梯度NiCrAlY涂层的高温腐蚀行为

IMR OpenIR

	梯度NiCrAlY涂层的高温腐蚀行为
	于大千
学位类型	硕士
导师	孙超
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料工程
关键词	电弧离子镀梯度涂层预氧化高温氧化热腐蚀 Arc Ion Plating The Gradient Coating Pre-oxidation Treatment High-temperature Oxidation Hot Corrosion
摘要	"摘要本论文工作采用电弧离子镀技术及后续真空扩散退火工艺在镍基高温合金上制备了均匀NiCrAlY涂层(此后简称均匀涂层)和梯度NiCrAlY涂层(此后简称梯度涂层)。分析了2种涂层的组织结构，对比研究了2种涂层静态空气下1000和1100 ℃的恒温氧化行为以及1100 ℃的循环氧化行为。对梯度涂层进行预氧化处理，得到预氧化后的梯度NiCrAlY涂层(此后简称预氧化涂层)。分析了预氧化涂层氧化膜的结构，并对比研究了均匀涂层、梯度涂层、预氧化涂层3种涂层静态空气下在75 wt.%Na2SO4+25 wt.%K2SO4混合盐中900 ℃和700 ℃的热腐蚀行为。均匀涂层和梯度涂层在退火后组织致密，与基体结合良好。均匀涂层由γ′/γ相和少量β-NiAl相、α-Cr相组成，成分分布均匀；梯度NiCrAlY涂层具有外层富Al、内层富Cr结构，其中外层由β-NiAl相和少量γ′/γ相、α-Cr相组成。均匀涂层和梯度涂层在1000 ℃恒温氧化1500 h后样品表面仍为连续致密的Al2O3膜，但此时均匀涂层的Al含量已经低于基体的Al含量，而梯度涂层外层的Al含量却仍为8.15 wt.%(EDS)。均匀涂层和梯度涂层1100 ℃的恒温氧化实验表明，梯度涂层具有较低的退化速率和良好的氧化膜修复能力。氧化初期过后，梯度涂层的动力学曲线斜率为均匀涂层的2/3。均匀涂层和梯度涂层在1100 ℃循环氧化65次后，梯度涂层外层仍存在连续的β-NiAl相，氧化膜为厚度约6 μm左右的α-Al2O3；而均匀涂层的Al含量已经低于维持涂层发生选择性氧化所需的临界Al含量，氧化膜为约2 μm左右的混合氧化物层。总的来说，在高温氧化过程中，梯度涂层的初始Al含量较高；氧化过程中其富Cr区两侧出现了对富Al区的Al向基体扩散起阻碍作用的Cr(W)析出带。这两方面使梯度涂层长时间维持更多的Al存储相，提升了氧化膜的迅速生成及再生成能力，从而使涂层具有较好的抗氧化性能。均匀涂层、梯度涂层、预氧化涂层3种试样在900 ℃Na2SO4+K2SO4混合盐中的热腐蚀实验表明，预氧化涂层因为其表面存在的双层氧化膜(外层混合氧化物层+内层Al2O3层)，在热腐蚀过程中，一定程度上将涂层和熔盐隔离，降低了氧、硫向涂层的扩散，降低了涂层/Al2O3膜界面的氧、硫分压，使保护性的Al2O3膜得以持续、缓慢地生长。因此，在900 ℃Na2SO4+K2SO4混合盐中，预氧化涂层的抗热腐蚀性能略优于梯度涂层，并远远优于均匀涂层。均匀涂层、梯度涂层、预氧化涂层3种试样在700 ℃Na2SO4+K2SO4混合盐中均表现出良好的抗热腐蚀性能。 "
其他摘要	"ABSTRACT High temperature corrosion behavior of the gradient NiCrAlY coating Daqian Yu (Materials Engineering) Supervised by Prof. Chao Sun The thesis is focused on the fabrication and the high-temperature corrosion behavior of NiCrAlY coating. A conventional NiCrAlY coating and a gradient NiCrAlY coating have been prepared by the combined method of arc ion plating and subsequent diffusion treatment on Ni-base superalloy substrate (specimens are hereafter termed as the conventional coating and the gradient coating). The microstructures, morphologies, isothermal oxidation behavior at 1000 and 1100 °C and cyclic oxidation behavior at 1100 °C have been investigated on the two kinds of coatings. The pre-oxidation treatment has been conducted for some of the gradient coating, then they were termed as the preoxidized coating. The microstructures and morphologies of the scale of the preoxidized coating have been characterized. The hot corrosion behavior in 75 wt.% Na2SO4+ 25 wt.% K2SO4 mixed salt at 900 and 700 °C of the conventional coating, the gradient coating and the preoxidized coating have been investigated. The conventional coating with uniform components is composed of γ′/γ phase, β-NiAl phase and some α-Cr precipitate phase. While the gradient NiCrAlY coating has showed layered microstructure, i.e., an Al-enriched outer layer and a Cr-enriched inner layer, primarily consists of β-NiAl phase, γ′/γ phase and some α-Cr precipitate phase in the outer layer. A compact and continuous alumina scale could be observed on the surface of the conventional coating and the gradient coating at 1000 °C isothermal oxidation test for 1500 h. Nevertheless, the Al content of conventional coating has been lower than the substrate, while the Al content of the outer layer of gradient coating has still been 8.15 wt.%. Isothermal oxidation at 1100 °C has indicated that the gradient coating possesses slower degradation speed and better ability of forming and healing the protective α-Al2O3 scale than the conventional coating. After the initial stage of oxidation, the gradient coating has maintained a slower oxidation rate in the following full period of oxidation, whose curve slope is two-thirds of the conventional coating. The gradient coating has exhibited better than the conventional coating at 1100 °C cyclic oxidation test. The masssive β-NiAl phase, as reservoir phase of Al, can be observed in the outer layer of gradient coating, and the thickness of α-Al2O3 scale on gradient coating is about 6 μm. While the Al content of conventional coating has decreased to 3 wt.% which is greatly lower than the substrate, and the scale is composed of mixed oxides containing α-Al2O3, Cr2O3 and Ni(Al,Cr)2O4. As a result, the gradient coating has maintained higher Al content during long-term oxidation due to the massive β-NiAl phase obtained in the outer layer after vacuum annealing and the Cr(W) zones precipitated beside the Cr-enriched inner layer during the oxidation. Adequate β-NiAl phase, as reservoir phase of Al, directly delay the process of Al depletion; Cr(W) zones, to a certain extent, slow down the degradation by hindering the diffusion of Al from the gradient coating to the substrate. Consequently, the ability of forming and healing the protective α-Al2O3 scales in the gradient coating have been enhanced, which has eventually improved the high-temperature oxidation properties. Hot corrosion of conventional coating, gradient coating and preoxidized coating at 900 °C in Na2SO4+ K2SO4 mixed salt has indicated that the preoxidized coating is sightly better than the gradient coating and greatly better than the conventional coating. The two-layer scale of preoxidized coating consists of a mixed oxidizes outer layer and a single α-Al2O3 inner layer, which partly separates the salt from the substrate and retards the diffusion of O and S toward the coating. The conventional coating, the gradient coating and the preoxidized coating have all behaved well at 700 °C in Na2SO4+ K2SO4 mixed salt. "
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64555
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	于大千. 梯度NiCrAlY涂层的高温腐蚀行为[D]. 北京. 中国科学院金属研究所,2012.