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7 Cards in this Set
- Front
- Back
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What are the 3 items of which a metallurgist or engineer must be aware before sectioning a specimen to prepare it for light microscopy? Briefly explain why they are important. |
1 - Be aware that the sample will be damage 2 - If the sample is to big and has to burn it, burn well away from the area of interest, and sectioning after, or the microstructure will be altered. 3 - The material must be sectioned in 2 different planes, the longitudinal and the transversal, so that you be able what happened in the microstructure 3d. |
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Metallographic specimen preparation is tedious, but why is it important to avoid poor technique? |
It is important to avoid erroneous results |
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Provide 5 sectioning techniques and indicate when you would use each technique. |
Fracturing - Used in brittle material Shearing - Used in thin, soft material Sawing - Used in thicker, soft material Abrasive cutting - most common used, because it gives a good finishing Wire Saws - When it needs to produce a Damage-free. |
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Briefly explain 3 conditions in which edge retention would be important. List 3 ways good edge retention could be accomplished. |
Edge retention can be improved through 1 - the use of backup materials near the edge of interest. 2 - addition of filler material to castable resins 3 - plating prior to mounting. |
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Why would a cold-mount or hot-press mount be selected? What are the procedures of each? |
Cold mount - Used when you have a thin, fragile or friable samples. Put the sample in a in a phenolic ring form with the desire diameter mix the hardener and the resin in a different cup, and put inside the ring. Wait 24hrs for cure. Hot-press - Simple and highly automated. Put the material at the hot press machine with bakelite, with pressure of 3000psi and 300°F. |
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What are 3 typical defects in Bakelite? What would be the cause of each? |
Radial Split - Too large section and Sharp cornered specimen Burst - Too short a cure period, Insufficient pressure. Edge Shrinkage - Excessive shrinkage of plastic away from sample. |
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What are 3 typical defects in cold-mounts? |
Cracking - Resin to Hardener incorrect Bubbles - Too violent agitation Soft Mount - Resin to hardener ration incorrect. |
