{"title":"Investigation of scale formation and degeneration of silicide coating on Nb–Si based alloy in the temperature range from 1250 °C to 1560 °C","authors":"Weiping Zhang, Yanqiang Qiao, Xiping Guo","doi":"10.1016/j.intermet.2024.108395","DOIUrl":null,"url":null,"abstract":"<div><p>Nb silicide coatings modified with active elements have good oxidation resistance, but there is a lack of systematic research on their oxidation behavior at high temperatures above 1250 °C. The aim of this work is to investigate the oxidation behavior of an Al–Y modified silicide coating on Nb–Si based alloy in the temperature range from 1250 °C to 1560 °C. After oxidation at 1250 °C, the scale displays a typical layered structure consisting mainly of a TiO<sub>2</sub> outer layer, an amorphous SiO<sub>2</sub> matrix layer embedded with TiO<sub>2</sub> and ZrSiO<sub>4</sub>, and an inner layer consisting of SiO<sub>2</sub> and Cr<sub>2</sub>O<sub>3</sub>. Above 1350 °C, the evaporation reaction of Cr<sub>2</sub>O<sub>3</sub> into CrO<sub>3</sub> (g) is significantly accelerated and Cr<sub>2</sub>O<sub>3</sub> disappeared gradually with temperature or time. The TiO<sub>2</sub> layers covering on the scales formed at 1250–1500 °C grow along the crystallographic orientation of [100]. The micropores formed on the surface of TiO<sub>2</sub> should be attributed to the further oxidation of Cr<sub>2</sub>O<sub>3</sub> into volatile oxide CrO<sub>3</sub> (g). The scales exhibit a similar structure consisting mainly of a SiO<sub>2</sub> glass matrix embedded with ZrSiO<sub>4</sub> and a surface TiO<sub>2</sub> layer until 1500 °C. Above the eutectic temperature of SiO<sub>2</sub>–TiO<sub>2</sub> system, the scale is mainly composed of a matrix layer of SiO<sub>2</sub>–TiO<sub>2</sub> eutectic embedded with block TiO<sub>2</sub> particles, and a thin SiO<sub>2</sub> interface layer at 1560 °C. The degeneration path of the (Nb,X)Si<sub>2</sub> coating is (Nb,X)Si<sub>2</sub> → (Ti,Nb)<sub>5</sub>Si<sub>4</sub> → γ-(Nb,X)<sub>5</sub>Si<sub>3</sub>.</p></div>","PeriodicalId":331,"journal":{"name":"Intermetallics","volume":null,"pages":null},"PeriodicalIF":4.3000,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Intermetallics","FirstCategoryId":"88","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0966979524002140","RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
引用次数: 0
Abstract
Nb silicide coatings modified with active elements have good oxidation resistance, but there is a lack of systematic research on their oxidation behavior at high temperatures above 1250 °C. The aim of this work is to investigate the oxidation behavior of an Al–Y modified silicide coating on Nb–Si based alloy in the temperature range from 1250 °C to 1560 °C. After oxidation at 1250 °C, the scale displays a typical layered structure consisting mainly of a TiO2 outer layer, an amorphous SiO2 matrix layer embedded with TiO2 and ZrSiO4, and an inner layer consisting of SiO2 and Cr2O3. Above 1350 °C, the evaporation reaction of Cr2O3 into CrO3 (g) is significantly accelerated and Cr2O3 disappeared gradually with temperature or time. The TiO2 layers covering on the scales formed at 1250–1500 °C grow along the crystallographic orientation of [100]. The micropores formed on the surface of TiO2 should be attributed to the further oxidation of Cr2O3 into volatile oxide CrO3 (g). The scales exhibit a similar structure consisting mainly of a SiO2 glass matrix embedded with ZrSiO4 and a surface TiO2 layer until 1500 °C. Above the eutectic temperature of SiO2–TiO2 system, the scale is mainly composed of a matrix layer of SiO2–TiO2 eutectic embedded with block TiO2 particles, and a thin SiO2 interface layer at 1560 °C. The degeneration path of the (Nb,X)Si2 coating is (Nb,X)Si2 → (Ti,Nb)5Si4 → γ-(Nb,X)5Si3.
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