Tailoring an abnormal gradient with nano-dislocation networks via hybrid laser-quenching/USRP: A breakthrough in wear resistance of steel

Abstract

Dynamic sealing interfaces of petroleum plug valves suffer severe wear-induced failure under extreme conditions, necessitating alternatives to traditional carburization—a process limited by interfacial brittleness, multi-step pollution, and low automation. This study proposes a hybrid process combining Laser Quenching (LQ) and Ultrasonic Surface Rolling Process (USRP) to fabricate a multiscale-strengthened layer on AISI 4140 steel. The layer exhibits a unique "anomalous grain gradient–nano dislocation architecture" accompanied by carbon supersaturation. While LQ produces a hardened layer reaching 800 μm in depth, thermal boundary effects lead to anomalous grain coarsening at the surface (surface martensite: 2.74 μm vs. subsurface: 1.58 μm). USRP effectively counteracts this through high-frequency dynamic strain, implanting a high-density nano-dislocation network into coarse martensite. This results in an exceptional nanohardness exceeding 10 GPa, challenging the classical "coarse-grain softening" paradigm. The wear volume is reduced by 74.4 %, attributed to three synergistic mechanisms: an ultra-high strength barrier (combining nano-dislocation cell pinning and carbon-supersaturated martensite) that confines plastic deformation to sub-micron depths, suppressing material loss at its source; a hard gradient-supported tribo-oxide layer reducing friction and preventing direct metallic contact; and a wear-adaptive response involving dislocation-cell-catalyzed martensite nanonization and stress-induced ω phase transformation, establishing a self-reinforcing cycle of "damage→nanonization/phase transformation→hardening". These mechanisms achieve profound coupling through a "pre-engineered gradient–hard substrate-supported oxide formation–dynamic adaptive response" framework. This work advances theoretical understanding of non-equilibrium structural evolution under multi-field coupling while delivering an adaptive, transformative, and environmentally sustainable surface strengthening solution for petroleum valves and critical engineering components.