Effect of Frictional Contact Surface on Maximum Pressing Load during Equal Channel Angular Pressing Process

Equal channel angular pressing (ECAP) is one of the advanced manufacturing methods for the production of nanostructured samples. The ECAPed materials showed exceptional mechanical properties with simultaneous high strength and good elongation features. Recently, the application of ECAP method for the production of industrial samples has widely been reported. Due to the required high pressing load in ECAP process, the length of the produced samples is limited. This study investigates the rooms for the reduction in the pressing load by change in frictional surfaces. Here, a novel design of ECAP punch and die is proposed, where most of the friction surfaces are changing from 'soft sample-to-brittle die' to 'brittle die-to-brittle punch' contact surfaces. By changing the contact surfaces between punch and die, the opportunity for the preparation of frictional surfaces is provided and the total frictional surfaces is reduced. The results of the numerical analysis and experimental measurements showed that about 2.2-9.8% reduction in the maximum required pressing load is feasible. Further reduction is also possible by more surface preparation. Optical microscopy is used to investigate the contact surfaces after the process, and scanning and transmission electron microscopies are used to analyze the rate of the grain refinement of the samples after conventional and novel ECAP processes. The experimental finding is supported by 3D finite element analysis (FEM). The calculated maximum required pressing force in novel and conventional ECAP dies is in good agreement with the experimental measurements. The FEM analysis revealed that the reduction in the pressing load by the modification of frictional surfaces is a practical approach.