Metallography is an informative tool in the processing of materials. It is essential in helping classify problems and failures. Microstructural examinations and visual evaluations of fracture surfaces provide insight into the mechanism of component and assembly failures. A-Lab's state of the art instrumentation and qualified personnel rapidly and competently prepare metallurgical samples for evaluation of case depth, plating thickness (Referee Method), inclusion ratings, grain size, surface defects, and heat treat evaluation. Metallurgical examination is a required tool for welder and procedure qualification. Our Metallography Department can act as an extension of your company's research and development, quality control, and production control departments, by providing a sounding board on technical issues.
As metal cools from heat treating, the grains will grow. If the temperature of cooling is slow, a larger grain size will be produced. The grain size is a critical characteristic for most metals in that it will determine the usability of the material in its application. ASTM rates grain size on a decreasing scale of #1 to #10, in which grain size of #1 is coarse and #10 is fine. ASTM grain size of #5 is considered the boundary between coarse and fine grain. Typical specification for a fine grain material is specified as ASTM #5 or finer.
Case hardening by carburizing, induction hardening, or flame hardening, at times will require evaluation to a print or specification. Test methods available are microscopic (visual) and by microhardness traverse. Typical depths of cases by visual means will state at the point at which 50% martensite is present. A microhardness traverse effective case is at the point at which the hardness drops below HRC 50.
ASTM E45 rates four types on inclusions based on sizes and quantity. The rating is useful in evaluation of a materials conformance to a specification, machinability, and explaining causes of failures. The four types of inclusions rated are: Sulfide, Alumina, Silicate, and Oxide.
Density / Porosity
Evaluation of the basic properties of sintered powder metal parts involved evaluation of the density, and/or the interconnected porosity. This is performed in accordance with ASTM B328. Structural analysis, microstructural evaluation, and microhardness are also performed on heat treated powder metal samples.
Grain Orientation / Macrostructure
Grain orientation or grain flow of forgings is evaluated by macroscopic examination of etched cross sections of the parts. Characteristics that are evaluated are grain run-out, blown grain size, pipe, laminations, etc.
In performing Failure Analysis, all the tools that our laboratory have may be utilized. For example, if a bolt fails in the field, we will first visually examine the sample and photograph the part prior to any destructive testing. Additional tests can include non-destructive testing such as mag-particle, penetrant, chemical analysis, mechanical testing, and microstructural analysis. These tests will help isolate the cause of failure.
Scanning Electron Microscope
SEM is a highly useful tool in evaluation of fracture surface for origin of failures and type of fracture progression. It is also a useful evaluation of small particles for shape, size, and surface texture. Equipped with an Energy Dispersive Spectroscopy (EDS), an added analysis tool in which the x-ray emission from the electron beam is evaluated for elemental composition. Surface contaminants, inclusions, corrosion pits, etc. are located by the SEM and analyzed by the EDS. These tools along with metallographic evaluation are useful in determining failure modes.