96 Prakt. Met. Sonderband 41 (2009)
3 Results and discussion N as the is0
min) only mar
Sectioning and rough grinding can be a violent process capable of introducing massive damages in treatments wit
samples. For this reason, it is important that the material removing processes used for this alloy are ness state is al
applied using equipment, techniques and consumables which minimize damage. The grinding and physical mech:
polishing processes were manually applied since the use of automated methods are likely to lead to the present rep
undesired material thinning outcomes, such as sudden separation or a complete loss of the already hardness state «
rather thin micro specimen from the embed mass. Mitigating against such outcomes reasonably
compensates for the disadvantages (long processing time and poor reproducibility of surface qual- Table 4. List of
ity) of manually applied grinding or polishing operations. Figure 1a,b representative images of etch- Spediien
polished micro specimen sections. It can be seen from the images that the etch-polished surfaces 400 °C/15min
were well finished. Pores can be observed in the images. There appears to be no marked difference Solution treated
between the images taken from the as-cast and the heat treated micro specimens. In Figure 2a-d the _ Age hardened
images obtained for the Trial 1 etched micro specimens are presented. Clearly optical contrast is
weak in these images. In comparison to the microstructure of the as-cast micro specimen (Figure
2a), it is observed that the grain boundaries of the heat treated micro specimens are largely darkened 4 Conclu
(except for Figure 2c due to image contrast), indicating that segregation must have occurred at those
sites. Over-etching is likely responsible for the dark image in Figure 2c. The well revealed micro-
structures are presented in Figure 3a-d for the micro specimens etched using Trail 2 procedure. Seg- This study has
regated phases at the grain boundaries are noticeable in these images. The large particles observed Cu ternary allo
especially in Figure 3c and 3d are likely from precipitates of second phases in the micro specimen nium peroxide.
and etched inclusions from the preparation consumables. Images obtained by DIC also provide es- though polishir
sential information on grain size and the location of second phases (which appear bright in the im- scratches on th
age). It is obvious that the etching option applied in Trial 2 produces better results as the micro- steps as this wi
structures are better resolved. As expected the average grain size (predominantly equiaxed) of the hardness in the
as-cast micro specimens is generally smaller than that of the heat treated micro specimens (Table 4) hardened state.
where thermally assisted grain growth must have occurred. The porosity (Table 4) in the micro-
specimens is below 1% indicating a good casting process, particularly the mould filling behaviour.
The knowledge derived from this microstructural investigations are as follows: (i) The elimination 5 Acknov
of scratches from such a ductile alloy is almost impossible even for polishing and grinding at pains-
taking circumstances. The scratches retained on the etched micro specimens most probably devel- We are eratefu
oped as a result of broken-off hard particles at the polishing stage, contaminating the polishing cloth grate
a .. (IMF III) Forsc
and thus creating fine scratches even at the end polishing stage. (ii) The chloride-based etchant schungsgemein
(Trial 1) did not sufficiently react to reveal optically resolvable microstructure in the micro speci-
mens. The images appeared in some cases as though a white powder was smeared over the speci-
men and in other cases as though a black powder was smeared. It is unclear why this is so however
a possible source of these effects might be traced to the Ag contained in this alloy (25.0 wt.-% Ag 6 Referen
or ~29.3 at.-% Ag). Silver reacts with chlorine containing compounds to form an opaque white pre-
cipitate of AgCl (i.e. Ag’ aq) + Cl ag) >AgCl) which darkens upon exposure to light. [1] K. Ober
The results from the heat treatments are in this report being used to assess the viability of incorpo- Nauheir
rating the ageing process into a larger production chain. The micro hardness test results have been [2] G. Beck
listed in Table 4. It can be seen that the hardness state in the as-cast condition is quite comparable Degusse
with that of the age hardened material. As expected the solution treatment (750°C for 15 min), [3] T. Shira
which is typically characterized by the formation of a disordered solid solution single phase alloy, [4] P.P.Co
leads to a softening of the material. Heat treatment of the as-cast material at 400°C for 15 min as [51 G. Baur
