Influence of α‐Precipitate Orientation and Distribution on the Deformation Behavior of the Additively Manufactured Metastable β‐Titanium Alloy Ti‐5553 Assessed by Cyclic Nanoindentation

Abstract

The metastable β‐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. Herein, cyclic nanoindentation is applied up to a maximum cycle number of 105 to elucidate the influence of the local phase distribution on the cyclic deformation behavior of Ti‐5553, made by laser powder bed fusion of metals (LPBF‐M), in the (α + β)‐solution annealed state. By combining the localized cyclic mechanical loading and high‐resolution transmission electron microscopy, the influence of the presence and orientation of αp‐precipitates within the β‐grains on the cyclic deformation behavior and mechanisms is unraveled. αp‐phase orientation and distribution significantly contribute to the effectiveness of the precipitates as barriers to dislocation motion. A high density and trapping of dislocations are observed at α/β interfaces. The occurrence and size of the pile‐up surrounding the indents are correlated with the cyclic deformation behavior, and, thus, with the presence of αp‐precipitates. The gained improved knowledge of the phase‐dependent deformation behavior helps to better understand the fatigue performance of this alloy also on the macroscale.