Influence of He implanted surface layer on the mechanical properties of Fe-3%Si alloy

Change in the mechanical properties of single and polycrystals of Fe-3%Si alloys implanted with 100 keV He+ ions is investigated at room and liquid nitrogen temperatures. The main results are as follows: the implanted single crystals exhibit the increase in yield stress with dose; Coarse slip bands are formed at a dose of 3 × 1020 ions m−2; the implantation to a dose of 4 × 1021 ions m−2 leads to cleavage fracture at liquid nitrogen temperature, which results from surface cracks associated with deformation twins; the implanted polycrystals show stress-strain curves similar to those of the non-implanted ones at room temperature, while surface cracks are formed at grain boundaries as well as in grains at 4 × 1021 ions m−2; Surface cracks at grain boundaries cause cleavage at liquid nitrogen temperature. These results indicate that the hardening and embrittlement of He-implanted layers markedly affect the mechanical properties of bulk materials.