Cutting and machining
The first step in preparing a specimen for metallographic analysis is to locate the area of interest. Sectioning or cutting is the most common technique for revealing the area of interest. The cut must be flat with minimal microstructural damage and free from heat affected zones.
MM section is equipped with several techniques for cutting but also machining: standard and slow-speed saw, diamond wire cutting, or Computed Numerical Control (CNC) milling and turning. The election of the appropriate technique will depend on the sample itself and the analysis which will be carried out afterwards.
Sample mounting
When small pieces are beign manipulated, or when they require surface polishing, samples are mounted in a resin. The purpose of it is to facilitate their manipulation, proving protection to the edges of the specimen. Moreover, mounted specimens are easier to fix into automated machines and also to hold them manually. The orientation of the specimen can also be easily controlled.
Metallographic mounting is accomplished by casting the specimen into a mouldable plastic material or by compression mounting the plastic under pressure and temperature. The section is equipped with both hot and cold mounting machines. Conductive resins are available when analysis into an electron microscope is foreseen.
Surface preparation
Samples are normally grinded and polished after cutting and/or mounting in a resin. The purpose of abrasive grinding is to remove the damage layer possibly induced by the sectioning and to restore the microstructural integrity of the specimen for accurate analysis. Apart from the mechanical polishing machines (manual and automatic ones), MM section is equipped also with a Vibrometre for a finer polishing, required in some applications like EBSD. Small sections of samples can be eventually polished by ion milling.
Some applications require the deposit of a thin layer on top of samples to make them conductive. Gold and a carbon vacuum coating systems are available.
Sample preparation examples