Preparation and thermal stability of ultra-fine and nano-grained commercially pure titanium wires using CONFORM equipment

Abstract

Processes based on severe plastic deformation (SPD) capable of producing microstructures with sizes of the order of nanometres are gaining increasing importance. One of the available ways to make production more efficient is to combine the CONFORM continuous extrusion process with the ECAP method. This paper describes our initial experience with this combined process in a CONFORM 315i machine, equipped with a specially designed die chamber. Trials were performed to explore the impact of the CONFORM equipment's settings on the microstructure of the Ti wire. The feedstock consisted of CP-Ti grade 2 bar with a diameter of 10 mm. The decisive parameter for the entire process, i.e., the die-chamber temperature, was varied and controlled. Specimens with grain sizes of 1.4 μm and 420 nm were obtained. Using these specimens, the temperatures at which the recovery processes began to take effect were determined by thermal analysis.

Effect of severe plastic and heavy cold deformation on the structural and mechanical properties of commercially pure titanium

“…It is possible to say that the additional deformation causes the subgrains to rotate into highangle grain boundaries, typically with an equiaxed shape of the grains. 5,7,9 The subsequent rotary swaging led to a further increase in the mechanical properties, but the strengthening mechanism was different this time. Instead of the formation of equiaxed grains, the grains became elongated in the direction of forming, with a much higher dislocation density (Figure 3).…”

“…This method uses continuous angular pressing through a die chamber of a modified design to produce ultrafine structures and nanostructures of the materials. [5][6][7] The design modification reflects the principles of the ECAP method (equal-channel angular pressing), as described in studies. [5][6][7] Continuous operation is the key advantage of this forming method.…”

“…[5][6][7] The design modification reflects the principles of the ECAP method (equal-channel angular pressing), as described in studies. [5][6][7] Continuous operation is the key advantage of this forming method. The processing of CP titanium Grade 2 with the CONFORM SDP machine was described in multiple papers.…”

“…5,7 The main outcomes were the improved mechanical properties (ultimate tensile strength (UTS) = 698 MPa, 0.2 % offset yield stress (0.2 OYS) = 637 MPa), no significant decrease in the elongation, and an equiaxed ultrafine-grained (UFG) microstructure. 7 The present study proposes a process route which involves CONFORM SPD forming and rotary swaging (RS) in order to enhance the mechanical properties of a workpiece. [8][9][10] The effects of severe plastic deformation and work hardening are thus combined.…”

Continuous Production of Pure Titanium with Ultrafine to Nanocrystalline Microstructure

“…As a result, the near-surface region is likely to undergo partial recovery. For UFG materials, reduction in recrystallization temperatures was reported in several studies [11,32,33].…”