Vicker test

Standard Test Method for
Vickers Hardness of Materials
E92-82(reapproved 1997)
BY:-
NAMAN SONI(12BME051)
NIMESH SUTHAR(12BME052)
ABHISHEK THAKKAR(12BME53)
NAISHAL THAKKAR(12BME054)
ADITYA VAGHASIYA(12BME55)

Scope
This test method covers the determination of the
Vickers hardness of metallic materials, using applied
loads of 1 kgf to 120 kgf, the verification of Vickers
hardness testing machines, and the calibration of
standardized hardness test blocks.
Two general classes of standard tests are recognized :
 Verification, Laboratory or Referee Tests.
 Routine Tests.

Reference Documents
ASTM Standards:
 E 4 Practices for Force Verification Testing Machines.
 E 140 Hardness Conversion Tables for Metals
(Relationship between Brinell Hardness, Vickers
Hardness Rockwell Hardness, Rockwell Superficial
Hardness, Knoop Hardness and Seleroscope Hardness).
 E 384 Test Method for Microhardness of Materials.

Terminology
Vickers hardness number, HV – a number related to
the applied load and the surface area of the permanent
impression made by a square-based pyramidal
diamond indenter having included face angles of 136°
can be calculated by :
 HV = 2P sin (α/2)/d2 =1.8544P/d2

Formula
HV = 2P sin (α/2)/d2 =1.8544P/d2
Where:
P = load, kgf
d = mean diagonal of impression, mm
α = face angle of diamond = 136°

Terminology
Vickers hardness test – an indentation hardness test
using calibrated machines to force a square-based
pyramidal diamond indenter having specified face
angles, under a pre-determined load, into the surface
of the material under test and to measure the
diagonals of the resulting impression after removal of
the load.
VH test are made at test loads of 1 kgf to 120 kgf.

Contd…
For practical purposes the Vickers hardness number is
constant when a square-based diamond pyramid with
a face angle of 136° is used with applied loads of 5 kgf
and higher.
At lower test loads Vickers hardness numbers may be
load dependent.
In table 2 the Vickers hardness numbers for a test load
of 1kgf are given.

Contd…
For obtaining hardness numbers when other test loads
are used, the Vickers hardness number obtained from
table 2 is multiplied by the test load in kilograms-
force.

Using table 3 determine:
HV = 4.47 at 0.644 mm
diagonal length
at 1kgf load.
50*4.47 = 224 HV
for 50 kg test load

A)GENERAL DESCRIPTION & TEST PROCEDURE
 Apparatus
 Test specimen
 Verification of apparatus
 Procedure
 Measurement of Impression
 Accuracy
 Conversion to other Hardness scales or tensile strength
values
 Report
 Precision and Bias

1)APPARATUS
A. Testing machine:-
supports the specimen.
Permits the indenter and the specimen to be brought
into contact gradually and smoothly under a
predetermined load,which is applied for a fixed period
of time.
 Design should be such that no rocking or lateral
movement of indenter or specimen is permitted while
load is applied or removed
 Measuring microscope is usually mounted in such a
manner that the impression in the specimen may be
readily located in the optical field.

B. Indenter:-
Should be Highly polished, pointed, square-based
pyramidal diamond with face angles of 136 ̊± 30min.
All four faces shall be equally inclined to the axis of the
indenter(within ±30min) and meet at sharp point , i.e.
the line of junction between opposite faces shall not be
more than 0.001 mm in length.
It should be examined periodically and if it is loose in
the mounting material, chipped or cracked,it should be
discarded or reconditioned.

 NOTE:-
Point of the indenter is of considerable importance
where the test load is light and the impression is small.
It should be periodically checked by examining an
impression made in a polished steel block, under a
magnification of 600× or more, using a vertical
illuminator ,and extent of defect is measured with a
filar micrometer. Diamond pyramid indenter should
not be used for tests in which the maximum length of
such a defect exceeds 5% of the length of the
impression diagonal

C. Measuring Microscope:-
 Divisions of micrometer scale of measuring
microscope shall be so constructed that the length of
the diagonals of an impression in a properly surface
finished specimen can be measued to within
±0.0005 mm or ±0.5% , whichever is larger.

2)TEST SPECIMENS
A. Thickness:-
 It should be at least one and half times the length of
the diagonal of an indenter. It should be such that,no
bulge or marking showing the effect of the load
appears on the side of the specimen opposite the
impression.
B. Finish:-
 It should be so prepared that the ends of the
diagonals are clearly defined and can be read with
precision of ±0.0005 mm or ±0.5% of the length of
the diagonals , whichever is larger.

