METALLOGRAPHY TESTING SERVICES
NHML is able to characterize the microstructure of metals and alloys by metallography. Metallography in the most basic sense consists of the selection and preparation (sectioning, mounting, grinding, polishing, and etching) of specimens for microscopic examination. Metallographic techniques may also be applied to ceramic and polymer in some cases. This is the technique that is used to examine the internal structure of a metal. The appearance of the “microstructure” is a key to failure analysis. It is also used to better understand the material and its mechanical behavior. At NHML, laboratory techniques such as microscopy and spectroscopy are combined with a thorough knowledge of thermodynamics, engineering metallurgy, polymer chemistry and applied mechanics to understand and explain the behavior of materials. The scientific understanding is balanced by real-world understanding of manufacturing and design applications.
A wide variety of material is available regarding the preparation of specimens for microscopic examination from a number of sources including the following:
ASTM E3 Preparation of Metallographic Specimens Volume 03.01
ASTM E7 Standard Terminology Relating to Metallography
ASTM E1268 Assessing the Degree of Banding or Orientation of Microstructures
ASTM E407 Microetching Metals and Alloys
*Metals Handbook Volume Nine Metallography and Microstructures
Most samples are sectioned using a band saw, diamond saw, or a water cooled abrasive saw.
Samples are mounted in epoxy and wet ground on successively finer grades of abrasive using manual or automatic laps.
Coating or oxide thickness measurements
Weld and heat affected zone examinations
Plating thickness & adhesion
Grain size determinations
Heat treating including case depth and hardness
Extent & size of porosity
Inclusion content and rating (non-metallic..)
Intergranular attack (IGA) and intergranular oxidation (IGO)
Depth of surface imperfections or corrosion
Extent of decarburization of steels
Examination of grain boundary precipitates
Examination of the extent of cold working of the sample