1、Designation: B933 14Standard Test Method forMicroindentation Hardness of Powder Metallurgy (PM)Materials1This standard is issued under the fixed designation B933; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of the micro-indentation hardness of powder metallurgy (PM) materials.The test meth
3、od differs from the approach used for pore-freematerials in terms of the precautions required to deal with theporosity.1.2 A method for converting the directly measured indenta-tion lengths to other hardness scales, for example, HRC isdescribed in Appendix X1.1.3 This standard does not purport to ad
4、dress all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B243 Termino
5、logy of Powder MetallurgyE384 Test Method for Knoop and Vickers Hardness ofMaterialsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions of powder metallurgy (PM) terms can befound in Terminology B243. Additional descriptive in
6、forma-tion is available in the Related Materials section of Vol 02.05of the Annual Book of ASTM Standards.4. Summary of Test Method4.1 Microindentation hardness testing uses a calibratedmachine to force a pyramidal-pointed diamond indenter intothe surface of the test material under a known test load
7、. Themicroindentation hardness value is calculated from the indent-ing force divided by the projected area of the resultingindentation.NOTE 1This test method is designed specifically for use on porousPM materials. It is intended to be a companion to Test Method E384.There are specific differences th
8、at are intentional; otherwise, the details onequipment and procedures in Test Method E384 shall be adhered to. Thespecific differences relate to the presence of porosity in the PM materials.Special precautions are required during sample preparation to reveal poresand heterogeneous microstructural fe
9、atures so that appropriate test loca-tions may be selected.5. Significance and Use5.1 Microindentation hardness testing provides a measure ofthe hardness of the microstructural constituents of a porousmaterial. It indicates the hardness the material would have ifthere were no pores present and the m
10、aterial was tested usingmacroindentation hardness methods.5.2 Microindentation hardness tests allow the evaluation ofspecific phases, microstructural constituents, and regions orgradients too small for macroindentation hardness testing.6. Apparatus6.1 Microindentation Hardness Testing Machine, capab
11、le ofapplying the required load, equipped with a Knoop or Vickersindenter, and provision for measuring the length of the diago-nals of the indentation.6.2 Apparatus requirements are summarized in method TestMethod E384.7. Reagents and Materials7.1 Metallographic Etchants, suitable for the material b
12、eingtested.8. Test Specimen8.1 Specimen Mounting:8.1.1 Sample mounting is recommended for convenience insurface preparation, edge retention, and ease of testing. Thesample should be supported adequately in the mountingmedium.8.2 Specimen Preparation:1This test method is under the jurisdiction of AST
13、M Committee B09 on MetalPowders and Metal Powder Productsand is the direct responsibility of Subcommit-tee B09.05 on Structural Parts.Current edition approved April 1, 2014. Published April 2014. Originallyapproved in 2004. Last previous edition approved in 2009 as B93309. DOI:10.1520/B0933-14.2For
14、referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardC
15、opyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States18.2.1 Guidelines for grinding and polishing specimens areprovided in Appendix X2.8.2.2 Care should be taken to ensure that the true areafraction of porosity is revealed throughout the ent
16、ire crosssection of the specimen. It is essential in surface preparation toremove all smeared metal and to identify pores clearly so thatthey may be avoided during testing.8.2.3 The specimen should be lightly etched prior to micro-indentation hardness testing. Careful etching is necessary asheavy et
17、ching obscures features and interferes with the mea-surement of the diagonals of the indentation.8.2.4 For heat treated steels, swabbing with or immersion in2 % nital for 4 to 7 s gives an appropriate structure.9. Procedure9.1 Support the specimen so that its surface is perpendicularto the axis of t
18、he indenter.9.2 Select a suitable location for testing and an appropriateload and magnification for the test. A 100 gf load is recom-mended for hardened materials. Lower loads may be used forsofter materials or when small regions need to be tested. Forthe best precision, use the highest load compati
19、ble with thefeature to be tested. Magnification ranges for various indenta-tion lengths are as follows:Indentation Length(m)MagnificationMax Min125 600 2009.3 Apply the test load.9.4 Examine the indentation for possible sources of errorsuch as distorted or unusually large indentations. The twosectio
20、ns of each diagonal should agree within 20 % of eachother. Discard any distorted or unusually large indentations.Unusually large indentations sometimes occur due to thepresence of pores directly under the indentation.9.5 Measure the length of the diagonals of the indentation,taking care to avoid bac
