Microstructure and Mechanical Properties of the Commercially Pure Copper Tube After Processing by Hydrostatic Tube Cyclic Expansion Extrusion (HTCEE)

A newly introduced severe plastic deformation process for the production of relatively long ultrafine-grained (UFG) tubes, hydrostatic tube cyclic expansion extrusion (HTCEE), was applied up to two passes on commercially pure copper tubes to study the mechanical characteristics and microstructure of the HTCEE processed samples. In HTCEE process, the pressurized hydraulic fluid around the piece has a main role in the reduction of the friction load leading to a decrease in the required pressing force. After the second pass of HTCEE, a UFG microstructure with an average grain size of similar to 127 nm was observed. In two-pass HTCEE processed tub, more refined and also more homogeneous microstructure was achieved compared to the one-pass HTCEE processed and annealed samples. This type of microstructure caused the increment of yield strength from 75 to 310 MPa, (similar to 4.13 times higher), ultimate tensile strength from 207 to 386 MPa (similar to 1.86 times higher) and microhardness from similar to 59 to similar to 143 Hv (similar to 2.42 times higher). Simultaneously, elongation to failure was lessened from similar to 55 to 37%. In other words, a remarkable increase in the strength and hardness was attained besides a low loss of ductility. Also, microhardness measurements revealed a more homogeneous distribution of hardness in the two-pass processed sample. SEM fractography analysis demonstrated that mostly ductile fracture happened in the HTCEE processed samples. Also, the influence of the HTCEE process on the equivalent plastic strain and also the required force was examined via FEM simulation using Abaqus software. It seems that HTCEE process, by applying low deforming force, possesses the potential of production of tubes with long length having a simultaneous good ductility and strength. Graphic