Tubular pure copper grain refining by tube cyclic extrusion–compression (TCEC) as a severe plastic deformation technique

Tube Cyclic Extrusion–Compression (TCEC) method is a novel severe plastic deformation technique developed for grain refining of cylindrical tubes to ultrafine grained (UFG)/nanostructured ones. In this method, tubes are fully constrained and deformed between chamber and mandrel with a small neck zone. The principle of TCEC technique which was adopted to impose severe plastic strains to the tubular materials was explained. Also, the deformation and grain fragmentation mechanism during TCEC was analyzed. The material deformation characteristics during TCEC were numerically simulated by FE code of ABAQUS/Explicit. The FEM results demonstrated that TCEC technique was able to impose extremely high plastic strains. The TCEC method was successfully applied to a commercially pure copper (99.99%) and significant grain refinement was achieved. TEM observation demonstrated the refinement of grains from the initial size of 45 μm to 200–350 nm after four processing cycles of TCEC. Microhardness measurements were carried out across the thickness of the initial and processed tubes. The results show good homogeneity of hardness distribution and an increase to 102 Hv from initial value of 55 Hv after four TCEC cycles. Mechanical properties of the specimens were extracted from tensile tests. The obtained results documented notable increase in the yield and ultimate strengths, whereas the uniform and total elongations decreased. Fracture surfaces after tensile tests were investigated by scanning electron microscopy (SEM), and the observed morphology indicates ductile fracture mode after four cycles of TCEC

Repetitive forging (RF) using inclined punches as a new bulk severe plastic deformation method

A new bulk severe plastic deformation method based on repetitive forging (RF) using inclined punches is proposed. This process consists of two half cycles. In the first half cycle, a square cross section deforms to parallelogram by forging with two inclined punches, and the parallelogram cross section is forged back to square using two flat punches in the second half cycle. This method was applied to commercially pure copper and significant grain refinement was achieved after four passes of RF. The results showed that significant improvement in the mechanical properties was obtained. Notable increase of yield and ultimate strengths corresponding to 358 MPa and 381 MPa after four passes of RF from the initial values of 121 MPa and 230.5 MPa is detectable. Microhardness increases to about 100 Hv after four passes of RF from the initial value of 53 Hv. Finite element (FE) results illustrate that RF is able to impose extremely high plastic strains to the materials. In the RF process, the processed samples have the same dimensions and geometry as those of the initial sample without any waste material and there is no need for back pressure. (C) 2012 Elsevier B.V. All rights reserved

TEM analysis and determination of dislocation densities in nanostructured copper tube produced via parallel tubular channel angular pressing process

Parallel tubular channel angular pressing (PTCAP) is a recently developed novel intense plastic deformation method appropriate for fabrication ultrafine-grained and nanostructured cylindrical tubes. In the present work a commercially pure copper was processed via multi-pass PTCAP and the effects of number of passes on grain refinement and the dislocation density were studied. TEM analysis showed that after first pass elongated subgrains with interior tangled dislocations were formed. After pass number two the density of interior dislocations through the elongated grains was decreased. In the next stages of deformation, at pass number three, elongated grains almost disappeared and equiaxed grains with grain size about 150 nm are formed as a result of dynamic recovery. The dislocation densities were measured by hardness indentation size effect using the Nix–Gao model. The results showed that increase in the number of PTCAP passes leads to decrease in the dislocation densities. The dislocation density is decreased to 2.48×109 cm−2 after fourth passes from 18.1×109 cm−2 after first pass. TEM results verified calculated values from the Nix–Gao model. Microhardness of the PTCAP processed tube through four passes increased to ∼142 HV from initial value of about 62 HV. Also, significant increase takes place after single pass and in the next passes the hardness value is saturated

Excellent energy absorption capacity of nanostructured Cu–Zn thin-walled tube

The present study shows that nanostructured (NS) thin-walled tubes possess an excellent energy absorption capacity, which was increased about four times compared to their course grained counterparts. Different deformation modes of axisymmetric concertina folding, three lobes diamond, and two lobe diamond forms were observed in annealed, single pass and two pass parallel tubular channel angular pressing (PTCAP) processed tubes, respectively