21、klash by moving only in one direction.For Knoop microindentation hardness, read the length of thelarger diagonal to 0.1 m. For Vickers microindentationhardness, measure both diagonals to the nearest 0.1 m andcalculate the average.9.6 Make additional indentations. Space the indentations, sothat adjac
22、ent tests do not interfere with each other. Theminimum spacing between tests is illustrated in Fig. 1.10. Calculation or Interpretation of Results10.1 The Knoop or Vickers microindentation hardness num-bers may be calculated using the following formulae or byusing tables in Test Method E384.10.1.1 K
23、noopUsing the units of force and length com-monly employed, that is, for force P in gf, and a long diagonald in micrometres, the Knoop hardness is calculated:HK 5 14229 P/d210.1.2 VickersUsing the units of force and length com-monly employed, that is, for force P in gf, and the mean of thetwo diagon
24、als d in micrometres, the Vickers hardness iscalculated:HV 5 1854.4 P/d210.1.3 For indentation diagonals measured in millimetres,tables of HK and HV values are tabulated in Test Method E384.11. Report11.1 Report the following information:11.1.1 The identification of the sample and the location atwhi
25、ch the microindentation hardness was measured,11.1.2 The type of indenter, Knoop or Vickers,11.1.3 The magnification used,11.1.4 The identity, or description of the phase or micro-structural constituent measured,FIG. 1 Minimum Spacing Between IndentationsB933 14211.1.5 The type of etchant used, the
26、duration, and method ofetching, and11.1.6 The average of at least five acceptable measurementsshall be reported as the microindentation hardness of thematerial, microstructural constituent, or other feature mea-sured.11.1.7 Knoop (HK) or Vickers (HV) microindentation hard-ness shall be reported alon
27、g with the test load used, forexample, 400 HK 100 gf or 400 HV 100 gf. This is thepreferred method. However, an alternative method expressingthe load in kilograms force may be used in accordance withISO, for example, 400 HK 0.1 or 400 HV 0.1. Report HK andHV values to the nearest whole number.12. Pr
28、ecision and Bias12.1 The repeatability r and reproducibility R of measure-ments were determined in accordance with Practice E691.Members of the Powder Metallurgy Parts Association of theMetal Powder Industries Federation conducted the interlabo-ratory test program. The test sample was prepared from
29、heattreated FL-4605. One Knoop and oneVickers microindentationhardness indent was made in the surface of the test sample, andthese indentations were measured by 12 participating labora-tories.12.2 The mean Knoop microindentation hardness value was701 HK 100 gf with a repeatability of 22 and a reprod
30、ucibilityof 76. Duplicate microindentation hardness results from onelaboratory should not be considered suspect at the 95 %confidence level unless they differ by more than 22. For thesame test specimen, Knoop microindentation hardness resultsfrom two different laboratories should not be consideredsu
31、spect at the 95 % confidence level unless they differ by morethan 76.12.3 The mean Vickers microindentation hardness valuewas 716 HV 100 gf with a repeatability of 43 and a reproduc-ibility of 178. Duplicate microindentation hardness resultsfrom one laboratory should not be considered suspect at the
32、95 % confidence level unless they differ by more than 43. Forthe same test specimen, Vickers microindentation hardnessresults from two different laboratories should not be consideredsuspect at the 95 % confidence level unless they differ by morethan 178.13. Keywords13.1 Knoop microindentation hardne
33、ss; microindentationhardness; PM; powder metallurgy; Vickers microindentationhardnessAPPENDIXES(Nonmandatory Information)X1. CONVERSION TO OTHER HARDNESS SCALESX1.1 It is sometimes desired to express microindentationhardness values in terms of equivalents to other hardnessscales, for example, HRC. T
34、here is no direct conversion frommicroindentation hardness to HRC.Approximate values can beobtained through the procedure described in this appendix.X1.1.1 The following procedure describes a method forconversion to HRC.X1.1.2 Obtain four or five standard HRC test blocks thatspan the range from the
35、low 20s HRC to the 60s HRC.X1.1.3 Remove a small portion from each standard testblock, being careful to avoid any procedure that might affectthe hardness of the test block material, and make a metallo-graphic mount with the standardized face of the test block atthe surface of the mount.X1.1.4 Polish
36、 the specimens using standard procedures (seeAppendix X2).X1.1.5 Using either a Knoop or a Vickers indenter and a100 gf test load (other loads might be used for a conversion tohardness scales such as HRB or HRF), make five indentationsat various points in each of the standard specimens.X1.1.6 Measur
37、e the length of the diagonals of the indenta-tions.X1.1.7 Prepare a graph with the filar units, micrometres, orKnoop/Vickers microindentation hardness number on they-axis (ordinate) and HRC on the x-axis (abscissa). Plot allmeasured diagonals and, using regression analysis (regressionof y on x), con
38、struct a best-fit curve to the data points.X1.1.8 In future tests, take any diagonal reading and use thegraph to convert to HRC.NOTE X1.1The graph that is constructed applies to the specificinstrument used for the microindentation hardness test, the test load used,and the person performing the test.
