OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 2.37 GPa. Based on the microstructural data and phase composition, the increased hardness is likely due to the dissolution of the primary β-phase and the precipitation of secondary coherent phases within the grain volume. Annealing the rolled sample at 400°C decreased the microhardness from 2.52 GPa to 2.25 GPa.As annealing did not alter the phase composition of the rolled sample, the change in microhardness is attributed solely to structural modifications within the material. During the tribological tests, the change in the coefficient of friction (CoF) over time was recorded (Fig. 5, a), from which the average value was calculated (Fig. 5, b). When the printed bronze sample (Sample 1) was subjected to friction, the CoF remained relatively constant throughout the test at 0.245, with the amplitude of fluctuations not exceeding 0.02. In addition to changing the mechanical properties, multi-directional forging also affected the tribological properties of the investigated bronze. At the start of the test, the CoF for Sample 2 was 0.2, but then decreased to 0.14 within the first 300 seconds. Then the CoF gradually increased to 0.172, and its short-term fluctuations did not exceed 0.05. After rolling (Sample 3), the CoF changed insignificantly; its average value was 0.189, and short-term fluctuations were 0.03. Heat treatment of the sample after multi-directional forging led to an increase in the average CoF to 0.18, and short-term fluctuations to 0.05 (Fig. 5, a, Sample 4). During friction, the CoF monotonically increased from the beginning to the end of the test. Heat treatment of the sample after rolling led to an increase in the average CoF to 0.226, and short-term fluctuations to 0.05 (Fig. 5, a, Sample 5). The change in CoF during friction was not monotonic. At the initial stage, the CoF increased, but then decreased approximately in the second half of the test. Fluctuations in the coefficient of friction reflect dynamic alterations during the sliding friction process. The greater their amplitude, the more unstable the friction process becomes, which may reflect a change in the conditions of contact interaction between the steel ball and the bronze. Based on the obtained results, it can be noted that SPD contributes to a reduction in the CoF compared to the as-printed material. Heat treatment of the samples after SPD led to an increase in the CoF and an increase in the amplitude of its fluctuations. Based on the analysis of optical image data, characteristic regions reflecting the condition of the wear track surface on the bronze samples were identified (Fig. 6). After friction of the as-printed bronze, fine microgrooves formed on the track, oriented along the direction of the friction force, along with dark areas Fig. 4. Microhardness of Cu-Al-Si-Mn bronze samples a b Fig. 5. Coefficients of friction as a function of time during sliding tests (a) and their average values (b)
RkJQdWJsaXNoZXIy MTk0ODM1