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Metallography. The objective of our experiment is to learn specimen preparation techniques in metallography and study the microstructures of typical engineering alloys. The objective of the lab report is to explain the techniques that were learned and u

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Introduction

METALLOGRAPHY LAB #3 APRIL 28, 2005 METALLURGY 331 OBJECTIVE This laboratory experiment and report have 2 separate objectives: The objective of our experiment is to learn specimen preparation techniques in metallography and study the microstructures of typical engineering alloys. The objective of the lab report is to explain the techniques that were learned and use them to help identify the specific alloy that was provided for the experiment. INTRODUCTION The term metallography has been in use since the 1700's, however at that time it was defined as the description of metals and their properties. It was not used in its modern sense, the process of preparing a metallic sample and observing or recording its microstructure, until 1892. Since then, there have been constant advancements in technology, which have provided a far superior procedure which is in use today. The metallographic preparation process can be subdivided into 5 categories: - sectioning - mounting - grinding - polishing - etching Sectioning can be defined as the removal of a conveniently sized, representative specimen from a larger sample. There are different methods of sectioning which include fracturing, shearing, sawing, abrasive cutting, and electric discharge machining. For our experiment we used an abrasive cutting machine. Abrasive cutting is the most widely used method of sectioning and there are 2 types of abrasive cutters, consumable and non-consumable. Consumable abrasive cutters are beneficial because it is fast, accurate, economical and there are an almost innumerable number of consumable wheels available which provide more control over the conditions required than do other methods of sectioning. ...read more.

Middle

In order to verify the type of metal that we were given for this experiment we not only had to perform the metallographic preparation process we also had to develop a selection process to match the microstructure of the unknown specimen with known metals. For the preparation process we employed the 5 steps: sectioning, mounting, grinding, polishing and etching. - For sectioning procedure we used the Buehler Metallurgical Cutting Apparatus which is a non-consumable abrasive cutting device. When the specimen is placed in the clamps make sure there is enough material exposed to cut a 1/4" section. This device uses coolant which can get messy at times, so it is recommended to use latex gloves while operating. - Once the specimen was properly sectioned it was mounted using Bakelite, a thermosetting resin. The resin was heated and placed under pressure in an automatic curing apparatus. - For the grinding procedure we used the Buehler Handimet Grinder. This circular grinder has 2 flat grinding surfaces with increasingly fine grit abrasives used to sand and buff metal surfaces. To properly grind the surface of the specimen, the following steps were followed: o Open water line located behind grinder. o Turn coolant on by turning coolant knob slightly counterclockwise. o Starting on the 240 grit surface, place the prepared specimen face down on the abrasive surface, and begin sliding specimen against abrasive in a forward and backward motion. ...read more.

Conclusion

They both have high amounts of pearlite, and the ferrite concentrations are rather evenly distributed throughout the sample. The main difference between the two is the size of their microstructure. I believe this may have occurred from two different magnifications being used. The magnification of the picture we captured was higher than of the one in the ASM Handbook. Because of these reasons, I do believe that these two metals are one in the same. Performing this experiment has helped me to understand how to apply the metallographic preparation process to help identify an unknown material. The results indicate that I may need a little more practice to increase my precision in this procedure, but I have a good understanding of the principles behind it. CONCLUSION The research that was performed in this experiment was beneficial to my overall understanding of the metallographic process and I realize that there is room for improvement in my execution of this process. The next time that I perform this process I will be mindful of the angle at which the specimen is being held during the grinding, sanding, and polishing processes, so as to provide a flat surface. By doing this it should eliminate the fuzzy appearance of most of the material in the image. Additionally, once I complete the etching process I will try to eliminate the delay between removal of the specimen from the etching solution and taking the picture under the microscope. This wasted time is the reason why corrosion began to propagate across the specimen. ...read more.

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