Effect of surface self-nanocrystallization and Si infiltration on Si diffusion behavior, hardness and magnetic properties of pure Fe

Surface nanocrystallization of pure Fe was performed using an improved surface treatment process. The phase transformation and Si infiltration depth of the pure Fe before and after surface mechanical attrition treatment (SMAT) were compared by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results indicated that nanocrystallization of Fe surface was achieved using SMAT, which resulted in deeper penetration of Si. Prolonging time of SMAT and Si infiltration also resulted in increasing microhardness, with the hardness first increasing with increasing distance from the surface and then decreasing. Furthermore, longer Si infiltration time, nanocrystallization of Si and longer SMAT time resulted in higher saturation magnetization (MS). The greatest Si penetration depth (150 μm), maximum hardness (280 HV), and maximum MS (1.849 × 10⁶ A/m) were achieved after SMAT for 45 min and Si infiltration for 9 h. The interaction between adjacent grains after surface nanocrystallization leads to a region of the magnetic domain wall structure located at the grain boundary, which causes the remanence enhancement effect.