Exp.1: Preparation of Specimens for Metallographic Examination Eng. Ahmed Al-Afeefy Eng. Ahmed Y. Manama

Objective To learn and gain experience in the preparation of metallographic specimens. To examine and analyze the microstructures of metals and metallic alloys.

Introduction 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.

Introduction Such microscopic studies can provide constitutional information about the specimen under investigation, including: The size and shape of the grains, The presence of micro defects, The nature and distribution of secondary phases.

Introduction 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), Mounting, Grinding, Polishing, Etching , Microscopic examination.

Procedures Sectioning (cutting): The preparation starts by cutting a small representative piece of the metal to be studied. Cutting can change the microstructure of a sample. Minitom

Procedures Cleaning Specimens must be kept clean in order to reveal accurate microstructures. Metason

Procedures Mounting Small samples are generally mounted in plastic for convenience in handling and to protect the edges of the specimen being prepared. LaboPress-3

Hot Mounting Cylinder dia. Resin heating Cooling 30 mm Type Time Temp. Force Rate [min] [oC] [kN] PolyFast 4-6 180 20 2-3 HIGH MultiFast (block)

Optimizing the amount of resin 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, and the cylinder may all be damaged. Min no. of Spoons = Height of 1 Spoon (15 mm) of Resin after Mounting in an Empty Cylinder Cylinder dia: 30 mm Resin: mm inch PolyFast 11.3 0.44 MultiFast (black) 8.9 0.35

Procedures Grinding The entire process is designed to produce a scratch free surface by employing a series of successively finer abrasives. Rotating Discs

Grinding Surface MD-Primo 220 MD-Largo Abrasive SiC DP-Suspension Grit / Grain size - 9µm Lubricant Water Green/Blue rpm 300 150 Force(N) 120 180 Time (min) Until Plane 5

Procedures Polishing To remove deformations from grinding and obtain a surface that is highly reflective. (rotating discs covered with soft cloth ) Rotating Discs

Polishing Surface Abrasive Grit / Grain size Lubricant rpm Force(N) MD-Dac MD-Nap or MD-Chem Abrasive DP-Suspension OP-S or OP-U Grit / Grain size 3µm - Lubricant Green/Blue rpm 150 Force(N) 190 60 Time (min) 5

Procedures Etching Etching occurs when the acid or base is placed on the specimen surface. The purpose of etching: Grinding and polishing operations produce a highly deformed, thin layer on the surface which is removed chemically during etching. Etching is used to highlight, and sometimes identify, microstructural features or phases present. LectroPol-5:

Procedures Microscopic examination Next week