Strengthening mechanisms of laser cladded CoCrFeNiSnx composite coatings: Microstructure and tribological properties

In order to demonstrate the feasibility of Sn to improve tribological properties, CoCrFeNiSn_x (x = 0, 0.5, 0.75, 1, x values are molar ratios) high-entropy alloy composite coatings were prepared separately by laser cladding technique and their microstructures and wear behavior were investigated at room temperature (25 °C) and 600 °C. The relevant results showed that all the coatings consist of face-centered cubic (FCC) solid solution and Ni₃Sn₂ phase. The microhardness of the coatings gradually increased with increasing Sn content to 787.69 HV_0.5. High hardness, high work-hardening capacity, fine-grain strengthening of Ni₃Sn₂ as a heterogeneous nucleation point and blocking effect of Sn on dislocation movements. These enhancement behaviors acted synergistically to give the CoCrFeNiSn₁ coating the best tribological properties, with good wear resistance (2.5 × 10⁻⁶ mm³ / N·m) at room temperature, which was reduced by 89.49 % comparison with Sn-free coating. At 600 °C, a highly dense oxide film consisting of SnO₂, CoO and NiO oxides and a friction film reconstructed from Cr₂O₃ acted synergistically on surface of the coating, reducing the wear rate due to oxidative wear by 63.52 % compared to the substrate. This study was expected to offer some data support for the application of Q235 steel in wear-critical areas.