In recent years ultrafine grained materials (UFG) have been studied extensively due to their outstanding mechanical and physical properties. Many of these submicrometer scaled materials have been produced using severe plastic deformation (SPD) processing techniques. In the medical sector titanium and its alloys are the most commonly used materials because of their enhanced mechanical and corrosion properties. The objective of this work was to study the deformation and fracture behaviour of ultrafine grained Ti45Nb and Ti13Zr13Nb. As characterization techniques micro hardness measurements, nanoindentation, electron microscopy, tensile and fracture toughness measurements were used. The high pressure torsion (HPT) treated samples showed a strongly elongated microstructure and a saturation effect regarding the grain refinement. Due to the grain refinement, with a saturation grain size below one micrometer, an increase in hardness and strength was obtained. Investigations with transmission electron microscopy exhibited a pure body centred cubic beta-phase for Ti45Nb, and the formation of an omega-phase because of the hydrostatic pressure during deformation. Due to the anisotropy of the microstructure, tensile tests in two different orientations were made. Ti45Nb showed, contrary to Ti13Zr13Nb, a measurable anisotropy in strength. Simultaneously to the hardening the ductility decreased. While Ti13Zr13Nb, with an elongation at fracture below one percent, became quite brittle, Ti45Nb exhibited a better deformability with an elongation at fracture of seven percent. Nanoindentation was used to determine the influence of severe plastic deformation on the Young`s modulus, which is an important parameter for the use as an implant material. While the Young`s modulus of Ti13Zr13Nb increased due to the deformation process, the Young´s modulus of Ti45Nb remained unchanged. To investigate the fracture behaviour, compact tensile samples with three different orientations were used. Comparing the two studied alloys, Ti45Nb showed a higher fracture toughness. As a result of this work one can conclude that ultrafine grained Ti45Nb is more appropriate as an implant material than Ti13Zr13Nb using this specific deformation technique. Further investigations should be performed to develop suitable heat treatments aiming for a better ductility of Ti13Zr13Nb.
|Translated title of the contribution||Mechanical properties of ultrafine grained titanium alloys|
|Award date||26 Jun 2015|
|Publication status||Published - 2015|
Bibliographical noteembargoed until null
- ultrafine grained
- titanium alloy