Study of the mechanical properties of alloy 36NKhTYu in relation to the mechanisms underlying the precipitation of the γ' and η phases

The nature of the dispersion (precipitation) hardening of the alloy 36NKhTYu is examined. It is shown that the increase observed in the resistance of the alloy to the motion of dislocations inside the grains during the continuous precipitation of the γ' phase is due to the presence of long-range order in the hardening particles. In addition to this, there is also a considerable increase in that part of the yield stress which is associated with the grain boundaries; this is because of the precipitation of carbides at grain boundaries and the corresponding sharp increase in slip localization. Overaging is characterized by a reduction in the resistance to the motion of the dislocations inside the grains, and a diminishing influence of the grain boundaries (ultimately to no influence at all). These results are in satisfactory agreement with calculations based on the Orowan theory, and also with the assumption that, as overaging progresses, the range of the dislocations is reduced from a distance equal to the grain size to a distance equal to that separating the particles ofγ′ phase, while localized slip is replaced by uniform slip. When the precipitation of theη phase reaches a well-developed stage, the yield stress is reduced. The result of the present investigation confirm our earlier conclusion as to the substantial hardening (strengthening) of the meterial which occurs as a result of the discontinuous precipitation of theγ′ phase.