Efficient finishing strategy on rough high-entropy alloy film by abrasive flow machining with unique viscoelastic media: effect, mechanism and modeling

Current deposition processes on high-entropy alloy (HEA) film would inevitably remain the rough peaks on the superficial surface, generating some potential risks when subjected to the thermal shock or radiation. To break the limitation of traditional finishing processes, an efficient finishing strategy was timely proposed, entitled abrasive flow machining (AFM) process, to eliminate above humps and peaks and improve the surface quality. When observing the initial film topography, the excessively deposited HEA atoms generated the humps on the film top surface, apparently leading to the inevitable rough profile. While, benefiting from the unique elasticity and viscous flow nature, the abrasive media presented desired machinability on the initially-smooth film surface and successfully subdued the convex peaks to a rather lower value. To deeply probe the excellent finishing effect, the micro structure of polymer melt and abrasive media were observed to exhibit the pseudo-network structure and tight combination state. The apparent rheological properties were subsequently measured to characterize the media viscoelasticity and describe the unique conversion effect. Considering the continuous grain collision with rough profile, the finishing mechanism on HEA film was systematically elucidated as the direct fracture or yield deformation accumulation on the convex peaks. Subsequently, to quantitatively illustrate the squeeze and driven effect during the finishing effect, the mechanics models were built from the media perspective and verified by comparing the theoretical and the measured values of film yield strength by comprehensively integrating the rheological properties and the melt-grain interaction in the flow field. The thickness reduction rate and the general energy consumption involved in the finishing process by rigid grains was discussed to exhibit and demonstrate the efficient characterization on HEA film surface with initially smooth state. Overall, the present work provides the efficient finishing strategy on the HEA film or other coatings to further improve its surface quality.