ME 336 SPRING 2018 MATERIALS SCIENCE LABORATORY METALLOGRAPHY Objectives:  Gain experience in sample preparation, namely grinding, polishing, and etching.  Understand how different pre-conditions (i.e. microstructures) influence properties. Suggested Reading:  Callister 9th ed, Sections 4.9, 4.10, and 4.11  Hugh W. Coleman and W. Glenn Steele, Experimentation and Uncertainty Analysis for Engineers, 2nd ed., New York: Wiley, 1999, pp. 16-54. Mechanical preparation includes grinding and polishing—both processes for improving the surface conditions and making them suitable for optical analysis. These techniques are a abrading operations; therefore, they work harden the surfaces (~0.001”). Additional etching and or electro-polishing further lessen the surface roughness of a metal sample and yield a mirrorlike surface. In contrast, all mechanical polishing procedures leave a layer of disturbed structure (scratches, stains, embedded abrasives, etc.). The mechanically finished surface will not have the properties reported for the bulk metal, regardless of the thickness of the disturbed surface or the mechanical process employed (i.e. hardness measurements on a metallography sample will not reflect reality). For many metals, electro-polishing’s mirror-like luster is the goal; however, some materials require additional functional or technical advantages of electro-polishing not attainable by mechanical polishing means. Experimental Procedure: In all grinding/polishing procedures, ensure that the sample is perpendicular to the grinding/polishing surface, so the sample can remain planed. When grinding, hold sample securely. Do not touch the surface with anything!       Grind the sample—use only a small, steady stream of water when grinding or polishing Turn the sample 90 degrees each time you move to another size grit paper and hold for about 90-120s Grind using 240, 400, and 600 grit paper. After each grinding period, rinse with a little ethanol and dry using the air hose. If the sample has really deep scratches after the 600 grit grinding cycle, you will need to start over, as the surface topography is not conducive to yielding a good image. Upon finishing the grinding sequence, place sample under the microscope and take a number of images. After imaging coat the polishing wheel with 5 micron Al2O3 powder and polish for two minutes. Remember to rotate the sample. Rinse with ethanol and dry again with air hose.      Turn sample again and repeat using 0.3 micron Al2O3 powder. Take another series of images under the microscope. Etch the sample. If it’s a steel/ferrous sample, you will be using nital, nitric acid/ethanol mixture; if it is an aluminum sample, you will be using Keller’s Reagent. The TA will do the etching procedure. Look for grain boundaries, not phases. Note: After a general focus at lowest magnification (shortest lens), go to a higher magnification. Then focus on an area of interest and then return one magnification lower for the image. Lab Requirements:  Images of phases in the steel/metal  Identification of each phase seen on representative sample  Determine average grain size. Use ASTM grain size number or the alterative intercept method. This is given in equation 4.16 and 4.19 in Callister, 9th ed. Homework/Pre-lab: 1. White balance is the process of removing unrealistic color casts, so that objects which appear white in our eyes are rendered white in photos. Discuss one shortcoming of using automatic white balance adjustment. 2. How would you polish 1018 steel? Assume cost is not a factor. 3. What etchants should you use for titanium alloys? Copper alloys? 4. Problem 4.46 in your Callister textbook. Twin Prep 5 v= 50 RPM + Water first did the sample with 250 grid paper 1.3min bir t = t. 5 min 2. we moved to 400 grid pasa to the mored it 60. grid paper t=130g 7.30 min both 4 + We pour Alcohol to samples S- then we dry the sample from Alcohol 6. then take picture the sample using mxroscope polish drop 1 Alennium oxide in the polish wheel 2- hold the sample the weet is rotate to polish hold it 2 both for t = 2 min 4 나 0.5 first on the wheel again do it with thon we pour sane nlcohol in both simple Cclean it 조 tre pic by using -crascope for both sample bommary M 40x etching drop Nital sa emple For til min We Know the metal by mesuring hrain honary machine erro microscope ) white polichid - china Tsope Grinding 2 scale: 40x me gan Eictive G M
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