| ZHAO Yongsheng,GE Chao,WU Ying,CHEN Chunlun,LIU Yan,CHEN Hui.Effect of Laser Cladding Process on Microstructure and Mechanical Properties of CoCrMo Cobalt-based Alloy Coating[J],53(23):216-227 |
| Effect of Laser Cladding Process on Microstructure and Mechanical Properties of CoCrMo Cobalt-based Alloy Coating |
| Received:January 27, 2024 Revised:July 22, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.23.019 |
| KeyWord:CoCrMo cobalt-based alloy 24CrNiMo steel brake disc microstructure tensile properties wear resistance |
| Author | Institution |
| ZHAO Yongsheng |
School of Materials Science & Engineering, Southwest Jiaotong University, Chengdu , China |
| GE Chao |
School of Materials Science & Engineering, Southwest Jiaotong University, Chengdu , China |
| WU Ying |
School of Materials Science & Engineering, Southwest Jiaotong University, Chengdu , China |
| CHEN Chunlun |
School of Materials Science & Engineering, Southwest Jiaotong University, Chengdu , China |
| LIU Yan |
School of Materials Science & Engineering, Southwest Jiaotong University, Chengdu , China |
| CHEN Hui |
School of Materials Science & Engineering, Southwest Jiaotong University, Chengdu , China |
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| Abstract: |
| As the speed of high-speed trains continues to increase significantly, the 24CrNiMo cast steel material used in brake discs is increasingly found inadequate in meeting the rigorous braking performance requirements necessary for these advanced high-speed trains. This inadequacy necessitates the exploration of alternative materials that can withstand the higher stress and thermal demands placed on brake systems. Cobalt-based alloys, recognized for their exceptional mechanical properties, including superior strength, excellent wear resistance, and high-temperature stability, are now being widely utilized in demanding applications such as rail transportation, aerospace, and other high-performance fields. The work aims to investigate the impact of laser cladding technology on the microstructure and mechanical properties of CoCrMo cobalt-based alloy cladding coatings. The primary goal is to enhance the strength, wear resistance, and overall durability of the brake disc friction surface to meet the elevated performance demands of modern high-speed train brake systems. In the experimental setup, 24CrNiMo steel brake discs serve as the substrate material, and CoCrMo cobalt-based alloy powder is used for cladding. The study meticulously examines how variations in single-factor laser cladding process parameters, such as laser power, scanning speed, and powder feeding rate, affect critical aspects including melt width, melt height, melt depth, and dilution rate. Comprehensive evaluations are conducted by various techniques, including optical microscopy (OM), scanning electron microscopy (SEM), microhardness testing, friction and wear testing, and tensile testing, to assess the microstructure and mechanical properties of the cladding coatings under different conditions. The experimental results indicate that both melt width and dilution rate increase as the laser power increases, while melt height and melt depth remain relatively stable across different power settings. The dilution rate also increases with increasing scanning speed, but melt height and melt width decrease with increasing scanning speed. Moreover, the melt height increases as the powder feeding rate rises, whereas the dilution rate decreases as the feeding rate increases. Despite variations in process parameters, the microstructure of the cladding coating exhibits minimal changes, predominantly consisting of γ-Co, Ni-Cr-Co-Mo solid solution, and a small amount of ε-Co phase. The microstructure is characterized mainly by columnar and cellular crystals. The microhardness of the cladding coating increases with increasing laser power and powder feeding rates, but decreases with the increasing scanning speed, reaching a peak value of approximately 304HV0.2. The tensile strength and yield strength demonstrate an increasing trend with the increasing laser power but decrease with the increasing scanning speed. After fracture, the elongation increases with laser power, initially rises and then decreases with the increasing scanning speed, and decreases with the increasing powder feeding rates. Under varying process parameters, the maximum tensile strength achieved is (1 202±60) MPa, with a maximum elongation of (17.4±1.3)%. Although laser power does not significantly affect wear resistance, higher laser power and powder feeding rates or lower scanning speed, result in improved wear resistance, with abrasive wear and adhesive wear identified as the primary wear mechanisms. Overall, the laser cladding process has a significant impact on the melt width, melt height, and dilution rate, though its effect on the microstructure of the cladding coating is relatively minor. By optimizing the laser cladding process parameters, it is possible to substantially enhance the hardness and tensile properties of the cladding coating, although the impact on wear resistance remains somewhat limited. |
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