39、 A separate graph needs to be plottedfor each operator, each test instrument, and for each load used formicroindentation hardness testing.X1.1.9 Precision of the Graphical Conversion:X1.1.9.1 Seven laboratories participated in an interlabora-tory study. Each laboratory developed a regression line fo
40、rtheir own instrument. The regression line was plotted based onthe results (six-reading averages) of measurements on fiveHRC standard test blocks with hardness ranging from 25.4HRC to 63.2 HRC. The seven laboratories found the hardnessof a circulated unknown sample to average 56.5 HRC.X1.1.9.2 With
41、this test method, 95 % of any future readingswould be expected to repeat in a laboratory within 4.0 HRCpoints at this level; for six-reading averages within 1.6 HRCpoints. For a laboratory to duplicate any of the otherlaboratories, 95 % of the readings should be within 5.3 HRC;for six-reading averag
42、es within 4.5 HRC.B933 143X2. SAMPLE PREPARATIONX2.1 The methods described in this appendix are provenpractices for metallographic preparation of porous PM materi-als for microindentation hardness testing. It is recognized thatother procedures or materials used in preparation of a samplemay be equal
43、ly as good and can be used on the basis ofavailability and preference of individual laboratories.X2.2 Method 1 :X2.2.1 The porous samples should be free of oil or coolant.Remove any oil using Soxhlet extraction. Mount and vacuumimpregnate samples with epoxy resin, to fill porosity and toprevent the
44、pickup of etchants. Use a sample cup or holder toform the mount. Pour epoxy resin over the sample in the cup toa total depth of about 0.75 in. (19 mm). Evacuate the cup tominus 26 in. of mercury (88 kPa) and hold at that pressure for10 min.Then restore ambient air pressure to force the resin intomos
45、t of the sample. Cure at room temperature or at 122 F(50 C).X2.2.2 Grind on 240, 400, and 600 grit wet SiC paper, on arotating wheel, and change the polishing direction 90 aftereach paper. Etch samples for 1 min in their normal etchant, forexample, 2 % nital, to begin to open the porosity. Roughpoli
46、shing for 8 to 12 min total on 1 m alumina (Al2O3), longnapped cloth (for example, Struers felt cloth), at 250 rpm, and300 gf load, using an automated polisher opens smeared pores.This rough polishing opens and exaggerates the pores. Toreturn the pores to their true area fraction, polish for 4 min a
47、t125 rpm on a shorter nap cloth (for example, Struers MOLcloth), with 1 m diamond paste. Final polishing is done for 20to 30 s using 0.05 m deagglomerated alumina, and a longnapped cloth (for example, Buehler Microcloth), at 125 rpm,and 75 gf load, on an automated polisher. Polishing may alsobe done
48、 by hand for the times indicated. The first twopolishings require moderate pressure and the final polishrequires light pressure.X2.2.3 The metallographic structure should be free ofsmeared porosity. Generally at 800 to 1000, the edge of asmeared over pore will appear as a thin gray line outlining on
49、eside of the pore, and occasionally outlining most of the pore.X2.2.4 The specimen should be etched prior to microinden-tation hardness testing. Careful etching is necessary becauseheavy etching obscures features and may interfere with themeasurement of the diagonals. For heat-treated steels, swab-bing with or immersion in 2 % nital for 4 to 7 s gives anappropriate structure. Martensite will be very light and thedarker etching non-martensitic transformation products such asupper bainite or fine pearlite will be evident by contrast.Materials with complex, multi-const
