| DU Jia-jun,MI Jia-liang,SHI Lu-bing,CHEN Chao,LIU Zhong-ming,WANG Wen-jian,DING Hao-hao.Laser Cladding of 18CrNiMo7-6 Gear Steel and Its Scuffing Load Capacity[J],52(9):420-429 |
| Laser Cladding of 18CrNiMo7-6 Gear Steel and Its Scuffing Load Capacity |
| Received:July 08, 2022 Revised:February 28, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.09.038 |
| KeyWord:laser cladding 18CrNiMo7-6 gear material microstructure scuffing damage |
| Author | Institution |
| DU Jia-jun |
Tangshan Research Institute, Southwest Jiaotong University, Hebei Tangshan , China |
| MI Jia-liang |
China Academy of Launch Vehicle Technology, Beijing , China |
| SHI Lu-bing |
Zhengzhou Research Institute of Mechanical Engineering Co., Ltd., Zhengzhou , China;Tribology Research Institute, Southwest Jiaotong University, Chengdu , China |
| CHEN Chao |
Zhengzhou Research Institute of Mechanical Engineering Co., Ltd., Zhengzhou , China |
| LIU Zhong-ming |
Zhengzhou Research Institute of Mechanical Engineering Co., Ltd., Zhengzhou , China |
| WANG Wen-jian |
Tangshan Research Institute, Southwest Jiaotong University, Hebei Tangshan , China;Tribology Research Institute, Southwest Jiaotong University, Chengdu , China |
| DING Hao-hao |
Tangshan Research Institute, Southwest Jiaotong University, Hebei Tangshan , China;Tribology Research Institute, Southwest Jiaotong University, Chengdu , China |
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| Abstract: |
| As a typical failure of gear surface in high-speed and heavy-duty gear transmission system, scuffing is affected by the operating parameters, lubricating medium, material, surface roughness and surface hardness of the gears. Many manufacturing technologies have been widely used to improve the scuffing load capacity of gear. As a new surface strengthening and modification technology, laser cladding technology can effectively improve the wear resistance and scuffing load capacity of matrix materials, so it has a high application prospect for improving the scuffing load capacity of gear. The gear material selected in the test was 18CrNiMo7-6 gear steel. The cladding material was NiCr20 alloy powder with the addition of different contents of ZrO2 powder and MoS2 powder. The NiCr20 alloy powder and ZrO2 powder used were spherical particles with particle sizes of 100 μm and 50 μm respectively, while the MoS2 powder was lamellar particles with the size of about 10 μm. Before each laser cladding test, the cladding powders were mechanically mixed and dried, and the surface of the samples were subject to ultrasonic cleaning in the ethanol bath. Two kinds of laser cladding alloy coatings were prepared on the surface of 18CrNiMo7-6 gear material by coaxial laser cladding technology with ZrO2, MoS2 and NiCr20 alloy powders in different proportions. In the laser cladding, the laser power used was 500 W, the scanning speed was 2 mm/s, and the powder feeding rate was 11.1 g/min. After preparation, the microstructure and hardness profile of the coatings were observed. Scuffing tests for the laser cladding samples and carburized treated samples were carried out on the MJP-30 A rolling contact friction and wear testing machine. In the scuffing test, the load was increased step by step from 500 N according to the interval of 300 N. Each level of load acted for 3 minutes until the sample was scuffed, the sudden increase of friction coefficient was taken as the scuffing failure index. In the test, the rotating speeds of the upper and lower samples were set at 500 r/min and 200 r/min respectively, and the lubricating oil flow was 0.5 L/min. After the test, the damage of the samples were observed by optical microscope. The results indicated that the carburized gear sample was mainly composed of lath martensite and retained austenite and its surface hardness reached around 572HV0.5; the NiCr20-3%ZrO2 (mass fraction, the same below) coating was mainly composed of dendritic and cellular phases and its hardness reached around 620HV0.5; the NiCr20-3%ZrO2-1%MoS2 coating was composed of dendritic phases, cellular phases and black flower shaped particles and the hardness reached around 486HV0.5. The friction coefficient of the NiCr20-3%ZrO2 cladding sample and the NiCr20-3%ZrO2-1%MoS2 cladding sample was lower than that of the carburized gear sample. Compared with the carburized gear sample, the scuffing loads of the two cladding samples were increased by 8.41% and 44.86%, respectively. The carburized gear sample presented typical thermal scuffing damage features, and the critical flash temperature was calculated to be 207 ℃. This critical flash temperature was not reached in the failure of NiCr20-3%ZrO2 cladding sample and it presented a fatigue spalling damage of the cladding layer. The self-lubricating effect of the NiCr20-3%ZrO2-1%MoS2 cladding sample inhibited the rapid development of the scuffing damage after reaching the critical flash temperature. The failure was finally caused by the surface spalling with the initiation and expansion of surface fatigue cracks when the load was continued to increase to the critical failure load. Compared with carburization strengthening of gear surface, NiCr20-3%ZrO2-1%MoS2 laser cladding strengthening can effectively improve the scuffing load capacity. |
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