Micro hardness testing involves forcing a diamond indenter with a specific geometry into the surface of a test piece under a small load, then using a microscope to measure the resulting indentation to determine the hardness; there are three main types of tests that differ by the indenter shape and how indentation size is measured; micro hardness testing is useful for measuring small parts, surface layers, and the hardness of individual micro-constituents.

1. Micro Hardness Testing

2. Micro Hardness Testing
• Forcing a diamond indenter of specific geometry into
the surface of the test piece with a load (1 to 50,000
gf).
• Three type of test: i) Knoop ii) vicker iii)ultrasonic.
• IN knoop and vicker, size of resulting un-recovered
indentation by using a microscope.
• Measured change in the frequency of a vibrating
diamond-tipped rod (no microscope).
• All these testing methods produce an indentation
depth of less than 19 micron.

3. Knoop indenter
Knoop indenter.
Highly polished,
rhombic-based
pyramidal diamond
that produces a
diamond shaped
indentation
Ratio between long and short diagonals of
about 7-1.The pyramid shape has an
angle, (longitudinal) 172-30, transverse
angle of 130-0.

4. Vickers indenter
• Vicker indenter.
• Highly polished
• pointed square base
• pyramidal diamond
• with face angles of 136

5. Vicker Indenter

6. Interesting information
• For same load the vicker indenter penetrates
about twice as far into the specimen as the
Knoop indenter.
• Therefore the vicker test is less sensitive to
minute differences in surface condition than
knoop test.

7. Difference in Knoop and vicker
The basic differences are:
• i) diamond indenter shape ii) Load
• Knoop indenter. Highly polished, rhombic-based
pyramidal diamond that produces a diamond shaped
indentation.
• Ratio between long and short diagonals of about 7-1.The
pyramid shape has an angle, (longitudinal) 172-
30, transvers angle of 130-0.
• Vicker indenter. Highly polished pointed square base
pyramidal diamond with face angles of 136.

8. Measuring the Indentation
A microscope in conjunction with the hardness tester
is used to determine the size of indentation. Proper
magnification is important for accurate
measurements. max---min
Indentation length (micron) Mag.( max---min) Less
then 76 measurement. 400
• 76-----------125 800---------300
• More then 125 600---------200
• The ends of indentation diagonals must be brought
into sharp focus.

9. Testing equipment
• Tester vary primarily in load range capabilities. (micro-
hardness to mac-rohardness)
• Most of them accommodate either the knoopor or vicker
indenters.
• Application of load by dead weight or by weights and a lever.
• Load from 1-10 gf are directly applied to the top of the
indenter.
• Application.
• Research and development, micro-constituents, small
parts, foil and wire ,hardened parts.

10. Specific Application
• Measuring hardness of too small work pieces.
• Measuring hardness close to edges
• Foil or wire too thin or too small
• Monitoring of carburising or nitriding
operations
• Hardness of individual constituents (micro)
• Measuring hardness of surface layers such as
plating etc.

11. Strength from Brinell Hardness
Steel:
Su = 3.45 HB (MPa)
Cast Iron:
Su = 5.35HB -500
(MPa)
Brass:
Su = 2.9HB + 50
(MPa)