Comprehensive Evaluation of the Properties of Ultrafine to Nanocrystalline Grade 2 Titanium Wires

Abstract

This paper describes the mechanical properties and microstructure of commercially pure titanium (Grade 2) processed with Conform severe plastic deformation (SPD) and rotary swaging techniques. This technology enables ultrafine-grained to nanocrystalline wires to be produced in a continuous process. A comprehensive description is given of those properties which should enable straightforward implementation of the material in medical applications. Conform SPD processing has led to a dramatic refinement of the initial microstructure, producing equiaxed grains already in the first pass. The mean grain size in the transverse direction was 320 nm. Further passes did not lead to any additional appreciable grain refinement. The subsequent rotary swaging caused fine grains to become elongated. A single Conform SPD pass and subsequent rotary swaging resulted in an ultimate strength of 1060 MPa and elongation of 12%. The achieved fatigue limit was 396 MPa. This paper describes the production possibilities of ultrafine to nanocrystalline wires made of pure titanium and points out the possibility of serial production, particularly in medical implants.

Characterization of the Microstructure, Local Macro-Texture and Residual Stress Field of Commercially Pure Titanium Grade 2 Prepared by CONFORM ECAP

“…In reference [39], Palán et al simulated the conditions which prevailed in the C-ECAP machine. The authors results indicated that the temperature, the strain rate, and the velocity distribution were very inhomogeneous in the die.…”

“…Furthermore, as discussed at the end of section 3.2., different conditions prevailed in different parts of the C-ECAP machine. In reference [39] (Figure 2), it was shown that in the corners and the adjacent areas, the strain rate and velocity distribution was practically zero. This may be additional evidence that the real shear plane can be different from the predicted one ( Figure 11).…”

Continuous Production of Pure Titanium with Ultrafine to Nanocrystalline Microstructure

“…At COMTES FHT, the method has been modified in order to refine the structure during the forming process; and thus Conform SPD ( Figure 1) was developed. This Conform SPD significantly improved the final mechanical properties [10,11,15]. The grain refinement is achieved thanks to the shear deformation and high hydrostatic pressure inside the processing chamber die which was designed based on experiences with the ECAP procedure [16,17].…”

Structure and Properties of High-Strength Ti Grade 4 Prepared by Severe Plastic Deformation and Subsequent Heat Treatment

“…It is essentially equivalent to the CONFORM ECAP method, but it has a narrower channel angle of 90 • , which provides more severe deformation. The main advantage of these methods is that they allow continuous production [9]. The combination of Conform SPD with rotary swaging was also found to be very effective [10,11].…”

“…The ductility decreases with increasing strength, which worsens workability of the material. Possible solving of this problem is to apply subsequent heat treatment after severe plastic deformation, as it was described for Ti grade 2 [9]. Suitable heat treatment in this case leads to release of internal stresses but does not cause grain coarsening.…”