ASTM B933-04
(Test Method)Standard Test Method for Microindentation Hardness of Powder Metallurgy (P/M) Materials
Standard Test Method for Microindentation Hardness of Powder Metallurgy (P/M) Materials
SIGNIFICANCE AND USE
Microindentation hardness testing provides a measure of the hardness of the microstructural constituents of a porous material. It indicates the hardness the material would have if there were no pores present and the material was tested using macroindentation hardness methods.
Microindentation hardness tests allow the evaluation of specific phases, microstructural constituents, and regions or gradients too small for macroindentation hardness testing.
SCOPE
1.1 This test method covers the determination of the microindentation hardness of powder metallurgy (P/M) materials. The test method differs from the approach used for pore-free materials in terms of the precautions required to deal with the porosity.
1.2 A method for converting the directly measured indentation lengths to other hardness scales, for example, HRC is described in Appendix X1.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:B933–04
Standard Test Method for
Microindentation Hardness of Powder Metallurgy (P/M)
Materials
This standard is issued under the fixed designation B 933; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope microindentation hardness value is calculated from the indent-
ing force divided by the projected area of the resulting
1.1 This test method covers the determination of the micro-
indentation.
indentation hardness of powder metallurgy (P/M) materials.
The test method differs from the approach used for pore-free
NOTE 1—This test method is designed specifically for use on porous
materials in terms of the precautions required to deal with the P/M materials. It is intended to be a companion to Test Method E 384.
There are specific differences that are intentional; otherwise, the details on
porosity.
equipment and procedures in Test Method E 384 shall be adhered to. The
1.2 Amethod for converting the directly measured indenta-
specific differences relate to the presence of porosity in the P/M materials.
tion lengths to other hardness scales, for example, HRC is
Specialprecautionsarerequiredduringsamplepreparationtorevealpores
described in Appendix X1.
and heterogeneous microstructural features so that appropriate test loca-
1.3 This standard does not purport to address all of the
tions may be selected.
safety concerns, if any, associated with its use. It is the
5. Significance and Use
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
5.1 Microindentationhardnesstestingprovidesameasureof
bility of regulatory limitations prior to use.
the hardness of the microstructural constituents of a porous
material. It indicates the hardness the material would have if
2. Referenced Documents
there were no pores present and the material was tested using
2.1 ASTM Standards:
macroindentation hardness methods.
B 243 Terminology of Powder Metallurgy
5.2 Microindentation hardness tests allow the evaluation of
E 384 Test Method for Microindentation Hardness of Ma-
specific phases, microstructural constituents, and regions or
terials
gradients too small for macroindentation hardness testing.
E 691 Practice for Conducting an Interlaboratory Study to
6. Apparatus
Determine the Precision of a Test Method
6.1 Microindentation Hardness Testing Machine, capable of
3. Terminology
applying the required load, equipped with a Knoop or Vickers
3.1 Definitions of powder metallurgy (P/M) terms can be
indenter, and provision for measuring the length of the diago-
found in Terminology B 243. Additional descriptive informa-
nals of the indentation.
tion is available in the Related Materials section of Vol 02.05
6.2 Apparatus requirements are summarized in method Test
of the Annual Book of ASTM Standards.
Method E 384.
4. Summary of Test Method
7. Reagents and Materials
4.1 Microindentation hardness testing uses a calibrated
7.1 Metallographic Etchants, suitable for the material being
machine to force a pyramidal-pointed diamond indenter into
tested.
the surface of the test material under a known test load. The
8. Test Specimen
8.1 Specimen Mounting:
This test method is under the jurisdiction of ASTM Committee B09 on Metal
8.1.1 Sample mounting is recommended for convenience in
PowderandMetalPowderProductsandisthedirectresponsibilityofSubcommittee
B09.05 on Structural Parts.
surface preparation, edge retention, and ease of testing. The
Current edition approved April 1, 2004. Published April 2004.
sample should be supported adequately in the mounting
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
medium.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
8.2 Specimen Preparation:
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B933–04
8.2.1 Guidelines for grinding and polishing specimens are Unusually large indentations sometimes occur due to the
provided in Appendix X2. presence of pores directly under the indentation.
8.2.2 Care should be taken to ensure that the true area
9.5 Measure the length of the diagonals of the indentation,
fraction of porosity is revealed throughout the entire cross
taking care to avoid backlash by moving only in one direction.
section of the specimen. It is essential in surface preparation to
For Knoop microindentation hardness, read the length of the
remove all smeared metal and to identify pores clearly so that
larger diagonal to 0.1 µm. For Vickers microindentation
they may be avoided during testing.
hardness, measure both diagonals to the nearest 0.1 µm and
8.2.3 The specimen should be lightly etched prior to micro-
calculate the average.
indentation hardness testing. Careful etching is necessary as
9.6 Make additional indentations. Space the indentations, so
heavy etching obscures features and interferes with the mea-
that adjacent tests do not interfere with each other. The
surement of the diagonals of the indentation.
minimum spacing between tests is illustrated in Fig. 1.
