부산대학교 도서관

The results on thermal stability of the microstructure and mechanical properties of Zr--1 wt.% Nb and Ti 45 wt.% Nb ultrafine-grained alloys subjected to long-term thermal annealing at a temperature of 400[degrees]C are presented. It is shown that in a Zr--1 wt.% Nb ultrafine-grained alloy an increase in the annealing duration from 5 to 360 hr leads to a growth of the structural elements (grains, subgrains, fragments) of the [sigma]-Zr matrix phase and [beta]-Nb particles. This is a consequence of the recrystallization processes, which gives rise to softening of the alloy and a decrease in their microhardness and yield stress. It is found out that an annealing treatment for as long as 360 hr does not affect the structural element size of [beta]-phase in the Ti--45 wt.% Nb alloy but favors a noticeable grain growth in [alpha]- and [omega]-phases. It is demonstrated that disordering of the Ti--45 wt.% Nb alloy and a decrease in its mechanical characteristics are due to the recovery processes at the grain boundaries, an increase in the nanosized grains of [alpha]- and- [omega]-phases, and their decreased contribution to dispersion hardening. Keywords: Zr--1 wt.% Nb and Ti--45 wt.% Nb alloys, ultrafine-grained microstructure, thermal stability, phase composition, mechanical properties.
UDC 539.4, 539.25 INTRODUCTION The advances in modern medical materials science dictate special requirements to the development of new materials based on bioinert metals. At present, a good deal of [...]