Structural changes and tribological performance of thermosetting polyimide induced by proton and electron irradiation

• Proton irradiation induced more extensive changes in structure and friction behavior than electron irradiation.
• The effect of combined irradiation was less than that of the sum of electron and proton irradiation.
• Three forms of irradiations all induced the high initial friction coefficient and the low steady-stage friction coefficient.
• The initial friction stage means a fast-wearing adhesive process while the steady-state of the system is a three-body abrasion.

The structural changes and tribological performance of thermosetting polyimide were investigated by electron, proton or both combined irradiations at 25 keV in a ground-based simulation facility. Three forms of irradiations could lead to the formation of the carbonized layer on the polymer surface that could increase the hardness and adhesive force of the material. Proton irradiation induced more extensive changes in structure and friction behavior than electron irradiation by reason of the higher linear energy transfer value, and combined irradiation resulted in the largest impact, but which was less than the sum of the radiation effects of electron and proton. Moreover, the experimental results indicated that the changes in friction behavior are closely related with the carbonized layer, which was easily worn out in friction process and could introduce a shift from adhesion wear to three-body abrasive wear that reduced the wear rate and the friction coefficient. The friction process of irradiated samples could be divided into the initial stage and the steady stage. Three forms of irradiations all induced the high friction coefficient in the initial stage and the low friction coefficient in the steady stage, and the wear rate of the irradiated samples decreased in the order: electron irradiation>proton irradiation>combined irradiation.