OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 containing oxidized material (Fig. 6, a). Signs of plastically displaced material are visible at the edges of the track, indicating substantial plastic deformation of the material. Following friction of the bronze sample with the structure produced by multi-directional forging (Fig. 6, b), fragments of detached wear particles are observed on the surface, in addition to microgrooves and extended regions of oxidized material. Rolling significantly influenced the post-friction condition of the material (Fig. 6, c). The resulting image reveals that the wear track consists of microgrooves without noticeable oxidation or wear debris. After annealing the multi-directionally forged sample (Fig. 6, d), the microgrooves are preserved and become more pronounced; the traces of oxidation approximately coincide with those observed on the deformed Sample 2. Concurrently, individual wear particles are absent. Annealing the rolled sample (Fig. 6, e) had a minimal effect on the morphology of the wear track surface; only a slight increase in its width was observed, suggesting an increase in the wear volume. Fig. 6. Optical images of the wear track surfaces of Cu-Al-Si-Mn bronze samples. Sample 1 (a), sample 2 (b), sample 3 (c), sample 4 (d) and sample 5 (e) a b c d e Annealing promotes increased material plasticity; therefore, the amount of wear particles on the heattreated samples after SPD by multi-directional forging decreased. This is attributed to a reduced likelihood of fracture of the ductile bronze material due to deformation induced by the steel counterbody. Following the tribological tests, the surface condition of the steel balls was also investigated (Fig. 7). Signs of adhesive material transfer were observed on the surfaces of all the balls, a characteristic feature of bronze-steel friction pairs [31]. Bronze particles detaching during sliding friction adhered to the surface of the steel counterbody due to adhesive bonds. This process results in the formation of a protective layer, acting as a third body between the sample and the counterbody. The state of this layer is dependent on the wear characteristics of the softer material – the bronze. Previous results indicated that the wear of as-printed bronze results in the formation of microgrooves on its surface accompanied by minor oxidation. Correspondingly, grooves and minor areas with oxidized material are also observed on the surface of the ball (Fig. 7, a). Increased oxidation during friction of bronze Sample 2 and Sample 4 (following multi-directional forging and subsequent annealing) is reflected in the formation of an adherent layer on the counterbody’s surface. Instead of microgrooves, the formation of a mechanical mixture of non-uniform thickness, composed of bronze and oxidized material, is observed (Fig. 7, b, d).
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