# Oxidation-Reduction of Ti-6 Al-4V in Direct Energy Deposition Subject to Minimum Argon Consumption
## 4 Results  
Figures 10-12 illustrate the variation in the oxygen concentration across different locations (A, B, and C) for shielding gas flow rates of 20, 25, 30, and 35 SCFH, as well as the oxygen concentration observed without the attachments.  
Figure 11: Graph for location B with flow rates of 20, 25, 30, and 35 SCFH of argon compared to the oxygen concentration without the attachments.  
Figure 10: Graph for location A with flow rates of 20, 25, 30, and 35 SCFH of argon compared to the oxygen concentration without the attachments.  
At location B in Figure 11, the results show that as the flow rate of the shielding gas increases, the time taken to reduce the oxygen concentration decreases. All tested flow rates were able to bring the oxygen levels down from 200,000 PPM to nearly 0 PPM. Given the resolution of the sensor (0.2%), a reading of 0 PPM can be interpreted as approximately 200 PPM, which is still considered a safe level for deposition.  
Locations B and C exhibit a similar trend in shielding gas behavior, both achieving 0 PPM oxygen concentration. However, location C reaches 0 PPM more rapidly than location B. The data for locations B and C show tightly packed curves, indicating that the flow rates have a negligible effect on the oxygen concentration. Unlike location A, the broader bases of the attachment design at locations B and C facilitate a higher volume of shielding gas, effectively overcoming the resistance presented by the mesh and steel wool.  
Based on the results at the three locations, 25 SCFH provided an adequate level of shielding, offering a balance between gas flow rate and effective coverage. As shown in Figure 13, the numerical simulations in Ansys Fluent further support this finding, demonstrating that the argon concentration thickens in the shielding area with an increasing flow rate. However, at 20 SCFH, a patch of the oxygen-rich area was detected due to turbulence in the argon flow and insufficient supply.  
It is observed that while all flow rates eventually achieve 0 PPM oxygen levels, the time required to reach optimal shielding conditions was, on average, 40 s. Given that Ti-6 Al-4V is a highly reactive alloy, even this delay can result in oxidation, particularly in deposition paths requiring short-term shielding. Therefore, using a higher flow rate for the initial few seconds and then reducing the flow rate to 25 SCFH is recommended to optimize the shielding gas usage while maintaining effective coverage.  
Figure 12: Graph for location C with flow rates of 20, 25, 30, and 35 SCFH of argon compared to the oxygen concentration without the attachments.  
\[\text{t}_{\text{total}}=\text{t}_{\text{sen}}+\text{t}_{\text{loc}}+\text{t}_{ \text{rel}}+\text{t}_{\text{gas}} \tag{1}\]  
\(\text{t}_{\text{total}}\) = the total delay in providing optimal shield gas on the deposit.  
\(\text{t}_{\text{sen}}\)= the delay in the oxygen sensor used; 0.7 s.  
\(\text{t}_{\text{loc}}\)= the delay caused by the controller in determining the actual location of the system; 10 ms.  
\(\text{t}_{\text{rel}}\)= the delay caused by the relays to activate; 20 ms.  
\(\text{t}_{\text{gas}}\)= the time taken by the Ar gas to reach the deposition path.  
From the equation, it can be seen that the total depends on three constants and a variable. The variable \(\text{t}_{\text{gas}}\) depends on many factors, including the atmospheric air in the test area.