热喷涂技术应用及研究进展与挑战

热喷涂作为重要的表面工程技术之一,是通过在材料表面制备材料保护涂层与功能涂层,赋予基体材料没有,但服役环境所必须的表面性能的方法。由于热喷涂可以制备从超过50%孔隙缺陷含量到接近完全致密的任意材料的涂层,基于缺陷控制可满足从可磨耗、耐高温隔热、耐磨损与耐腐蚀等不同服役要求,经过100余年的发展已经形成了包括等离子喷涂、超音速火焰喷涂、电弧喷涂、普通火焰喷涂等一系列方法,已经成为在众多产业领域,包括航天航空、交通运输、石油化工、电力能源、冶金钢铁、纺织与造纸、机械制造等,提高产品寿命与竞争力不可或缺的技术。制备可以提供耐磨损、耐环境腐蚀防护、耐高温隔热防护等保护涂层是热喷涂尤为重要的应用方面,热喷涂作为可显著提升结构零件耐磨损的涂层制备方法应用非常广泛,但在动载如冲蚀、空蚀、疲劳磨损、或高应力磨料磨损条件下,涂层材料的耐磨性能尚不能完全发挥;由于涂层总是存在一定的孔隙,难以以制备态直接用作长效耐腐蚀防护涂层,适当的封孔处理成为其用作耐腐蚀涂层的必要条件;包括以燃气轮机热障涂层为代表的耐高温隔热涂层等在航空与地面重型燃机中的应用,在欧美热喷涂市场中约占比60%,随着我国燃气轮机技术的发展,该市场潜力有望逐步得到发掘。热喷涂耐磨损涂层性能的进一步提升不仅需要开发新型硬质耐磨材料以及宽温域自润滑材料,还需要结合材料开发,发展可使粒子间结合充分的涂层制备方法,其次,基于涂层结构特征与服役性能关系控制磨损服役条件,防止源于粒子间脱落的加速磨损是确保长效磨损保护的基础。如何制备在喷涂态即可满足腐蚀介质不浸渗的致密涂层依然是热喷涂耐腐蚀涂层制备需要攻克的挑战。冷喷涂、等离子喷涂、物理气相沉积、液料热喷涂等新方法近年来发展迅速,与这些方法相配套的材料制备技术的发展将是这些新方法得到广泛应用的基础。新能源、医疗、民生、半导体等对导电、催化、生物活性、绝缘、耐刻蚀等功能涂层的需求也将有力推动热喷涂技术的发展。本文将结合目前热喷涂技术在国内外的应用现状与存在的问题,展望热喷涂技术进一步发展过程中有待解决的主要挑战性技术问题,为本领域技术人员合理认识热喷涂技术的特点,直面挑战,深入开展开发与基础研究,推动技术提供参考。

Applications, Research Progresses and Future Challenges of Thermal Spray Technology

Thermal spraying has been developed to a well-established coating technology to provide materials surfaces with protective and functional coatings with different properties and performances which are required by service conditions of engineering parts where the substrate do not pocess. As one of the most important surface engineering technologies, the most distinct feature of thermal spraying is that the coating application developments are primarily based on microstructure defect control technologies, and the coatings can be sprayed with different levels of porosity. Moreover, the processing ability to deposit coatings with different microstructure of porosity level from more than 50% to near zero of dense one which looks like wrought bulk makes thermal spray coatings able to fulfill different service requirements from abradable, thermal barrier, wear-resistant to corrosion-resistant. Based on over 100 year research and development, several spray technologies such as plasma spraying, arc spraying, high velocity oxy-fuel spraying, conventional flame spraying have been established for wide applications in different industrial fields. Typical fields include aeronautics and aerospace, transportation, petroleum and chemicals, power and energy, metallurgy and steel manufacturing, textile and paper industries, machinery manufacturing etc. Thermal spraying has become indispensable to above industrial fields to prolong service lifetime of engineering parts and improve their properties as well as cost performance.The most important applications of thermal spraying are to provide engineering parts with excellent anti- wear, anti-corrosion, high temperature protections in the form of materials protective coatings. Among wide applications, thermal spraying is most popularly employed to deposit protective coatings against wear. HVOF WC-Co coatings can provide materials with excellent abrasive wear resistance. However, excellent wear-resistant potential of coating materials themselves is not utilized yet under wear conditions of dynamic loading such as erosion, cavitation and fatigue wear, and high stress wear conditions. It should be understood that as-sprayed coating cannot be directly used as materials protection against corrosion, since pores are inevitably present in coating. Thus, sealing treatment using proper organic or inorganic sealants must be applied to thermal spray coatings which are used in a corrosive environment. It has been reported that high temperature protections by thermal spray coatings for aero gas turbine and industrial gas turbine account about 60% of thermal spray market share in Northern American and Europe. Therefore, market potential in such field is expected to expand thermal spray market in China gradually with increasing application of gas turbine.The challenges facing further improvement of wear resistance of thermal spraying coatings include development of high performance anti-wear new coating materials and self-lubricating materials in a necessary temperature range, and also processing technology to create the coating with sufficiently bonded lamellae based on spray powder design. Moreover, it is also effective to use the coating in the conditions without significant spalling of lamellae by establishing the relationship between coating microstructure and service conditions. The challenge for anti-corrosion is how to deposit a dense coating that aggressive gas or liquid phase does not penetrate. Moreover, emerging new thermal spray technologies including cold spraying, plasma spraying physical vapor deposition, and liquid feedstocks thermal spraying have been developed in last two decades and are expected to explore new applications such as cold spraying in additive manufacturing and remanufacturing along with corresponding powders manufacturing technology. The great demand for high performance functional coatings such as electrical conduction, catalyst, bioactivity, insulation, anti-plasma eching in new energy, medical, semiconductors etc will lead to further development of new applications fields of thermal spraying.In this review paper, the applications and research progresses of thermal spraying will be summarized. The typical features of thermal spray coatings dominating coating application performances will be discussed. Moreover, typical challenges for future development of thermal spray technology from powders and processing technologies to fundamental researches will be put forwarded. It would be expected to provide engineers involving in thermal spray coatings with a reasonable understanding to coating features and current problems and future challenges.