不同温度下柔性刷丝HVOF涂层摩擦磨损及氧化行为研究

Flexible Bristle-HVOF Coating Interface Wear and Tribological Oxidation Behavior at Different Temperature

目的研究不同温度下柔性刷丝HVOF涂层接触界面的摩擦磨损行为。方法在销盘摩擦磨损试验机上采用法向载荷2 N,转速900 r/min,对L605刷丝材料与HVOF涂层配副进行不同温度下的摩擦磨损试验,分别利用扫描电镜(SEM)、能谱仪(EDX)和X射线光电子能谱仪(XPS)对摩擦试验后不同温度(200~600℃)下的刷丝端面进行观察,并对其表面化学成分的价态进行分析。结果柔性刷丝界面的摩擦因数在0.5~0.9之间,且摩擦因数随着温度的升高而降低,摩擦因数曲线的波动程度则随温度的升高而加剧。随温度的升高,柔性刷丝界面的摩擦磨损状态由三体磨损逐渐转向二体磨损。摩擦界面EDX分析表明,接触界面的氧含量分布存在差异,随温度升高,刷丝表面氧含量增加,且XPS结果表明,不同温度工况下摩擦磨损界面氧元素的结合能并不相同。结论柔性刷丝接触界面的磨损机制以氧化磨损为主,在400℃以下,柔性刷丝界面的磨损机制主要表现为氧化磨损和磨粒磨损,再转变为氧化磨损与黏着磨损共同作用。此外,柔性刷丝界面形成不同的磨损氧化产物,当温度高于400℃时,氧元素的结合能呈现双峰。

Brush seal is a dynamical flexible contact structure with a tribo-pair in dynamic seal.The flexible bristle and the HVOF coating are used as the tribo-pair that effects on the seal-ability of the brush seal.In order to investigate the tribology behavior of the flexible bristle contact interface,the normal load of 2 N and the rotational speed of 900 r/min were used in the L605 bristle material friction tests by the pin-on-disc friction tester at different temperature.Scanning electron microscope is used to analyze the worn morphology of the bristle tips.Energy dispersive spectrometer and X-ray photoelectron spectroscopy were applied to analyze the chemical component of the worn surface,especially chemical states of oxygen element that could be used to character the oxidation phenomenon of the bristles tribological behavior.Two bristle tips connected in the shape of"8"could be observed on the worn bristles at 600℃,the hexagonal type bristle tips appeared under the condition of 400℃.In addition,the XPS results showed that the oxygen chemical state of the tribological interface varied as the temperature ranged from 200℃to 600℃.Especially,as the temperature increased over 400℃,the O 1s binding energy peaks of worn surface existed in several different chemical states.The atom weight percentage of the oxygen elements was 34.15%,27.48%and 14.88%at the temperature of 600℃,400℃and 200℃,respectively.As the temperature increased from 400℃to 600℃,the O 1s peak was split into two different peaks which were 529.8 eV and 531.3 eV binding energy.When the environment temperature was 200℃,the peak site of O 1s binding energy was at 530.6 eV.As the temperature increased from 200℃to 600℃,the friction coefficient value of the flexible bristle contact interface was declined from 0.9 to 0.5,while the variation of the friction coefficient presented strong wave.The temperature conditions could affect the steady state of the worn morphological contact interface.As the temperature increased,the flexible bristle frictional system from a third-body tribological system transferred into a two-body tribological system.The bristle cylinder contacting with the cylinder was the line contact mode and the circle usually changed into the polygonal shape after the friction tests.Specifically,the top tips were shown in the"8"shaped morphology with two bristle cylinder glued together after friction tests at 600℃.The flexible bristle contact interface state changed as the temperature increased and it was like that the bristle tips contacted with the flat coating sample under the flat contact condition,the tips of bristle changed from the coarse surface to the plough surface,and then to the smooth surface with the local oxidative layer spalling.The wear particles changed from the tiny nano-size particles,to common micron-size particles and then the thin slices as the temperature increased from 200℃to 600℃.The wear mechanism of the flexible bristle frictional pair presented oxidative wear mixed with abrasive wear,and then transferred into oxidative wear with adhesion wear.