To support the above analysis, further investigations were carried
out. Fig. 13 shows a C-scan image along with an image from a
metallographic cross section prepared from the scanned sample. The
weld nugget and some areas with partial liquation of lower melting
point grain boundary phase are shown in micrograph; whilst in the
C-scan image, the weld nugget and areas corresponding to liquation
in the metallographic cross section are circled. Comparing these
images obtained by two different techniques; it can be seen that the
shape and size of the weld nugget are similar in both of the images;
areas of liquation are visible metallographically and correspond to
areas depicted in the C-scan image.
The chances of sectioning a weld and polishing/grinding to reveal
all of the features described are extremely low. Attempts were made
using different welds and Fig. 14 revealed the ring feature in the
microstructure at the interface. This also shows how the weld
nugget has developed asymmetrically with respect to the ring,
which correlated with the NDT image. It is therefore suggested that
the NDT technique is capable of revealing microstructural feature of
a weld nugget providing an understanding of features of the process.