PSI - Issue 59

Sviatoslav Motrunich et al. / Procedia Structural Integrity 59 (2024) 58–65 Sviatoslav Motrunich et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction In contemporary medical practice, a diverse array of materials is employed, encompassing chrome-nickel stainless steel, cobalt alloys with chromium, ceramics, polymers, and titanium and its alloys, as noted by Wang (2022). But it was found that elements such as nickel, cobalt and chromium are gradually released from implants made of stainless steel and alloys of cobalt with chromium due to corrosion in the fluids of the human body, giving it a toxic effect has been documented by Okazaki (2005) and Woźniak (2021). So, titanium-based alloys currently are recognized as the best materials for implantation in clinical practice. This is due to the unique combination of properties of titanium alloys, such as high strength, low density (and therefore high specific strength), good corrosion resistance, inertness to the biological environment (i.e. surrounding tissue implants), increased biocompatibility, low modulus elasticity and high ability to connect with bones and other tissues. This has been emphasized in the works of Niinomi (1998), Scerri (2015), Alontseva (2020), and Cassar (2012). Presently, the most widely employed materials in the manufacturing of implants are commercial grades of titanium and alloys such as Ti-6Al-4V, as highlighted by da Silva (2017). But as was shown the long-term operation of implants and prostheses made of these materials raises certain concerns due to the gradual release of aluminum and vanadium ions. It has been observed that the release of aluminum and vanadium ions can potentially lead to long-term health issues, including the progression of Alzheimer's disease, neuropathy, and osteomalacia (a systemic disease associated with the softening of bones due to a lack of bone mineralization tissues), as discussed by Nag (2005).This circumstance prompted the developers of materials to create new alloys for prostheses that contain alloying additives compatible with the human body, or lowering their modulus of elasticity and reducing possibilities of stress shielding. This development is discussed by Hidalgo (2023) and Moltasov (2022). Recently developed materials are Ti-6Al-7Nb and Ti-13Nb1-13Zr, which have good affinity to the human body and also have been approved by the ASTM standard, as discussed by Hidalgo (2023) and Kumar (2023).. However high requirements to medical alloys are set mainly on the quality of materials, which are constantly being improved and become more rigid. Any imperfections of chemical and structural homogeneity in titanium alloys lead to a decrease in the strength and fatigue life of the medical products. Obtaining quality titanium alloy ingots is associated with difficulties due to the high sensitivity of titanium to impurities introduced, especially to oxygen, nitrogen, hydrogen, carbon and interaction with many chemical elements, as a result of which solid solutions or chemical compounds are formed. Furthermore, one of the primary structural imperfections in titanium alloys is the presence of non-metallic inclusions, as highlighted by Akhonin (2022). Currently, not all methods of titanium alloys ingot production to make it possible to obtain high-quality metal, and when the technological process of titanium alloys manufacturing is violated, defects form in the ingot, which reduce the quality of the metal. Thus, the solution to the problem of obtaining high-quality ingots of high-strength titanium alloys from various charge materials is quite relevant. Electron beam cold hearth melting (EBCHM) is the most effective method of vacuum metallurgy for obtaining alloys, including refractory and highly reactive ones, with an ultra-low content of gases, volatile impurities and non metallic inclusions. With EBCHM, it is possible to adjust the melting rate of the ingot within wide limits, thanks to an independent heating source, which, in turn, allows you to adjust the duration of the metal's stay in the liquid superheated state, as explained by Akhonin (2019). EBCHM is a technology that allows almost complete removal of refractory inclusions of high and low density. Thus, EBCHM allows for a substantial enhancement in the quality of ingots produced from titanium alloys, as emphasized by Paton (2006). However, high-strength titanium alloys have a high content of alloying elements, which somewhat complicates their production by the EBCHM method, since when smelting ingots of medical titanium alloys by the EBCHM method, there is a problem of ensuring the given chemical composition of the ingot, since melting in a relatively deep vacuum contributes to the selective evaporation of alloying elements with high vapor elasticity, such as aluminum, etc., as highlighted by Akhonin (2023). Also, the concentration in the ingot of chemical elements with a vapor elasticity lower than titanium, such as niobium, can lead to its increase.