443888973-METALLOGRAPHY-presentation-test failuresNew-ppt.pptx

443888973-METALLOGRAPHY-presentation-test failuresNew-ppt.pptx

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2. Preparation of Specimens for Metallographic Examination 2

3. Metallography

4. Objective To prepare the specimens surfaces to be examined for their microstructure study by the microscope . To learn and to gain experience in the preparation of metallographic specimens. 4

5. Metallography Cutting Grounding – emery paper (240, 300, 400, 600) Polishing (0.5, 0.1, 0.05μ) Etching –Nitol/ Kellers Solution Microscopy

6. Grounding grinding is a subset of cutting, as grinding is a true metal cutting process. Abrasive :The use of Premium SiC abrasive paper is the most efficient and practical technique for grinding metallic metallographic specimens. Although many qualities of silicon carbide are readily available, only the premium grade SiC powder provides the most consistent results and highest grinding rates. Each grain of abrasive functions as a microscopic single-point cutting edge and shears a tiny chip that is analogous to what would conventionally be called a "cut" chip (turning, milling, drilling, tapping, etc.) 6

7. Soft non-ferrous metals - Initial grinding is recommended with 320 grit SiC abrasive paper followed by 320 400, 600 and , 800 grit SiC paper. because These materials are relatively soft they do not easily break down the SiC paper. The initial grinding with 320 grit is generally sufficient for minimizing initial deformation and yet maintaining adequate removal rates. For extremely soft materials such as tin, lead and zinc it is also recommended that the abrasive paper be lightly coated with a paraffin wax. The wax reduces the tendency of the SiC abrasive to embed into the soft specimen. Grinding Soft non-ferrous metals

8. Ferrous metals - are relatively easy to grind with the depth of deformation being a major consideration. 120 grit SiC abrasives provide a good initial start with subsequent use of 240 or 320, 400, 600 and 800 grit SiC. Super alloys - are generally of moderate hardness but have extremely stable elevated temperature characteristics and corrosion resistance. the procedures for preparing super alloys is very similar to that for most non-ferrous metals. Grinding Ferrous metals

9. Sample Preparation The purpose of this practice is to understand how to prepare and interpret metallographic samples systematically. Gather information about chemical composition, heat treatment, processing, phase diagram. Cut representative sample. Mount sample, grind and polish. Examine un etched sample. Etch lightly and examine again. Etch further if necessary. Compare with microstructure expected from equilibrium phase diagram

10. Spheroidal Graphite Cast Iron

11. Abrasive Material 11 Materials used for the abrading particles are: garnet : commonly used in woodworking emery : commonly used to abrade or polish metal aluminium oxide : perhaps most common in widest variety of grits; can be used on metal (i.e. body shops) or wood silicon carbide : available in very coarse grits all the way through to micro-grits, common in wet applications alumina-zirconia : (an aluminium oxide– zirconium oxide alloy), used for machine grinding applications chromium oxide : used in extremely fine micron grit ( micrometre level) papers ceramic aluminum oxide : used in high pressure applications, used in both coated abrasives, as well as in bonded abrasives.

12. Polishing is the process of creating a smooth and shiny surface by rubbing it or using a chemical action, leaving a surface with a significant reflection Aluminum Oxide (0.5, 0.1, 0.05μ) Polishing

13. PROCESS 13 The specimen must 1. Be free from scratches, stains and others imperfections which tend to mark the surface. 2. Reveal no evidence of chipping due to brittle inter metallic compounds and phases. 3. Be free from all traces of disturbed metal. 4. The specimen has to be grounded with the help of abrasive papers. 5. Polishing enhances the surface and makes it suitable to observe its grain structure under Microscope.

14. Grain The micro structure of many metallic or ceramic materials consists of many grains. A grain is portion of the materials within which the arrangement of the atoms is nearly identical but the orientation or crystal structure of atoms are different. Microstructure of Aluminum 14

15. Etching: Sample material Etchant Composition Remarks Carbon steel (usually 2%) (nitric acid) HNO 3 1 -5 ml Ethyl alcohol 100ml Few seconds (15 Sec) Carbon steel Picric Acid Picric acid 4g Ethyl alcohol 100ml Few seconds (15 Sec) Aluminum Hydrofluoric acid HF ( conc.) 0.5ml H 2 O 99.5ml Swab for 15 sec. 15

16. REFERENCES http://sembach.com/uploads/images/brevier/bild18.gif http://www.springerimages.com/img/Images/Springer/JOU=11661/VOL=2011.42/ISU=9/ART=688/MediaObjects/MEDIUM_11661_2011_688_Fig26_HTML.jpg http://www.springerimages.com/img/Images/Springer/JOU=11661/VOL=2011.42/ISU=11/ART=749/MediaObjects/MEDIUM_11661_2011_749_Fig1_HTML.jpg http://www.sfsa.org/tutorials/uplock/images/Grains.Jpg http://ars.els-cdn.com/content/image/1-s2.0-S0043164804002364-gr11.jpg THANK YOU 16