Microstructures
by George Langford, Sc.D., Massachusetts Institute of Technology, Cambridge, MA, 1966
Copyright©2005 by George Langford
Non Ferrous Alloys - Lesson 3 - Eighth specimen
Electrodeposited copper at 200X
 This photomicrograph was taken at 200X, and the next one is at 1000X.  The etchant was ammonium peroxide -  hydrogen peroxide.  The material is copper.

How was this microwave guide formed ?

Why would you say it was not cast ?

The wave guide was made on a pattern made from poly(methyl methacrylate) - PMMA - and coated with silver.  It was then electroplated heavily with copper from a copper sulphate bath.  This particular specimen was removed from the bath several times, producing a layered structure.
Electrodeposited copper at 1000X
 The bent "annealing" twins are indicative of a highly faulted and strained microstructure, a result of the high deposition rate necessary to form such a massive electrodeposited thickness (six millimeters).  Note the absence of any normal grain structure, the columnar grains, and the lack of porosity.

This excellent microstructure was produced by a process called electroforming (no endorsement intended).  The silver was leached away by acid treatment from the inside of the waveguide after removing the PMMA with a solvent.

Specimen 9 is next on the agenda.