*3.2. Metallographic Testing*

The microscopic observations made it possible to determine the microscopic structure of the materials studied. The observations, carried out using a light microscope, did not show internal defects in the layers due to welding methods and material defects in the case of HARDOX 400 sheet, ABRECOPLATE, and CDP plates, Figure 7.

(**a**) (**b**)

**Figure 7.** Microstructure of layers resistant to abrasive wear. (**a**) NANO; (**b**) ABRECOPLATE; (**c**) CDP; (**d**) ABRADUR 64; (**e**) WC; (**f**) HARDOX 400; Reagents selected for abrasion resistant material.

Metallographic examinations carried out on a scanning microscope technique (SE) revealed large amounts of primary carbide precipitates highly dispersed in the zone of the nanocrystalline matrix, as shown in Figures 8 and 9.

**Figure 8.** Microstructure of a nanocrystalline layer with eutectic like carbides of NANO (Fe-Cr-Nb-B).

**Figure 9.** Microstructure of a nanocrystalline layer with carbide precipitates of NANO (Fe-Cr-Nb-B).

SEM analysis showed that the observed carbide precipitates which appeared larger in size were niobium and chromium carbides, shown in Figures 10 and 11.

(**a**)

(**b**)


**Figure 10.** (**a**) SEM image of the nanostructural layered microstructure over the EDS analysis area—a precipitation of niobium carbide; (**b**) the EDS spectrum with the above indicated spot-separation of niobium carbide and results of the quantitative elemental analysis.


**Figure 11.** (**a**) SEM image of the nanostructural layer microstructure over the EDS analysis area—a precipitation of chromium carbide; (**b**) the EDS spectrum showing the above indicated spot-separation of chromium carbide and results of the quantitative elemental analysis.

The size of the crystallographic grains of the Fe-Cr-Nb-B nanocrystalline microstructure was measured using an Xpert PRO X-ray diffractometer by PANalytical and a computerized radiation recording system equipped with a cobalt lamp at 40 kV and 30 mA current with a strip detector, in the Bragg angle range of 30–120◦. Based on calculations of crystalline sizes carried out using the Scherrer Equation (2), it was found that the average grain size of the layered microstructure measured in the direction perpendicular to the deposited substrate was approximately 20 nm.

$$D = \frac{K \cdot \lambda}{B\_{\text{struct}} \cdot \cos \theta} \tag{2}$$

where: *D*—the average size of the crystallite in the direction perpendicular to the planes of deflection; *K*—Scherrer constant (0.98); *λ*—wavelength; *Bstruct*—width of reflexes; *θ*—the angle of reflection.

Analysis of the diffraction pattern of the nanocrystalline layers of Fe-Cr-Nb-B showed the presence of reflections from the three types of carbides (Figure 12):


**Figure 12.** The diffraction pattern of the nanocrystalline Fe-Cr-Nb-B layer.
