Gradient Dual-Phase Structure Design in Brass: A New Strategy for Balancing Mechanical and Tribological Properties

This study introduces a novel gradient dual-phase structure design in brass, achieved through ultrasonic severe surface rolling (USSR) processing, which enables an unconventional asymmetric bilayer structure—comprising a hardened surface layer (>1 mm thick) and a ductile substrate—distinct from conventional hard-soft-hard sandwich configurations in gradient nanostructured materials. Microstructural characterization reveals a gradient dual-phase (α + β′) structure in the hardened layer, progressively transitioning into a homogenized dual-phase structure in the substrate. This unique architecture endows the USSR brass with exceptional mechanical properties, including a yield strength of 582.4 ± 31.0 MPa, ultimate tensile strength of 775.3 ± 33.9 MPa, and retained ductility (9.3 ± 1.0%), demonstrating an outstanding strength-ductility synergy. The USSR brass also demonstrates superior wear resistance with a 42.32% reduction in wear volume and 40.82% decrease in coefficient of friction compared to its as-received counterpart under oil lubrication. This architectural paradigm establishes a robust framework for engineering high-performance brass that simultaneously achieve an exceptional strength-ductility balance and enhanced wear resistance.