表面界面特性对碳薄膜摩擦行为的影响机制

Along with the rapid development of mechanical systems to high efficiency,high integration,high reliability,and high precision,the moving parts are playing more and more important roles in reliable operation of machines. More importantly,the surface and interface of the moving parts are payed more and more attention with the continuous reduction in size of machines and parts.To provide efficient lubrication so as to reduce friction and wear now becomes a key point to make sure the moving parts move smoothly.Solid lubrication is a supplyment or substitute to liquid lubrication, particularly, in the cases of extreme or harsh conditions.Therefore, to pursue super low firction or super lubricity solid lubricant materials has been a long time dream for people.Carbon based thin films, generally,called diamond like carbon (DLC),are considered as the solid lubricants with super low friction to be used in practice among many solid lubricants after many years investigation.However,due to the types of the DLC films are various according to the ratios of sp3 to sp2 hybird carbon and the content of hydrogen in the films,their tribological behaviors are diversity in different conditions,for example,pure DLC films demonstrated higher friction in dry air but lower friction in humidity air,while the hydrogenated DLC films showed reverse behaviors,lower friction in dry air but higher friction in humidity air.Many explanations were proposed to give answers to above phenomena,such as dangling bonds prsent in pure DLC would induce strong interaction force between the sliding surfaces to higher friction while reacted with water from humidity air to lower friction;capillary force would reinforce the interaction force between the rubbing faces in the case of hydrogenated DLC films. These proposed explanations are also diversity,and sometimes are contrary to one another.In order to give a integrate explanation in theory to the diversity friction behaviors of DLC films,based on the theoritical analyses,we are planning in this project to design the friction counter pairs according to their surface chemical properties.Pure DLC could be seen as lewis acid since of a large amount OH groups on the surface generated once exposed to air,hydrogenated DLC films could be considered as neutral due to hydrogenated surface,and fluorated DLC could be acted as lewis base;and counterparts Al2O3 is lewis acid,Si3N4 is neutral,and glass,Na2SiO4 is lewis base. Hope to verify the impact of surface wettability and chemical acid or base properties on the friction behaviors of various DLC films through experiments,to elicit unitary answer to the diversity friction behaviors of various DLC films in different conditions,and to reveal the roles of DLC films'surface and interface properties in the friction mechanism at molecular or atomic level.

针对碳薄膜摩擦学行为在不同环境下的多样性，本项目基于理论分析,即，纯DLC，a-C，路易斯酸；含氢DLC，a-C:H，中性；含氟DLC，a-C:F薄膜，弱路易斯碱。对偶：Al2O3，路易斯酸；Si3N4，中性；Na2SiO4，玻璃，路易斯碱。当纯DLC，a-C，暴露在空气中后, 薄膜表面的自由悬键与空气中的H2O进行加成反应后，表面为羟基OH。因此，a-C薄膜应该具有最大表面能和最小水接触角，即最大亲水性，a-C:H薄膜次之， a-C:F:H薄膜具有最小表面能和最大水接触角，即最小亲水性或最大疏水性。设计制备不同表面化学特性DLC薄膜、选择摩擦对偶配副，通过试验验证并揭示表面润湿性和界面酸碱理论匹配对碳薄膜摩擦学行为的影响机制，统一归纳碳薄膜摩擦性能的多样性，从分子或原子水平揭示碳薄膜摩擦行为及其与表面界面化学特性的相关性规律。

针对碳薄膜摩擦学行为在不同环境下的多样性，本项目基于表面润湿性和界面酸碱理论匹配分析，主要开展了两个方面的研究工作，取得的重要结果对工程应用中摩擦配副的合理选择具有极其重要的意义。（1）考察了不同类型DLC薄膜（a-C，a-C:H，a-C:H:F）互相作为摩擦对偶配副，在干燥大气环境和潮湿环境下的摩擦学特性。结果表明，干燥大气环境下，摩擦界面的静电作用（吸引力或排斥力）是导致其摩擦行为不同的主要原因。而潮湿环境下，摩擦副表面吸附水润湿行为则是导致其摩擦行为不同的主要原因；（2）考察不同类型DLC薄膜与Al2O3（路易斯酸），Na2SiO3（玻璃，弱路易斯碱）配伍的摩擦学行为。结果表明，摩擦配副界面间的静电相互作用对薄膜摩擦行为有显著影响。如, 当摩擦配副为路易斯酸-路易斯酸或路易斯碱-路易斯碱时，摩擦界面间的静电斥力会降低摩擦界面间的剪切力，从而使摩擦系数显著降低。而当摩擦配副为路易斯酸-路易斯碱时，界面间的静电引力则会导致更高的摩擦系数。