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Here is a complex brazed joint between Kovar (iron - 27%
nickel - 17% cobalt) and oxygen free high conductivity (OFHC)
copper. The braze metal is copper - 30% gold. Note the following features of this microstructure: (a) Coring in
the braze metal;
(b) Shrinkage porosity in the braze metal; and (c) Penetration along the grain boundaries of both substrates. |
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The second photomicrograph, at 500X magnification, shows the
microstructure of the Kovar with its zone of grain boundary
penetration, an alloying zone, and a zone of disintegration where
alloyed Kovar grains dispersed into the molten braze metal. The etchant was potassium bichromate. |
| The next series of images in Specimen 8 show an unsuccessful attempt to coat a low carbon steel with a heat resistant alloy by welding. |