*Article* **Microstructural Analysis and Mechanical Propertiesof TiMo20Zr7Ta15Six Alloys as Biomaterials**

**Adriana Savin 1,\*, Mihail Liviu Craus 1,2,\*, Alina Bruma 3, František Novy 4, Sylvie Malo 5, Milan Chlada 6, Rozina Steigmann 1, Petrica Vizureanu 7, Christelle Harnois 5, Vitalii Turchenko 2 and Zdenek Prevorovsky 6**


Received: 24 September 2020; Accepted: 23 October 2020; Published: 28 October 2020

**Abstract:** TiMoZrTaSi alloys appertain to a new generation of metallic biomaterials, labeled high-entropy alloys, that assure both biocompatibility as well as improved mechanical properties required by further medical applications. This paper presents the use of nondestructive evaluation techniques for new type of alloys, TiMo20Zr7Ta15Six, with x = 0; 0.5; 0.75; 1.0, which were obtained by vacuum melting. In Ti alloys, the addition of Mo improves tensile creep strength, Si improves both the creep and oxidation properties, Zr leads to an α crystalline structure, which increases the mechanical strength and assures a good electrochemical behavior, and Ta is a β stabilizer sustaining the formation of solid β-phases and contributes to tensile strength improvement and Young modulus decreasing. The effects of Si content on the mechanical properties of the studied alloys and the effect of the addition of Ta and Zr under the presence of Si on the evolution of crystallographic structure was studied. The influence of composition on fracture behavior and strength was evaluated using X-ray diffraction, resonant ultrasound spectroscopy (RUS) analyses, SEM with energy dispersive X-ray spectroscopy, and acoustic emission (AE) within compression tests. The β-type TiMo20Zr7Ta15Six alloys had a good compression strength of over 800 MPa, lower Young modulus (69.11–89.03 GPa) and shear modulus (24.70–31.87 GPa), all offering advantages for use in medical applications.

**Keywords:** titanium alloys; microstructure; mechanical properties; resonant ultrasound spectroscopy; acoustic emission; inhomogeneities
