“…The adverse effects of metal ions include the cytotoxicity of trace amounts of vanadium (V) and aluminum (Al) ions in Ti–6Al–4V alloy and the allergy-related characteristics of nickel (Ni) ions [ 2 , 3 , 4 ]. Recently, many types of Ti alloy containing noncytotoxic elements such as zirconium (Zr), niobium (Nb), tantalum (Ta), and molybdenum (Mo) have been developed for various medical applications [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Ti–15Zr–4Nb–(0 to 4) Ta alloy, which is an alpha (α)–beta (β)-type alloy, has been developed in Japan as a highly biocompatible alloy [ 17 ], and it is standardized in JIS T 7401-4 [ 18 ].…”