1、Designation: B933 14B933 16Standard 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 l
2、ast revision. 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 microindentation hardness of powder metallurgy (PM) materials. The te
3、stmethod differs from the approach used for pore-free materials in terms of the precautions required to deal with the porosity.1.2 This procedure covers tests made with the Knoop or Vickers indenters under loads in the range from 1 to 200 gf.1.3 Automated testing is not generally suitable for use wi
4、th porous PM materials, because acceptable indentations requireavoiding placing indentations in the immediate vicinity of a pore, a condition not guaranteed with automated placement of theindentations. Any automated testing shall allow for review of indentations post-test to reject any distorted or
5、unusually largeindentations in accordance with 9.4.1.4 A method for converting the directly measured indentation lengths to other hardness scales, for example, HRC is describedin Appendix X1.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It
6、 is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B243 Terminology of Powder MetallurgyE384 Test Method for Microindentation Hardness
7、 of MaterialsE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method3. Terminology3.1 Definitions of powder metallurgy (PM) terms can be found in Terminology B243. Additional descriptive information isavailable in the Related Materials section of Vol 02.05 o
8、f the Annual Book of ASTM Standards.4. Summary of Test Method4.1 Microindentation hardness testing uses a calibrated machine to force a pyramidal-pointed diamond indenter into the surfaceof the test material under a known test load. The microindentation hardness value is calculated from the indentin
9、g force dividedby the projected area of the resulting indentation.NOTE 1This test method is designed specifically for use on porous PM materials. It is intended to be a companion to Test Method E384. There arespecific differences that are intentional; intentional such as restricting the applied load
10、 to a maximum of 200 gf; otherwise, the details on equipment andprocedures in Test Method E384 shall be adhered to. The specific differences relate to the presence of porosity in the PM materials. Special precautionsare required during sample preparation to reveal pores and heterogeneous microstruct
11、ural features so that appropriate test locations may be selected.5. Significance and Use5.1 Microindentation hardness testing provides a measure of the hardness of the microstructural constituents of a porousmaterial. It indicates the hardness the material would have if there were no pores present a
12、nd the material was tested usingmacroindentation hardness methods. Loads are limited to a maximum of 200 gf to reduce the likelihood of interference from theporosity.1 This test method is under the jurisdiction ofASTM Committee B09 on Metal Powders and Metal Powder Products and is the direct respons
13、ibility of Subcommittee B09.05on Structural Parts.Current edition approved April 1, 2014April 1, 2016. Published April 2014April 2016. Originally approved in 2004. Last previous edition approved in 20092014 asB93309. DOI: 10.1520/B0933-14. 14. DOI: 10.1520/B0933-16.2 For referencedASTM standards, vi
14、sit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standardsstandards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an A
15、STM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as publishe
16、d by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.2 Microindentation hardness tests allow the evaluation of specific
17、phases, microstructural constituents, and regions orgradients too small for macroindentation hardness testing.6. Apparatus6.1 Microindentation Hardness Testing Machine, capable of applying the required load, equipped with a Knoop or Vickersindenter, and provision for measuring the length of the diag
18、onals of the indentation.6.2 Apparatus requirements are summarized in method Test Method E384.7. Reagents and Materials7.1 Metallographic Etchants, suitable for the material being tested.8. Test Specimen8.1 Specimen Mounting:8.1.1 Sample mounting is recommended for convenience in surface preparation
19、, edge retention, and ease of testing. The sampleshould be supported adequately in the mounting medium.8.2 Specimen Preparation:8.2.1 Guidelines for grinding and polishing specimens are provided in Appendix X2.8.2.2 Care should be taken to ensure that the true area fraction of porosity is revealed t
