ISSN 0031-918X, The Physics of Metals and Metallography, 2014, Vol. 115, No. 6, pp. 600–608. © Pleiades Publishing, Ltd., 2014. Original Russian Text © S.V. Grib, A.G. Illarionov, A.A. Popov, O.M. Ivasishin, 2014, published in Fizika Metallov i Metallovedenie, 2014, Vol. 115, No. 6, pp. 638–647. 600 INTRODUCTION Titanium alloys are extensively used in medicine to manufacture orthopedic, cardiologic, and dental implants due to their rather high level of strength, cor- rosion resistance, and better biocompatibility among widely used metal biomaterials, such as comochroms (cobalt-molybdenum-chromium alloys) and stainless steel [1]. One of the requirements imposed on metallic biomaterials is a low elastic modulus that is compara- ble to that of the human bone (20–30 GPa), and the absence of toxic alloying elements in the alloy. Ini- tially, much attention was paid to the commercial (α + β) titanium alloys, such as Ti–6Al–4V ELI and Ti–6Al–7Nb [2]. However, these alloys were charac- terized by high biomechanical incompatibility due to their relatively high elastic moduli (110–120 GPa). Moreover, these alloys release toxic vanadium and alu- minum ions in human body, which retards recovery. Currently, research in the field of metallic biomaterials is focused on new β-titanium–zirconium alloys which contain no toxic elements and have lower elastic mod- uli (42–85 GPa) as compared with stainless steels (210 GPa) widely used in medicine and Co–Mo–Cr- based alloys (240 GPa) [1, 3]. The development of Ti–Zr–Nb-based alloys used for medical applications can be promising if one con- siders the following aspects. First, the elements of this system are initially characterized by relatively low Young’s moduli compared with other metals that are used in medical alloys (Table 1). Second, these elements are nontoxic and, there- fore, they do not cause adverse responses in human body [1]. Third, niobium acts as a β-phase stabilizer in the Ti–Zr–Nb system and, in the case of its sufficient content, it is capable of stabilizing the β phase during quenching. This ability is important for the behavior of the elastic modulus, since it tends to minima in tita- nium alloys that are in metastable β states (Fig. 1). Zirconium acts as a neutral hardener in titanium alloys, but it can produce a β stabilizing effect in β tita- nium alloys, thus lowering the temperature of marten- sitic transformation and suppressing the formation of an athermal ω phase [6]. Fourth, titanium and nio- bium have close atomic radii (0.145 and 0.146 nm), Development and Investigation of the Structure and Physical and Mechanical Properties of Low-Modulus Ti–Zr–Nb Alloys S. V. Grib a , A. G. Illarionov a , A. A. Popov a , and O. M. Ivasishin b a Yeltsin Ural Federal University, ul. Mira 19, Ekaterinburg, 620002 Russia b Kurdyumov Institute of Metal Physics, National Academy of Sciences of Ukraine, bul’v. Akademika Vernadskogo 36, Kiev, 03680 Ukraine e-mail: stella_grib@mail.ru Received May 28, 2013; in final form, June 18, 2013 Abstract—The criteria for the optimization of chemical composition of Ti–Zr–Nb alloys have been selected that allow for obtaining materials with low elastic moduli and which have been used to melt alloys 50Ti–(50 – x) Zr–xNb, at 15 < x < 20 at %. Transmission electron microscopy and X-ray diffraction analysis have been used to study the phase composition of the as-cast alloys and alloys after homogenizing annealing. The minimum elastic modulus (69 GPa) and minimum microhardness (2440 MPa) have been found in the almost single-β-phase alloy with a maximum niobium content (17.1 at %). An increase in the volume fraction of α'' phase in the alloys with a lower niobium content (to 15 at %) promotes the growth of values of these properties. The phase transformations that occur during the continuous heating of homogenized alloys have been studied. The dependence of the temperature of the polymorphic (α + β)–β transformation on the ratio of the alloying elements in the studied alloys have been shown. Keywords: low-modulus alloys, Ti–Zr–Nb alloys, structure, phase composition, properties DOI: 10.1134/S0031918X14030041 STRENGTH AND PLASTICITY Table 1. Young’s moduli of several chemical elements [4] Chemical element Ti Zr V Nb Ta Mo Young’s modulus, GPa 120 97 135 100 185 325