Application of the selected area diffraction from carbon extraction replicas for the study of carbide reactions and the inclusions in steel

Abstract

In recent years the applications of the electron microscope to the study of carbides and nonmetallic inclusions in steel, have greatly increased as the result of the development of the extraction replica technique. With extraction replicas the distribution and shape of carbides or nonmetallic inclusions are clearly defined in the electron microscope. When several different types of particles are present at the same time diffraction patterns from individual particles can be obtained by means of the selected area diffraction technique and this method becomes particularly valuable if the microscope is adapted for operation at very high voltages. In preparing the extraction replica the time required to extract the particles onto the replica is short, therefore the risk of changes occurring is less than with particles extracted by the various electrolytic isolation techniques. The disadvantages of the extraction replicas are that there is a limit to the size and shape of the particles which can be extracted, whilst the treatments after extraction have to be more delicate than with electrolytically isolated residues. In view of the low accuracy obtainable in the determination of lattice parameters from electron diffraction patterns, it is better to use both the extraction replica-electron diffraction technique and the electrolytically isolated residue-X-ray diffraction methods together, as in this way accurate results may be obtained.