1、Designation: C 1326 08Standard 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 () 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 The values stated in SI units are t
3、o be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to 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 an
4、d determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 730 Test Method for Knoop Indentation Hardness ofGlassC 849 Test Method for Knoop Indentation Hardness ofCeramic WhitewaresE4 Practices for Force Verification of Testing MachinesE 177 P
5、ractice for Use of the Terms Precision and Bias inASTM Test MethodsE 384 Test Method for Microindentation Hardness of Ma-terialsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodIEEE/ASTM SI 10 Standard for Use of the InternationalSystem of Units (SI) (
6、The Modern Metric System)2.2 European Standard:CEN ENV 843-4 Advanced Technical Ceramics, Mono-lithic Ceramics, Mechanical Properties at Room Tempera-ture, Part 4: Vickers, Knoop, and Rockwell SuperficialHardness Tests32.3 ISO Standard:ISO 9385 Glass and Glass CeramicsKnoop HardnessTest43. Terminolo
7、gy3.1 Definition:3.1.1 Knoop hardness number (HK), nan expression ofhardness obtained by dividing the force applied to the Knoopindenter by the 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
8、172 308 and130 008.4. Summary of Test Method4.1 This test method describes an indentation hardness testusing a calibrated machine to force a pointed, rhombic base,pyramidal diamond indenter having specified face angles,under a predetermined load, into the surface of the materialunder test and measur
9、es the surface projection of the longdiagonal of the resulting impression after removal of the load.NOTE 1A general description of the Knoop 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 ad
10、vancedceramics.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 loading. Inaddition, the length correction factor for the resolution limits of opticalmicroscopes is not utilized.5. Significance and Use5.1 For advanced ceram
11、ics, Knoop indenters are used tocreate indentations. The surface projection of the long diagonalis measured with optical microscopes.5.2 The Knoop indentation hardness is one of many prop-erties that is used to characterize advanced ceramics. Attemptshave been made to relate Knoop indentation hardne
12、ss to otherhardness scales, but no generally accepted methods are avail-able. Such conversions are limited in scope and should be used1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.01 onMechanical Properties
13、and Performance.Current edition approved Aug. 1, 2008. Published September 2008. Originallyapproved in 1996. Last previous edition approved in 2003 as C 1326 03.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book o
14、f ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from European Committee for Standardization (CEN), 36 rue deStassart, B-1050, Brussels, Belgium, http:/www.cenorm.be.4Available from International Organization for Standardization (ISO), 1,
15、 ch. dela Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.with caution, except for special cases where a reliable basis forthe conversion has been obtain
16、ed 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 load, and cracking is much less of a problem (1).5On the other hand, the long slender tip
17、 of the Knoop indenta-tion is more difficult to precisely discern, especially in mate-rials with low contrast. The indentation loads chosen in this testmethod are designed to produce indentations as large as may bepossible with conventional microhardness equipment, yet notso large as to cause cracki
18、ng.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 ratio of theapplied load divided by the projected indentation area on thespecimen surface. It is assumed t
19、hat 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 of contact of the fourfaces of the undeformed indenter.)5.6 A full hardness characterization includes meas
20、urementsover a broad range of indentation loads. Knoop hardness ofceramics usually decreases with increasing indentation size orindentation force (load). The trend is known as the indentationsize effect (ISE). Hardness approaches a plateau constanthardness at sufficiently large indentation size or f
21、orces (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 hardness iseither close to or on the plateau, but not so large as to introduceexcessive cracking. A comprehen
22、sive 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 tips can interfere withinterpretation of the exact tip location. The loads chosen forthis test method are s
23、ufficiently 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 of the long diagonal length (2)(unlike Vickers indentations in ceramics).6.2 Cracking or spalling from the
24、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 influenceupon measured hardness, provided that the tip impressions arestill readable and the tips are not dislodged
25、 (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 in a pore.6.4 At higher magnifications in the optical microscope, itmay be difficult to obtain a sharp cont
26、rast 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. Apparatus7.1 Testing Machines:7.1.1 There are two general types of machines available formaking this test.
27、 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 microscope. Descriptions of the various ma-chines are available (46).7.1.2 Design of the machine should be such that
28、 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.The machine should be designed so that vibrations induced atthe beginning of a test will be damped out by the
29、 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 calibration when needed.7.2 Indenter:7.2.1 The indenter shall meet the specifications for Knoopindenters. See Te
30、st 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 of the long diagonal. A perfect Knoop indenter has thefollowing angles:7.2.2.1 Included longitudinal angle
31、 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 morethan 1 % from this value.7.2.4 The offset at the indenter tip shall not exceed 1.0 m.See Test Method E 384.5Th
32、e boldface numbers in parentheses refer to the list of references at the end ofthis test method. FIG. 1 Knoop Indenter Showing Maximum Usable DimensionsC 1326 0827.2.5 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
33、mounting material, chipped, or cracked, it shallbe replaced.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 hi
34、gher than customarily used forhardness testing. Such usage 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.Indenters may also be inspected with an optical micr
35、oscope 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 uncertainties
36、 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 The numer
37、ical 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 NAof a lens increases. The range of NAspecifiedby this test method corresponds to 40 to 1003 objective lenses. The higherpower lenses may ha
38、ve 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 variety of ad
39、vanced 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 long as
40、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 roughness sh
41、ould 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 for most a
42、dvanced 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). (Extra
43、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 surfaces. The
44、 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 indentation shou
45、ld 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 Standard
46、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 PlacementPlace the spe
47、cimen 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 one leg (on
48、e 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 tolerance is mo
49、re 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 9.81 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 a
