| 引用本文: | 孔俊超,王刚,许雪艳,徐兵,陈梦强,祝小康.粉末润滑粗糙界面的摩擦特性数值模拟及光学原位观测[J].中国表面工程,2024,37(4):229~239 |
| KONG Junchao,WANG Gang,XU Xueyan,XU Bing,CHEN Mengqiang,ZHU Xiaokang.Numerical Simulation and Optical in-situ Observation of Friction Characteristics of Rough Interface of Powder Lubrication[J].China Surface Engineering,2024,37(4):229~239 |
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| 摘要: |
| 固体粉末润滑剂可用于航空航天和高温成型等恶劣环境，润滑剂的润滑特性已成为制约大型锻件成形的关键因素。建立离散元数值模型分析不同粉末层厚度和粗糙度的初压力链和配位数，再利用面接触原位观察试验机分析 30 个行程中粉末层形态、摩擦特性参数和真实接触面积比。结果表明：粉末层厚度为 15 μm 时，易发生擦伤、点状剥落和分层剥落等，部分区域金属基体初始裸露，摩擦因数先增加后趋于定值，主要为微凸体直接接触承载，接触界面颗粒数少、配位数迅速下降、 力链持续时间短，摩擦磨损状态恶劣。粉末层厚度为 30 μm 时，粉末完全覆盖接触区域，摩擦因数先增加后降低，真实接触面积比大，界面颗粒数多、配位数降低缓慢、力链持续时间长，载荷波动较小且真实接触面积比大，摩擦磨损状态良好。选取较大粉末层厚度（30 μm）和适当的表面粗糙度（Ra 0.409 μm）时，粉末平整性好且碳元素含量高，接触界面的力链分布均匀，配位数大且持续时间长，能形成平整、稳定的粉末润滑膜。基于离散元数值模拟和光学原位观测研究不同粗糙度和粉末层厚度的摩擦接触界面摩擦特性，可为机械工程领域的接触界面形成平整、稳定且润滑性能良好的粉末润滑膜提供理论指导和机理分析。 |
| 关键词: 光学原位观测 表面粗糙度 粉末层厚度 摩擦因数 真实接触面积比 |
| DOI：10.11933/j.issn.1007-9289.20230810001 |
| 分类号:TH117 |
| 基金项目:巢湖学院自然科学研究重点项目（XLZ-202205）；巢湖学院科技创新与服务团队项目（kj22kctd02）；巢湖学院校企合作项目（hxkt20220091，hxkt20220125）；巢湖学院教学研究重点项目（ch22jxyj05） |
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| Numerical Simulation and Optical in-situ Observation of Friction Characteristics of Rough Interface of Powder Lubrication |
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KONG Junchao1，WANG Gang2，XU Xueyan1，XU Bing1，CHEN Mengqiang1，ZHU Xiaokang1
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1.College of Mechanical Engineering, Chaohu University, Hefei 238000 , China ；2.Institute of Tribology, Hefei University of Technology, Hefei 230009 , China
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| Abstract: |
| Solid powder lubricants are used in aerospace, high-temperature molding, and other harsh environments where oil lubrication is unsuitable for mechanical engineering. It is essential to find a lubricant that protects against high temperatures, which is a key constraint in the formation of large forgings. A discrete-element numerical model was established to analyze the initial pressure chain and coordination number of different thicknesses and surface roughness of a powder layer based on the linear-bond model. The upper specimen was a 1.5 mm × 4 mm 304 pin, whereas the glass of Sailboat 7101 (25.4 mm × 76.2 mm × 1 mm) was selected for the lower specimen. The graphite spray used for the test was produced by Kangtai, Germany, and was characterized by high adhesion and temperature resistance. The specified thickness of the powder layer was obtained by repeated spraying. An M-Drive micro-stepper motor was used to drive the specimen in a linear reciprocating motion at different speeds, and a metallurgical microscope was equipped with a 10× objective lens to observe the selected powder layers in real time. The morphology, friction characteristics, and real contact-area ratio of the powder layer during 30 strokes were analyzed using an in-situ surface contact observation machine. A confocal laser scanning microscope(VK-X250) was used to observe the three-dimensional contour surface morphology of the upper specimens. The real contact-area ratio is an important parameter for characterizing the abrasion status of specimens and is calculated using the grayscale and binary modes of MATLAB. A 3D surface profilometer, scanning electron microscope, and energy-dispersive X-ray spectroscope were used to characterize the morphology and elements of the worn surfaces. The results showed that the metal matrix in the local area of the specimen was initially exposed when the thickness of the powder layer was 15 μm. The interface of the lower specimen showed severe abrasion marks, whereas the 3D morphology parameters (Sa and Sz) of the upper specimen were larger, and the carbon content was lower. Because the number of particles and the contact between particles are small, the coordination number decreases rapidly, and the force chain duration is short. Hence, abrasions, spot flaking, and stratified shedding occurred at the interface. The friction coefficient increased and then tended to a larger value, whereas the real contact area was the direct contact of asperities which reached 19.13% after 30 strokes. This indicates that the worn interface was severe, and lubrication was ineffective. When the powder-layer thickness was 30 μm, the contact area was completely covered during the initial period, and the powder-lubrication layer peeled off in subsequent periods. The interface of the lower specimen exhibited large flakes of powder, whereas the 3D morphology parameters of the upper specimen decreased, and the carbon content increased. A large number of particles and contacts leads to a slow decrease in the coordination number; therefore, the force chain lasts for a long time. The friction coefficient increased and then decreased to a small value, whereas the load was lower, and the real contact-area ratio was large. Therefore, a dense and complete powder-lubrication layer can be formed, which can provide a certain lubrication effect at this time. When the powder-layer thickness was large (30 μm) and the surface roughness was appropriate (Ra = 0.409 μm), a powder layer with good uniformity (Sa and Sz were small) and a high carbon content was formed. Along with the uniform distribution of the force chain, large number of coordination, and long duration, the powder layer was lubricated well under these test conditions. This study provides theoretical guidance and mechanistic analysis for the formation of a smooth and stable powder-lubrication layer in the machining field using numerical simulations and experimental research. |
| Key words: optical in-situ observation surface roughness powder-layer thickness friction factor true contact-area ratio |
