# Grain Orientation and Hardness in the Graded Interlayer of Plasma Sprayed W on CuCrZr
## 2 Materials and Methods  
The examined sample was a cylinder with a diameter of 30 mm and a height of 10.6 mm; a cross-section is shown in Figure 1.  
The CuCrZr alloy forming the substrate had the following nominal composition: Cr 0.65, Zr 0.05, Cu to balance (wt%). Deposition was performed through PS technique in controlled atmosphere (a mix of Ar-H\({}_{2}\) gases) at a pressure of 600 mbar. Figure 2 shows a schematic view of the PS apparatus. Figure 1: Cross-section of examined sample. The main deposition parameters were selected on the basis of some preliminary tests: torch speed of 800 mm/s, torch-surface distance of 180 mm, substrate temperature of \(180\pm 5\) \({}^{\circ}\)C. The thickness of W coating was \(\sim\)1.6 mm while that of the interlayer was \(\sim\)1.2 mm. The interlayer was made of a mixture of pure Cu and W and was obtained by depositing eight layers with nearly the same thickness (150 \(\upmu\)m) and different composition by adjusting the powder feed rates. The composition of the layers forming the interlayer gradually changed with increasing amounts of W moving from the substrate to the coating. The volume fractions of W and Cu in each deposited layer are reported in Table 1.  
Observations using light microscopy (LM) (Union Optical Co., Ltd., Tokyo, Japan) and scanning electron microscopy (SEM) Hitachi SU70 (Hitachi, Tokyo, Japan) were carried out on the cross-section of the sample after surface polishing by means of increasingly fine grinding papers. To characterize the interlayer structure, SEM observations were also carried out on the fracture surface of the samples broken in three-point bending tests. We carried out XRD (Philips, Eindhoven, The Netherlands) measurements on the CuCrZr substrate, interlayer, and W coating by illuminating the cross-section and shifting the sample with increasing steps of 250 \(\upmu\)m. A schematic view of the experimental set-up is shown in [19]. In this way, five zones of the interlayer were examined (1-5, moving from substrate to coating). The rectangular X-ray spot had constant length of 15 mm and width changing with 2\(\Theta\) angle. At the maximum angle of analysis (2\(\Theta\) = 75\({}^{\circ}\)), the spot width was about 250 \(\upmu\)m. Since the step of analysis and the width of X-ray spot had substantially the same value, the whole interlayer was examined without overlapping zones. Given that the width of the X-ray spot was larger than each deposition step (150 \(\upmu\)m), the five zones did not correspond to the single deposition steps. The Cu-\(K\alpha\) radiation (\(\lambda\) = 0.15408 nm) was used to collect XRD patterns in the 2\(\Theta\) angular range 35-150\({}^{\circ}\) with 2\(\Theta\) steps of 0.05\({}^{\circ}\) and counting time of 5 s per step. The peaks at \begin{table}
\begin{tabular}{c c c} \hline
**Deposition Steps** & & **Interlayer Composition** \\ \hline  & Cu vol.\% & W vol.\% \\ Substrate (CuCrZr) & - & - \\
1 & 90 & 10 \\
2 & 85 & 15 \\
3 & 79 & 21 \\
4 & 71 & 29 \\
5 & 59 & 41 \\
6 & 42 & 58 \\
7 & 18 & 82 \\
8 & 10 & 90 \\ Coating & 0 & 100 \\ \hline \end{tabular}
\end{table} 
Table 1: Composition of the layers deposited in each step. Figure 2: Schematic view of the PS apparatus. 2\(\Theta\) angles \(>75^{\circ}\) demonstrated negligible intensity and were comparable to the background values; thus, they were not considered in the analysis. To evaluate possible textures in the examined zones, the relative intensities of the XRD reflections were compared to those reported in the JCPDS-ICDD database (W-File 4-806, Cu-File 4-0836) [20] referring to metals with random grain orientation. To determine the dislocation density, high precision peak profiles of the most intense reflections were recorded with 2\(\Theta\) steps of 0.005\({}^{\circ}\) and counting time of 20 s per step. Hardness (\(H\)) was been measured through the nano-indentation technique by using a Hysitron(r) Inc. triboscope nanoindenter Ubi-1(r) (Minneapolis, MN, USA).