铸铁材料在边界润滑条件下形成薄片状磨屑的塑性流动机制

The Mechanism of Plastic Flow for Cast Iron Materials in Forming Flake-Like Debris under Boundary Lubrication Condition

本文在铸铁材料油润滑线接触滑动磨损状态研究的基础上,对边界润滑区典型的薄片状磨屑之形成过程进行了考察。通过对磨损表面的几何形貌、磨屑的形态和内部显微组织变化的分析,提出了薄片状磨屑的塑性流动形成机制。作者认为,薄片状磨屑的形成是磨损表面材料在局部应力和摩擦热的作用下以3种方式发生塑性流动的结果:当摩擦方向垂直于磨削加工条纹时为单侧塑性流动;当摩擦方向平行于磨削加工条纹时为双侧塑性流动;而在峰顶平台(磨削加工粗糙条纹磨合后形成的微平台)较大且载荷较高时,则为平台上的材料沿着摩擦方向向前挤压流动。

The object, which was based upon the research on sliding wear of cast iron materials under the condition of linear contact lubricated, has examined the process forming typical of flake-like debris (thickness is about 1-3μm) in boundary lubrication region. The analysis results shown that the formation of the flake-like debris is because of the consequences of plastic flow of material on wear surface affected by local stress and frictional heat. The ways of plastic flow are as follows: Thin layers on the tops of asperities deform and flow plastically along a side direction which is perpendicular to the direction of grinding marks; Thin layers are extruded from the edges of every deforming asperity when frictional direction is parallel to the direction of grinding marks; And when the area of bearing-load regions on the tops increases with wear progress and the load is higher, thin layers is extruded to flow forward along the direction of friction. Furthermore, according to the examination of the characteristics of wear scar on worn surfaces, the shape of wear debris and the change of interior microstructures in debris, a mode of plastic flow process for forming the flake-like debris is discussed in the paper as following: a. Plastic flow is occured on the tops of the asperities resulting from concentrated load and frictional heat, and then the material is extruded from the interfaces between contacted asperities to form thin flowing layers. b. The thin flowing layers are repeatedly affected by the frictional force or the asperities on the frictional interface so that the layers may be torn and fallen out from the stress concentrated and defects on the layers to form the flake-like debris. c. With increasing of the load and area of bearing-load regions on the tops of the asperities, the plastic flow occurs at the local micro- regions on where the born load may be much higher than other ones. Thin flowing layers are firstly produced at the micro-regions with higher stress, and then extruded forward to cover onto the tops. The covering layers have weaker bonding to the substrate. d. The covering layers generally show flake-like tongues separated from the substrate. The tongues are repeatedly acted by frictional force and asperities in friction interface, they are ultimately torn and fallen out as flake-like debris. On the basis of the mode of the plastic flow to forming flake-like debris and the results from quantitative analysis of debris in wear process, wear mechanism dominated in initial stage of boundary lubrication in our experiment is the plastic flow wear.