Characterization of the fatigue behavior of additively manufactured β-metastable titanium alloy Ti-5Al-5V-5Mo-3Cr on different length scales
The β-metastable titanium alloy Ti-5Al-5V-5Mo-3Cr (Ti-5553) has recently found growing interest as medical implant material due to its advantageous mechanical properties when compared to the up-to-date standard alloys. Besides biocompatibility, implant materials need to exhibit sufficient fatigue resistance. This thesis investigates the fatigue and cyclic deformation behavior on different length scales of Ti-5553, made by laser powder bed fusion of metals (LPBF-M), with distinct microstructures resulting from different heat treatments. The nano-scale investigation reveals how the α-precipitates orientation and distribution influence the deformation behavior of Ti-5553 in the (α+β)-solution annealed state (ST) during cyclic nanoindentation. In addition, quasi-static and cyclic nanoindentation tests were conducted to investigate the mechanical properties of LPBF-M Ti-5553 in the “as-built”, (α+β)-solution annealed and aged (STA) and β-annealed, slowly cooled, and aged (BASCA) conditions. Microstructural variations notably influence the nanohardness, reduced elastic modulus, plasticity, and cyclic deformation behavior of Ti-5553. The macro-scale perspective summarizes the cyclic deformation behavior of shot-peened Ti-5553 specimens in Hanks’ balanced salt solution (HBSS). Changes in the free corrosion potential and the corrosion current are highly sensitive indicators for fatigue-induced damage on a rough surface, which was correlated to the microscopic examination, fracture surface features, and fatigue crack development. The gained deeper understanding of the mechanical performance of this promising β-metastable alloy across different microstructures and different length scales helps establish a foundation for predicting fatigue characteristics and optimizing LPBF-M Ti-5553 alloy performance, especially in the context of implant materials.
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