Macroscopic and Microscopic Examination of Metals Tushar Aneyrao

Macroscopic and Microscopic Examination of Metals -Tushar Aneyrao

Macroscopic

Macroscopic Metallographic Examinations Cutting Grinding Buffing Cleaning (Alcohol) Superfinishing Itching Cleaning (Water) Observation

Microscopic

Microscopic Examination Cutting Mounting in Mold Grinding Cleaning (Water and Alcohol) Drying Buffing Irching Cleaning Observation under Microscope

IMPERFECTION IN CRYSTALS

Crystalline Defects The arrangement of Atoms and Molecules in most of the Crystalline Material is not perfect. l. OR l. Crystals Inherently posses imperfections, and referred to as crystalline defects. l

Classification of Imperfections Lattice vibration l. Point Defect l. Line Defect l. Surface defect or Planar Defect l

Lattice Vibration Atoms are not stationary in there designed position l. Atoms are vibrating about their mean position l. Frequency of Vibration Depend on the Temperature. l

Point Defect

SUBSTITUTIONAL DEFECT A Substitutional defect is introduced when one atom or ion is replaced by a different type of atom or ion.

INTERSTITIAL DEFECT Atoms which occupy a site in the crystal structure at which there is usually not an atom, or two or more atoms sharing one or more lattice sites such that the number of atoms is larger than the number of lattice sites.

Line Defects l A part of line of atoms will be missing from its regular site. l Movement of dislocation is necessary for plastic deformation. l This Dislocation is a boundry between the slipped region and unslipped region and lies in the slipped plane. l There are two basic types of dislocation l Edge dislocation l Screw dislocation.

Edge Dislocation

Screw Dislocation

Mechanism of Plastic Deformation Below Elastic Limit- Temporary deformation � Above elastic limit- Permanent deformation �

Stress Strain curve for Mild Steel

Slip It represents permanent displacement of one part of crystal relative to other as shown in figure �

Twin It is the process in which the atoms in part of the crystal subjected to stress rearranged so that the orientation of path change in such a way that dissorted part become mirror image of other part. �

Slip and twin