Micro Vickers hardness test

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Micro Vickers hardness test

The Vickers hardness test was developed in 1924 by Smith and Sandland. The test evaluates

hardness in a manner similar to Brinell taking the ratio between the load applied and the surface

area of the resulting impression.

It was decided that the indenter shape should be one based on the following

To be capable of producing geometrically similar impressions, irrespective of size.

The resulting impression should have well defined points of measurement.

The indenter should have high resistance to self-deformation.

The Vickers hardness test method consists of indenting the test material with a diamond

indenter, in the form of a right pyramid with a square base and an angle of 136 degrees between

opposite faces subjected to a load of 1 to 100 kgf. The full load is normally applied for 10 to

15 seconds. The two diagonals of the indentation left in the surface of the material after removal

of the load are measured using a microscope and their average calculated. The area of the

sloping surface of the indentation is calculated. The Vickers hardness is the quotient obtained

by dividing the kgf load by the square mm area of indentation.

The corresponding units of HV are then kilograms-force per square millimetre (kgf/mm²). To

calculate Vickers hardness number using SI units one needs to convert the force applied from

kilogram-force to newtons by multiplying by 9.806 65 (standard gravity) and convert mm to

m. To do the calculation directly, the following equation can be used

HV = 𝐹

𝐴

1.8544𝐹

𝑑2

Where

F = applied load in gf

D = average of dia n mm

In micro Vickers hardness test a load of 1gf – 1000gf is applied.

Indenter

In this test diamond cone is used as indenter. As diamond has sharp edge so the dia of indenter

is easy to find due to sharp edge. Angle between the opposite faces of the indenter is 136o, and

use full angle is 120o.

Micro Vickers hardness test

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Figure 1 indenter and impression

Micro Vickers Test Method

All Vickers ranges use a 136° pyramidal diamond indenter that forms a square indent.

The indenter is pressed into the sample by an accurately controlled test force.

The force is maintained for a specific dwell time, normally 10 – 15 seconds.

After the dwell time is complete, the indenter is removed leaving an indent in the sample

that appears square shaped on the surface.

The size of the indent is determined optically by measuring the two diagonals of the

square indent.

The Vickers hardness number is a function of the test force divided by the surface area

of the indent. The average of the two diagonals is used in the following formula to

calculate the Vickers hardness

Calculation

Applied load = 1.961 N

Dwell time = 10 sec

First diagonal = d1= 48.78 µm

Second diagonal = d2=48.78 µm

Average = d = 48.78 µm

HV = 1528.26 N/mm2

Advantages

The major advantages of the Vickers test method are

Simple conducting of the test

Micro Vickers hardness test

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Can be used for an extremely broad hardness range

Independent of the hardness value of the test load in the macro range

Suitable for testing small parts, thin sheet material and layers

Can be used to test structural constituents

Determination of case hardening depth possible with the corresponding equipment

Disadvantages

The major disadvantages of the Vickers test method are

More time required for test surface preparation and the exact measurement of the test

impression

Diamond indenter susceptible to damage

Increasing susceptibility to shocks with decreasing test load

Shape deviation of indenter and test surface preparation influence the hardness result

with small test impressions

Micro Vickers hardness test

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References:

http://www.instron.us/wa/applications/test_types/hardness/vickers.aspx?ref=https://w

ww.google.com.pk/

http://www.instron.us/wa/applications/test_types/hardness/vickers.aspx?ref=https://w

ww.google.com.pk/

ASM metals handbook volume 8 mechanical testing and evaluation