polish the sample surface with grid papers up to grade 1200, then alumina powder. BSEM images were 
then directly obtained in a field emission scanning microscope, Philips XL30 SFEG, working with a 15 
kV acceleration voltage. Image analysis was performed with the software Aphelion [4] on at least 50 
images (magnification 2000) per sample. In the case of long heat treatments, y matrix, carbides and 8 
phase presented distinct ‘chemical’ contrast, thus they were easily discriminated by a simple grey-level 
thresholding (if present, y' and y’’ phases are too fine to be detected at this magnification). In the case of 
shorter heat or thermo-mechanical treatments, carbides and 8 phase had to be separated through a simple 
algorithm, illustrated in Figure 3, which is based on a morphological erosion (with an octogone of size 2) 
followed by a partial geodesic reconstruction (alternate dilation and intersection applied three times). LM 
observation required an additional electrolytic etching of the polished surface, using a solution of 10% 
phosphoric acid in water and an etching time of 20s under 3.5V. 8 phase appeared in strong dark contrast 
and can be easily discriminated by thresholding. Image analysis was performed in the usual industrial 
conditions, using a Quantimet 900 system, on at least 30 LM images per sample (magnification 500). 
In order to understand the bias resulting from the chemical etching, we also analysed the topology of the 
polished/etched surfaces using atomic force microscopy (AFM). A few images were obtained with a Parks 
AFM used as a nanoprofilometer. 
J MN + 
= 1 in solvus 8 (=1000;C) I y+ carbides 
5 re : 
2 www  yroarbides +8 
eb an a AED Vd 
ab Toh Wa Lt Fig. 1: Schematisation of a typical 
f i mom fhrecipitation. an Inconel 718 alloy Results 
= Time Tez 
been inve 
relability 
iustrated 
ry Efi 
Nes 
hus astm 
mien 
0 Um i0Mm 
em] —] 
a ++ 
Fig. 2 : Typical microstructures of an Inconel 718 alloy observed by scanning microscopy in back- 
scattered electron mode ; y matrix appears in dark grey, ö phase (inter- and intragranular particles) and 
carbides (coarser equiaxed particles) in bright: a) 5 precipitation resulting from an isothermal heat 
treatment at 980°C for 9 h.) ; b) 8 precipitation resulting from a forming process around 980°C 
The ven 
RS 
ip the at 
M6