Influence of stresses on phase transitions in helium ion implantation steels

In experiments on irradiation of alloys by α-particles through absorptive filters the irreversible phase - structural transformations in polymorph alloys under high-temperature after irradiation annealing was determined. In zones, implanted with helium of investigated samples of steels with carbon content from 1 to 7 atomic %, the grain size and quantitative ratio of pearlite-ferrit phases was change after annealing at the temperature above of temperature of polymorphs transformation of iron. The reason causing the microstructure changes in implanted by helium samples of steels, under our judgement, is stress fields from the helium, introduced into a material. Irradiation through absorptive filters by helium ions leads to non-uniform distribution of He on length of ions run. Ions of He stopped in rather small areas, where it the concentration can reach large values. He atoms, concentrated in small areas, cause the dilatation (volumetric extension) of material in these areas and at increase of temperature initiate irreversible microstructure changes in steel. We calculate spatial distribution of stresses and values of dilatation in a material with zones containing helium for interpretation of experimental results. The stresses due to implanted ions can be calculated using the techniques developed for thermoelastic phenomena. According to this investigation the process of microstructure changes it is possible to present as follows: the irradiation by α-particles through the absorptive filter results in specific distribution of internal stresses in a material - the local regions with high values of stresses will be formed. At low temperatures, i.e. temperatures lower than the temperature of α-γ phase transformation material does not undergo visible structural changes. At increase of temperature above the temperatures of α-γ phase transformation the local internal stress fields stimulate irreversible microstructure changes in these regions resulting in changes of a quantitative ratio ferrite-pearlite and of grain size. Experimentally observable increase of microhardness H is outcome of microstructural changes