉末熔点的温度下以超音速冲击到基底上而形成部件。 “冷”部分特别具有吸引力，因为它为制造迷人的材料开辟了道路，否则无法加工，例如具有非常不同熔点的材料。 这是一项航空航天工业特别感兴趣的技术，作为制造和维修部件的一种手段。 该项目旨在提高对这一进程的基本认识，以期： (i)理解过程：虽然已经知道了很多，但颗粒结合冶金的许多方面需要更彻底地探索。 此外，还有许多与冷喷涂相关的工艺变量，但一些更关键的参数在冷喷涂期间无法测量，这些参数是冷喷涂期间的粉末速度、输送速率和温度。 这些参数可能变化的后果需要通过实验和工艺建模来探讨。 验证的过程模型将实现与基于霍普金森杆方法的冷喷涂“模拟器”的帮助下。 通过这种方式，可以物理模拟已知的“速度”和温度值，并且可以使用结果来帮助验证模型。 (ii)研究后处理热机械处理的效果：后处理对于降低加工硬化和孔隙率以及增加颗粒/颗粒结合是必要的。 控制这些机制将被探索，以优化热机械处理。 (iii)探索金属-金属复合材料的冷喷涂：冷喷涂不同金属粉末的混合物可以改善“冷喷涂性能”，创造新材料，帮助后处理，并使人们更深入地了解冷喷涂的机理。 具有不同硬度和塑性流动性能的粉末混合物将被初步研究，因为初步工作已经揭示了一些有希望的结果和有趣的现象。

Cold spray is a deceptively simple concept, in which plastically deformable powders are formed into components by 'merely' impacting on to a substrate at supersonic velocities at temperatures far from the powder melting point. The 'cold' part is particularly beguiling because it opens the way for making fascinating materials which otherwise could not be processed, e.g. materials which have very different melting points. It is a technology of particular interest to the aerospace industry as a means to manufacture and repair components. This project seeks to improve the fundamental understanding of the process, with a view to: (i) Understanding the process: Although much is known, many aspects of the metallurgy of particle bonding need to be explored more thoroughly. As well, there are many process variables connected with cold spray, but some of the more critical parameters cannot be measures during cold spray, these being powder velocity, delivery rates and temperature during cold spray. The consequences of possible variations in these parameters needs to be explored by experimentation and process modelling. Validation of the process model will be achieved with the help of a cold spray 'simulator' based on the Hopkinson bar approach. In this way, known values of 'velocity' and temperature can be physically simulated and the results can be used to help validate the model. (ii) investigating the effect of post processing thermomechanical treatments: post processing is necessary to reduce the work hardening and the porosity, as well as increase particle/particle bonding. The mechanisms controlling these will be explored in order to optimise thermomechanical treatments. (iii) exploring cold spraying of metal-metal composites: cold spraying mixtures of different metal powders could improve 'cold sprayability', create novel materials, aid post processing and bring more insight into the mechanisms of cold spraying. Mixtures of powders with different hardnesses and plastic flow properties will be initially examined, since preliminary work has revealed some promising results and interesting phenomena.