Continuous Production of Pure Titanium with Ultrafine to Nanocrystalline Microstructure

Abstract

This work deals with the application of the Conform SPD (Severe Plastic Deformation) continuous extrusion process for ultrafine to nanostructured pure titanium production. The process has been derived from the Equal Channel Angular Pressing (ECAP) technique but, unlike ECAP, it offers continuous production of high-strength wire. This study describes the Conform SPD process combined with subsequent cold working (rotary swaging technique), its potential for commercial application, and the properties of high-strength wires of pure titanium. High-strength wire of titanium Grade 4 is the product. Titanium Grade 4 reaches ultimate strengths up to 1320 MPa. This value is more than twice the ultimate strength of the unprocessed material. The typical grain size upon processing ranges from 200 to 500 nm. Process development supported by FEM analysis together with detailed microstructure characterization accompanied by mechanical properties investigation is presented.

Commercialization of bulk nanostructured metals and alloys

“…Coiling will be applied to high-strength variants of nanostructured grades of CP Ti, which have been produced with strength levels exceeding 1320 MPa and the fatigue endurance limit above 900 MPa. 21,22 These levels of mechanical properties for ultrafine grain commercially pure titanium outperform most titanium alloys.…”

“…23 This combination of processes is suitable for producing wires of diameter up to 1 mm with enhanced mechanical and fatigue properties. 22,24 The superior properties of nanostructured alloys, mainly for medical applications, offset the higher prices of such materials. Other potential price-insensitive applications include luxury jewelry, where SPD-processed materials offer higher strength, hardness, and better wear resistance.…”

Mechanical properties of Titanium processed by ECAP

“…Products made by this technique are characterised by high strength properties (Figure 2), and they can be potentially used at subsequent super-plastic forming [1][2][3]. Magnitude of deformation, development of structure and resulting mechanical properties achieved by this technique depend notably on: homologous temperature Th, size of grain dz, deformation speed   , homologous tension in die () density of structural failures, on purity, etc [4][5][6]. Obtaining of the required final structure depends primarily on geometry of todie, obtained magnitude and speed of deformation and temperature.…”