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Questions and Answers
What is a major disadvantage of having a significant difference in hardness between the mounting medium and the specimen?
What is a major disadvantage of having a significant difference in hardness between the mounting medium and the specimen?
Which type of mounting uses heat and pressure to surround the specimen with molding materials?
Which type of mounting uses heat and pressure to surround the specimen with molding materials?
What defines cold mounting materials primarily?
What defines cold mounting materials primarily?
Which characteristic is NOT associated with thermosetting molding materials?
Which characteristic is NOT associated with thermosetting molding materials?
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What is a benefit of using clamps for mounting specimens?
What is a benefit of using clamps for mounting specimens?
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What is the maximum temperature resistance of Polyvinyl Chloride?
What is the maximum temperature resistance of Polyvinyl Chloride?
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Which material is not resistant to strong acids?
Which material is not resistant to strong acids?
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What is the pressure rating of Methyl Methacrylate?
What is the pressure rating of Methyl Methacrylate?
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Which of the following materials has the highest temperature resistant capacity?
Which of the following materials has the highest temperature resistant capacity?
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What is a characteristic feature of Polystyrene?
What is a characteristic feature of Polystyrene?
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At what temperature does Polyvinyl Chloride begin to melt?
At what temperature does Polyvinyl Chloride begin to melt?
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What is the PSI rating for Methyl Methacrylate?
What is the PSI rating for Methyl Methacrylate?
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Which material can be classified as resistant to most acids?
Which material can be classified as resistant to most acids?
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What is the primary purpose of mounting specimens?
What is the primary purpose of mounting specimens?
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Which cutting method is specifically designed to avoid damage to sample orientation?
Which cutting method is specifically designed to avoid damage to sample orientation?
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What are the risks associated with mechanical deformation during specimen mounting?
What are the risks associated with mechanical deformation during specimen mounting?
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Which of the following is a benefit of using cold curing resin as a mounting medium?
Which of the following is a benefit of using cold curing resin as a mounting medium?
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What is an important consideration when choosing the mounting method for a specimen?
What is an important consideration when choosing the mounting method for a specimen?
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How can cutting a sample incorrectly lead to erroneous results?
How can cutting a sample incorrectly lead to erroneous results?
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What is a secondary purpose of mounting specimens?
What is a secondary purpose of mounting specimens?
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Which of the following is NOT a method of sectioning mentioned?
Which of the following is NOT a method of sectioning mentioned?
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What is the main purpose of grinding in specimen preparation?
What is the main purpose of grinding in specimen preparation?
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Which grit size range is classified as coarse abrasives?
Which grit size range is classified as coarse abrasives?
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How often must the direction of grinding be changed?
How often must the direction of grinding be changed?
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What is important to inspect during the grinding process?
What is important to inspect during the grinding process?
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Why is equal pressure important during grinding?
Why is equal pressure important during grinding?
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What occurs if sectioning is done carelessly?
What occurs if sectioning is done carelessly?
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What should be done after each grinding step?
What should be done after each grinding step?
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What is a potential consequence of not completely removing deformed metal in the grinding process?
What is a potential consequence of not completely removing deformed metal in the grinding process?
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What is the temperature range for Bakelite in °C?
What is the temperature range for Bakelite in °C?
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Which resin is attacked by strong acids and alkalies?
Which resin is attacked by strong acids and alkalies?
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What is the abraded area of the specimen for testing in mm²?
What is the abraded area of the specimen for testing in mm²?
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What is the polishing rate for Diallyl phthalate in μm/min?
What is the polishing rate for Diallyl phthalate in μm/min?
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What is the coefficient of thermal expansion for Bakelite in in./in.?
What is the coefficient of thermal expansion for Bakelite in in./in.?
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What is the minimum heat distortion temperature for Diallyl phthalate in °C?
What is the minimum heat distortion temperature for Diallyl phthalate in °C?
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At what speed is the specimen rubbed during the abrasion test in mm/min?
At what speed is the specimen rubbed during the abrasion test in mm/min?
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Which option best represents the transparent property of Bakelite?
Which option best represents the transparent property of Bakelite?
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What is the primary focus of metallography?
What is the primary focus of metallography?
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Which of the following is NOT one of the five major operations in sample preparation?
Which of the following is NOT one of the five major operations in sample preparation?
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What is the desired condition of a well-prepared metallographic specimen?
What is the desired condition of a well-prepared metallographic specimen?
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When examining defects in metallographic specimens, what method is often used?
When examining defects in metallographic specimens, what method is often used?
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What is an important aspect of sectioning metallographic specimens?
What is an important aspect of sectioning metallographic specimens?
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What role does etching play in the metallographic examination process?
What role does etching play in the metallographic examination process?
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Which of the following describes microstructure in metallography?
Which of the following describes microstructure in metallography?
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Why is it important for a metallographic specimen to be free from polishing scratches?
Why is it important for a metallographic specimen to be free from polishing scratches?
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Study Notes
Metallography and Sample Preparation
- Metallography is the study of the microstructure of metals and their alloys
- It's a branch of materials science, relating the constitution and structure of metals and alloys to their properties
- It involves observing and determining the chemical and atomic structure, and spatial distribution of the constituents, inclusions or phases in metal alloys
What is Microstructure?