8.2.4 For heat treated steels, swabbing with or immersion in
9.7 Discardanyvalueifbyincludingthisvaluethehardness
2 % nital for 4 to 7 s gives an appropriate structure.
range of the other points is more than doubled. In all cases of
a discarded value, make a replacement.
9. Procedure
9.1 Support the specimen so that its surface is perpendicular
10. Calculation or Interpretation of Results
to the axis of the indenter.
10.1 TheKnooporVickersmicroindentationhardnessnum-
9.2 Select a suitable location for testing and an appropriate
bers may be calculated using the following formulae or by
load and magnification for the test. A 100 gf load is recom-
using tables in Test Method E 384.
mended for hardened materials. Lower loads may be used for
10.1.1 Knoop—Using the units of force and length com-
softer materials or when small regions need to be tested. For
monly employed, that is, for force P in gf, and a long diagonal
the best precision, use the highest load compatible with the
d in micrometres, the Knoop hardness is calculated:
feature to be tested. Magnification ranges for various indenta-
tion lengths are as follows:
HK 5 14229 P/d
Magnification
Indentation Length (µm)
10.1.2 Vickers—Using the units of force and length com-
Max Min
<76 . . . 400 monly employed, that is, for force P in gf, and the mean of the
76 to 125 800 300
two diagonals d in micrometres, the Vickers hardness is
>125 600 200
calculated:
9.3 Apply the test load.
HV 5 1854.4 P/d
9.4 Examine the indentation for possible sources of error
such as distorted or unusually large indentations. The two 10.1.3 For indentation diagonals measured in millimetres,
sections of each diagonal should agree within 20 % of each tables of HK and HV values are tabulated in Test Method
other. Discard any distorted or unusually large indentations. E 384.
FIG. 1 Minimum Spacing Between Indentations
B933–04
11. Report ratory test program. The test sample was prepared from heat
treatedFL-4605.OneKnoopandoneVickersmicroindentation
11.1 Report the following information:
hardnessindentwasmadeinthesurfaceofthetestsample,and
11.1.1 The identification of the sample and the location at
these indentations were measured by 12 participating labora-
which the microindentation hardness was measured,
tories.
11.1.2 The type of indenter, Knoop or Vickers,
12.2 The mean Knoop microindentation hardness value was
11.1.3 The magnification used,
701 HK 100 gf with a repeatability of 22 and a reproducibility
11.1.4 The identity, or description of the phase or micro-
of 76. Duplicate microindentation hardness results from one
structural constituent measured,
laboratory should not be considered suspect at the 95 %
11.1.5 Thetypeofetchantused,theduration,andmethodof
confidence level unless they differ by more than 22. For the
etching, and
same test specimen, Knoop microindentation hardness results
11.1.6 The average of at least five acceptable measurements
from two different laboratories should not be considered
shall be reported as the microindentation hardness of the
suspect at the 95 % confidence level unless they differ by more
material, microstructural constituent, or other feature mea-
than 76.
sured.
12.3 The mean Vickers microindentation hardness value
11.1.7 Knoop (HK) or Vickers (HV) microindentation hard-
was 716 HV 100 gf with a repeatability of 43 and a reproduc-
ness shall be reported along with the test load used, for
ibility of 178. Duplicate microindentation hardness results
example, 400 HK 100 gf or 400 HV 100 gf. This is the
from one laboratory should not be considered suspect at the
preferred method. However, an alternative method expressing
95 % confidence level unless they differ by more than 43. For
the load in kilograms force may be used in accordance with
the same test specimen, Vickers microindentation hardness
ISO, for example, 400 HK 0.1 or 400 HV 0.1. Report HK and
resultsfromtwodifferentlaboratoriesshouldnotbeconsidered
HV values to the nearest whole number.
suspect at the 95 % confidence level unless they differ by more
than 178.
