Porous polyimide materials (PPIs) having different porosity with a constant pore size were fabricated to further understand the effect of porosity on the friction properties in the boundary lubrication, mixed lubrication and elastohydrodynamic lubrication (EHL) regime, respectively. The tribological behaviors of non-porous polyimide (PI0) immersed in poly-α-olefin oil bath and PPIs impregnated with poly-α-olefin were firstly compared, and the effects of load and porosity on the friction performances were investigated. Results show that as the speed increases, the PPIs impregnated with oil exhibit the same friction coefficient (COF) change trend as PI0 immersed in poly-α-olefin oil, which is consistent with the stribeck curve, but the COFs in whole velocity range are higher, and the EHL arrived at a higher speed. The EHL critical speed of PPIs impregnated with oil, as well as the COFs during whole lubricating regime are closely related to the load and the porosity of the material. It mainly depends on two opposite effects of porosity on the friction properties. On one hand, PPIs with higher porosity will release more oil from pores under compression to form a lubricating film, on the other hand, higher porosity will lead to higher contact pressure under the same load, and provide larger contact areas as a result of the increase in the elastic collapse area, which will aggravate the solid–solid direct rubbing and increase the COFs.

Graphic Abstract

中文翻译：

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孔隙率对不同润滑方式下含α-烯烃的聚酰亚胺多孔聚酰亚胺摩擦性能的影响

制造具有不同孔隙率和恒定孔径的多孔聚酰亚胺材料（PPI），以进一步了解孔隙率分别对边界润滑，混合润滑和弹性流体动力润滑（EHL）方案中的摩擦性能的影响。首先比较了无孔聚酰亚胺（PI0）浸入聚α-烯烃油浴中的摩擦学行为和浸渍有聚α-烯烃的PPI的摩擦学行为，并研究了载荷和孔隙率对摩擦性能的影响。结果表明，随着速度的增加，浸油的PPI的摩擦系数（COF）的变化趋势与PI0浸入聚α-烯烃油中的趋势相同，这与stribeck曲线是一致的，但是在整个速度范围内更高，而EHL则以更高的速度到达。浸油的PPI的EHL临界速度以及整个润滑过程中的COF都与材料的载荷和孔隙率密切相关。它主要取决于孔隙率对摩擦性能的两个相反的影响。一方面，孔隙率较高的PPI会在压缩状态下从孔隙中释放出更多的油，从而形成润滑膜，另一方面，孔隙率越高，在相同载荷下会导致更高的接触压力，并且由于接触压力的增加而提供更大的接触面积。弹性塌陷面积增加，这将加重固-固直接摩擦并增加COF。

图形摘要