## 1 Introduction  
Titanium has excellent specific strength and corrosion resistance and is widely used in aerospace, the defense industry, and biomaterials [1; 2; 3; 4; 5]. In particular, titanium has lower elastic modulus and higher specific strength than cobalt alloys, stainless steel, alumina, etc., and is widely used as biomaterials. However, commercially pure titanium (c.p. Ti) has comparatively low mechanical properties, such as tensile strength, making it unsuitable for certain applications. Further, it has been reported that the aluminum contained in a commercial titanium alloy, Ti-6 Al-4V, can cause Alzheimer's disease [6], and vanadium can cause allergies and serious complications due to the release of toxic ions [7]. Therefore, it is required to develop biocompatible beta-titanium alloys in order to replace these components [8] and, at this time, niobium, zirconium, tantalum, and molybdenum are attracting attention as alloy elements that are not harmful to the human body [9]. Actually, many beta-titanium alloys, such as Ti-3 Zr-5 Fe-5 Mo, Ti-14 Mn, Ti-10 Fe-10 Ta, Ti-27 Nb-7 Fe-8 Cr, Ti-33 Zr-3 Fe-4 Cr, and Ti-7.5 Mo, have been recently developed.  
In fact, a beta-titanium alloy has excellent heat treatment characteristics compared to the \(\alpha+\beta\) alloy and represents an increase in elongation due to its BCC structure, including a low elastic modulus, and then is used not only in biomaterials but also in various other fields. However, the \(\beta\)-stabilizer elements, tantalum, niobium, and zirconium, inevitably increase costs due to their expensive price, resulting in many restrictions on the use of beta titanium [10; 11]. Thus, several studies have been actively conducted to replace expensive alloy elements, such as tantalum, niobium, and zirconium, with inexpensive elements (Fe, Mo, Mn, etc.) [12; 13].  
Iron, an inexpensive element, has a strong \(\beta\)-stabilizer effect and a good reinforcing effect on non-toxic and non-allergic titanium alloys [14]. In addition, it is reported to improve the sintering reaction of titanium alloys [15] because it represents a faster diffusion rate than the atom of titanium itself in the \(\beta\) phase as a rapidly diffused element [16]. Likewise, molybdenum is a biocompatible \(\beta\)-stabilizer element and when molybdenum is added to a titanium alloy, it has been reported to have high corrosion resistance [17; 18; 19; 20], lower the elastic modulus, and increase the strength [21].  
The titanium alloy obtained through the existing ingot metallurgy (IM) process results in significant process costs, such as multiple vacuum remelting, alloying additions, homogenization, hot deformation and annealing, etc. [22]. However, it is relatively easy to manufacture complex parts in a powder metallurgy (PM) process [23], and simpler work processes and facilities are used for comparing it with the ingot process. In addition, unlike the ingot process, Ti and alloy elements are heated to a temperature lower than the melting point, which has the advantage of significantly reducing costs [24; 25].  
Therefore, this study designed a biocompatible Ti-Mo-Fe high-strength beta-titanium alloy and applied the powder metallurgy process technology using hydrogenation-dehydrogenation (HDH) titanium powder to ensure excellent price competitiveness. Further, changes in the microstructure of the Ti-xMo-4 Fe (x = 3.4, 5) powder alloys with different Mo contents were examined and then it was evaluated and analyzed in connection with mechanical properties. The results were compared with the properties of ingot alloys of the same alloy system.