OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 2 2023 Parameters of the plasma-jet hard-facing process Specimen No. Current, А Processing method 1 120 one track 2 140 3 160 comparing the intensities of the characteristic X-rays from each element that is present in the sample with the intensity of the same radiation emitted by the standard. The study of the phase composition of coatings after plasma-jet hard-facing was carried out on an X-ray diffractometer Shimadzu XRD-7000 using CuKα radiation. The samples were scanned in step-by-step scanning mode in the range of 5°–85° with 5° steps at 40 kV and 40 mA. The microhardness of the alloyed layer was measured using a Shimadzu HMV-2 microhardness tester. Results and discussion In the process of samples’ microscopic investigation, it was found that the method of plasma melting of a coating containing amorphous boron and a binder of BF-6 glue makes it possible to form coating layers without cracks and pores. Figure 2, a shows the microstructure of the cross section of the first sample after plasma-jet hard-facing. The first zone is characterized by the presence of a hypereutectic-type structure, which consists of primary crystals of FeB and Fe2B of various morphology, located in a eutectic matrix consisting of Fe2B and α-Fe (figure 3). The boride morphology varies from oval (figure 4, a) to columnar (figure 4, b). In addition, iron borides with incomplete overgrowth of faces were observed in the hard-faced layer (figure 4, c). In the region of the coating near the base metal, the structure of the layer 100 µm wide is represented only by eutectic colonies (figure 4, d), because the boron concentration is not sufficient to isolate borides. At the bottom of the hard-faced layer, a heat-affected zone is formed, characterized by the presence of coarse grains, the formation of which is due to heating to high temperatures. Next is a zone with the structure of the base metal. The boron content in the hard-faced layer is 12.35 %. Fig. 1. Plasma-jet hard-facing scheme 1 – power source; 2 – argon bottle; 3 – oscillation detector; 4 – control block; 5 – electric motor; 6 – specimen with smearing, 7 – plasma torch; 8 – camera, 9 – infrared thermometer
RkJQdWJsaXNoZXIy MTk0ODM1