Submitted by curator on Fri, 10/16/2015 - 13:31
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Inv. 32-21-368
Fragmented end of a boss
A cut from the fragmented edge: magnification, 200x
Etchant: Ammonium hydroxide + hydrogen peroxide
(Sn, <0.012%; As, 0.55%; Ni, 0.37%)
The metal is heavily penetrated by pitting and intergranular corrosion, but in sound regions there are large polyhedral grains that, in their twinning and slight distortion, indicate a treatment of annealing after light cold-working. Scattered through the metal are some large pores introduced during casting. Inclusions vary in size appreciably, and some are elongated in a way that implies both hot- and cold-working deformation. The edge most likely was cold-worked, but the finer grained structure that would confirm that treatment is all but lost to corrosion.
Microhardness VHN: 112 ± 10 (n=5)
Uniform; data scatter (with the VHN ranging 127 to 101) is most likely due to the presence of intergranular corrosion products.
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