44  Prakt. Met. Sonderband 38 (2006) 
avel 
orde 
2. EXPERIMENTS pixe 
chai 
2.1 SPECIMEN PREPARATION poin 
Table 1: Chemical composition of alloy 80A in weight percent: 
CW hg _ Mn Cr Mo Co AL 3. F 
| 0.06 a] 0.04 _ 0.03 75.1 0.06 2.52 1.67 
Au 
Samples of Böhler L306 VMR (Alloy 80A, composition see Table 1) were cut from hot dete 
rolled pieces, thus ensuring a completely recrystallized, fine-grained and homogeneous grail 
microstructure. Afterwards a solution heat treatment was performed at 1220°C for 60 The 
seconds. This short annealing time was chosen to avoid excessiv grain growth and led to poin 
an initial grain size of about 120 um (see Fig. 1a). Hot compression tests were carried out a pe 
on a Gleeble-3800 Hydro Wedge testing system. The specimens were cooled down to the part! 
test temperature of 1120°C and were compressed at a constant strain rate of 0.1 s to spec 
different strains (up to 0.92); Fig. 1b shows the relevant stress strain curve. The soak time scat 
was chosen between 0 and 100s before cooling down the specimen to room temperature. The 
An example of the obtained microstructure of a specimen with a strain of 0.3 and without usin 
following soaking is displayed in Fig. 1c. The cylindrical compression samples (h = 12 mm, 
d = 10 mm) were cut to both longitudinal (specimen centre) and transversal cross sections. 
The latter sections were chosen at one fourth of the specimen height, since finite element 
calculations of the compression tests proved that in this section from the centre to half the 
radius, the local and the global strain rate correspond [13] 
oar or ok = RET Fic 
Me , ET , “Ss = on a rare Spe 
Fig. 1: a) Grain map of a hot rolled nickel based alloy 80A specimen after 60 sec solution 
heat treatment at 1220°C b) Stress-strain curve for T= 1120°C and ¢ = 0.1 s™ 
c) Grain map of a specimen with a strain of 0.3. As a 
was 
inter 
2.2 EBSD INVESTIGATIONS mate 
For the SEM-investigation the specimens were embedded in an epoxy resin and ground 
and polished down to granularity of 0.25 ym of diamond paste. The final polishing step 3.1 
was performed with an alkaline colloidal silica solution (0.04 um granularity) for 30 
minutes. The measurements and analyses were performed on a Zeiss DSM 982 Gemini The 
(Carl Zeiss SMT AG, Oberkochen, Germany) equipped with an EBSD-system from EDAX- coole 
TSL (SIT camera, OIMTM 4.5 software). The microscope was operated with a primary repre 
electron energy of EO = 20 keV and a specimen current of Isp = 2.8 nA. The patterns were with