- Microstructure is the structure of a prepared specimen revealed by a microscope
- Dimensions of structural features range from subatomic particles to macrostructural features like porosity
Sample Preparation
- Preparing metallographic specimens requires five major operations:
- Sectioning
- Mounting
- Grinding
- Polishing
- Etching
- A well-prepared specimen:
- Represents the sample accurately
- Has no surface damage (disturbed or flowed metal) caused by mechanical deformation
- Is free from scratches and pits from polishing
- Is flat enough to examine at high magnification
- Sectioning:
- Important for process control and investigating defects in finished/partially finished products or parts that have failed in service
- Can require more than one specimen or sectioning operation
- Failed parts may require specimens at the failure origin and surrounding areas
- Sectioning methods include: crushing, cutting, sawing, and abrasive cutting
- When cutting samples, preserve the axes orientation (rolling, transverse, normal) to avoid erroneous results
Mounting of Specimens
- Mounting is for handling convenience and protecting/preserving specimen edges and defects
- Specimens may require mounting for use with automatic devices or microscope stages
- Mounting also facilitates specimen identification by marking the mount
- Mounting often uses a cold curing resin or hot mounting compound for small specimens
Mounting Methods
- Mounting should not injure the specimen's microstructure
- Mechanical deformation and heat are potential sources of damage
- The mounting medium should be compatible with the specimen in terms of hardness and abrasion resistance and chemically resistant to the polishing and etching solutions
Clamp Mounting
- Clamps are commonly used for mounting thin metal sheets
- Several specimens can be clamped in a sandwich form
- The clamp hardness should be similar to or greater than the specimen material
Compression (Hot) Mounting
- Involves molding around the specimen using heat and pressure
- Materials include bakelite, diallyl phthalate resins, and acrylic resins
- Thermosetting resins require heat during the molding process, while thermoplastic resins also require pressure
Cold Mounting
- Uses materials including: polyesters, epoxides, and acrylics
- Compared to hot mounting, cold mounting is faster for large numbers of specimens
Grinding
- Grinding is an essential stage in specimen preparation
- It uses abrasive grit to progressively reduce surface deformation
- Grit size ranges from 40 to 600 mesh
- Grinding direction should be changed to ensure complete removal of deformed metal
Grinding (continued)
- Grind to lessen the depth of deformation to a point that polishing steps can remove remaining damage.
- Grind with different abrasive grit sizes
- Microscopic examination can aid in evaluating the grinding sequence and ensure the scratch size uniformity
Most Grinding
- The specimen is manually held against the abrasive
- Equal pressure is applied on both sides to prevent a convex surface
- Clean the specimen after grinding to remove any abrasive particles
Grinding (continued)
- Abrasive types include silicon carbide, aluminum oxide, emery and diamond particles.
- These abrasives are typically bonded onto paper or cloth backing material
Polishing
- Polishing is the final specimen preparation step, aiming for a flat, scratch-free, and mirror-like surface
- The surface should be of at least the same quality as obtained by grinding using a 1200-grit abrasive
- Polishing also prepares the surface for subsequent metallographic (microscopic) examination
Etching
- Etching enhances microstructure (grain size, phase features) by selectively altering features based on composition, stress, or crystal structures
- Etching is necessary to visualize structures that have little or no difference in reflectivity (especially microstructural features with weak color or similar hardness differences)
- Common etching is through selective chemical etching using different formulas
Specimen Storage
- Polished and etched specimens need protection from atmospheric corrosion
- Desiccators and vacuum desiccators provide this protection
- Stored specimens maintain their condition
Materials Characterization
- Used to examine material structure and properties (Methods include: SEM, AFM, Microscopy, mechanical measurements, XRD, XPS, etc.)
Optical Microscopy
- Microstructure is directly related to the material's physical, chemical, and mechanical properties
- Diverse variations of optical microscopy are used in material characterization for assessing the structural state of a material
Scanning Electron Microscopy (SEM)
- Images the sample surface by scanning it with a high-energy beam of electrons
- Information about sample surface topography, composition, and properties (like electrical conductivity) are obtained through interacting with atoms on the sample
SEM - X-ray Analysis (EDS)
- Qualitative and quantitative elemental analysis using x-rays
- Analyzes the surface and near-surface region
Scanning Tunneling Microscopy (STM)
- Atomic-level imaging using a tunneling current between a tip and a sample
- Produces high-resolution images of the surface
- Used in various environments (vacuum, air, liquid)
Atomic Force Microscopy (AFM)
- Topographical imaging of surfaces, semiconductors, conductors and insulators
- Creates images using a nano-scale tip to probe the surface
X-ray Photoelectron Spectroscopy (XPS)
- Quantitative spectroscopic analysis of elemental composition and chemical and electronic states
- Uses XPS spectra, obtained by irradiating the sample with x-rays while measuring the electrons that escape
X-ray Diffraction (XRD)
- Uses x-rays to determine the crystalline structure of materials
- Often used for powdered or bulk samples
- Bragg's Law is a key equation to understand how it works.
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Description
Explore the fascinating field of metallography, which involves studying the microstructure of metals and their alloys. This quiz covers key aspects of sample preparation methods and the importance of microstructural analysis. Test your understanding of techniques such as sectioning, grinding, and polishing.
