Podcast
Questions and Answers
What is the primary focus of metallography?
What is the primary focus of metallography?
What factors significantly influence the properties of materials?
What factors significantly influence the properties of materials?
What is the maximum magnification commonly used in metallographic optical microscopy?
What is the maximum magnification commonly used in metallographic optical microscopy?
What is the purpose of polishing a specimen in metallography?
What is the purpose of polishing a specimen in metallography?
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What are non-metallic inclusions observed during macro investigation?
What are non-metallic inclusions observed during macro investigation?
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Why is etching performed on a polished specimen?
Why is etching performed on a polished specimen?
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What type of microscope is primarily used to examine microstructures in metallography?
What type of microscope is primarily used to examine microstructures in metallography?
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What is the significance of sectioning a specimen in metallographic examination?
What is the significance of sectioning a specimen in metallographic examination?
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What is the maximum area typically allowed for metallographic examination specimens?
What is the maximum area typically allowed for metallographic examination specimens?
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Why is it important to mount small metallographic specimens?
Why is it important to mount small metallographic specimens?
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Under what conditions does hot mounting typically occur?
Under what conditions does hot mounting typically occur?
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What is a significant difference between hot mounting and cold mounting?
What is a significant difference between hot mounting and cold mounting?
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What occurs during the cold mounting process?
What occurs during the cold mounting process?
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What grinding sequence is recommended for metallographic specimens?
What grinding sequence is recommended for metallographic specimens?
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What is the purpose of grinding metallographic specimens?
What is the purpose of grinding metallographic specimens?
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How should the grinding process ideally be carried out?
How should the grinding process ideally be carried out?
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What is the primary purpose of using a stream of water during the grinding process?
What is the primary purpose of using a stream of water during the grinding process?
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Why is it important to rotate the specimen 90° during the transfer to finer abrasive papers?
Why is it important to rotate the specimen 90° during the transfer to finer abrasive papers?
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What is the ideal surface condition you aim for during the final polishing operation?
What is the ideal surface condition you aim for during the final polishing operation?
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What type of cloth is typically used for the polishing operation?
What type of cloth is typically used for the polishing operation?
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What should be done after the final polishing is complete?
What should be done after the final polishing is complete?
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How should the specimen be moved during polishing to ensure uniform surface removal?
How should the specimen be moved during polishing to ensure uniform surface removal?
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What is the recommended hand pressure during the final polishing operation?
What is the recommended hand pressure during the final polishing operation?
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Why is it crucial to wash both the specimen and your hands between grinding steps?
Why is it crucial to wash both the specimen and your hands between grinding steps?
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What is the primary purpose of using a metallurgical microscope at a magnification of usually 100X?
What is the primary purpose of using a metallurgical microscope at a magnification of usually 100X?
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Why should a polished metallographic specimen be stored in a desiccator?
Why should a polished metallographic specimen be stored in a desiccator?
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What is the significance of etching a polished metal surface?
What is the significance of etching a polished metal surface?
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Which of the following methods is NOT used for etching a polished surface?
Which of the following methods is NOT used for etching a polished surface?
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What should be done immediately after the bright metallic shine of the polished surface disappears during etching?
What should be done immediately after the bright metallic shine of the polished surface disappears during etching?
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What materials are typically needed for the metallurgical examination of specimens?
What materials are typically needed for the metallurgical examination of specimens?
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What issue should be avoided when handling a polished metallographic specimen?
What issue should be avoided when handling a polished metallographic specimen?
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After etching, what is the recommended procedure to prepare the specimen for observation?
After etching, what is the recommended procedure to prepare the specimen for observation?
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Study Notes
Metallographic Examination Lab
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Objective:
- Learn specimen preparation for metallographic examination
- Learn how to use an optical microscope
- Learn to identify structural features
Background
- Material properties depend heavily on their internal structure.
- The interior structure dictates how a material performs in various applications.
- Microstructures of materials define how they handle industrial processes.
- Metallography is the study of microscopic structures of metals.
Macro Investigation
- Visual examination with naked eyes or magnification up to 5x.
- Characterized by: grain shape, size, cavities, and non-metallic (e.g., slag, oxides) inclusions.
Micro Investigation
- Higher magnification reveals more details of structure, e.g., phases, distributions, and micro-segregation.
- Optical technique is the most common method for structural examination.
Specimen Preparation for Microscopic Examination
- Sectioning: Select sample representative of the whole material. Keep area small (e.g., 15 mm x 15 mm). Avoid altering microstructure during cutting process. Use low-speed cutting saw.
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Mounting:
- Used for smaller samples, embedding in thermosetting/thermoplastic polymer matrix.
- Hot and cold methods are used for mounting
- Convenience and handling important factors
- Protection of edges for micrograph taking
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Grinding:
- Successive finer emery papers (240, 320, 400, 600)
- Purpose: gradually reduce thickness of distorted surface layer from sectioning.
- Wet grinding with water is best practice to prevent scratching sample and clogging emery paper. Continuous 90° rotation of the specimen during grinding helps remove coarse surface striations.
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Polishing:
- Use revolving cloth wheels with fine abrasive material for final surface smoothness.
- Remove scratches left from grinding.
- Employ suspensions of aluminum oxide with varying particle sizes (15, 6, and 1 micron).
- Ensure uniform surface removal throughout using a constant clockwise rotation.
- Important: wash specimen and hands between steps and after polishing
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Etching:
- Enhance visibility of structural features like grain boundaries, plastic deformation, etc.
- Chemical reagents applied to polished surface.
- Use cotton gauze/vessel and rinse with water, methyl alcohol before drying under hot air
Microscope Use
- Magnification typically 100X for revealing structural features like porosity, microcracks, and non-metallic pieces.
Equipment
- Metallurgical microscope, emery papers (various grits), polishing wheel, polishing agent (paste or powder), suitable etchant.
Procedure
- Follow the step-by-step procedures provided in the experiment or lecture.
Required
- Sketch and explain microstructure observed
- Highlight any challenges faced during preparation and the final surface appearance
- Explain the importance of grain size.
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Description
This quiz focuses on the essential techniques for metallographic examination, including specimen preparation and the use of optical microscopes. Participants will learn to identify and analyze microstructures of materials that impact their properties and performance. The content is crucial for understanding the relationship between material structures and their industrial applications.
