Composition Design Of β-(Ti,Zr)-(Mo,Sn)-Nb Alloys With Low Young’s Moduli Based On A Cluster Model And Their Properties

Since BCC β-Ti alloys exhibit low elastic modulus, good biocompatibility, excellent corrosion resistance, and good comprehensive mechanical properties, they are widely applied into the biomedical field and have the greatest potential to be used as biological implant materials.β-Ti alloys are metastable, so various alloying elements are needed to stabilize the (3structure and achieve low Young’s modulus. Although several empirical methods were proposed to guide composition design, such as Mo equivalent method, d-electronic alloy theory, electronic concentration theory, they all lack a quantitative description of solid solution structures in complex systems, which is essential for the understanding on the composition rules of the seemingly complex alloys.We have proposed a structural model of "Cluster-plus-glue-atoms" in the long-term research of complex alloys, composed of a cluster part and a glue aotm part, the former being the nearest coordination polyhedron and the latter connecting clusters. Thus a cluster formula is given as [cluster](glue atom)x, x being1-3. In this paper, a binary monotectoid [MoTi14]Mo1is proposed for (Ti,Zr)-(Mo,Sn)-Nb systems as the basic cluster formula and a general cluster formula [(Mo,Sn)(Ti,Zr)14]Nbx (x=1,2,3) is formed by adding alloying elements substituting the basic formula according to their mixing enthalpies with the base Ti. The designed alloys were prepared into alloy rods of3mm and6mm in diameter and those alloys with x=1were also solid-solutioned in950℃for2h. XRD, OM and EPMA were used to examine the micorstructure and element distributions of alloys; the densimeter was used to obtain the density values of alloys; the tensile properties were tested by universal tensile testing machine (MTS); the corrosion resistances were studied in Hank’s artificial body fluid by electrochemical workstation. Experimental results showed that when low-E Ti, Nb or Zr substitutes for Mo at glue part or Sn substitutes for Mo at cluster center of the basic formula [MoTil4]Mo1, the ternary alloys have a lower modulus values, where the [SnTi14]Mo1alloy has an E value of61GPa after solid-solution. The substitution of Mo by Nb reduces the structural stability of [SnTi14]Nbi alloy, and the further substitutiton of Sn by Mo0.5Sn0.5at cluster center and partial Ti by Zr at the cluster shell not only secure the stability of alloys but also achieve the lowest Young’s modulus, exemplified by the alloy [(Mo0.5Sn0.5)(Ti13Zr)]Nb1(Ti81.25Mo3.13Sn3.13Zr6.25Nb6.25at.%, Ti68.1Mo5.2Sn6.5Nb10.2Zr10.0wt.%), which exhibts a lowest E with E=48GPa in the suction-cast state and E=43GPa after solid-solution. This suction-cast alloy also shows good mechanical properties with σb= 715MPa and ε=7.6%. Meanwhile, β-Ti alloys with low Young’s moduli designed by the cluster model have good corrosion resistances in Hank’s fliud with a corrosion potential of about-0.3V that is comparable of reference alloy Ti-6Al-4V with a corrosion potential of-0.285V.