12. Precision and Bias
13. Keywords
12.1 The repeatability r and reproducibility R of measure-
ments were determined in accordance with Practice E 691. 13.1 Knoop microindentation hardness; microindentation
Members of the Powder Metallurgy Parts Association of the hardness; P/M; powder metallurgy; Vickers microindentation
Metal Powder Industries Federation conducted the interlabo- hardness
APPENDIXES
(Nonmandatory Information)
X1. CONVERSION TO OTHER HARDNESS SCALES
X1.1 It is sometimes desired to express microindentation X1.1.7 Prepare a graph with the filar units, micrometres, or
hardness values in terms of equivalents to other hardness Knoop/Vickers microindentation hardness number on the
scales, for example, HRC. There is no direct conversion from y-axis (ordinate) and HRC on the x-axis (abscissa). Plot all
microindentationhardnesstoHRC.Approximatevaluescanbe measured diagonals and, using regression analysis (regression
obtained through the procedure described in this appendix. of y on x), construct a best-fit curve to the data points.
X1.1.8 In future tests, take any diagonal reading and use the
X1.1.1 The following procedure describes a method for
graph to convert to HRC.
conversion to HRC.
X1.1.2 Obtain four or five standard HRC test blocks that
NOTE X1.1—The graph that is constructed applies to the specific
span the range from the low 20’s HRC to the 60’s HRC.
instrument used for the microindentation hardness test, the test load used,
and the person performing the test. A separate graph needs to be plotted
X1.1.3 Remove a small portion from each standard test
for each operator, each test instrument, and for each load used for
block, being careful to avoid any procedure that might affect
microindentation hardness testing.
the hardness of the test block material, and make a metallo-
graphic mount with the standardized face of the test block at
X1.1.9 Precision of the Graphical Conversion:
the surface of the mount.
X1.1.9.1 Seven laboratories participated in an interlabora-
X1.1.4 Polish the specimens using standard procedures (see
tory study. Each laboratory developed a regression line for
Appendix X2).
their own instrument. The regression line was plotted based on
X1.1.5 Using either a Knoop or a Vickers indenter and a the results (six-reading averages) of measurements on five
100 gf test load (other loads might be used for a conversion to
HRC standard test blocks with hardness ranging from 25.4
hardness scales such as HRB or HRF), make five indentations HRC to 63.2 HRC. The seven laboratories found the hardness
at various points in each of the standard specimens.
of a circulated unknown sample to average 56.5 HRC.
X1.1.6 Measure the length of the diagonals of the indenta- X1.1.9.2 With this test method, 95 % of any future readings
tions. would be expected to repeat in a laboratory within 4.0 HRC
B933–04
points at this level; for six-reading averages within 1.6 HRC ries, 95 % of the readings should be within 5.3 HRC; for
points. For a laboratory to duplicate any of the other laborato- six-reading averages within 2.2 HRC.
X2. SAMPLE PREPARATION
X2.1 The methods described in this appendix are proven specimen may require sectioning to provide a workable speci-
practices for metallographic preparation of porous P/M mate- men.Sectioningmaybemadeemployingahacksaw,bandsaw,
rialsformicroindentationhardnesstesting.Itisrecognizedthat abrasive, or diamond wheel. A hacksaw is sufficient for soft
other procedures or materials used in preparation of a sample materials. However, if harder materials are of interest, then an
may be equally as good and can be used on the basis of abrasive or diamond wheel may be required.
availability and preference of individual laboratories. X2.3.2 Heat should be avoided to prevent occurrence of
possiblechangesinmicrostructure.Ifslowfeedsareemployed,
X2.2 Method 1:
a coolant may not be necessary to avoid temperature build-ups.
X2.2.1 The porous samples should be free of oil or coolant.
Ifabrasivewheelsareused,thenacoolantisoftennecessaryto
Remove any oil using Soxhlet extraction. Mount and vacuum
avoid overheating of the specimen.
impregnate samples with epoxy resin, to fill porosity and to
X2.3.3 If a coolant is employed, it may be retained within
prevent the pickup of etchants. Use a sample cup or holder to
the pores. The lubricant must be removed prior to the prepa-
form the mount. Pour epoxy resin over the sample in the cup to
ration of the specimen for examination. This may be accom-
a total depth of about 0.75 in. (19 mm). Evacuate the cup to
plished by using a Soxhlet extractor or an ultrasonic cleaner.
minus 26 in. of mercury (88 kPa) and hold at that pressure for
The extraction condenser is the most efficient and the least
10min.Thenrestoreambientairpressuretoforcetheresininto
expensive.
most of the sample. Cure at room temperature or at 122°F
X2.3.4 Generally, specimens to be evaluated for microin-
(50°C).
dentation hardness are mounted to provide edge retention.
X2.2.2 Grind on 240, 400, and 600 grit wet SiC paper, on a
There are many kinds of mounting compounds available. Most
rotating wheel, and change the polishing direction 90° after
common materials include ep
...
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