Exp.5: Preparation of Specimens for Metallographic Examination

1 To prepare the specimens surfaces to be examined by the microscope. To learn and to gain experience in the preparation of metallographic specimens. Exp.4: Preparation of Specimens 02/22/20 2

Metallography is basically the study of the structures and constitution of metals and alloys, using metallurgical microscopes and magnifications, so that the physical and mechanical properties of an alloy can be related to its observed microstructure. Such microscopic studies can provide an abundance of constitutional information about the specimen under investigation, including the size and shape of the grains (crystallites), the presence of micro defects (such as segregation, hair cracks, and nonmetallic inclusions), and the nature and distribution of secondary phases. The metallographic examination can be used in quality control and to predict and/or explain the

mechanical properties. Exp.4: Preparation of Specimens 02/22/20 3 Proper preparation of metallographic specimens to determine microstructure and content requires that a rigid step-by-step process be followed. In sequence, the steps include sectioning (cutting), ultrasonic cleaning, mounting, course grinding, fine grinding, and polishing, etching and microscopic examination. Specimens must be kept clean and preparation procedure carefully followed in order to reveal accurate microstructures Exp.4: Preparation of Specimens

02/22/20 4 Minitom: Small, automatic precision cut-off machine sectioning all metallographic and ceramic specimens. Metason: Ultrasonic Cleaning: For effective ultrasonic cleaning of metallographic, ceramic, and mineralogical specimens LaboPress-3 :Semi-automatic mounting press for hot mounting of all materials. Exp.4: Preparation of Specimens

02/22/20 5 for LaboPol (grinding and polishing machine): Machines for grinding, lapping and polishing for 200 or 230 mm discs. LaboForce : Specimen movers for semi-automatic preparation of materialographic specimens on LaboPol grinding and polishing machines. LectroPol-5: Automatic, microprocessor

controlled electrolytic polishing and etching of metallographic specimens Exp.4: Preparation of Specimens 02/22/20 6 Exp.4: Preparation of Specimens 02/22/20 7 It is important to supply enough resin during mounting. If the amount of resin is too small to cover the specimen

after curing, the specimen, the ram and the cylinder may all be damaged. 1.2 hight sample Min no. of Spoons = height of one spoon of re sin The factor 1.2 is multiplied to eliminate variation in the resin densities and the measuring during mounting. Height of 1 Spoon (15 ml) of Resin after Mounting in an Empty Cylinder Exp.4: Preparation of Specimens 02/22/20 8

Exp.4: Preparation of Specimens 02/22/20 9 Surface Abrasive Grit / Grain size Lubricant rpm Force(N) Time (min) MD-Primo 220 MD-Largo SiC

DP-Suspension - 9m Water Green/Blue 300 150 120 180 Until Plane

5 Exp.4: Preparation of Specimens 02/22/20 10 Surface Abrasive Grit / Grain size Lubricant rpm Force(N) Time (min) MD-Dac MD-Nap or MD-Chem

DP-Suspension OP-S or OP-U 3m - Green/Blue - 150 150 190 60

5 Exp.4: Preparation of Specimens 02/22/20 11 Exp.4: Preparation of Specimens 02/22/20 12 Exp.4: Preparation of Specimens 02/22/20 13

Describe the steps involved in the preparation of a metallographic sample: Sectioning (cutting) Plastic coating of the samples Mounting Grinding Polishing

Etching Why should the specimen be roughly washed after each stage during either grinding or polishing? Why is fine grinding performed wet? What is the purpose of etching metallographic samples? What are the advantages of electrolytic polishing? Exp.4: Preparation of Specimens 02/22/20 14