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This study explored the corrosion resistance of 7075-T6 aluminum alloy by immersing it in a 3.5% NaCl solution to induce corrosion damage, and subsequently repairing the sample surface using ultrasonic nanocrystal surface modification (UNSM). UNSM was found to effectively repair the defects on the surface of the pre-corroded sample and improve its stress corrosion crack (SCC) resistance. The improvement in corrosion resistance and SCC resistance of sample was mainly due to the compressive residual stress and grain refinement caused by UNSM, which not only improved the pitting resistance but also effectively inhibited the initiation and extension of stress corrosion cracks. • UNSM refined the grains and increased the hardness of the surface layer. • UNSM introduced compressive residual stresses in the surface layer. • UNSM improved the corrosion resistance and SCC resistance of aluminum alloy. • UNSM can effectively repair corrosion damage of aluminum alloy. [ABSTRACT FROM AUTHOR]

In this research, a surface plastic deformation layer was induced on 300M ultra-high strength steel using ultrasonic nanocrystal surface modification (UNSM). The UNSM-treated and control specimens were then nitrided at 450 °C for 6 h. After gas nitriding, the microstructure, corrosion and wear resistance of 300M steel with and without UNSM pre-treatment were investigated. After nitriding, the UNSM-treated specimens generated a dense surface nitride layer that was thicker than that of the control specimens. The high defect density and refined lath martensite induced by UNSM were found to accelerate the nitrogen diffusion and efficiency. X-ray diffraction patterns revealed that α-Fe phase occupied the largest proportion in the nitriding layer of specimens without UNSM pre-treatment. However due to the higher nitriding efficiency, the main phase of UNSM-treated specimens after nitriding was found to be ε-Fe 2-3 N. Compared with the specimens without pre-treatment, UNSM-treated specimens exhibited higher surface hardness as well as higher corrosion and wear resistance after nitriding. Unlabelled Image • Refined and distorted lath martensite generated in UNSM-treated 300M steels resulted in much higher nitriding efficiency. • UNSM + nitriding generated a denser and deeper surface nitride layer that contributed to higher corrosion resistance. • UNSM + nitriding induced high surface hardness that contributed to higher wear resistance of 300M steel. [ABSTRACT FROM AUTHOR]

Surface severe plastic deformation was induced in Inconel 718 alloy using ultrasonic nanocrystal surface modification (UNSM). Low-temperature gas nitriding was carried out on non-processed and UNSM-processed Inconel 718 samples. The microstructure and material properties were characterized using X-ray diffraction, scanning electron microscopy, the Vickers hardness test, and wear and corrosion testing. The results demonstrated that gas nitriding efficiency was significantly enhanced by the UNSM treatment. Higher nitrogen concentration was observed in the surface layer of the UNSM samples. The nitride layer in the UNSM + nitriding sample exhibited an increased hardness over that of the nitriding sample and the UNSM treated sample. Additionally, both wear resistance and corrosion resistance were significantly improved in the UNSM + nitriding sample. [ABSTRACT FROM AUTHOR]