Laser-assisted structural trasformations and specific features of evolution of local mechanical properties of Co-based amorphous alloy

The influence of laser irradiation modes on the structural-phase state and microhardness of amorphous ribbons of the Co70Fe3Mn3.5Mo1.5Si11B11 alloy is presented. It is established that a decrease in the laser beam scanning speed leads to the devitrification of the amorphous alloy and the formation of a nanocomposite consisting of an FCC β-Co solid-solution matrix and Co2B and Co2Si phases. A complex non-monotonic variation in microhardness was observed. The highest mechanical properties (up to 2300 HV) were recorded at the pre-crystallization stage of treatment for samples which, according to X-ray diffraction (XRD) data, still remained X-ray amorphous. This result is explained in terms of the spatially constrained diffusion of metalloid atoms (B, Si), which promotes the formation of a structure with a high density of ultrafine nanoclusters acting as effective barriers to shear-band propagation.