# Grain Orientation and Hardness in the Graded Interlayer of Plasma Sprayed W on CuCrZr
## 3 Results and Discussion  
The micrographs at different magnifications in Figure 3a,b show the interlayer where Cu and W splats exhibit a complex and irregular morphology. The W coating and the interlayer showed good adhesion and no cracks were observed. Figure 3: The stratified structure of the interlayer is shown at different magnifications in LM (**a**) and SEM (**b**) micrographs. The fracture surface of the samples broken in the three-point bending tests were examined through SEM observations to investigate the specific microstructural features of both metals in the interlayer. Figure 4 shows representative micrographs recorded at different distances from the substrate. Figure 4: (**a–h**). Fracture surface of samples broken in three-point bending tests. Micrographs were recorded in zones of the interlayer at different distances from the substrate and in the W coating. Labels indicate the zones and the distance from the substrate, expressed in microns, red arrows indicate some unmolten particles. To make the identification of the areas of W and Cu in (**c**) easier, they are evidenced by markers. The zones from 1 to 5 indicated in each photo correspond to those of the XRD measurements. In all the examined zones, Cu and W can be identified because they exhibit quite different fracture modes. The Cu areas show large amounts of dimples, revealing a typical ductile fracture mode. By contrast, W always exhibits a brittle inter-crystalline mode of fracture. For example, the specific features can be seen in the areas indicated by markers in Figure 4c. Some unmolten particles, indicated by red arrows in the first micrograph of Figure 4, can be observed in different positions of the interlayer and W coating. It was demonstrated that W has a complex and fine layered structure arising from the impact of metal droplets on its surface. Each layer consists of many columnar grains whose thickness \(d_{T}\) (see Figure 5) is usually that of the layer, while the length substantially corresponds to the size of the original impacting droplet. The morphology of W grains is substantially the same across the interlayer and coating: the average thickness \(d_{T}\) is \(\sim\) 6 \(\upmu\)m, while the grain width \(d_{W}\) ranges from 0.5 to 1 \(\upmu\)m. In fact, the grains exhibit an irregular lamella-like shape, with one dimension much larger than the other two. The W layers are about parallel to the deposition surface in zones 1 and 2, where Cu is the prevalent element, whereas in zone 5, they display different orientations. The XRD patterns collected in the different zones across the interface are shown in Figure 6.  
Figure 5: Complex and fine layered structure of W. Each layer consists of many columnar grains whose thickness \(d_{T}\) is usually that of the layer, while the length substantially corresponds to the size of the original impacting droplet. The thickness \(d_{T}\) and width \(d_{W}\) are indicated in the figure. The examined zones of the interlayer correspond to successive shifts (250 \(\upmu\)m) of the sample under the X-ray beam, starting from the substrate to the coating. To evaluate possible preferred grain orientations, the relative intensities of W and Cu peaks in each XRD pattern displayed in Figure 6 were determined and compared to data taken from the JCPDS X-ray database (Cu-4-836 and W-4-806 files), referring to the metals with randomly oriented grains. The relative intensities of the diffraction peaks after normalization to the most intense reflection (\(I=100\)) are reported in Table 2. For each zone, the central position of the X-ray spot is indicated. The relative intensities of the XRD reflections reported in the JCPDS X-ray database [20] correspond to those of the material with randomly oriented grains. If the examined material has a texture, the intensities diverge from the reference values: the greater the difference, the stronger the texture. On this basis, an index was used to quantitatively describe the strength of each texture component.