Lab report (Metallographic specimen preparation and examination) PDF

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Metalluregy lab (report (3

Name:

Mohamed Abdurrahman Mohamed

ID: 3371 Report of metallographic SAMPLE PREPARATION FOR MICROSCOPY

Metallographic specimen preparation and examination :Objectives

The objective of this experiment is to describe metallographic and its application to study the microstructure of materials and to provide experience of metallographic preparation techniques together with practical examples of fracture analysis and Quantitative meta1lography . Students will observe grain boundaries and phases in different metallic samples using an optical microscope.

:Safety Optical metallography involves the use of etchants (standard solutions containing a variety of chemicals such as strong acids and solvents) which can be very corrosive and poisonous. You must wear gloves and goggles and handle the chemicals with extreme care. You must not have direct skin or eye contact with the etchants. Etchants .must be used in well ventilated area. Do not try to smell the etchants

:Introduction Def: Metallographic is the study of the physical structure and components of metals,

typically using microscopy. And Our understanding of the behavior of materials depends on our ability to relate properties to microstructures. The microstructure is the geometric arrangement of grains and the different phases present in a material. Materials engineers can predict the general behavior of materials by observing their microstructure. Besides the crystallographic nature of a material, imperfections inside a material have an even greater influence on the mechanical properties, i.e. tensile, fatigue, creep, fracture toughness, impact properties. Some defects such as missing planes of atoms, called dislocations, are responsible for plastic deformation of crystalline solids. Others such as grain boundaries, precipitates, twins and cracks alter stress distribution in a material and the accompanying motion of dislocations. Some defects such as missing atoms and dislocations cannot be observed optically except by their effects, i.e. strain, etch pits, slip lines. Other defects such as grain boundaries, twins, precipitates, can be observed readily in the microscope.

:Microscope examination

Prepared specimens should be examined with the unaided eye after etching to detect any visible areas that have responded to the etchant differently from the norm as a guide to where microscopical examination should be employed. Light optical microscopy (LOM) examination should always be performed prior to any electron metallographic (EM) technique, as these are more time-consuming to perform and the instruments are much more expensive. Further, certain features can be best observed with the LOM, e.g., the natural color of a constituent can be seen with the LOM but not with EM systems. Also, image contrast of microstructures at relatively low magnifications, e.g.,...