1 CHAPTER TWO METALLOGRAPHY & MICROSCOPY 1. INTRODUCTION: 1. INTRODUCTION: • Materials characterisation has two main aspects: Materials characterisation has two main aspects: Accurately measuring the physical, mechanical and chemical Accurately measuring the physical, mechanical and chemical properties of materials properties of materials Accurately measuring (determining) the structure of a material Accurately measuring (determining) the structure of a material Atomic level structures Atomic level structures Microscopic level structures Microscopic level structures • A critical part of materials science & technology is to seek relationships A critical part of materials science & technology is to seek relationships between: between:
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CHAPTER TWO
METALLOGRAPHY & MICROSCOPY
1. INTRODUCTION:1. INTRODUCTION:
•• Materials characterisation has two main aspects:Materials characterisation has two main aspects:
�� Accurately measuring the physical, mechanical and chemical Accurately measuring the physical, mechanical and chemical
properties of materialsproperties of materials
�� Accurately measuring (determining) the structure of a materialAccurately measuring (determining) the structure of a material
•• A critical part of materials science & technology is to seek relationships A critical part of materials science & technology is to seek relationships
What is metallography (Materiallography)?What is metallography (Materiallography)?
•• The study of structure of materialsThe study of structure of materials
•• It includes the techniques used to:It includes the techniques used to:
�� Prepare specimens for examination, Prepare specimens for examination,
�� Examine the specimens and Examine the specimens and
�� Interpreting the structures.Interpreting the structures.
What is a microstructure?What is a microstructure?
•• Most engineering materials of great importance are based on metals, Most engineering materials of great importance are based on metals, they are crystalline in the solid form.they are crystalline in the solid form.
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•• Metals also are normally polycrystalline, meaning they consist of Metals also are normally polycrystalline, meaning they consist of
many small crystals, called grains.many small crystals, called grains.
•• In some cases, these grains can be viewed with the naked eye and In some cases, these grains can be viewed with the naked eye and
these structures are called these structures are called MACROSTRUCTURESMACROSTRUCTURES
•• The structural features of small grains are observed using an optical The structural features of small grains are observed using an optical
microscope, or an electron microscope. These structures are called microscope, or an electron microscope. These structures are called
MICROSTRUCTURESMICROSTRUCTURES..
•• TheThe structuralstructural featuresfeatures presentpresent inin aa materialmaterial areare aa functionfunction ofof thethe
Specimen preparation consists of :Specimen preparation consists of :
The number, location and orientation of the samples examined are important The number, location and orientation of the samples examined are important
parameters in selection samples.parameters in selection samples.
Specimens are Specimens are examined using optical examined using optical
and /or electron and /or electron microscopesmicroscopes
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SectioningSectioning
•• Abrasive cutting is the most common cutting method Abrasive cutting is the most common cutting method
•• The cutting tool (disc) is made of silicon carbide (SiC) The cutting tool (disc) is made of silicon carbide (SiC)
of Diamond particlesof Diamond particles
•• use coolant fluid (lubrication) to avoid overheating of use coolant fluid (lubrication) to avoid overheating of
specimen and possible change in material structurespecimen and possible change in material structure
Electric Discharge Machining Electric Discharge Machining
(EDM) cutting(EDM) cutting
Mounting: Mounting: Provides a safe and efficient mean of handling samples (particularly Provides a safe and efficient mean of handling samples (particularly
small and irregular specimens)small and irregular specimens). There are two types of mounting:. There are two types of mounting:
1.1. Hot mounting: Hot mounting: requires compression pressure and heat and is done using requires compression pressure and heat and is done using
mounting machinesmounting machines
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MountingMounting
2.2. Cold mounting: Cold mounting: uses epoxy resin hardened at room temperatureuses epoxy resin hardened at room temperature
Grinding and PolishingGrinding and Polishing•• Grinding removes the damage on the specimen surface produced by sectioningGrinding removes the damage on the specimen surface produced by sectioning
•• Grinding is done using abrasive paper with different grit size Grinding is done using abrasive paper with different grit size
•• After grinding is complete, the specimen is polishedAfter grinding is complete, the specimen is polished
•• Image quality, in all optical instruments, is limited by distortions which Image quality, in all optical instruments, is limited by distortions which
arise from optical defects called aberrationsarise from optical defects called aberrations