1、Designation: C 1326 03Standard Test Method forKnoop Indentation Hardness of Advanced Ceramics1This standard is issued under the fixed designation C 1326; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A
2、number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the Knoopindentation hardness of advanced ceramics.1.2 This standard does not purport to
3、address 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:2C 730 Test
4、 Method for Knoop Indentation Hardness ofGlassC 849 Test Method for Knoop Indentation Hardness ofCeramic WhitewaresE 4 Practices for Force Verification of Testing MachinesE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 380 Practice for Use of the International System of U
5、nits(SI) (the Modernized Metric System)E 384 Test Method for Microhardness of MaterialsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 European Standard:CEN ENV 843-4 Advanced Technical Ceramics, Mono-lithic Ceramics, Mechanical Properties at Room
6、 Tempera-ture, Part 4: Vickers, Knoop, and Rockwell SuperficialHardness Tests32.3 ISO Standard:ISO 9385 Glass and Glass CeramicsKnoop HardnessTest43. Terminology3.1 Definition:3.1.1 Knoop hardness number (HK), nan expression ofhardness obtained by dividing the force applied to the Knoopindenter by t
7、he projected area of the permanent impressionmade by the indenter.3.1.2 Knoop indenter, na rhombic-based pyramidal-shaped diamond indenter with edge angles of 172 308 and130 008.4. Summary of Test Method4.1 This test method describes an indentation hardness testusing a calibrated machine to force a
8、pointed, rhombic base,pyramidal diamond indenter having specified face angles,under a predetermined load, into the surface of the materialunder test and measures the surface projection of the longdiagonal of the resulting impression after removal of the load.NOTE 1A general description of the Knoop
9、indentation hardness testis given in Test Method E 384. The present test method differs from thisdescription only in areas required by the special nature of advancedceramics.NOTE 2This test method is similar to Test Methods C 730 and C 849,but differs primarily in the choice of load and the rate of
10、loading. Inaddition, the length correction factor for the resolution limits of opticalmicroscopes is not utilized.5. Significance and Use5.1 For advanced ceramics, Knoop indenters are used tocreate indentations. The surface projection of the long diagonalis measured with optical microscopes.5.2 The
11、Knoop indentation hardness is one of many prop-erties that is used to characterize advanced ceramics. Attemptshave been made to relate Knoop indentation hardness to otherhardness scales, but no generally accepted methods are avail-able. Such conversions are limited in scope and should be usedwith ca
12、ution, except for special cases where a reliable basis forthe conversion has been obtained by comparison tests.5.3 For advanced ceramics, the Knoop indentation is oftenpreferred to the Vickers indentation since the Knoop longdiagonal length is 2.8 times longer than the Vickers diagonalfor the same l
13、oad, and cracking is much less of a problem (1).5On the other hand, the long slender tip of the Knoop indenta-tion is more difficult to precisely discern, especially in mate-rials with low contrast. The indentation loads chosen in this test1This test method is under the jurisdiction of ASTM Committe
14、e C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.01 onProperties and Performance.Current edition approved October 1, 2003. Published November 2003. Originallyapproved in 1996. Last previous edition approved in 1999 as C 1326 99.2For referenced ASTM standards, visit the
15、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.3Available from European Committee for Standardization, Brussels, Belgium.4Available from International
16、 Standards Organization, Geneva, Switzerland.5The boldface numbers in parentheses refer to the list of references at the end ofthis test method.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.method are designed to produce indentatio
17、ns as large as may bepossible with conventional microhardness equipment, yet notso large as to cause cracking.5.4 The Knoop indentation is shallower than Vickers inden-tations made at the same load. Knoop indents may be useful inevaluating coating hardnesses.5.5 Knoop hardness is calculated from the
18、 ratio of theapplied load divided by the projected indentation area on thespecimen surface. It is assumed that the elastic springback ofthe narrow diagonal is negligible. (Vickers indenters are alsoused to measure hardness, but Vickers hardness is calculatedfrom the ratio of applied load to the area
