Mechanical Properties and Plastic Deformation Mechanism of Additively Manufactured Novel Metastable β Ti–42Nb and Near β Ti–20Nb–6Ta Alloy

Abstract β- Titanium alloys experience more and more attention as a new generation of materials for biomedical applications as they offer superior corrosion resistance, excellent biocompatibility, and exceedingly low Young’s moduli. Additive manufacturing with laser powder bed fusion is a promising technology to process these alloys in a cost-effective way and to tailor their properties for the needs of biomedical applications. In this work, the mechanical properties of the novel metastable β Ti–42Nb and near β Ti–20Nb–6Ta alloy processed by laser powder bed fusion were investigated. The d-electron alloy design method was used to predict the resulting Young’s Modulus and dominant plastic deformation behavior prior to experimental testing. To correlate the mechanical properties with microstructural aspects of the titanium alloys X-ray diffraction, scanning electron microscopy and electron backscatter diffraction were performed. Based on microhardness and tensile testing, Ti–42Nb and Ti–20Nb–6Ta showed superior ductility and lower Young’s modulus in comparison with laser powder bed fusion-processed pure titanium and Ti–6Al–4V. In contrast to the prediction made by the d-electron alloy design method, the orthorhombic α ″ phase of Ti–20Nb–6Ta displayed an even lower Young’s modulus than the β phase of Ti–42Nb, with a higher strength at the same time. Subsequent microstructure analysis after tensile testing with X-ray diffraction and scanning electron microscopy revealed no stress-induced phase transformation or apparent twin formation for both β titanium alloys. These findings aligned well with the prediction made by the d-electron alloy design method.