| LI Jingkui,WANG Ruichao,PAN Linlin,ZOU Xiaodong,YANG Ke.#$NPEffect of LaB6 on Microstructure and High-temperature Oxidation Resistance of Inconel625 Alloy Coating Fabricated by Plasma Transferred Arc Surfacing[J],54(6):98-107, 142 |
| #$NPEffect of LaB6 on Microstructure and High-temperature Oxidation Resistance of Inconel625 Alloy Coating Fabricated by Plasma Transferred Arc Surfacing |
| Received:April 18, 2024 Revised:June 13, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2025.06.008 |
| KeyWord:plasma transferred arc surfacing Inconel625 alloy LaB6 high-temperature oxidation resistance La-Ti-O composite oxides grain refinement |
| Author | Institution |
| LI Jingkui |
School of Mechanical and Automation Engineering, Wuyi University, Guangdong Jiangmen , China;Guangdong Provincial Key Laboratory of Material Joining and Advanced Manufacturing, China-Ukraine Institute of Welding, Guangdong Academy of Sciences, Guangzhou , China |
| WANG Ruichao |
School of Mechanical and Automation Engineering, Wuyi University, Guangdong Jiangmen , China |
| PAN Linlin |
Guangdong Provincial Key Laboratory of Material Joining and Advanced Manufacturing, China-Ukraine Institute of Welding, Guangdong Academy of Sciences, Guangzhou , China |
| ZOU Xiaodong |
Guangdong Provincial Key Laboratory of Material Joining and Advanced Manufacturing, China-Ukraine Institute of Welding, Guangdong Academy of Sciences, Guangzhou , China |
| YANG Ke |
Guangdong Provincial Key Laboratory of Material Joining and Advanced Manufacturing, China-Ukraine Institute of Welding, Guangdong Academy of Sciences, Guangzhou , China |
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| Abstract: |
| To ensure the security of heat exchanger tubes in garbage incinerators under high-temperature conditions, it is common to prepare a high-temperature-resistant coating on the surface of the heat exchanger tubes. Nickel-based superalloys, due to their excellent mechanical properties, oxidation resistance, and thermal stability at elevated temperatures, are considered a favorable choice for protective coatings on the heat exchanger tubes. However, due to the coarse microstructure resulting from PTA surfacing and its potential impact on the high-temperature performance of the coating, it becomes necessary to enhance the high-temperature oxidation resistance of the IN625 coating to extend the service life of the heat exchanger. In this study, 1wt.% LaB6 particles with an average particle size of 1 μm were introduced into the IN625 alloy. After that, the IN625 and IN625/LaB6 coatings with and without LaB6 particles were fabricated by plasma transferred arc (PTA) surfacing. Subsequently, the microstructure, hardness, and high-temperature oxidation resistance of the two coatings at 1 000 ℃ were evaluated. The IN625 sample exhibited a typical columnar grain structure. With the addition of LaB6 particles, the microstructure of IN625/LaB6 sample transformed into a mixed structure of columnar and equiaxed grains. Notably, the IN625/LaB6 sample showed increased precipitation of phases, including dendritic Laves phases and La-Ti-O composite oxides. The fine dispersed La-Ti-O composite oxides acted as inhibitors of grain growth at high temperature, resulting in refined grain size and significantly improving microhardness (increasing from 225.7HV0.3 to 268.92HV0.3). Furthermore, during the initial stage (first 50 h) of 1 000 ℃ high-temperature oxidation, the oxidation kinetics curves for both samples followed the parabolic law, although the IN625/LaB6 sample exhibited a lower oxidation rate. After 50 h oxidation, the oxidation constant of IN625 sample increased significantly from (14±1)×10−2 mg2/(cm4.h) to (72±4)×10−2 mg2/(cm4.h), while that of sample B remained relatively stable. A hybrid structure with the outer layer of NiO/CrNbO4/NiCr2O4 oxides was formed on the surface of IN625 sample. With the incorporation of LaB6 particles, the area of spalling zone and the NiO oxide with poor adhesion to matrix in the outer layer decreased remarkably. In contrast to that, a continuous and uniform δ-Ni3Nb layer was formed at the oxide scale/matrix interface, and more CrNbO4 oxides were formed in the outer layer. This change could be attributed to the grain refinement in the IN625/LaB6 sample, which facilitated more Cr transport through grain boundaries to form a dense oxide scale on the surface of matrix. The substantial consumption of Cr near the oxidation interface increased the activity gradient of Nb, promoting the outward diffusion of Nb. As a result, a continuous and uniform δ-Ni3Nb layer formed at the oxide scale/matrix interface, along with additional CrNbO4 on the oxide scale surface. Both of these phases acted as diffusion barriers for cations and anions during high- temperature oxidation, leading to a reduction in the oxidation constant from (72±4)×10−2 mg2/(cm4.h) to (26±3)×10−2 mg2/(cm4.h). The addition of LaB6 particles facilitates the transformation of some columnar grains to equiaxed grains and grain refinement in the IN625/LaB6 coating, resulting in improved hardness and significantly enhancing high-temperature oxidation resistance at 1 000 ℃. |
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