19、 of contact of the fourfaces of the undeformed indenter.)5.6 A full hardness characterization includes measurementsover a broad range of indentation loads. Knoop hardness ofceramics usually decreases with increasing indentation size orindentation force (load). The trend is known as the indentationsi
20、ze effect (ISE). Hardness approaches a plateau constanthardness at sufficiently large indentation size or forces (loads).The test forces or loads that are needed to achieve a constanthardness vary with the ceramic. The test force specified in thisstandard is intended to be sufficiently large that ha
21、rdness iseither close to or on the plateau, but not so large as to introduceexcessive cracking. A comprehensive characterization of theISE is recommended but is beyond the scope of this testmethod which measures hardness at a single, designated load.6. Interferences6.1 Cracking from the indentation
22、tips can interfere withinterpretation of the exact tip location. The loads chosen forthis test method are sufficiently low that tip cracking, if itoccurs, will cause tiny, rather tight cracks at the indentation tipsin advanced ceramics. Such cracks will have a negligibleinterference on measurements
23、of the long diagonal length (2)(unlike Vickers indentations in ceramics).6.2 Cracking or spalling from the sides of the Knoopimpression may also occur, possibly in a time-dependentmanner (minutes or hours) after the impression is made. Smallamounts of such lateral cracking have little or no influenc
24、eupon measured hardness, provided that the tip impressions arestill readable and the tips are not dislodged (2).6.3 Porosity (either on or just below the surface) mayinterfere with measuring Knoop hardness, especially if theindentation falls directly onto a large pore or if the indentationtip falls
25、in a pore.6.4 At higher magnifications in the optical microscope, itmay be difficult to obtain a sharp contrast between theindentation tip and the polished surface of some advancedceramics. This may be overcome by careful adjustment of thelighting as discussed in Test Method E 384 and Refs (2, 3).7.
26、 Apparatus7.1 Testing Machines:7.1.1 There are two general types of machines available formaking this test. One type is a self-contained unit built for thispurpose, and the other type is an accessory available forexisting microscopes. Usually, this second type is fitted on aninverted-stage microscop
27、e. Descriptions of the various ma-chines are available (46).7.1.2 Design of the machine should be such that the loadingrate, dwell time, and applied load can be set within the limitsset forth in 10.5. It is an advantage to eliminate the humanelement whenever possible by appropriate machine design.Th
28、e machine should be designed so that vibrations induced atthe beginning of a test will be damped out by the time theindenter touches the sample.7.1.3 The calibration of the balance beam should be checkedmonthly or as needed. Indentations in standard referencematerials may also be used to check calib
29、ration when needed.7.2 Indenter:7.2.1 The indenter shall meet the specifications for Knoopindenters. See Test Method E 384.7.2.2 Fig. 1 shows the indenter and its maximum usabledimensions. The diagonals have an approximate ratio of 7:1,and the depth of the indentation is approximately 1/30 thelength
30、 of the long diagonal. A perfect Knoop indenter has thefollowing angles:7.2.2.1 Included longitudinal angle 172 30 min 00 s.7.2.2.2 Included transverse angle 130 00 min 00 s.7.2.3 The constant Cp(defined in 12.2) for a perfect indenteris 0.07028. The specifications require a variation of not moretha
31、n 1 % from this value.7.2.4 The offset at the indenter tip shall not exceed 1.0 m.See Test Method E 384.7.2.5 The four faces of the indenter shall meet at sharpedges.7.2.6 The diamond should be examined periodically, and ifit is loose in the mounting material, chipped, or cracked, it shallbe replace
32、d.NOTE 3This requirement is from Test Method E 384 and is especiallypertinent to diamond indenters that are used to measure hardness ofceramics. In addition, these indenters sometimes are used to precrackadvanced ceramic specimens at loads higher than customarily used forhardness testing. Such usage
33、 can lead to indenter damage. The diamondindenter can be examined with a scanning electron microscope, or indentscan be made into soft copper to help determine if a chip or crack is present.FIG. 1 Knoop Indenter Showing Maximum Usable DimensionsC 1326 032Indenters may also be inspected with an optic
34、al microscope with at least500X power, but care should be taken to avoid damaging the microscopelens.7.3 Measuring Microscope:7.3.1 The measurement system shall be constructed so thatthe length of the diagonals can be determined with errors notexceeding6 0.0005 mm.NOTE 4Stage micrometers with uncert
