*3.5. Scratch Test Results*

Scratch tests enabled the determination of kinetic friction coefficient µ, scratch depth *h*, and friction force T on the outer surface of the surfaced layer. For scratch testing, one sample from powder plasma surfaced and powder laser surfaced pipes were chosen. The surfaced layers subjected to scratch testing had a comparable iron content of under 7%. Scratch test was performed on slightly leveled by grinding surface to exclude the impact of layers convexity on the results. As a result, powder laser surfaced layer (sample L4), with mean iron weight content of 5.1%, has slightly lower (0.38) mean outer surface kinetic coefficient of friction, than powder plasma surfaced layer (sample P2, Fe—5.2 wg.%), for which mean outer surface kinetic coefficient of friction was 0.39. Obtained results correlate with a higher mean microhardness of the sample L4 surfaced layer (Tables 10 and 11). In cases of both P2 and L4 scratch test results regions with a lower and higher coefficient of friction are visible. These results can be attributed to changes in surface scratch resistance due to partial heat treating of the previous surfacing pass by the next pass. The scratch test results are presented in Figures 9 and 10.

presented in Figures 9 and 10.

**Table 11.** Average microhardness HV0.3 measured on the cross‐section of 16Mo3 steel pipes laser

Base material (16Mo3) 163.5 166.3 168.2 161.8 160.3 164.0 163.7 160.6 163.2 Heat affected zone 259.5 249.7 240.5 251.2 253.7 253.0 250.5 250.7 249.9 Surfaced layer 234.2 231.4 229.0 265.9 254.3 252.0 245.2 204.1 186.7

Scratch tests enabled the determination of kinetic friction coefficient *µ*, scratch depth *h*, and friction force T on the outer surface of the surfaced layer. For scratch testing, one sample from powder plasma surfaced and powder laser surfaced pipes were chosen. The surfaced layers subjected to scratch testing had a comparable iron content of under 7%. Scratch test was performed on slightly leveled by grinding surface to exclude the impact of layers convexity on the results. As a result, powder laser surfaced layer (sample L4), with mean iron weight content of 5.1%, has slightly lower (0.38) mean outer surface kinetic coefficient of friction, than powder plasma surfaced layer (sample P2, Fe—5.2 wg.%), for which mean outer surface kinetic coefficient of friction was 0.39. Obtained results correlate with a higher mean microhardness of the sample L4 surfaced layer (Tables 10 and 11). In cases of both P2 and L4 scratch test results regions with a lower and higher coefficient of friction are visible. These results can be attributed to changes in surface scratch resistance due to

**Sample Designation L1 L2 L3 L4 L5 L6 L7 L8 L9 Mean Microhardness HV0.3**

clad with Inconel 625 superalloy powder (Table 7).

**Microhardness Test Area**

3.5. Scratch Test Results

**Figure 9.** Coefficient of friction for Inconel 625 superalloy layer obtained in the process of plasma powder transferred arc surfacing (sample P2) and of laser surfacing (sample L4). **Figure 9.** Coefficient of friction for Inconel 625 superalloy layer obtained in the process of plasma *Materials*  powder transferred arc surfacing (sample P2) and of laser surfacing (sample L4). **2020**, *12*, x FOR PEER REVIEW 15 of 17

**Figure 10.** Coefficient of friction as a function of scratch length for Inconel 625 superalloy layers obtained in the process of plasma powder transferred arc surfacing (sample P2) and of laser surfacing (sample L4). **Figure 10.** Coefficient of friction as a function of scratch length for Inconel 625 superalloy layers obtained in the process of plasma powder transferred arc surfacing (sample P2) and of laser surfacing (sample L4).

#### **4. Conclusions 4. Conclusions**

process

will be presented.

The aim of this study was to compare robotized powder plasma transferred arc surfacing and powder high power diode laser surfacing parameters on structure, chemical composition, geometry, base material content and mechanical properties of nickel‐based superalloy Inconel 625 layers surfaced on 16Mo3 pressure vessel grade steel pipe. The carried comparative analysis enabled the formation of the following conclusions: The aim of this study was to compare robotized powder plasma transferred arc surfacing and powder high power diode laser surfacing parameters on structure, chemical composition, geometry, base material content and mechanical properties of nickel-based superalloy Inconel 625 layers surfaced on 16Mo3 pressure vessel grade steel pipe. The carried comparative analysis enabled the formation of the following conclusions:

1. In the case of both powder plasma surfacing and powder laser surfacing narrow parameter range enabling the formation of nickel‐based superalloy Inconel 625 layer with dependable fusion into 16Mo3 steel pipe base material, minimal content of base material, iron content on the outer surfaced layer surface under 7 wg.%, and low HAZ depth is present. 2. Achieving low base material content in the surfaced layer and reducing detrimental 1. In the case of both powder plasma surfacing and powder laser surfacing narrow parameter range enabling the formation of nickel-based superalloy Inconel 625 layer with dependable fusion into 16Mo3 steel pipe base material, minimal content of base material, iron content on the outer surfaced layer surface under 7 wg.%, and low HAZ depth is present.

microstructural changes in the base material is possible, even when high surfacing linear energy is used, by application of intensive liquid cooling of inner pipe surface during the

reduced in the case of PPTA and HPDDL surfacing. As a result, additional material usage

from Ni‐Si, with lattice parameters close to pure Nickel were found.

B.W.. All authors have read and agreed to the published version of the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.

can be reduced in the case of tested technologies.

3. Singular layer depth in case of powder plasma and laser surfacing was two times lower than

4. In the powder plasma surfaced and powder laser surfaced layers no additional phases, aside

5. The nickel‐based superalloy Inconel 625 surfaced layers manufactured by powder laser

In the future, results of holding temperature impact on nickel‐based superalloy Inconel 625 layer

**Author Contributions:** Conceptualization, A.C.; Data curation, A.C.; Formal analysis, A. and B.W.; Funding acquisition, A.C.; Investigation, A.C.; Methodology, A.C.; Project administration, B.W.; Resources, A.C.; Supervision, A.C.; Validation, B.W.; Visualization, B.W.; Writing‐original draft, A.C.; Writing‐review & editing,

surfacing exhibit higher hardness compared to powder plasma surfaced layers.

**Funding:** This research was financed from the own resources of the Silesian University of Technology.


In the future, results of holding temperature impact on nickel-based superalloy Inconel 625 layer will be presented.

**Author Contributions:** Conceptualization, A.C.; Data curation, A.C.; Formal analysis, A.C. and B.W.; Funding acquisition, A.C.; Investigation, A.C.; Methodology, A.C.; Project administration, B.W.; Resources, A.C.; Supervision, A.C.; Validation, B.W.; Visualization, B.W.; Writing-original draft, A.C.; Writing-review & editing, B.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was financed from the own resources of the Silesian University of Technology.

**Conflicts of Interest:** The authors declare no conflict of interest.
