# Technological Processes for Steel Applications in Nuclear Fusion
## 6 Solid State Bonding
### Corrosion and Contamination
Due to the mentioned outliers in the test results (e.g., T0 \(-\)80 \({}^{\circ}\)C or T2 \(-\)90 \({}^{\circ}\)C), this conclusion should better be treated as a tendency and not stressed too much. On the other hand, down to test temperatures of at least \(-\)70 \({}^{\circ}\)C, there is no brittle fracture, independent of the oxidation period. In other words, the maximum LTUS after treatments T0-T4 is \(-\)70 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{c c} \hline \hline
**ID** & **Surface Treatment/Preparation/Condition** \\ \hline \multirow{2}{*}{T0} & Reference surface = dry milled, similar to procedure \# 4 in Table 4, \\  & then _immediately_ sealed by EB-welding \\ \hline T1 & Reference surface, 24 h in humidor (70\% rel. humidity), then EB-welded \\ \hline T2 & Reference surface, 48 h in humidor (70\% rel. humidity), then EB-welded \\ \hline T3 & Reference surface, 72 h in humidor (70\% rel. humidity), then EB-welded \\ \hline T4 & Reference surface, 14 days in humidor (70\% rel. humidity), then EB-welded \\ \hline \multirow{2}{*}{T5} & Reference surface, sealing with WD40 (spray oil), \\  & 14 days in humidor (70\% rel. humidity), cleaning with isopropanol in ultrasonic \\  & bath and drying with wipes, then EB-welded \\ \hline \multirow{2}{*}{T6} & Reference surface, sealing with WD40 (spray oil), \\  & 14 days in humidor (70\% rel. humidity), cleaning with soap and drying with \\  & wipes, then EB-welded \\ \hline \multirow{2}{*}{T7} & Surface milled with coolant (industrial standard), drying with wipes, \\  & then EB-welded \\ \hline \multirow{2}{*}{T8} & Surface milled with coolant (industrial standard), cleaning with isopropanol in \\  & ultrasonic bath and drying with wipes, then EB-welded \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Preparation and fabrication details of the surface contamination study. The different surface treatments are denoted as T0–T8. The effect of oxidation protection by using spray oil has been studied on two additional samples (T5 and T6). One has been cleaned with isopropanol after 14 days oxidation in air with a relative humidity of 70%. The other has been cleaned with industrial soap. The sample T4 from the previous study has been taken as a reference. As can be seen from Figure 29, oiling the surfaces may reduce oxidation, but obviously only isopropanol removes the oil without residues, since cleaning with soap leads to the same or even worse results compared to unprotected oxidation (scattering of the results impedes a definite assessment). Figure 28: Charpy test results of the samples with different oxidation periods prior to diffusion bonding at 25 MPa, 1150 \({}^{\circ}\)C for 2 h and after post-veld heat treatment of 980 \({}^{\circ}\)C/0.5 h + 760 \({}^{\circ}\)C/2 h. Oxidation times at 70% relative humidity: 0 h (T0), 1 day (T1), 2 days (T2), 3 days (T3), 14 days (T4). The circles represent results with the base material (EUROFER97/2, heat 993402). Figure 29: Charpy test results of samples with different cleaning and contamination treatments prior to diffusion bonding at 25 MPa, 1150 \({}^{\circ}\)C for 2 h and after post-veld heat treatment of 980 \({}^{\circ}\)C/0.5 h + 760 \({}^{\circ}\)C/2 h. For comparison, the results with the base material (EUROFER97/2, heat 993402) are plotted by circles. Details of the contamination treatments are given in Table 5.  
Finally, the influence of milling with coolant (as is standard in industry) on the weld quality was also studied by two samples. One sample was just wiped dry after milling (T7), the other was cleaned with isopropanol (T8). Figure 29 shows that the use of milling coolant has no effect on the diffusion bond process if the coolant is removed with isopropanol. Without cleaning, that is, just by drying the surfaces with wipes, the weld performance is clearly deteriorated. With the exception of treatment T7, this study leads to the same conclusion as the oxidation study: All samples (except for T7) show the same upper shelf energies and LTUS amounts to \(-70\)\({}^{\circ}\)C, even in the worst case.