35、ainties less than this shall beused to establish calibration constants for the microscope. See TestMethod E 384. Ordinary stage micrometers which are used for determin-ing the approximate magnification of photographs may be ruled too coarseor may not have the required accuracy and precision.7.3.2 Th
36、e numerical aperture (NA) of the objective lensshall be between 0.60 and 0.90.NOTE 5The apparent length of a Knoop indentation will increase asthe resolving power and NA of a lens increases. The range of NA specifiedby this test method corresponds to 40 to 1003 objective lenses. The higherpower lens
37、es may have higher resolution, but the contrast between theindentation tips and the polished surface may be less.7.3.3 A filter may be used to provide monochromaticillumination. Green filters have proved to be useful.8. Test Specimens8.1 The Knoop indentation hardness test is adaptable to awide vari
38、ety of advanced ceramic specimens. In general, theaccuracy of the test will depend on the smoothness of thesurface and, whenever possible, ground and polished speci-mens should be used. The back of the specimen shall be fixedso that the specimen cannot rock or shift during the test.8.1.1 ThicknessAs
39、 long as the specimen is over ten timesas thick as the indentation depth, the test will not be affected.In general, if specimens are at least 0.50 mm thick, thehardness will not be affected by variations in the thickness.8.1.2 Surface FinishSpecimens should have a ground andpolished surface. The rou
40、ghness should be less than 0.1 mrms. However, if one is investigating a surface coating ortreatment, one cannot grind and polish the specimen.NOTE 6This requirement is necessary to ensure that the surface is flatand that the indentation is sharp. Residual stresses from polishing are ofless concern f
41、or most advanced ceramics than for glasses or metals.References (2) and (7) report that Knoop hardness was insensitive tosurface finish for surfaces prepared with 1 m or finer diamond abrasive.Hardness was only affected when the surface finish had an opticallyresolvable amount of abrasive damage (7)
42、. (Extra caution may beappropriate during polishing of transformation toughening ceramics, suchas some zirconias, since the effect upon hardness is not known.)8.1.3 Radius of CurvatureCare should be used whenrelating hardness values obtained on curved surfaces to thoseobtained on polished, flat surf
43、aces. The hardness values ob-tained will be affected even when the curvature is only in thedirection of the short diagonal.9. Preparation of Apparatus9.1 Verification of LoadMost of the machines availablefor Knoop hardness testing use a loaded beam. This beam shallbe tested for zero load. An indenta
44、tion should not be visiblewith zero load, but the indenter should contact the sample.Methods of verifying the load application are given in PracticesE4.9.2 Separate Verification of Load, Indenter, and MeasuringMicroscopeProcedures in Test Method E 384, Section 14,may be followed.9.3 Verification by
45、Standard Reference MaterialsStandardreference blocks, SRM No. 2830, of silicon nitride that areavailable from the National Institute of Standards andTechnology6can be used to verify that an apparatus produces aKnoop hardness within6 5 % of the certified value.10. Procedure10.1 Specimen PlacementPlac
46、e the specimen on the stageof the machine so the specimen will not rock or shift during themeasurement. The specimen shall be clean and free of anygrease or film.10.2 Specimen Leveling:10.2.1 The surface of the specimen being tested shall lie ina plane normal to the axis of the indenter.10.2.2 If on
47、e leg (one half) of the long diagonal is more than10 % longer than the other, or if the ends of the diagonal are notboth in the field of focus, the surface of the specimen may notbe normal to the axis of the indenter. Align the specimensurface properly, and make another indentation.NOTE 7This tolera
48、nce is more stringent than the 20 % that is specifiedin Test Method E 384, but is less stringent than requirements in TestMethods C 730 and C 849.10.2.3 Leveling the specimen to meet these specifications isfacilitated if one has a leveling device.710.3 Magnitude of Test ForceA test force of either 9
49、.81 N(1 kgf) or 19.61 N (2 kgf) is specified. 19.61 N is preferred.9.81 N may be used if the higher force is not available on theapparatus, if cracking is a problem, or if preferred for a specificrequirement. If cracking is a problem at 9.81 N, lower forcesmay be used and the reporting procedure of 12.6 shall be used.(The precision might be less and the bias greater with the lowerforces.) If additional forces are used (for example to measurethe indentation size effect trend), then the reporting procedureof 12.6 shall be used for each data set.NOTE 8“Load” a
