title: Thermal stability and phase transformations of martensitic Ti-Nb alloys.
abstract: Aiming at understanding the governing microstructural phenomena during heat treatments of Ni-free Ti-based shape memory materials for biomedical applications, a series of Ti-Nb alloys with Nb concentrations up to 29 wt% was produced by cold-crucible casting, followed by homogenization treatment and water quenching. Despite the large amount of literature available concerning the thermal stability and ageing behavior of Ti-Nb alloys, only few studies were performed dealing with the isochronal transformation behavior of initially martensitic Ti-Nb alloys. In this work, the formation of martensites (α' andα″) and their stability under different thermal processing conditions were investigated by a combination of x-ray diffraction, differential scanning calorimetry, dilatometry and electron microscopy. The effect of Nb additions on the structural competition in correlation with stable and metastable phase diagrams was also studied. Alloys with 24 wt% Nb or less undergo a [Formula: see text] transformation sequence on heating from room temperature to 1155 K. In alloys containing >24 wt% Nbα″ martensitically reverts back toβ0, which is highly unstable against chemical demixing by formation of isothermalωiso. During slow cooling from the single phaseβdomainαprecipitates and only very limited amounts ofα″ martensite form.
authors.affiliation: IFW-Dresden, PO Box 270116, D-01171 Dresden, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Bönisch
authors.affiliation: IFW-Dresden, PO Box 270116, D-01171 Dresden, Germany.
authors.forename: Mariana
authors.initials: M
authors.lastname: Calin
authors.affiliation: University of Vienna, Faculty of Physics, A-1090 Vienna, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Waitz
authors.affiliation: University of Vienna, Faculty of Physics, A-1090 Vienna, Austria.
authors.forename: Ajit
authors.initials: A
authors.lastname: Panigrahi
authors.affiliation: University of Vienna, Faculty of Physics, A-1090 Vienna, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Zehetbauer
authors.affiliation: IFW-Dresden, PO Box 270116, D-01171 Dresden, Germany.
authors.forename: Annett
authors.initials: A
authors.lastname: Gebert
authors.affiliation: TU Dresden, Institut für Strukturphysik, D-01062 Dresden, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Skrotzki
authors.affiliation: IFW-Dresden, PO Box 270116, D-01171 Dresden, Germany; TU Dresden, Institut für Werkstoffwissenschaft, D-01062 Dresden, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Eckert
keywords: 10.07; biomedical applications; differential scanning calorimetry; dilatometry; martensite; niobium; thermal stability; titanium