![]() ![]() Elements manufactured from Co-based alloys with low carbon guarantee safe use (there is no risk of unexpected cracking due to the fragility of the material), but at the same time they wear out faster. In biomedical applications, the carbon content has to be limited, to avoid the risk of the carbides’ transformation into a brittle tetragonal intermetallic σ Co 7Cr 8 phase. Good wear resistance of cobalt alloys is usually attributed to increased strengthening and formation of carbides or nitrides. Reducing the density of stacking faults can be achieved by the addition of tungsten. In the substructure of Co-based alloys, a significant concentration of stacking faults is visible, which results from the low stacking fault energy value. The role of molybdenum is grain refinement and strengthening of the matrix. The purpose of chromium is to increase the corrosion resistance. Co-based alloys, especially for medical applications, contain added chromium and molybdenum. The γ → ε transformation is associated with the decreasing value of the stacking fault energy, and the martensite ε phase is greatly known to reduce ductility due to the relatively lower number of effective slip systems. It is also worth noting that the reverse transformation ε → γ is rare in Co-based alloys, and the ε phase is much more stable than the γ phase at room temperature. ![]() ![]() Thus, especially at high cooling rates, the transformation is retained below the phase boundary in a metastable state. However, the γ → ε transformation in Co and its alloys is very slow, due to the limited chemical driving forces available at the transformation temperature. In equilibrium conditions, only the ε phase exists. The structure of a Co-based alloy consists of a low-temperature phase ε (hexagonal close-packed (hcp)) and a phase γ (face-centered cubic (fcc)), which is formed at a higher temperature. By combining the characteristic features of the matrix and the reinforcing phase, the analyzed material gains an additional advantage, namely a higher resistance to abrasive wear. The second factor was the structure of the cobalt matrix, with dominant content of the hexagonal phase. ![]() The better resistance to abrasive wear for SLS was explained by the presence of a hard, intermetallic phase, present as precipitates limited in size and evenly distributed in the cobalt matrix. Structure characterization, mainly with the use of transmission electron microscopy, was applied to investigate the differences in tribological properties. The aim of the present work was to analyze and compare the structure and wear resistance of Co-based alloy samples with low carbon content, produced by Selective Laser Sintering (SLS) and Powder Injection Molding (PIM). The high carbon improves the wear properties, but causes fragility and dangerous cracking of elements during use. Cobalt alloys are widely used in biomedicine, implantology, and dentistry due to their high corrosion resistance and good mechanical properties. ![]()
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