| LUO Fang,HU Jinxin,XUAN Danfeng.Effect of Mo Content on Microstructure and Properties of Stellite21 Surfacing Layer[J],54(11):221-230 |
| Effect of Mo Content on Microstructure and Properties of Stellite21 Surfacing Layer |
| Received:November 07, 2024 Revised:April 07, 2025 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2025.11.019 |
| KeyWord:triple eccentric butterfly valve plasma arc surfacing stellite21 cobalt-based alloy Mo content wear resistance corrosion resistance |
| Author | Institution |
| LUO Fang |
Zhijiang College of Zhejiang University of Technology, Zhejiang Shaoxing , China;Institute of Laser Advanced Manufacturing, Zhejiang University of Technology, Hangzhou , China;Zhejiang Provincial Collaborative Innovation Center of High-end Laser Manufacturing Equipment, Hangzhou , China |
| HU Jinxin |
Zhijiang College of Zhejiang University of Technology, Zhejiang Shaoxing , China;Institute of Laser Advanced Manufacturing, Zhejiang University of Technology, Hangzhou , China;Zhejiang Provincial Collaborative Innovation Center of High-end Laser Manufacturing Equipment, Hangzhou , China |
| XUAN Danfeng |
Zhijiang College of Zhejiang University of Technology, Zhejiang Shaoxing , China;Institute of Laser Advanced Manufacturing, Zhejiang University of Technology, Hangzhou , China;Zhejiang Provincial Collaborative Innovation Center of High-end Laser Manufacturing Equipment, Hangzhou , China |
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| Abstract: |
| The triple eccentric butterfly valves are widely employed in fluid systems (gas/liquid) as critical components for regulating flow direction, rate, and pressure. Their sealing surfaces, which ensure sealing and blockage functions, are prone to damage due to corrosion, erosion, abrasive wear, and other media-induced effects during operation. Enhancing operational reliability and extending service life remain key objectives for sealing surface materials. Plasma transferred arc (PTA) surfacing, an advanced surface modification technology, offers advantages such as high deposition quality, efficiency, low dilution rate, cost-effectiveness, and compatibility with high-temperature, high-hardness materials. Stellite21 cobalt-based alloy, a high-performance Co-Cr-Mo alloy, is renowned for its exceptional wear resistance, corrosion resistance, and high-temperature stability. Optimizing its composition by adjusting molybdenum (Mo) content holds significant research potential for further improving comprehensive properties. This study fabricates Stellite21-based surfacing layers via PTA technology and systematically investigates the influence of Mo contents on microstructure and performance. Stellite21 alloy powder and Mo powder are mixed and ball-milled for 2 hours with a planetary angle grinder to achieve uniform dispersion. Surfacing layers with different mass fractions of Mo (5.5wt.%, 7.5wt.%, 10wt.%, 12.5wt.%, and 15wt.%) are fabricated on the substrate surface with plasma arc surfacing welding equipment DML-V03BD. The plasma gas, powder feeding gas, and shielding gas are all argon. The welding current is 115 A, the powder feeding rate is 20 g/min, the swing width is 10 mm, the swing speed is 10 mm/s, and the rotation speed is 1 r/min. The samples are cut using an electric spark wire cutting machine, and the cross-sections are polished and etched with 8% FeCl3 solution. Then, the microstructure, composition distribution, and phase composition of the surfacing layers are analyzed by optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and X-ray diffractometer (XRD). The microhardness of the surfacing layers is tested with a Vickers hardness tester XHV-1000T-CCD. The friction coefficient of the surfacing layers is measured with a friction and wear testing machine HT-600, and the shape of the worn surface is measured with a laser scanning microscope system to calculate the wear volume. An electrochemical corrosion test is carried out in the electrochemical workstation, and the corrosion potential and corrosion current density are calculated according to the obtained a Tafel curve. Finally, the sample is soaked in 36 wt.% HCl solution for 120 h, and the immersion corrosion is carried out, and the weight loss coefficient is calculated. The results indicate that with the increase in the Mo content, the continuous growth of columnar crystals in the surfacing layer is inhibited, resulting in the formation of more short dendrites and equiaxed crystals, and the grains are continuously refined. The phases of the Stellite21 alloy surfacing layer mainly consist of cobalt-based solid solution γ-Co, Co7Mo6, Co3Mo, Mo2C, Cr23C6, etc. The Mo2C phase is concentrated at the grain boundaries. With the increase in the Mo content, the content of Cr23C6 decreases, while the contents of Co7Mo6, Co3Mo, and Mo2C relatively increase. The hardness of the surfacing layer increases with the increase in the Mo content. When the Mo content reaches 15wt.%, the microhardness reaches the maximum value of 398HV, which is approximately 19.5% higher compared with the surfacing layer with 5.5wt.% Mo. When the Mo content is 10wt.%, the friction coefficient and the wear volume of the surfacing layer are the lowest, decreasing by approximately 17.2% and 79.1%, respectively. Moreover, the surfacing layer also exhibits a high corrosion potential and low corrosion current density, which are ‒0.999 V and 1.552×10‒5 A/cm2, respectively. After immersion, the weight loss coefficient K decreases to the lowest, and the K value is 1.54%. In conclusion, when the Mo content is 10wt.%, the wear resistance and the corrosion resistance of the Stellite21 cobalt-based alloy surfacing layer can be maximized, thereby ensuring the operational reliability of the sealing surface of the triple eccentric butterfly valve. |
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