title: Elastic softening of β-type Ti-Nb alloys by indium (In) additions.
abstract: Recent developments showed that β-type Ti-Nb alloys are good candidates for hard tissue replacement and repair. However, their elastic moduli are still to be further reduced to match Young׳s modulus values of human bone, in order to avoid stress shielding. In the present study, the effect of indium (In) additions on the structural characteristics and elastic modulus of Ti-40 Nb was investigated by experimental and theoretical (ab initio) methods. Several β-type (Ti-40 Nb)-xIn alloys (with x ≤ 5.2 wt%) were produced by cold-crucible casting and subsequent heat treatments (solid solutioning in the β-field followed by water quenching). All studied alloys completely retain the β-phase in the quenched condition. Room temperature mechanical tests revealed ultimate compressive strengths exceeding 770 MPa, large plastic strains (>20%) and a remarkable strain hardening. The addition of up to 5.2 wt% indium leads to a noticeable decrease of the elastic modulus from 69 GPa to 49 GPa, which is closer to that of cortical bone (<30 GPa). Young's modulus is closely related to the bcc lattice stability and bonding characteristics. The presence of In atoms softens the parent bcc crystal lattice, as reflected by a lower elastic modulus and reduced yield strength. Ab initio and XRD data agree that upon In substitution the bcc unit cell volume increases almost linearly. The bonding characteristics of In were studied in detail, focusing on the energies that appeared from the EDOSs significant for possible hybridizations. It came out that minor In additions introduce low energy states with s character that present antibonding features with the Ti first neighboring atoms as well as with the Ti-Nb second neighboring atoms thus weakening the chemical bonds and leading to elastic softening. These results could be of use in the design of low rigidity β-type Ti-alloys with non-toxic additions, suitable for orthopedic applications.
authors.affiliation: IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden, Germany. Electronic address: m.calin@ifw-dresden.de.
authors.forename: Mariana
authors.initials: M
authors.lastname: Calin
authors.affiliation: IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden, Germany.
authors.forename: Arne
authors.initials: A
authors.lastname: Helth
authors.affiliation: University of Ioannina, Department of Materials Science & Engineering, Ioannina 45110, Greece.
authors.forename: Julio J
authors.initials: JJ
authors.lastname: Gutierrez Moreno
authors.affiliation: IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Bönisch
authors.affiliation: IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden, Germany.
authors.forename: Varvara
authors.initials: V
authors.lastname: Brackmann
authors.affiliation: IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden, Germany; TU Dresden, Institute of Materials Science, D-01062 Dresden, Germany.
authors.forename: Lars
authors.initials: L
authors.lastname: Giebeler
authors.affiliation: IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Gemming
authors.affiliation: University of Ioannina, Department of Materials Science & Engineering, Ioannina 45110, Greece.
authors.forename: Christina E
authors.initials: CE
authors.lastname: Lekka
authors.affiliation: IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden, Germany.
authors.forename: Annett
authors.initials: A
authors.lastname: Gebert
authors.affiliation: Justus Liebig University, Laboratory of Experimental Trauma Surgery, Giessen, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Schnettler
authors.affiliation: IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden, Germany; TU Dresden, Institute of Materials Science, D-01062 Dresden, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Eckert
mesh_terms: D000497:Alloys / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry*; D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000473:pathology; D004548:Elasticity; D006801:Humans; D007204:Indium / Q000737:chemistry*; D008422:Materials Testing; D046529:Microscopy, Electron, Transmission; D009985:Orthopedics; D010100:Oxygen / Q000737:chemistry; D011312:Pressure; D011474:Prosthesis Design; D013314:Stress, Mechanical; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D000497:Alloys; D001672:Biocompatible Materials; C581937:Ti-Nb-xZr alloy; D007204:Indium; D014867:Water; D010100:Oxygen
keywords: Ab initio; Bcc-phase; Biomedical material; Elastic modulus; Indium; Ti alloys