3.3 Influence of the annealing on the microstructure
The metastable bcc ß2 — phase decomposes into product phases with a higher stability by an
annealing at higher temperatures. In Fig. 10 the microstructures of betatized and annealed
specimens of the cast alloy are shown. The annealing at low temperature ( 500°C ) produces
two important changes in the microstructure ( Fig. 10a ). Firstly small particles of the y, —
phase are generated in the ß2 — grains. Secondly the transformation of the 3; — phase into the
orthorhombic ß; — phase takes place.
metastable 3, — ordered orthorhombic B+ yı
These observations are proved by the X — ray diffraction pattern presented in Fig. 11. In the
pattern the reflections of the y, — phase and the B; — phase appear. The annealing at higher
temperatures ( 600°C and 700°C ) produces coarser particles of the y, — phase and also the
transformation of the bee PB, — phase into the orthorhombic B; — phase, see Fig. 10b and 10c.
In the X — ray diffraction patterns of the betatized and annealed specimens ( Fig. 11) the
intensities of the marked vy, — reflections are dominant. Consequently it is correct to assume,
that the y, — phase is the predominant phase in the microstructures.
1m
os es
ERE
CTs Ce
nes ’ id Se
5 ¥
region “ ba
he 8 - A
maller m
\ TheX-
autem df x
’ Figure 10: Microstructures of betatized and annealed specimens of the cast alloy, a — annealing temperature
500°C, b — annealing temperature 600°C, c — annealing temperature 700°C,
annealing time: 30 minutes. air cooling
45