# Effect of Heat Treatment on Some Titanium Alloys Used as Biomaterials
## 4 Conclusions  
In this paper, the influence of heat treatment on the microstructure characteristics and mechanical properties of Ti-Mo-Zr-Ta alloys has been investigated. Thermal treatments are mainly used, focusing on superficial hardening, thus ensuring proper contact wear behavior; improving fatigue and corrosion resistance. The main results are as follows:  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Alloy**} & **Loading** & **Release** & \multirow{2}{*}{**Young Modulus**} & **Stiffness** & **Specimen Poisson** \\  & **Deformation** & **Deformation** & **[GPa]** & **[N/um]** & **Ratio** \\  & **[N]** & **[μm]** & **[GPa]** & **[N/μm]** & **[Ration]** \\ \hline Ti15 Mo7 Zr15 Ta & 13.52 \(\pm\) 0.2 & 10.39 \(\pm\) 0.1 & 41.89 \(\pm\) 0.3 & 2.03 \(\pm\) 0.1 & 0.23 \\ Ti15 Mo7 Zr15 Ta0.5 Si & 13.54 \(\pm\) 0.1 & 6.07 \(\pm\) 0.3 & 47.34 \(\pm\) 0.1 & 3.23 \(\pm\) 0.2 & 0.23 \\ Ti15 Mo7 Zr15 Ta0.75 Si & 13.54 \(\pm\) 0.2 & 6.73 \(\pm\) 0.4 & 66.24 \(\pm\) 0.1 & 4.26 \(\pm\) 0.1 & 0.23 \\ Ti15 Mo7 Zr15 Ta1 Si & 13.52 \(\pm\) 0.4 & 7.57 \(\pm\) 0.2 & 60.25 \(\pm\) 0.4 & 4.95 \(\pm\) 0.1 & 0.23 \\ Ti20 Mo7 Zr15 Ta & 13.52 \(\pm\) 0.2 & 6.62 \(\pm\) 0.2 & 50.43 \(\pm\) 0.3 & 4.25 \(\pm\) 0.3 & 0.23 \\ Ti20 Mo7 Zr15 Ta0.5 Si & 13.53 \(\pm\) 0.3 & 6.79 \(\pm\) 0.3 & 54.65 \(\pm\) 0.2 & 4.56 \(\pm\) 0.1 & 0.23 \\ Ti20 Mo7 Zr15 Ta0.75 Si & 13.52 \(\pm\) 0.1 & 5.89 \(\pm\) 0.4 & 54.25 \(\pm\) 0.3 & 4.65 \(\pm\) 0.2 & 0.23 \\ Ti20 Mo7 Zr15 Ta1 Si & 13.54 \(\pm\) 0.2 & 6.72 \(\pm\) 0.4 & 36.25 \(\pm\) 0.4 & 4.35 \(\pm\) 0.1 & 0.23 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Indentation results.  
Regarding the microstructural analyses, the variation of the \(\alpha\), \(\alpha+\beta\), and \(\beta\) type phases consists of differences in the chemical composition of the constituent elements. \(\beta\)-type structure formation is highlighted in Ti-Mo-Zr-Ta alloys, which contain a high percentage of \(\beta\) stabilizing elements (Mo, Ta, Si). Zirconium in concentrations below 7% also contributes to the refinement of the microstructure, thus allowing the formation of a homogeneous and evenly distributed structure. Therefore, elements like tantalum (5-15%), molybdenum (15-20%) and silicon in different concentrations (0.5, 0.75, and 1%), contribute to the formation of the \(\beta\) phase at titanium alloys.  
Based on the microhardness testing, it was observed that the hardness of some alloys has increased by approximately 5% for Ti15 Mo7 Zr15 Ta1 Si and Ti20 Mo7 Zr15 Ta0.5 Si, while for Ti15 Mo7 Zr15 Ta0.5 Si and Ti20 Mo7 Zr15 Ta an approximately 9% decrease has been noted. At the same time, a slight increase of 0.9% has been observed for Ti15 Mo7 Zr15 Ta0.75 Si. An influence of the heat treatment is highlighted in Ti15 Mo7 Zr15 Ta, Ti20 Mo7 Zr15 Ta0.75 Si, and Ti20 Mo7 Zr15 Ta1 Si; these changes come from the concentration of each beta stabilizer on the alloys.  
The results of the indentation test on the Ti-Mo-Zr-Ta alloys highlighted a reduced modulus of elasticity compared to the classic alloys, identifying the Ti20 Mo7 Zr15 Ta1 Si alloy (38.57 GPa) with the lowest value close to the human bone (15-30 GPa).  
In conclusion, the application of thermal treatments aims to achieve the proper properties of the metallic product in efficient economic and technical conditions. An improvement in hardness was seen in the alloys and a low modulus of elasticity, recommending them as alloys for orthopedic implants.  
M.S.B.: conceptualization, management; C.C.-M.: writing--original draft preparation, investigation; P.V.: methodology, financing, data curation; L.T.: investigation, writing--review and editing; J.N.: validation, investigation. All authors have read and agreed to the published version of the manuscript.  
This work was supported by a innovations grant of the TUIASI, project number MedTech_8/2022.  
Not applicable.  
All data provided in the present manuscript are available to whom it may concern.  
The authors declare no conflict of interest.