Plastic deformation mechanism of crystalline polymer materials in the equal channel angular extrusion process

The plastic deformation mechanism of polymer materials was observed during the equal channel angular extrusion process with polypropylene as crystal polymer. The variations of the crystalline morphology, microstructure, and microhardness were discussed during the process. The extent of plastic deformation increased from the top surface to the bottom surface, and the maximum molecular orientation increased from R = 1 near the top surface to R = 2.2 near the bottom surface. The plastic deformation at the surface was small, especially in the range of 400 μm distance from the top surface, without definite change of the crystalline structure. The plastic deformation was obvious when the sample was pressed into the outer corner of die. The spherulitic structure extended to the ellipsoidal shape along the 45° direction of the diagonal line because of the shear strain. The plastic deformation led to the destruction of spherulites near the bottom surface. However, the spherulites were not destroyed at center part, so their refinement as metallic material could not be expected. The variation of internal structure and material orientation increased along the direction of the maximum molecular orientation.