Spinodal decomposition in surface nanocrystallization induced by laser-shock processing of E690 high-strength steel: An experimental study

Spinodal decomposition during nanocrystallization on the surface of E690 high-strength steel induced by lasershock processing (LSP) was investigated by performing three laser-shock cycles with the optimal parameters, including laser energy of 7 J, spot diameter of 2 mm, and overlap rate of 70%.The microstructures and compositions of the surfaces of E690 high-strength steel samples before and after LSP were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). The mechanism of the micro shock-response of E690 high-strength steel based on spinodal decomposition was established. The results show that the sample surface underwent self-nanocrystallization after three overlapping laser-shock cycles, and spinodal decomposition occurred. The grain size was approximately 30 nm. The primary phase decomposed into a carbon-rich (manganese-poor) region and a carbon-poor (manganese-rich) region. The lattice constants of the two phases were similar, and the interface was approximately coherent. The peak positions and shapes in XRD patterns were consistent with the TEM and EDS results. The micro shock-response process clarifies the evolution of the microstructure and composition of E690 high-strength steel under LSP, and explains the experimental observation that residual compressive stress moves to a lower level during surface nanocrystallization induced by LSP.