综述:活性元素作用机理——氧化物“钉扎”模型

Review:Mechanism of Reactive Element Effect——Oxide Pegging

高温防护涂层在航空发动机或燃气轮机上有着广泛应用,活性元素在高温防护涂层上得到了大量应用,尤其在降低氧化层生长速率和提高其粘结性方面,但是目前活性元素的微观作用机制还存在较大争议。在提出的几种解释中,氧化物"钉扎"模型往往作为首要的考虑因素,是一个非常重要的模型,但目前依旧存在争议。本文综述了自氧化物"钉扎"现象发现以来该模型的发展,包括模型的提出、氧化物栓与氧化层粘结性的关系、如何提高"钉扎"效果、不同情况下氧化物栓的生成和长大等,并介绍了该模型存在的缺陷。最后对该模型在自身完善方面及该模型和活性元素效应的其他解释模型之间的相互作用机制方面的研究重点进行了展望,力图对氧化物"钉扎"现象及目前的研究方向有一个全面的认识,期望为活性元素效应的研究和热障涂层材料设计提供一定的基础。

High temperature protective coatings are involved in a wide variety of applications including aero engines and gas turbines.Reactive elements,including all rare-earth elements as well as Ti,Zr,and Hf,are increasingly used to modify high temperature protective coatings,and their main effects are reducing scale growth and improving scale adhesion.The mechanism through which reactive elements work is yet to be clearly understood.The current mechanism comprises"enhanced scale plasticity","graded seal mechanism","modification to growth process","chemical bonding","the vacancy sink model","oxide pegging","dynamic segregation theory",and"the sulfur effect theory".Among these,oxide pegging is perhaps the most important one,although some people may disagree.Oxide pegging is the result of the mechanical joining of an oxide to its corresponding alloy;it is a result of either the internal oxidation of added reactive elements or dispersed oxide particles growing in size and extending into the alloy.This paper offers an overview of the research progress on oxide pegging,including its proposed,the relationship between the peg and scale adherence,improving the"key-on"effect,and the peg formation and growth under different conditions(the doped reactive element with a low or high solid solute in the alloy,dispersed oxide added in the alloy,and two reactive elements doped into the alloy).Moreover,it sheds light on the model’s inability to explain the surface application of reactive elements on the alloy.Finally,the paper suggests future studies on this model,like focusing on how to obtain the ideal oxide pegging,developing a new model for oxide peg formation and growth with two or more reactive elements added to the alloy,and the cooperation effect between the oxide pegging and other mechanisms.The paper’s objective is to offer a better understanding of oxide pegging and to provide theoretical support for the studies on the reactive element effect and the design of materials in thermal barrier coating systems.