Hydrostatic tube cyclic expansion extrusion (HTCEE) as a new severe plastic deformation method for producing long nanostructured tubes

Abstract

In the current study, hydrostatic tube cyclic expansion extrusion (HTCEE) was proposed as a new severe plastic deformation (SPD) method for producing relatively long and large ultrafine-grained (UFG) tubes. In this process, a moving mandrel placed inside the hollow tube sample and also using high fluid pressure are the cores of this technology. To investigate the applicability of the process, commercially pure copper tube was processed and mechanical properties and microstructure were examined. It was shown that the grain size was reduced to below 150 nm after the only a single pass of HTCEE from the initial value of 65 μm. The results demonstrated that both yield and ultimate strengths were increased to 270 MPa and 345 MPa after one pass of HTCEE from the initial value of 75 MPa and 207 MPa respectively while the elongation was reduced to 41% from 55%. It is realized that the remarkable increase in the strength is obtained with a very low ductility loss. Microhardness was also enhanced to about 133 Hv from the initial value of 59 HV after HTCEE process while exhibiting excellent hardness homogeneity. Reducing the total load, increasing the processable tube length and interestingly achieving simultaneous strength and ductility are important advantages of HTCEE. This method seems to be very interesting and very promising for the future industrial application.