Browsing by Author "Bönisch, Matthias"
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- ItemProduction of porous β-Type Ti–40Nb alloy for biomedical applications: Comparison of selective laser melting and hot pressing(Basel : MDPI, 2013) Zhuravleva, Ksenia; Bönisch, Matthias; Prashanth, Konda Gokuldoss; Hempel, Ute; Helth, Arne; Gemming, Thomas; Calin, Mariana; Scudino, Sergio; Schultz, Ludwig; Eckert, Jürgen; Gebert, AnnettWe used selective laser melting (SLM) and hot pressing of mechanically-alloyed β-type Ti–40Nb powder to fabricate macroporous bulk specimens (solid cylinders). The total porosity, compressive strength, and compressive elastic modulus of the SLM-fabricated material were determined as 17% ± 1%, 968 ± 8 MPa, and 33 ± 2 GPa, respectively. The alloy’s elastic modulus is comparable to that of healthy cancellous bone. The comparable results for the hot-pressed material were 3% ± 2%, 1400 ± 19 MPa, and 77 ± 3 GPa. This difference in mechanical properties results from different porosity and phase composition of the two alloys. Both SLM-fabricated and hot-pressed cylinders demonstrated good in vitro biocompatibility. The presented results suggest that the SLM-fabricated alloy may be preferable to the hot-pressed alloy for biomedical applications, such as the manufacture of load-bearing metallic components for total joint replacements.
- ItemThermal stability and phase transformations of martensitic Ti-Nb alloys(Bristol : IOP Publishing, 2013) Bönisch, Matthias; Calin, Mariana; Waitz, Thomas; Panigrahi, Ajit; Zehetbauer, Michael; Gebert, Annett; Skrotzki, Werner; Eckert, JürgenAiming 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′ and α″) 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 transformation sequence on heating from room temperature to 1155 K. In alloys containing >24 wt% Nb α″ martensitically reverts back to β0, which is highly unstable against chemical demixing by formation of isothermal ωiso. During slow cooling from the single phase β domain α precipitates and only very limited amounts of α″ martensite form.