## 2 Experimental Procedure  
A plating bath (Figure 1) with a volume of 5 L was employed for the electrodeposition of the Ni-P alloy with a phosphorus acid-nickel salt system solution. The bath composition and concentration used for the Ni-P alloy electrodeposition are listed in Table 1. The solution was prepared using analytic-grade chemicals and pure water. The plating conditions used in this study were a bath temperature of 50 \({}^{\circ}\)C, a current density (C.D.) of 1.0-4.0 A/dm\({}^{2}\), a plating time of 40-180 min and an air pump used for stirring. In this study, no pH adjustments were made during the electrodeposition of the Ni-P alloy. A pure nickel plate was used as the anode. A stainless steel plate, which had an exposed surface area of 10 cm\({}^{2}\) (3 \(\times\) 3.3 cm\({}^{2}\), shown in Figure 1), was used as the cathode. Before plating, the stainless steel plate was mechanically polished with a #1000 emery paper, degreased with acetone, rinsed with tap water and dried with a dryer.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Composition** & **Concentration** \\ \hline NiSO\({}_{4}\) 6H\({}_{2}\)O & 1.0 M \\ NiCl\({}_{2}\) 6H\({}_{2}\)O & 0.2 M \\ H\({}_{3}\)BO\({}_{3}\) & 0.5 M \\ H\({}_{3}\)PO\({}_{3}\) & 0.12–0.5 M \\ C\({}_{6}\)H\({}_{5}\)Na\({}_{3}\)O\({}_{7}\) & 0.5 M \\ \hline \hline \end{tabular}
\end{table}
Table 1: Bath composition and concentration for Ni-P alloy electrodeposition.  
The chemical composition analysis of the Ni-11P plated layer was performed by X-ray fluorescence (XRF, Shimadzu XRF-1700, Shimadzu, Kyoto, Japan) at a voltage of 40 kV and a current of 95 mA at a scan rate of 8\({}^{\circ}\)/min with an aperture of 20 mm. The structure of the Ni-11P plated layer was investigated by X-ray diffraction (XRD, Rigaku RINT 2200 VF, Rigaku, Tokyo, Japan) analysis at 40 kV and 20 mA with Cu K\(\alpha\) radiation at a scan rate of 0.02\({}^{\circ}\)/s in the 2\(\theta\) range of 30-70\({}^{\circ}\). The thickness of the plated layer was measured with a micrometer. The surface morphology of the plated layer was investigated by a scanning electron microscopy (FE-SEM, HITACHI S-4300 SE/N, HITACHI, Tokyo, Japan) at an acceleration voltage of 10 kV and a probe current of approximately 10 \(\upmu\)A.  
The brazing of the stainless steel plate with the electroplated Ni-11P alloy layer was conducted using a hydrogen reduction furnace with a dew point of \(-\)50 \({}^{\circ}\)C. The brazing temperature and the holding time at the brazing temperature were set to 1020 \({}^{\circ}\)C and 10 min, respectively. Figure 2 shows the geometry and dimensions of the brazed joint specimen. Specimens for cross-sectional investigation were cut with a cutter, embedded in epoxy resin, and polished with a 1 \(\upmu\)m Al\({}_{2}\)O\({}_{3}\) suspension. The microstructure of the brazed joint was analyzed by an electron probe X-ray microanalyzer (EPMA, Shimadzu EPMA-1600, Shimadzu, Kyoto, Japan) at an acceleration voltage of 15 kV, a sample current of 34 nA for backscattered electrons (BSE) image observation and a current of 50-100 nA for mapping analysis.  
Shear tests were performed at room temperature with an Instron5567 universal testing machine (Instron, Grove, PA, USA) to evaluate the shear strength of the brazed joints. The cross-head speed for the shear tests was set to 10 mm/min. After the shear test, the fracture mode observation of the brazed joint was performed by the SEM and an optical microscopy (OM, VK-X150, KEYENCE, Osaka, Japan).  
Figure 1: Schematic illustration of the plating equipment.  
Figure 2: Geometry and dimensions of brazed joint specimen.