Homework_Solution__1 - MSE 250 LAB. # 2 MICROSTRUCTURE AND...

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1 MSE 250 LAB. # 2 MICROSTRUCTURE AND HARDNESS TESTING Purpose: This purpose of this laboratory is to provide instructions on the proper use of optical microscope as well as two hardness testers that will be used in future experiments. The exercise is divided into two parts. Part A is designed to provide some basics of reflective optical microscope, proper collection of image, and common quantitative method(s) used to evaluate microstructure of metallic specimen. Part B is the hardness testing, which is a simple and yet quantitative method used to provide a measure on the effectiveness of heat treatment or surface treatment of metallic samples. Class will be divides into groups for this experiment. Each group should not be more than four students. PART A: Metallographic specimen preparation Metallography is the study of the physical structure and components of metals. This is done with the assistant of microscope, typically a reflective optical microscope. The surface of a metallographic specimen is prepared by mechanical procedures follow by a chemical procedure to reveal the microstructure of specimen. Mechanical procedures are grinding followed by polishing. Both grinding and polishing are a series of successive steps of finer abrasive paper or particles to remove material from the sample surface until the desired surface quality is achieved. After the final step of polishing, specimens is washed one final time and dry with air. Chemical procedure is “etching” on metal surface is needed to reveal the microstructure of interest. The composition of etching solution depends on metal of interest. For copper and its alloys, solution containing ferric chloride, hydrochloric acid and water is used. For steel (iron- carbon alloy), solution containing nitric acid and methanol is used. (For safety reason, all specimens used will be polished and etched by your TA before the Lab.) Microstructure of polished/etched specimen is to be evaluated using the optical microscope. Like many engineering measurement, there is a standard approach to determine “size” of observed features. These features are often called micro-constituents. Grain is one such of micro-constituents. It should be noted that most if not all micro-constituents are 3-D objects, while metallographic observation is a 2-D cross-sectional measure at a particular plane. Shape and orientation of grains with respect to the specific cross-sectional plane can significantly affect the observation.
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This document was uploaded on 10/28/2011 for the course MSE 250 at Michigan State University.

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Homework_Solution__1 - MSE 250 LAB. # 2 MICROSTRUCTURE AND...

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