Effect of circular vs. ring laser beam shaping on microstructure and wear resistance of laser cladded Ni60 coatings

A comparative study was conducted on Ni60 hard-facing coatings fabricated by circular and ring laser beams, focusing on phase constituents, microstructural characteristics, microhardness, and wear resistance, with complementary finite element (FE) simulation of thermal behavior and solidification dynamics. The coating deposited by the ring laser (Ni60R) shows a higher formation of chromium carbides but fewer chromium borides compared to that by the circular laser (Ni60C). FE simulations revealed that the ring laser generates a more uniform temperature field with a lower peak temperature, leading to a reduced thermal gradient ( G ) and an increased solidification rate ( R ). The lower G / R ratio in Ni60R promotes the formation of columnar γ-Ni and columnar or dendritic chromium carbides. Moreover, the product G × R is lower at the lateral boundary and higher at the center of the ring laser molten pool, resulting in coarser γ-Ni and hard particles formation at the inter-track interface and finer crystal formation in the inner-track-center of Ni60R compared to Ni60C. Attributed to a denser formation of chromium carbides and lower dilution ratio, the hardness is improved from ∼550 HV 0.5 to ∼700 HV 0.5 , and the wear resistance is largely enhanced over 40% for the Ni60R coating. This study confirms that ring laser beam shaping can be served as an effective strategy to tailor the phase formation and crystal morphology, thereby improving the wear resistance of Ni60 coatings for practical applications.