20、hroughout the entire cross section of thespecimen. It is essential in surface preparation to remove all smeared metal and to identify pores clearly so that they may beavoided during testing.8.2.3 The specimen should be lightly etched prior to microindentation hardness testing. Careful etching is nec
21、essary as heavyetching obscures features and interferes with the measurement of the diagonals of the indentation.8.2.4 For heat treated steels, swabbing with or immersion in 2 % nital for 4 to 7 s gives an appropriate structure.9. Procedure9.1 Support the specimen so that its surface is perpendicula
22、r to the axis of the indenter.9.2 Select a suitable location for testing and an appropriate load and magnification for the test. A 100 gf load is recommendedfor hardened materials. Lower loads may be used for softer materials or when small regions need to be tested. For the bestprecision, use the hi
23、ghest load compatible with the feature to be tested. Magnification ranges for various indentation lengths areas follows:Indentation Length(m)MagnificationMax Min125 600 2009.3 Apply the test load.9.4 Examine the indentation for possible sources of error such as distorted or unusually large indentati
24、ons. The two sections ofeach diagonal should agree within 20 % of each other. Discard any distorted or unusually large indentations. Unusually largeindentations sometimes occur due to the presence of pores directly under the indentation.9.5 Measure the length of the diagonals of the indentation, tak
25、ing care to avoid backlash by moving only in one direction. ForKnoop microindentation hardness, read the length of the larger diagonal to 0.1 m. ForVickers microindentation hardness, measureboth diagonals to the nearest 0.1 m and calculate the average.9.6 Make additional indentations. Space the inde
26、ntations, so that adjacent tests do not interfere with each other. The minimumspacing between tests is illustrated in Fig. 1.10. Calculation or Interpretation of Results10.1 The Knoop or Vickers microindentation hardness numbers may be calculated using the following formulae or by usingtables in Tes
27、t Method E384.10.1.1 KnoopUsing the units of force and length commonly employed, that is, for force P in gf, and a long diagonal d inmicrometres, the Knoop hardness is calculated:HK514229 P/d210.1.2 VickersUsing the units of force and length commonly employed, that is, for force P in gf, and the mea
28、n of the twodiagonals d in micrometres, the Vickers hardness is calculated:HV51854.4 P/d210.1.3 For indentation diagonals measured in millimetres, tables of HK and HV values are tabulated in Test Method E384.B933 16211. Report11.1 Report the following information:11.1.1 The identification of the sam
29、ple and the location at which the microindentation hardness was measured,11.1.2 The type of indenter, Knoop or Vickers, and the load used,11.1.3 The magnification used,11.1.4 The identity, or description of the phase or microstructural constituent measured,11.1.5 The type of etchant used, the durati
30、on, and method of etching, and11.1.6 The average of at least five acceptable measurements shall be reported as the microindentation hardness of the material,microstructural constituent, or other feature measured.11.1.7 Knoop (HK) or Vickers (HV) microindentation hardness shall be reported along with
31、 the test load used, for example, 400HK 100 gf or 400 HV 100 gf. This is the preferred method. However, an alternative method expressing the load in kilograms forcemay be used in accordance with ISO, for example, 400 HK 0.1 or 400 HV 0.1. Report HK and HV values to the nearest wholenumber.12. Precis
32、ion and Bias12.1 The repeatability r and reproducibility R of measurements were determined in accordance with Practice E691. Membersof the Powder Metallurgy PartsAssociation of the Metal Powder Industries Federation conducted the interlaboratory test program.The test sample was prepared from heat tr
33、eated FL-4605. One Knoop and one Vickers microindentation hardness indent was madein the surface of the test sample, and these indentations were measured by 12 participating laboratories.12.2 The mean Knoop microindentation hardness value was 701 HK 100 gf with a repeatability of 22 and a reproducib
34、ility of76. Duplicate microindentation hardness results from one laboratory should not be considered suspect at the 95 % confidence levelunless they differ by more than 22. For the same test specimen, Knoop microindentation hardness results from two differentlaboratories should not be considered sus