C. Alignment:-
 Surface of specimen should be normal to the axis of
the indenter within ±1 ̊of angle. Opposite side
should be parallel upto maximum extent.
D. Radius of curvature:-
 It is a special case for spherical and cylindrical
surfaces. Correction factor must be applied to the
vicker hardness values obtained. Correction factor
are given in standard table corresponding to the
ratio of mean diagonal ‘d’ of indentation to the
diameter ‘D’ of the sphere or cylinder .

Example:
Diameter of sphere, D = 10 mm
Load =10 kgf
Mean diagonal of impression, d =0.150 mm
d/D = 0.150 / 10 = 0.015
From Tables 2 and 3 , HV= 824
From Table 4, correction factor = 0.983
Hardness of sphere = 824 * 0.983 =810 HV 10

3)VERIFICATION OF APPARATUS
 TWO METHODS:
Separate verification of load application , indenter ,
measuring microscope.
Verification by standardized test block method.

4)PROCEDURE
A. Magnitude of Test Load:-
 Test load of 1 kgf to 120 kgf may be used, depending
upon the requirements of the test. Tests on
homogeneous materials indicate that the Vickers
hardness number is nearly independent of the test
load, but this condition will not be present in cases
where there is a hardness gradient from the
specimen surface to the interior of the specimen.
Therefore magnitude of the test load should be
stated in the test report.

B. Application of Test load:-
 The time of application of the full test load shall be
10 to 15 sec. , unless otherwise specified.
 It should be applied and released smoothly without
shock or vibration.
C. Spacing of Indentation:-
 It should not be closer to any edge of the test
specimen or to another impression than a distance
equal to two and half times the length of diagonal of
the impression.

5)MEASUREMENT OF IMPRESSION
Both diagonals of the impression shall be measured
and their mean value is used as a basis for calculation
of the vicker hardness number.
In case of anisotropic materials ,such as heavily cold
worked , there may be a difference between the
lengths of the diagonals.In such cases,test specimen
should be reoriented so that the diagonals of a new
impression are approximately of equal length.

6)ACCURACY
It depends upon accuracy of test load , indenter ,
measuring device , support surface etc.
Under optimum condition of these factors the
accuracy that can be expected is equivalent of 4% of
the vicker hardness number of the standardized
reference hardness test blocks.

7) CONVERSION TO OTHER HARDNESS
SCALES OR TENSILE STRENGTH VALUES

8)REPORT
It shall include:-
The Vicker Hardness number,
The test load used,
The loading time , if other than 10 to 15 seconds.
9)PRECISION AND BIAS
Due to wide variety of materials tested by this method
and the possible variations in test specimens, the
precision of this method has not been established.
Generally it can be established by employing statistical
methods.

B) VERIFICATION OF VICKERS
HARDNESS TESTING MACHINE

1)SCOPE
• This part covers the procedure for verification of
Vickers Hardness Testing Machine and the procedure
that is recommended for use to confirm that the
machine is not properly adjusted in the intervals
between periodical routine check.
 The two methods are:
1. Separate Verification of Force Application,
Indenter, and Measuring Microscope which is
used for new and rebuilt machines.
2. Vertification by Standardized Test Block Method
which is used for verifying machines in service.

2)GENERAL REQUIREMENTS
• Before a Vickers hardness testing machine is verified the
machine shall be examined to ensure that
The machine is properly set up.
The indenter holder is mounted normally in the plunger.
 The force can be applied and removed without shock or
vibration in such a manner that the readings are not
influenced.

contd....
If the measuring device is integral with the machine, the
machine shall be examined to ensure that the change from
loading to measuring does not influence the readings.
 The method of illumination does not affect the readings.
The center of the impression is in the center of the field of
view.

3)VERIFICATION
A. Force Application
The applied force shall be checked by the use of dead
weights and proving levers, or by an elastic calibration
device .
Vickers hardness testing machines shall be verified at a
minimum of three applied forces including the test force
specified.
 A minimum of three readings should be taken at each
force. A Vickers hardness testing machine is acceptable
for use over a loading range within which the machine
error does not exceed + 1 %.

contd.....
B. Measuring Microscope
The measuring microscope or other device for measuring
the diagonals of the impression shall be calibrated against
an accurately ruled line scale.
 The errors of the line scale shall not exceed 0.05 μm
(0.00005 mm) or 0.05 % of any interval, whichever is
greater.
The measuring microscope shall be calibrated throughout
its range of use and a calibration factor chosen such that the
error shall not exceed + 0.5 %.

