Sample Preparation AND Optical Microscope FOR Metallographic Observation PDF

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SAMPLE PREPARATION AND OPTICAL MICROSCOPE FOR METALLOGRAPHIC OBSERVATION...

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INTRODUCTION OF SAMPLE PREPARATION AND OPTICAL MICROSCOPE FOR METALLOGRAPHIC OBSERVATION

1.Abstract Proper preparation of metallographic specimens to determine microstructure and content requires that a rigid step-by-step process be followed. The sample was under preparation process consisted of mounting, grinding, polishing, and etching and be observed with metallurgical microscope. The photomicrograph which was obtain from the metallographic examination be identify.

2.Introduction In the study of metallic materials, it is often to analyse the phases exist and grain size in the structure. Details of the structure of metals are not readily visible through naked eyes, but grain structures in metals may be seen with the aid of microscope. Metal characteristics such as grain sizes, effect of heat treatment, and carbon content of steels may be determined by studying the micrograph. For this purpose, the metal used in the metallurgical examination must be prepared and polished carefully before a good microscopic image can be seen. It is important to ensure that the surface is totally flat and smooth before microstructure observation under the microscope. Any irregularity will appear as a dark image and may create confusion to the observer who attempts to analyse a structure. In order to obtain this smooth flat surface, several preparatory steps are required. When a mirror-like metal surface has been obtained, the structure can be observed with the aid of optical microscope. Schematic diagram of an optical microscope is shown in the right figure. The optical microscope magnifies an image by sending a beam of light through the object as seen in the schematic diagram. The condenser lens focuses the light on the sample and the objective lenses (50X, 100X,200X, 400X) magnifies the beam, which contains the image, to the projector lens so the image can be viewed by the observer.

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3.Theory Metallography is the study of metals by using electron or optical microscopes. The structures seem coarse enough to be seen by the naked eye under low magnifications of macrostructures. During the examination with the naked eye on the surface of metal that's been polished and etched, meaningful information gathered. To let microstructures visible, high magnification is required. Microscopes very helpful in accomplishing this task. Optical microscopes are used for resolution roughly about half of micron while electron microscopes are used for specifically for atomic resolution. Most commonly used microscope is conventional type light microscope.

Figure 1 : Phase Diagram In microstructure allotropic, there had many types of microstructure like cementite,θ pearlite,P martensite,α' and austenite,γ as figure 1 above.[ CITATION Bhadeshia \l 2057 ] Cementite is definite carbide of iron(Fe3C). The characteristics of cementite which extremely hard cause high carbon present which also brittleness. Pearlite is mixture of ferrite and cementite. Its appearance look-like pearl and known for being tough that produced from slow cooling process. Martensite is hard and brittle and been produced from rapid quenching. It differs from austenite because being magnetic. Austenite is metallic and non-magnetic. Due to it properties commonly kind of stainless steel for cutlery application. Sample preparation is the key way in metallography, as polishing, grinding, etching will make sure that the sample has flat and mirror look-like surface in finish. False techniques in preparing a sample may result in altering the real microstructure and it will lead to erroneous conclusions. It is important to follow the right technique follows that the microstructure should not be altered. While preparation process, if not careful hot or cold working can occur. In industry, expertise that employed produce high quality metallographic samples that requires practice and training. 2

4. Experiment Procedure (a) Cutting: The sample have been cut into desirable size and shape for easily molded handle.

(b) Molding: Molding process is carried out to make the sample easier to hold throughout the polishing procedure.

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(c) Grinding: - Rough grinding: Rough scale and gross imperfections on the surface of sample have been removed. - Fine grinding: The specimen’s surface heve been improved by fine grinding until it shine and reflect light slightly.

(d) Polishing: - Rough polishing: To remove the imperfections that grinding has left. - Fine polishing: To remove all scratches and leave a mirror like finish on the surface.

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(e) Etching: Various etchants are used to selectively attack the surfaces of metals to reveal grain boundaries, phases, precipitates, inclusions and variations in composition

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5. Result

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6. Discussion Base on the experiment of Sample Preparation and Optical Microscope for Metallographic Observaion, we able to understand the procedure metallographic sample preparation. The stage of process to prepare the sample are cutting, hot mounting, grinding, polishing and etching. The process of cutting, we using the abrasive cutting machine by pressing the cutting knob slowly to bring the wheel into the sample. The process applied need to be constant and the next process is hot mounting. By add 10g of phenolic powder. The temperature 180 °C and the pressure at 200 bar. Next, the sample will undergo with grinding process. This process have two section which is coarse grinding and fine grinding and the main process is to remove material using fixed abrasive particles that produce chips of the specimen material. Next step is polishing. This is to obtain a plane surface with minimal damage that can easily be remove during polishing. The last process is etching. There are etchant used and the resulting structure. For the next process bye using the microscope. The microstructure of the specimen with four different type of lens is Magnification x50, Magnification x100, Magnification x200 and Magnification x400, the different microstructure has been drawn. We can see that under Magnification x50, the structure look need and tidy. Under the biggest Magnification x400, we can see the structure have few black spots known as defect.

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7. Conclusion Metallography is important part to us for guess the type of the material and the physical property of the microstructure by using an optical. From the experiment we saw the microstructure is effected with some physical property change like carbon and additional of alloying element or some processing technique like changing cooling rate. We also can observed the deformation type of the important in modifying the microstructure. As the conclusion, the change of material properties and processing techniques are very important. So, metallography is very important place in material science because the microstructure really important that effect the physical properties of material

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8. Reference 1. "Metallography, Materialography and Specimen Preparation." It´s All About Materialography -. N.p., n.d. Web. 21 Sept. 2016. 2. "Metallographic Examination." Metallographic Examination. N.p., n.d. Web. 21 Sept. 2016. 3. Callister, William D., and David G. Rethwisch. Materials Science and Engieering An Introduction. 9th ed. N.p.: Wiley, n.d. Print. pp. 421-422 4.Bhadeshia, H. K. (2008, - -). Interpretation of the Microstructure of Steels. Retrieved from University of Cambridge Web site: https://www.phasetrans.msm.cam.ac.uk/2008/Steel_Microstructure/SM.html

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9. Appendix

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