In-situ stirring and its effect on microstructure evolution and tribological performance in wide temperature induced via addition of dual-functional ceramics in laser directed energy deposition of FeCoCrNi-MoS2-SiC

Abstract

Extreme equipment has a critical need for coatings with exceptional wear resistance across a wide temperature range. Dual-functional MoS₂-SiC ceramics were innovatively incorporated into FeCoCrNi coating during laser directed energy deposition to enhance its tribological performance across a wide temperature range (RT to 800 °C). The microstructural evolution and tribological behavior over different temperature intervals were systematically investigated. Active element sulfur alters the surface tension distribution of the molten pool through the solute capillarity effect, competing with the thermocapillary-driven flow to generate an in-situ stirring effect at edge of the molten pool, leading to an increased thermal gradients (530.6 to 800.2 °C/mm) and cooling rate (1048.8 to 1604.9 °C/s), resulting in grain refinement (71.1 to 24.49 μm) and more uniform crystal orientation. The high mixing enthalpy promoted the formation of Cr₃S₄ particles at grain boundaries with hundreds of nanometers in scale, which played an important role in enhancing thermal stability of coating. The composite coating showed increased nanohardness (4.4 to 6.2 Gpa) and slightly reduced elastic modulus (190.6 to 181.1 Gpa), contributing to significantly enhanced tribological properties. At 600–800 °C, the enhancement was mainly due to the formation of a protective tribo-oxide layer composed of self-lubricating MoO₃ and oxidation-resistant SiO₂, accompanied by improved thermal stability, including the inhibition of grain coarsening in heat-affected zone and the suppression of dynamic recrystallization in thermo-mechanically affected zone. At 200–400 °C, the reduced oxidation rate and a strongly adherent oxide layer effectively suppressed adhesive wear.