Self-lubricating behavior of a laser-clad boride-reinforced coating on AlCoCrFeNi_2.1 eutectic high-entropy alloy

AlCoCrFeNi_2.1 eutectic high-entropy alloy (EHEA) combines strength and ductility, but its insufficient surface hardness and load-bearing capacity under severe sliding contact conditions lead to poor wear resistance. To improve its surface properties, this study employs laser cladding with pure boron powder, creating a boride-reinforced coating under laser powers of 800 and 1000 W and scanning speeds of 6 and 10 mm/s. The coating, consisting of Cr₂B and CrB, was formed in situ during the cladding process. The optimized coating exhibited a microhardness of 974 HV and nanohardness of 10.98 GPa, enhancing load-bearing and deformation resistance. Under water lubrication, the coating reduced the friction coefficient (COF) by 21.9% and the wear rate by 93% compared to the original EHEA. Meanwhile, compared to the widely used Ni-based WC coating, the boride-reinforced coating shows a 34.3% improvement in friction-reduction performance and a 84.1% enhancement in wear resistance, demonstrating an excellent effect in reducing friction and improving wear resistance under water-containing conditions. XPS analysis confirmed the formation of a boron-containing tribofilm (B₂O₃/H₃BO₃), enhancing the friction-reduction and wear-resistance properties. This rapid, controllable laser cladding technique offers a promising surface modification strategy for high-entropy alloys in industrial applications.