ENSC 330
Lab 3
Microstructures and Properties of Metals
Word 2000 document
March 4, 2003
Instructor: John Jones jones@sfu.ca –
Lab Support: Carl Chun, chunq@sfu.ca
1.0 Objectives
Make observations and physical measurements of the samples provided.
Polish and etch the samples.
1.2 Observe and draw the microstructure of the prepared metal samples.
1.3 Identify the samples, or their composition, from your observations of the microstructure and other physical properties.
1.4 Identify an application for each sample metal.
1.5 Comment on how the observed microstructure might affect the mechanical and electrical properties of the samples.
2.0 Notes (Read before going any farther)
2.1 Read entire lab thoroughly before starting, especially SAFETY and PROCEDURE sections.
2.2 Report any problems or breakage. You will not be penalized for problems, even if you helped to create them. We want only to fix problems, not to fix blame. Call Gary at 4527 (ASB8843).
2.3 Each group will sign out a package of unknown samples, identified only by an alphanumeric code. These are not disposable samples. They must be cared for and returned in good condition. Save your samples in the original envelope. If samples are lost, the lab will not be marked and you will have to pay for the replacement of the samples. Do not damage the samples.
3.0 Materials and equipment
Metal samples, identified only by alphanumeric code, abraded other side on 600 grit sandpaper
Polishing equipment
Wet paper, 800 grit
Wet paper, 16 micron
Polishing pad and powder, 25 micron
Polishing pad and powder, 10 micron
Polishing pad and powder/paste, 3 micron
Polishing pad and powder, 0.3 micron
Spatula
Shop towel
Etchants, as required
Nital, 2%
Picral, 4%
Ferric Chloride
Petri dish
Rubber gloves
Double pan balance
Magnet
Overflow cup
5 ml graduated cylinder
10 ml graduated cylinder
Photocopied pages from metallurgical book describing typical sample preparation
Microscopes, Bausch & Lomb, Leitz
Goggles or face shields
4.0 Safety (READ THIS SECTION)
4.1 Note position of nearest telephone. It will have emergency numbers marked on it.
4.2 All participants must wear eye protection (goggles or face shields) and gloves whenever anyone in the group is using etchants.
5.0 Procedure (read entire procedure before starting work)
5.1. Sign out numbered samples of metals.
5.2 Make physical observations and measurements of the samples using the equipment provided. Use eyes to observe colour, appearance, etc. Use brain to think of other non-destructive measurements you might make using equipment available. If you wish to try scratching sample make a very small mark only on the side of the sample, not on either face. Inspect sample under B&L microscope.
5.3. Polish the samples as follows:
Notes: - Do NOT polish the numbered face of the sample.
- Rinse/clean sandpaper and polishing pads frequently to remove abraded material and avoid cross-contamination between samples.
- Check sample frequently – some will polish easier than others – move to next phase when previous scratches gone and no further improvement in surface quality occurs.
5.3.1 Place the 800 grit and 16 micron sandpaper on a flat surface and sprinkle some water on.
5.3.2 Place the polishing pads on a flat surface and dampen them.
5.3.3 Take a small amount (about ½ spatula) of the correct polish and place on the pads. PADS ARE MARKED WITH THE POLISHING POWDER SIZE. USE ONLY THE CORRECT POLISHING POWDER.
5.3.4 Start on the 800 grit paper. Hold the sample firmly and move in a circular motion. Remove any gross scratches, marks or oxidation.
5.3.5 Move to the 16 micron paper. Remove finer visible marks.
5.3.6 Move to the 25 micron powder, and then successively to the 10, 3,and 0.3. You want to get as smooth a surface (near to a mirror finish) as is practical for the particular sample.
5.3.7 Rinse under running water and pat dry on a shop towel.
5.3.8 Do not touch polished surface with bare hands or contaminate with any other material.
5.4. IMPORTANT NOTE RE USE OF LEITZ MICROSCOPE: Most samples are not perfectly flat -- DO NOT DAMAGE OBJECTIVE LENSES BY SWINGING THEM OVER AND CONTACTING SLANTED SURFACES. Working distance (i.e. the distance between the objective lens and the sample) of the high power Leitz objectives (20X and 50X) is VERY short (less than 0.5 mm). Lenses cost $1K-2K each and are no longer available new. Position your sample to avoid contact with the lens while rotating objectives turret. If you don’t understand the above, ask Gary for help.
Observe the DRY metal samples under the B&L and Leitz microscopes AS SOON AS POSSIBLE (why??) after polishing them. If sample might benefit from more polishing, repeat some of the finer polishing steps. Turn off microscope lights when finished.
5.5. Sketch the microstructure of the metal samples. Note the magnification (objective lens power times eyepiece lens power) at which structures were observed.
5.6. If the sample might benefit from etching, etch as follows:
5.6.1 Use premixed 2% Nital etchant (2 ml HNO3, 100 ml ethanol) supplied for the following samples: FM.H1, FM.H2, FM.A4, FM.A5, FM.A7, FM.P18, FM.P19, FM.P20, FM.P21, FM.J9B, FM.L6. Note that a few samples can use either etchant.
5.6.2 Use premixed 4% Picral etchant (4 gm picric acid, 100 ml ethanol) supplied for the following samples: FM.P18, FM.P19, FM.P20, FM.P21, FM.M8, FM.M10, FM.M12, FM.L1, FM.M2, FM.M4, FM.M15, FM.J7, FM.L6.
5.6.3 Use ferric chloride solution (5 gm ferric chloride, 2 ml HCl, 95 ml ethanol) for the following samples: FM.C1, FM.B1, FM.D1, FM.E13, FM.L6
5.6.4 Wearing gloves and goggles, place the sample in the petri dish, apply a few drops of etchant to the polished sample surface for 2-3 minutes, wash with water, dry and observe again immediately. Sketch.
Note: You do not need to submit sketches for both etched and unetched samples. Merely use the information from both observations to give the best possible picture.
5.7. Identify the metals, or their composition, from your results.
5.8. Identify an application for each metal.
5.9. Comment on how the observed microstructure might affect or determine the mechanical and electrical characteristics of the metal sample.
5.10. Clean petri dish, counter tops, etc. and turn off microscope lights and fume hood light and fan.
5.11. Sign in and return samples. See Note 2.3 again.