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