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7 Cards in this Set

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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.

Metallographic specimen preparation is tedious, but why is it important to avoid poor technique?

It is important to avoid erroneous results

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.

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.

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.

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.

What are 3 typical defects in cold-mounts?

Cracking - Resin to Hardener incorrect

Bubbles - Too violent agitation

Soft Mount - Resin to hardener ration incorrect.