|
Grain boundary (GB) phase transitions can change drastically the
properties of polycrystals. The GB wetting phase transition can
occur in the two-phase area of the bulk phase diagram where the
liquid (L) and solid (S) phases are in equlibrium. The GB wetting
tie line appears in the L+S area. Above the temperature of the GB
wetting phase transition a GB cannot exist in equlibrium with the
liquid bulk phase. The liquid phase has to substitute the GB and
to separate both grains. The experimental data on GB wetting phase
transitions in the systems Al-Sn, Al-Ga, Al-Sn-Ga, Cu-In, Cu-Bi, Fe-Si-Zn,
Mo-Ni, W-Ni, Zn-Sn and Zn-In are analysed. The GB wetting tie line can
continue in the one-phase area of the bulk phase diagram as a GB solidus line.
This line represents the GB premelting or prewetting phase transitions. The GB
properties change drastically when the GB solidus line is crossed by a change
in the temperature or concentration. The experimental data on GB segregation,
energy, mobility and diffusivity in the systems Cu-Bi, Al-Ga, Al-Pb and
Fe-Si-Zn obtained both in polycrystals and bicrystals are analysed.
|