Review: Mechanism of Reactive Element Effect—Oxide Pegging

doi:10.11900/0412.1961.2020.00222

Acta Metall Sin

2021, Vol. 57

Issue (2): 182-190 DOI: 10.11900/0412.1961.2020.00222

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Review: Mechanism of Reactive Element Effect—Oxide Pegging

YANG Liang, LV Haotian, WAN Chunlei, GONG Qianming, CHEN Hao, ZHANG Chi, YANG Zhigang(

)

School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China

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YANG Liang, LV Haotian, WAN Chunlei, GONG Qianming, CHEN Hao, ZHANG Chi, YANG Zhigang. Review: Mechanism of Reactive Element Effect—Oxide Pegging. Acta Metall Sin, 2021, 57(2): 182-190.

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Abstract

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.

Key words: high temperature oxidation reactive element effect oxide pegging

Received: 28 June 2020

ZTFLH:

TB31

Fund: National Natural Science Foundation of China(52001182)

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	Liang YANG
	Haotian LV
	Chunlei WAN
	Qianming GONG
	Hao CHEN
	Chi ZHANG
	Zhigang YANG

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https://www.ams.org.cn/EN/10.11900/0412.1961.2020.00222 OR https://www.ams.org.cn/EN/Y2021/V57/I2/182

Fig.1 Structure of a two-layer thermal barrier coating^[1]

Fig.2 Schematic diagram of different routes (I, II or III) of interface crack propagation an oxide peg^[53,54]

Table 1 Mechanism of adding active element oxide to improve TGO adhesion^{[65,69,71-74]}

Fig.3 Schematic diagram of oxide peg formation in the alloy with two kinds of REs doped^[79]

Table 2 Mechanism of surface application of some reactive element oxides to improve TGO adhesion^[70,86,87]

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