## 3 Results and Discussion
### Hardness Tests  
Figure 13 shows the Vickers hardness profiles measured for samples fabricated with the parameters shown in Table 2. Through analysis of the results received, it can be observed that the average hardness value for the upper part of the clads deposited at a travel speed of 5 mm/s (768 HV1) is about 6-7% lower than for travel speeds of 10 and 15 mm/s (817 and 825 HV1, respectively). The reason for this phenomenon is that a much lower cooling rate is obtained for the slowest deposited clads, whereas for higher travel speeds, the cooling conditions remain relatively similar. Figure 12: XRD pattern received for samples of substrate material and the clad. Figure 13: Results of the hardness measurement for single clads with the specifying substrate, heat-affected and clad zones: (**a**) parameters sets 1 to 3 (travel speed: 5 mm/s), (**b**) parameters sets 4 to 6 (travel speed: 10 mm/s), (**c**) parameters sets 7 to 9 (travel speed: 15 mm/s). Upon a deeper analysis of the hardness profiles, it is possible to notice two areas of a significant decrease in the hardness value for certain process conditions. The first drop can be observed at the boundary of the clad and HAZ for travel speeds of 5 and 10 mm/s. This is due to the relatively low cooling rate, which is affected by the increase in the volume of additional material. This decrease is proportional to the wire feed rate and is inversely proportional to the travel speed. As a result, this phenomenon cannot be noticed at the highest travel speed of 15 mm/s, where similar solidification conditions of the clads were maintained. The visual evaluation of the clads carried out previously showed the presence of cracks in the samples fabricated with the lowest travel speed and higher wire feed rates. It can be pointed out that crack initiation may occur in the HAZ or its boundaries. Analysis of the hardness profile shows that directly in the HAZ, there are the greatest fluctuations in hardness, structure and residual stresses. Another important factor was the increase in the geometric notches that appeared as the amount of additional material increased. Fracture did not occur with higher process speeds due to a lower decrease in hardness value in this area. Moreover, the smaller volume of the deposited material reduced the shrinkage that contributes to cracking. The second drop located just below the HAZ is the result of tempering the substrate material that has not reached the austenitizing temperature during the process. However, the clads deposited with the highest travel speed again do not indicate the mentioned decrease in the hardness value because of the lower amount of heat introduced to the substrate material. In the HAZ itself, one can also notice a local maximum of hardness located in the area that had the highest heat dissipation rate during cooling from the austenitizing temperature, resulting in the hardening of this area. The maximum hardness value increases with the speed of the process. For the two lowest travel speeds, the value of the mentioned peak hardness slightly decreases as the wire feed rate increases. The effect of preheating on the distribution of the hardness profile of the clad was also analyzed for two extreme travel speeds (Figure 14). In both cases, the resultant hardness of the clads did not change significantly. In the HAZ, a decrease in the peak hardness of about 50 \(\div\) 60 HV was observed due to the reduced temperature gradient. In the case of the area of the substrate material, preheating causes an increase (Figure 14a) or appearance (Figure 14b) of the tempered zone. The received width of this zone is larger for a lower travel speed due to the higher heat input. Figure 14: Results of hardness measurement for single clads with selected parameters sets with high and low heat input. Comparison of the result with/without additional preheating (\(\Gamma_{0}\): 320 \({}^{\circ}\)C): (**a**) parameter set No. 1—high heat input, (**b**) parameter set No 7—low heat input.