PSI - Issue 81

Anatolii Babinets et al. / Procedia Structural Integrity 81 (2026) 353–359 355 The microstructure was examined using a Neophot- 32 optical microscope at magnifications from ×300 to ×600. Samples were prepared according to standard procedures; etching was performed in a 4% HNO ₃ solution. Hardness and microhardness were measured in the upper part of the last deposited layer according to standard methods. Thermal stability was evaluated based on cyclic heating and cooling tests: the sample surfaces were sequentially subjected to heating up to 600 °C by a gas burner and cooling down to 80 °C by a stream of running water with holding at the extreme point s (Fig. 1a). The evaluation criteria were the number of cycles until the appearance of thermal cracks and the average depth of their propagation. Wear resistance was determined from friction –sliding tests according to the “metal–metal” scheme at temperatures up to 600 °C by measuring the difference in sample mass before and after testing. The test conditions involved constant contact under a defined load between the flat surface of the sample and the surface of a rotating metallic ring counterbody heated to the working temperature (Fig. 1b).

a

b

Fig. 1. View of the setup units for studying the heat resistance (a) of the deposited metal and its wear resistance under high-temperature friction conditions according to the “metal–metal” scheme (b): 1 – test specimen; 2 – heat source (gas burner); 3 – ring (counterbody); 4 – lever with weights; 5 – ring rotation drive; 6 – cooling source (water jet); 7 – reciprocating motion drive. 3. Results and Discussion As shown by the data in Table 1, the chemical composition of the metal deposited with the reference (No. 1) and experimental (Nos. 2 – 5) MPWs is generally identical, except for the boron content. The introduction of B ₄ C additives contributes to a gradual increase in the hardness of the deposited metal: from a 7 – 10% increase at 0.01% boron content to a 20 – 25% increase at 0.05% boron. At the same time, it was found that the hardness of the metal deposited with MPW No. 5 (core granulometric composition 50 –100 µm) is higher than that of the metal deposited with MPW No. 2 of similar chemical composition but with a wider granulometric range (50 – 300 µm). This effect is evidently caused by changes in the microstructure of the deposited metal, which will be discussed below.

Table 1. Chemical composition and hardness of the top layer of metal in specimens deposited with experimental MPWs* No Content of chemical elements in the deposited metal, wt.% Hardness, HRC Fe C Cr Ni Mo Mn Si V B 1 0,43 1,89 1,51 0,50 0,73 0,87 0,37 – 50…53

2 3 4 5

0,42 1,88 0,41 1,89 0,42 1,87 0,43 1,86

1,52 0,48 0,75 1,50 0,47 0,78 1,51 0,51 0,80 1,54 0,54 0,83

0,89 0,35 0,89 0,31 0,81 0,33 0,83 0,37

0,01 0,02 0,05 0,01

54…56 58…61 60…62 56…58

Base

* Granulometric composition of MPWs Nos. 1 – 4 was 50 –300 µm; MPW No. 5 – 50 –100 µm Fig. 2 shows the appearance of the ground surfaces of the specimens after dye penetrant testing, and Fig. 3 shows the transverse macrosections of the specimens after chemical etching. From the presented figures, it is evident that the quality of the metal formation deposited by all experimental MPWs is satisfactory: the fusion line with the base metal is clearly defined, and macroscopic defects such as pores, lack of fusion, or slag inclusions are absent. At the same time, it was found that at a boron conte nt in the deposited metal ≥ 0.02%, crystallization cracks were observed in specimens No. 3 and 4. Further increase in boron concentration intensifies this phenomenon, increasing both the number and length of the crystallization cracks. These cracks predominantly pass through all layers of the deposited specimen, reaching the surface of the deposited metal, but do not propagate into the base metal. A comprehensive assessment of the welding and technological properties (Table 2) showed that all experimental MPWs are characterized by sufficiently high scores according to visual evaluation criteria. However, taking into account the formation of cracks, the best results were demonstrated by MPWs Nos. 1, 2, and 5. Analysis of process stability and melting productivity indicated that the most stable process occurs when using wire No. 5 with a core granulometric composition of 50 –100 µm. This