Additive manufacturing of dense and open-porous specimen made of beta-Titan-Niob and material-specific tailoring of their mechanical properties for individualised implant applications

• Applicants: Dr. Annett Gebert; Professorin Dr.-Ing. Martina Zimmermann
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins ; Biomaterials
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 419952351

In this project, fundamental studies are performed on structure-property relationships of lattice structures designed based on triply periodic minimal surfaces (TPMS) and processed from β-Ti-42Nb by laser powder bed fusion (LPBF). The numerical and experimental work aims to explore the combination of biomimetic design, biocompatible material and customizable fabrication for future bone implant applications. Initial work is focusing on the dependence of mesostructural imperfections such as surface roughness and shape deviation on process parameters and design. A regression model for predicting the occurrence of LPBF inherent lattice defects in different TPMS structures is derived from the nominal-actual deviation parameters determined by CT measurements. Furthermore, a process-physical modeling concept for the numerical reconstruction of the characteristic imperfect mesostructure is developed, which permits assertions about the mechanical implications associated with imperfections. The correlation of experimental and numerical data provides valuable insights into the relative contributions of the different defect types (roughness, shape deviation) to the overall structural degradation. On the basis of targeted process parameter modulation, graded TPMS lattices are manufactured with high shape and dimensional fidelity and the local mechanical properties are characterized by means of nanoindentation measurements, among other things. The studies aim to identify potential relationships between lattice morphology and the resulting properties, with particular emphasis on the influence of location in the lattice (center/periphery) and heterogeneous grading regions. The high-resolution material data are integrated into FE calculations through multi-material formulations and the numerical results are compared with the accompanying in situ DIC deformation evaluations. Fatigue tests on biomimetic TPMS scaffolds and concomitant SEM/EBSD analyses provide insights into the correlation of microstructural morphology and texture on the one hand and damage initiation and accumulation on the other hand. Here, in addition to the as-built configuration, alloy states refined by heat treatment are also considered. Finally, fatigue life calculation rules are deduced. Through the holistic research approach consisting of additive manufacturing technology, innovative materials science and efficient FE simulation, this project provides the basic prerequisite for the future use of biomimetic TPMS lattices made of the biocompatible LPBF-processed Ti-42Nb alloy as bone implants.

• DFG Programme: Research Grants
• International Connection: USA
• Co-Investigator: Professor Dr.-Ing. Markus Kästner
• Cooperation Partner: Professor Dr. Udo Schwarz