## 5 Nanoindentation of Diffusion-Bonded Interfaces
### Aluminium/Steel
\begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**Material 1** & **Material 2** & **Interlayer** & \begin{tabular}{l} **Bonding** \\ **Temperature** \\ **\({}^{\circ}\)C** \\ \end{tabular} & \begin{tabular}{l} **Bonding** \\ **Pressure** \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{l} **Bonding** \\ **Time (h)** \\ \end{tabular} & \begin{tabular}{l} **Indentation** \\ **Conditions** \\ \end{tabular} & **Reference** \\ \hline Al-Mg-Si & Low-C steel & None & 500–575 & 2.5 & 0.04–0.5 & 1 mN load & [51] \\ \hline Al-Mg-Si & Low-C steel & None & 500–575 & 2.5 & 0.04–0.5 & 0.5 mN load & [52] \\ \hline Al-Mg-Si & Low-C steel & None & 512 & 2.5 & 0.5 & 0.5 mN load & [53] \\ \hline \multirow{3}{*}{Al 6082} & \multirow{3}{*}{Stainless steel 316L} & \multirow{3}{*}{None} & \multicolumn{3}{l}{Roll bonded at \(150\,^{\circ}\)C, then \(\begin{array}{c}\text{annealed at}\\ \text{400-550}\,^{\circ}\text{C}\end{array}\)} & \multirow{3}{*}{N/A} & \multirow{3}{*}{0.2–3.0} & \multirow{3}{*}{3 mN load} & \multirow{3}{*}{[19]} \\  & & & & & & \\ \hline Al 1050 & OFHC Copper & None & 350–650 & Not given & 0.5 & Not given & [54] \\ \hline Aluminium & Copper & None & 450–475 & 12 & 1.5–2.0 & 10 mN load & [55] \\ \hline Tungsten & EUROFER97 steel & None & 1050 & Not given & 1.0–4.0 & \begin{tabular}{l} Max depth \\ 1000 nm \\ \end{tabular} & [56] \\ \hline Tungsten & EUROFER97 steel & Niobium & 1050 & Not given & 1.0 & \begin{tabular}{l} Max depth \\ 500 nm \\ \end{tabular} & [57] \\ \hline Tungsten & EUROFER97 steel & Vanadium & 1050 & Not given & 1.0 & Not given & [58] \\ \hline Tungsten & Ferritic steel & Nickel & 850–950 & 10 & 1.5 & 30 mN load & [17] \\ \hline Tungsten & Stainless steel 316L & Copper & 1050 & 150 & 0.5–2.0 & Not given & [59] \\ \hline W-7 Ni-3 Cu & Stainless steel 304 & Copper & 900 & 20 & 2.0 & 30 mN load & [64] \\ \hline Tungsten & High-Cr ferritic steel & Vanadium/Nickel & 1050 & 10 & 1.0 & 30 mN load & [60] \\ \hline Tungsten & \
\begin{tabular}{l} High-Cr ferritic \\ steel \\ \end{tabular} & Copper/Nickel & 1050 & 10 & 1.0 & 5 mN load & [61] \\ \hline Uranium & Copper & None & 350–650 & 168 & 3.3–4.0 & 8 mN load & [62] \\ \hline NiT & Ti\({}_{3}\)SiC\({}_{2}\) & None & 800–1000 & 20 & 1.0–10 &
\begin{tabular}{l} Max depth 250 \\ nm \\ \end{tabular} & [63] \\ \hline Tl-6 Al-4V & Al\({}_{5}\)(HfNbTiZ)\({}_{3}\)C & None & 800–1000 & 5 & 1.0 & 5 mN load & [11] \\ \hline Stainless steel 321 & Ti-5 Al-2.5 Sn & None & 750–950 & 10 & 0.5 & 20 mN load & [9] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Details of nanoindentation studies of diffusion-bonded materials from the published literature. close to the Al side of the interface was also found to be enriched in both Si and Cu; SAED indicated these regions to be Al\({}_{12}\)Fe\({}_{3}\)Si and AlFeSi. Nanoindentation enabled measurement of the hardness and elastic modulus of the interfacial regions to be measured, as well as those of the two parent alloys. The load used was 1000 uN and the indents were spaced approximately 5 um apart. The thickness of the interfacial region was between 1 um and 5 um. The hardness and elastic modulus values of AlFeSi(Cu) were lower than those of both Al\({}_{3}\)Fe and Al\({}_{2}\)Fe\({}_{5}\). These differences were attributed to different crystal structures, Al\({}_{3}\)Fe being orthorhombic and Al\({}_{12}\)Fe\({}_{3}\)Si cubic. Tensile tests of the bonded specimens showed that the addition of Si and Cu resulted in increased bond strength. [PERSON] et al. [52] performed a similar study of a 6000-series Al alloy bonded to low-carbon steel. In addition to the \"base\" Al alloy, Al alloy specimens with elevated levels of Si and Cu were also bonded to low-carbon steel specimens. Diffusion bonding was carried out under the same conditions as the previous study [51]. Nanoindentation measurements were performed at a load of 500 uN and an indent spacing of 2 um. EPMA of the diffusion-bonded interfaces revealed that the interfacial reaction layer was enriched in Si and Cu; this was particularly marked on the Al side.