# Effect of Heat Treatment on Some Titanium Alloys Used as Biomaterials
## 1 Introduction  
Biomaterials play an essential role in medicine today by restoring function and facilitating the healing of people after various accidents or diseases. These materials used for medical applications ensure appropriate treatment from a medical point of view and improve the quality of life through performance devices [1]. Due to their excellent properties, titanium and its alloys are still the most used materials in medical applications. They are mainly used in hard tissue replacement, and the fields of use are orthopedics, dentistry, and cardiovascular medicine [2, 3, 4]. In recent years, the utilization of titanium and titanium-based alloys with applications in biology and medicine has made tremendous progress promoting of innovative technologies and new materials [5]. Titanium-based alloys are distributed in three categories: \(\alpha\), \(\alpha+\beta\) and \(\beta\) alloys [6]. Reduced modulus of elasticity, greater corrosion resistance, and improved biocompatibility are all advantages of adding benign elements like Mo, Si, Zr, and Ta [7]. This is due to their superior mechanical, physical, and biological properties. New titanium alloys with harmless elements, long-term performance, and no rejection by the human body are being promoted in the present era. Other benefits include high specific strength, low density, and almost non-magnetic properties [8]. Titanium makes up roughly 0.5 percent of the Earth's crust. Titanium is a lightweight, high-strength, low-corrosion structural metal utilized in biocompatible materials as an alloy [9]. Pure titanium is ductile, electrically and thermally inert, and paramagnetic. Due to the production of a passive oxide surface coating, titanium has good corrosion resistance in a variety of conditions. It is biocompatible because of its great strength, low density, and exceptional corrosion resistance [10]. Titanium castings exhibit common casting defects like shrinkage, gas porosity, cold shuts and misruns. The surface defects, such as surface-connected porosity or cold shuts, can be improved with heat treatments [11]. Thermal and thermochemical treatments play an important role in achieving quality characteristics to obtain a certain complex of technological and/or use properties. Over time, various improvements of biocompatible materials have been opted for in order to obtain suitable properties for the human body [12; 13; 14]. Numerous types of research have confirmed that thermal treatments are beneficial for improving the properties of titanium alloys, Mo element significantly affects the \(\alpha\) microtexture of \(\alpha+\beta\) titanium alloys; strong prior \(\alpha\) colony microtexture exists before thermal deformation; the smaller \(\alpha\) colony will hinder the formation of a large-size micro-texture [15; 16]. The term \"biocompatibility\" refers to the interaction of a medical device's tissues and physiological systems with the tissues and physiological systems of the patient. Any device's overall safety evaluation includes a biocompatibility examination [17; 18; 19]. When choosing alloys for medical implants, in addition to the mechanical properties, biocompatibility is also an important aspect to consider, specifically the biocompatibility of the elements that make up the alloy. The alloys from the Ti-Mo-Zr-Ta system contain biocompatible elements, the cytotoxicity of the elements being demonstrated by other researchers [2; 5; 13]; the overall benefits of each element are highlighted in Table 1, both in the human body and in the sampled alloys [20]. In the literature research, many articles were found on titanium alloys being used in orthopedic and aerospace applications, being studied the microstructure, hardness, and biocompatibility properties in the cast form of the alloys [2; 3]. However, a proper study investigating the heat treatment process, microstructure, and mechanical properties relationship for this Ti-Mo-Zr-Ta system has not been found [15; 16].