S. Ali Sadough Vanini
Overview:
Materials science Lab. is one of the oldest Lab. in mechanical engineering higher education technical and engineering department. Materials science Lab started its activities since 1958 and over time expanded its size and quality in education and researches.
Research Focus/Goals:
Involves establishing relationships between:
Equipment (Experimental lab):
Metallographic and Materialographic Specimen; Preparation Systems; Light Microscopy; Image Analysis; Heat Treatment and Hardness Testing
• A systematic method to examine microstructure of Materials (mainly metallic materials).
• Can also be used to examine ceramics, polymers and semiconductors.
1- Sectioning
Why sectioning?
1. Size limitation of specimen to be examined under optical
microscope.
2. Locate area needs to be selected from a large sample.
2- Microtomy:
• Useful for preparing soft materials such as polymer samples.
• Steel, glass or diamond knives in a microtome can cut samples into very thin sections.
3- Grinding
1. Removes the damage from the surface produced by sectioning.
2. Grinding also produces damage which must be minimized by subsequent grinding with finer abrasives.
3. At the end of grinding phase, the only grinding damage present must be from the last grinding step.
4. Such damage will be removed by polishing. Grinding Materials: Abrasive paper (covered with silicon carbide grit).
Commonly a series of abrasive papers are used from coarse to fine.
Typical Grit Sequence: 120-, 240-, 320-, 400-, 600-, 1200-, 2400-, etc.
4- Polishing
After being ground to a 600-grit finish (or better), the sample is polished to produce a flat and scratch-free surface with high reflectivity.
Coarse polishing: abrasives in the range of 30 μm to ~3 μm using diamond grits of the appropriate size.
Fine polishing: abrasives in the range of 1μm or less using diamond grits of the appropriate size.
Final polishing: 0.25-0.05 μm diamond, silica, or alumina slurries.