35、pect at the 95 % confidence level unless they differ by more than 76.12.3 The mean Vickers microindentation hardness value was 716 HV 100 gf with a repeatability of 43 and a reproducibility of178. Duplicate microindentation hardness results from one laboratory should not be considered suspect at the
36、 95 % confidencelevel unless they differ by more than 43. For the same test specimen, Vickers microindentation hardness results from two differentlaboratories should not be considered suspect at the 95 % confidence level unless they differ by more than 178.13. Keywords13.1 Knoop microindentation har
37、dness; microindentation hardness; PM; powder metallurgy; Vickers microindentation hardnessFIG. 1 Minimum Spacing Between IndentationsB933 163APPENDIXES(Nonmandatory Information)X1. CONVERSION TO OTHER HARDNESS SCALESX1.1 It is sometimes desired to express microindentation hardness values in terms of
38、 equivalents to other hardness scales, forexample, HRC. There is no direct conversion from microindentation hardness to HRC. Approximate values can be obtainedthrough the procedure described in this appendix.X1.1.1 The following procedure describes a method for conversion to HRC.X1.1.2 Obtain four o
39、r five standard HRC test blocks that span the range from the low 20s HRC to the 60s HRC.X1.1.3 Remove a small portion from each standard test block, being careful to avoid any procedure that might affect the hardnessof the test block material, and make a metallographic mount with the standardized fa
40、ce of the test block at the surface of the mount.X1.1.4 Polish the specimens using standard procedures (see Appendix 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 to hardness scales such as HRB or HRF), make five indentations
41、atvarious points in each of the standard specimens.X1.1.6 Measure the length of the diagonals of the indentations.X1.1.7 Prepare a graph with the filar units, micrometres, or Knoop/Vickers microindentation hardness number on the y-axis(ordinate) and HRC on the x-axis (abscissa). Plot all measured di
42、agonals and, using regression analysis (regression 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 graph to convert to HRC.NOTE X1.1The graph that is constructed applies to the specific instrument used for the microindentation ha
43、rdness test, the test load used, and the personperforming the test. A separate graph needs to be plotted for each operator, each test instrument, and for each load used for microindentation hardnesstesting.X1.1.9 Precision of the Graphical Conversion:X1.1.9.1 Seven laboratories participated in an in
44、terlaboratory study. Each laboratory developed a regression line for their owninstrument. The regression line was plotted based on the results (six-reading averages) of measurements on five HRC standard testblocks with hardness ranging from 25.4 HRC to 63.2 HRC. The seven laboratories found the hard
45、ness of a circulated unknownsample to average 56.5 HRC.X1.1.9.2 With this test method, 95 % of any future readings would be expected to repeat in a laboratory within 4.0 HRC pointsat this level; for six-reading averages within 1.6 HRC points. For a laboratory to duplicate any of the other laboratori
46、es, 95 % ofthe readings should be within 5.3 HRC; for six-reading averages within 4.5 HRC.B933 164X2. SAMPLE PREPARATIONX2.1 The methods described in this appendix are proven practices for metallographic preparation of porous PM materials formicroindentation hardness testing. It is recognized that o
47、ther procedures or materials used in preparation of a sample may beequally as good and can be used on the basis of availability 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 vacuu
48、mimpregnate samples with epoxy resin, to fill porosity and to prevent the pickup of etchants. Use a sample cup or holder to formthe mount. Pour epoxy resin over the sample in the cup to a total depth of about 0.75 in. (19 mm). Evacuate the cup to minus 26in. of mercury (88 kPa) and hold at that pres
49、sure for 10 min. Then restore ambient air pressure to force the resin into most of thesample. Cure at room temperature or at 122 F (50 C).X2.2.2 Grind on 240, 400, and 600 grit wet SiC paper, on a rotating wheel, and change the polishing direction 90 after each paper.Etch samples for 1 min in their normal etchant, for example, 2 % nital, to begin to open the porosity. Rough polishing for 8 to 12min total on 1 m alumina (Al2O3), long napped cloth (for example, Struers felt cloth), at 250 rpm, and 300 gf load, using anautomated polisher opens smeared pores. This r
