Study of microstructure and mechanical properties of a Ti-11Mo-11Nb alloy

Abstract Among the commercially available titanium alloys, Ti6Al4V alloy is the most widely used in orthopedic applications. However, its high elastic modulus causes stress-shielding effect, while the vanadium and aluminium that dissociate from the parent material can cause long-term health problems, e.g., Alzheimer disease and neuropathy. As a result, metastable β-type titanium alloys are being developed as alternative materials, because they offer low elastic moduli and good biocompatibility. The microstructure and mechanical properties of a Ti-11Mo-11Nb alloy was studied. Microstructures and phases were analyzed with X-ray diffraction, optical, and scanning electron microscopy. Tensile and microhardness tests were also done. The microstructure of the Ti-11Mo-11Nb alloy is predominantly β phase, although the existence of secondary ω and martensite α″ phases cannot be entirely excluded. The reduced mechanical properties and brittleness in the alloy could be attributed to the coarse columnar β phase. The lower elastic modulus obtained can reduce the stress-shielding effect during application. Graphical abstract XRD patterns of the Ti-11Mo and Ti-11Mo-11Nb alloys with the identified phases (β and α″) and their corresponding optical micrographs [(a) Ti-11Mo and (b) Ti-11Mo-11Nb] as well as the scanning electron microscopy images [(c) Ti-11Mo and (d) Ti-11Mo-11Nb]. Inset below SEM micrograph (c) of Ti-11Mo alloy shows a higher magnification view of the circled area in the Ti-11Mo alloy specimen. This reveals the acicular structures of the orthorhombic α″ phase, which nucleate preferentially from grain and sub-grain boundaries into the interior of the β phase grains.