microscopic observation

1. M.KARTHIKEYAN
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
AAA COLLEGE OF ENGINEERING & TECHNOLOGY, SIVAKASI
karthikeyan@aaacet.ac.in
OML751 TESTING OF MATERIALS

2. UNIT IV MATERIAL CHARACTERIZATION TESTING
1. Macroscopic observations
2. Microscopic observations
3. Optical microscopy
4. Electron microscopy (SEM)
5. Electron microscopy (TEM)
6. Diffraction techniques,
7. Spectroscopic Techniques,
8. Electrical Techniques
9. Magnetic Techniques
Principles, Types, Advantages and Limitations, Applications.

3. 1. MACROSCOPIC OBSERVATIONS
 No optical aid is used
 Specimen preparation is necessary
 Magnification is not possible
 Can inspect a large area at a time
 Results are not much accurate
2. MICROSCOPIC OBSERVATIONS
 Electron microscope is used
 Specimen preparation is necessary
 Very high level of Magnification is possible
 Inspection is performed at a specific point at a time
 Results are accurate

4. • During Microstructure Analysis of metals and alloys,
a Microscopic Examination is conducted to study the
microstructural features of the material under
magnification.
• The properties of a material determine how well it will
perform under a given application, and these properties
are dependent on the structure of the material.
• Their microstructure analysis services range from simple
determination of parameters such as grain size or coating
thickness to full evaluation of abnormalities and failure
mechanisms such as inclusions, segregation, and surface
layers.

5. THE MICROSCOPIC EXAMINATION PROCESS
 A carefully prepared specimen and magnification are needed for
microscopic examination.
 Proper preparation of the specimen and the material’s surface
requires that a rigid step-by-step process be followed.
 The first step is carefully selecting a small sample of the
material to undergo microstructure analysis with consideration
given to location and orientation.
 This step is followed by sectioning, mounting, grinding,
polishing and etching to reveal accurate microstructure and
content.

6.  Detailed viewing of samples is done with a metallurgical
microscope that has a system of lenses (objectives and
eyepiece) so that different magnifications can be
achieved, for example 50X up to 1000X.
 Scanning Electron Microscopes (SEMs) are capable of
much higher magnifications and are utilized for highly
detailed microstructural study.