# Tantalum Alloy Welding: Does the Thermal Cycle Influence the Microstructure?
## 5 Conclusions  
The choice of welding process, parameters, and execution (based on bibliographic exploration) has produced a sound and flawless weld (no pores and lack of fusion or cracks). Visual inspection, surface non-destructive examinations (penetrant test), and bend-test confirmed its properties.  
In the B 521 tantalum alloy UNS Grade R05200, metallurgical variations are observed in the different areas of the joint consisting of coarse columnar, and dendritic structures, as well as a network of hexagonal recrystallized cells, none of them prone to cracking.  
It was determined that there is an increase in hardness from HV 120, in the base metal, to 237 HV 0.05 in the heat-affected zone to 425 HV 0.05 in the molten zone, which is the result of the microstructural transformations produced by the application of the thermal cycle and refractoriness of the tantalum alloy.  
There is a relationship between the mechanical properties (in this case represented by the hardness value) and microstructure observed in the different zones. This microstructure can be related to the maximum temperature reached and residence time in different temperature ranges. Below the recrystallization temperature, the longer the high temperatures, the bigger the grain growth and more developed the dendritic structures.  
Once the aforementioned relationship is confirmed, an interesting avenue of new studies is opened, which could involve the development of multiphysics simulation models, use of other simulation software, electron microscopy with a detection problem and more extreme welding parameters.  
Figure 10: Cooling cycle after welding for the five zones referred to in Table 5.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Zone (See Figure 8)** & **Max. T. (\({}^{\circ}\)C)** & **Time \textgreater{} 300 \({}^{\circ}\)C [s]** & **Location** \\ \hline (1) Melted metal & \textless{}4334.4 & 276 & Joint Point \\ (2) Fusion Line & \textless{}3604.2 & 258 & Fusion Line \\ (3) Recrystallization & \textless{}1450 & 221 & Fusion Line + 2 mm \\ (4) Grain growth & \textless{}850 & 186 & Fusion Line + 5 mm \\ (5) \({}^{\circ}\)Base\({}^{\circ}\) metal & \textless{}300 & 47 & Fusion Line + 50 mm \\ \hline \hline \end{tabular}
\end{table}
Table 5: Correlation thermal cycle microstructure.  
**Author Contributions:** Conceptualization, A.B.S., T.F.-C., I.R.-G. and L.S.T.; methodology, T.F.-C., I.R.-G., M.M.F. and L.S.T.; software, T.F.-C., I.R.-G., L.A.d.P. and L.S.T.; validation, T.F.-C., I.R.-G. and L.S.T.; investigation, A.B.S., T.F.-C., I.R.-G., L.S.T., L.A.d.P. and M.M.F.; resources, T.F.-C., I.R.-G. and L.S.T.; data curation, A.P.V.; writing--original draft preparation, T.F.-C., I.R.-G. and L.S.T.; writing--review and editing, A.B.S., A.P.V. and L.A.d.P.; visualization, A.P.V.; supervision, A.B.S. and A.P.V.; project administration, A.B.S., L.A.d.P. and M.M.F. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
**Infrared Consent Statement:** Not applicable.  
**Data Availability Statement:** Data available on request due to restrictions.  
We express our sincere gratitude to the University of Moa for their support and initiative, which has allowed for this project to be carried out.  
The authors declare no conflict of interest.