Metallography  
     

Objective

To develop an understanding of the principles of practical metallography and the examination of some typical microstructures.

 

Procedure

Examine the specimens at different magnifications.  Start with low power examination to obtain an overall picture.  Then, at successively higher magnifications, resolve the fine detail.  Draw a neat sketch of each specimen you examined at any suitable magnification.  The sketch should include the magnification used.

 

Answer the following questions inthe background section of your report:

ˇ        What is the significance of microstructure in the material properties?

ˇ        Give examples of some microstructure-dependent material properties.

ˇ        What is the significance of sample preparation in metallography?

ˇ        What are the important steps metallographic sample preparation?

ˇ        What are the differences in the microstructures formed by heterogeneous nucleation versus homogeneous nucleation?

 

SPECIMEN #
TYPE OF STRUCTURE
X1
 Pure Metal: Pure zinc, sand cast
X1A
 Impure Metal: Impure zinc, sand cast
X2
 Solid solution: Copper/4% Tin alloy, sand cast
X5
 Eutectic Type: Cu/8.4% P, eutectic alloy, sand cast
X6
 Hypoeutectic alloy: Cu/4.5% P, sand cast
X9
 Peritectic tvpe structure: Sn/10% Sb alloy, sand cast
X10
 Widmanstatten structure: Cu 58/ Zn 42, sand cast
X17
 Eutectoid reaction: 0.8 %C steel, 1 hr at 800ēC furnace cooled (fully annealed)
X18
 Eutectoid reaction: 0.8% C steel, 1 hr at 800ēC cooled in still air (normalized)
X19
 Hypoeutectoid steel: 0.35% C steel bar, furnace cooled from 870ēC.
X20
 Hypereutectoid steel: 1.3% C steel bar, furnace cooled from 970ēC
X25
 Martensite: 0.35% C steel, water-quenched from 875ēC
 

  

Note: Specimens 8-12 will require the use of the oil immersion lens.  Use the oil with the oil immersion lens only.

 

If the microstructure of a sample is not visible or the sample is bad, exchange the sample with one that is viewable.  If a suitable sample is not found, ask the T.A. to assist you in polishing and etching the sample so that the microstructure is visible.

 

Before leaving the lab, have your T. A. examine and grade your lab notebook.

 

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