C. Verification by Standardized Test Block Method
A Vickers hardness testing machine used only for routine
testing may be checked by making a series of impressions on
standardized hardness test blocks.
A minimum of five Vickers hardness reading shall be taken
on at least three blocks having different levels of hardness
using a test force or forces as specified by the user with the
test force applied for 12 s.

4)PROCEDURE OF
PERIODIC CHECKS BY THE USER
Make at least one routine check each day that the testing
machine is used.
 Before making the check, verify that the zero reading of the
measuring apparatus is correctly adjusted.
Make at least five hardness readings on a standardized
hardness test block on the scale and at the hardness level at
which the machine is being used.
If the values fall within the range of the standardized
hardness test block the machine may be regarded as
satisfactory; if not the machine should be verified by the
Standardised Block Method

5)REPEATABILITY AND ERROR
Repeatability
For each standardized block, let d1, d2, ··· d5 be the
arithmetic means of the two diagonals of the indentations,
arranged in increasing order of magnitude.
The repeatability of the machine under the particular
verification conditions is expressed by the quantity d5 − d1.
Error
The error of the machine under the particular verification
conditions is expressed by the quantity d’ − d, where d’= (d1 +
d2 + ··· d5)/5, and d is the reported mean diagonal of
impressions on the standardized hardness test block.

6)ASSESSMENT OF VERIFICATION
Repeatability
The repeatability of the machine verified is considered
satisfactory if it satisfies the conditions givenin Table 7.
Error
The mean diagonal for five impressions should not differ
from the mean diagonal corresponding to the Vickers
hardness of the standardized test block by more than 2 %
or 0.5 μm (0.0005 mm), whichever is greater.

C. CALIBRATION OF STANDARD
HARDNESS TEST BLOCKS FOR
VICKERS HARDNESS MACHINES

1)SCOPE
 This part covers the calibration of standardized
hardness test blocks for the verification of Vickers
Hardness Test machines as described in previous
parts.

2)MANUFACTURE
 Each metal block that is to be standardized should not
be less than 0.25 inch in thickness.
 Each block should be specially prepared and heated to
give the necessary homogeneity and stability of
structure.
 If the block is of steel, it should be demagnetized from
manufacturer and also mantained by user.
 The lower surface of the test block shall have a fine
ground finish.

 The test surface should be polished and free of
scratches which would interfere with measurements of
the diagonals of the impression.
 The mean surface roughness height rating should not
exceed 4 micro inch center line average.
 To ensure that no material is subsequently removed
from the test surface of the standardized test block, an
official mark of the thickness at the time of calibration
shall be marked on the test surface to an accuracy of ---
-0.005 to +0.005 inch.

3)STANDARDIZING PROCEDURE
 The standardized hadness test blocks shall be calibrated on
a Vickers hardness testing machine as per the requirements
of described in previous part ie.separate Verification of Force
Application, Indenter, and Measuring Microscope
 The control mechanism of Application of Load should be
of two type
1. A device such as spring to reduce velocity of
indentation
2. A device that can maintain a constant velocity of
indentation
 The full load shall be applied for 12 seconds.

4)NUMBER OF INDENTATIONS
 Preferably ten randomly distributed indentations shall
be made on each test block.
 If not possible, atleast five indentations shall be made.

5)MEASUREMENT OF THE
DIAGONAL OF THE INDENTATION
The illuminating system of the measuring microscope
shall be adjusted to give uniform intensity over the
field of view and maximum contrast between the
indentation and the undistributed surface of the block.
The Measuring microscope shall be graduated to read
0.001mm with estimates made to nearest ± 0.0002mm.
The Measuring microscope shall be checked by a stage
micrometer , or by other suitable means , to ensure
that the difference between reading corresponding to
any two division of the instrument is correct within
± 0.0005mm.
Indentation should be measured by two observers.

6)REPEATABILITY
 Let be the mean values of the
measured diagonals arranged in increasing order of
magnitude.
 Repetability is defined as for Ten readings or
for Five reading.

7)UNIFORMITY OF THE HARDNESS
 The repetability of hardness readings as measured by
mean of five-ten impressions should be within limits
as given in Table.
 Unless repetability is within limits , the block cannot
be regarded as sufficently uniform for standardization
purposes.

8)MARKING
After determining Hardness of the material , each block
should be marked with the following :
Arithmetic mean of the hardness values found in
standardization test.
 The name or mark of the supplier.
 Serial number of the block.
 Thickness of the test block or and official mark on the top
surface.
 All of the markings except the official mark or the
thickness should be placed on the side of the block , the
marking being upright when the test surface is the upper
face.

Vicker test

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Vicker test