Low-modulus β-type Ti-based alloys for biomedical applications
Titanium-based alloys are particularly attractive as orthopedic implants due to their excellent corrosion resistance, good biocompatibility and low Young’s modulus. When considering the performance of materials for implant applications, one of the principal features is the stiffness, which is directly proportional to the elastic (Young’s) modulus. A reduction of the Young's modulus to a value approaching that of bone will provide the necessary “isoelastic behavior” between implant material and bone. A useful parameter for metallic biomaterial characterization is the ‘elastic admissible strain’ defined as the ratio of strength over elastic modulus. The higher the elastic admissible strain the more desirable the material is for such applications (i.e. the modulus is lower and/or the strength is higher). Beta-type Ti-Nb alloys are in the current focus of research on new metallic materials for load-bearing orthopedic implants. They demonstrate the best match of mechanical compatibility in terms of low elastic Young’s) modulus values and appropriate strength which is of particular importance for the reduction of stress shielding effects that inhibit bone growth.
Elastic softening of Beta-type Ti-Nb alloys by indium (In) additions
The effect of indium (In) additions on the structural characteristics and elastic modulus of Ti-40Nb was investigated by experimental and theoretical (ab initio) methods. The elastic softening of ß Ti-40Nb by minor indium additions may be due to: i) the lattice expansion induced by the large atomic radius of indium, and most importantly, ii) the presence of antibonding low energy electron states between In neighbouring atoms that weaken the chemical bonds.
M. Calin, A. Helth, J.J. Gutierrez Moreno, M. Boenisch, V. Brackmann, L. Giebeler, T. Gemming, C.E. Lekka, A. Gebert, R. Schnettler, J. Eckert, Journal of the Mechanical Behavior of Biomedical Materials 39 (2014), 162-174 URL
Phase transformations in ball-milled Ti-40Nb and Ti-45Nb powders upon quenching from the beta-phase region
The aim of the present work was to stabilize a single ß-type phase in Ti-Nb ball-milled powders at room temperature. The influence of milling parameters, degree of oxidation and initial powders morphology were studied. The produced ß single phase powder can be further used to synthesize compacts with a very low Young's modulus for biomedical applications.
K. Zhuravleva, M. Boenisch, S. Scudino, M. Calin, L. Schultz, J. Eckert, A. Gebert, Powder Technology 253 (2014), 166-171 URL
Production of porous beta-type Ti-40Nb alloy for biomedical applications: Comparison of selective laser melting and hot pressing
The selective laser melting (SLM) and hot pressing of mechanically-alloyed β-type Ti–40Nb powder was used to fabricate macro-porous specimens. The properties determined were phase composition, morphology, total porosity, inner pore architecture, compressive strength, compressive modulus, and in vitro biocompatibility. The presented results suggest that the SLM-fabricated alloy may be preferable to the hot-pressed alloy for biomedical applications.
K. Zhuravleva, M. Boenisch, K.G. Prashanth, U. Hempel, A. Helth, T. Gemming, M. Calin, S. Scudino, L. Schultz, J. Eckert, A. Gebert, Materials 6 (2013), 5700-5712 URL
On the formation of an ultrafine-duplex structure facilitated by severe shear deformation in a Ti-20Mo beta-type titanium alloy
Severe plastic deformation in the form of equal channel angular pressing (ECAP) has been adopted to introduce severe shear strain into a β-type Ti–20 wt.% Mo alloy to elucidate the aging response of the severely deformed β matrix. An ultrafine-duplex (α + β) structure composed of equiaxed α precipitates formed inside the shear bands (SBs) created during ECAP, whereas acicular α precipitates were favoured outside the SBs. This distinct precipitation structure was correlated to the structural characteristics of the SBs: high disorder with dislocation cells characteristic of low-angle boundaries and enhanced atomic diffusivity.
W. Xu, X. Wu, M. Stoica, M. Calin, U. Kuehn, J. Eckert, K. Xia, Acta Materialia 60 (2012) Nr. 13-14, 5067-5078 URL
Deformation-induced nanostructuring in a TiNbTaIn beta alloy
Bulk ultrafine-grained and nanostructured metals and alloys exhibit unique mechanical properties and have attracted growing interest during the past decade. Depending on phase stability, the dominant deformation mechanism of body-centered cubic (bcc) structured beta-titanium alloys may vary from dislocation slip to twinning/martensitic transformation. The interaction between these mechanisms is believed to greatly facilitate grain refinement in the beta-type Ti-Nb-Ta-In alloys. Upon severe plastic deformation nanostructuring occurred more easily in the less-stabilized ß-titanium alloy (Ti-25.4Nb-7.1Ta-1.2In, at.%) with a low stacking fault energy (SFE). With decreasing SFE deformation twinning and martensitic transformation play a significant role in grain refinement.
W. Xu, K.B. Kim, J. Das, M. Calin, B. Rellinghaus, J. Eckert, Applied Physics Letters 89 (2006) Nr. 3, 31906/1-3 URL