1、Designation: C1326 13 (Reapproved 2018)Standard Test Method forKnoop Indentation Hardness of Advanced Ceramics1This standard is issued under the fixed designation C1326; 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. Scope1.1 This test method covers the determination of the Knoopindentation hardness of advanced ceramics. In this test, apointed
3、, rhombic-based, pyramidal diamond indenter of pre-scribed shape is pressed into the surface of a ceramic with apredetermined force to produce a relatively small, permanentindentation. The surface projection of the long diagonal of thepermanent indentation is measured using a light microscope.The le
4、ngth of the long diagonal and the applied force are usedto calculate the Knoop hardness which represents the materialsresistance to penetration by the Knoop indenter.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 UnitsW
5、hen Knoop and Vickers hardness tests weredeveloped, the force levels were specified in units of grams-force (gf) and kilograms-force (kgf). This standard specifiesthe units of force and length in the International System ofUnits (SI); that is, force in newtons (N) and length in mm orm. However, beca
6、use of the historical precedent and contin-ued common usage, force values in gf and kgf units areoccasionally provided for information. This test method speci-fies that Knoop hardness be reported either in units of GPa oras a dimensionless Knoop hardness number.1.4 This standard does not purport to
7、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, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.5 This international standard was d
8、eveloped in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced
9、Documents2.1 ASTM Standards:2C730 Test Method for Knoop Indentation Hardness of GlassC849 Test Method for Knoop Indentation Hardness of Ce-ramic WhitewaresE4 Practices for Force Verification of Testing MachinesE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE384 Test Method
10、for Microindentation Hardness of Mate-rialsE691 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) (The Modern Metric System)2.2 European Standard:3CEN ENV 843-4 Advanced Technical Ceram
11、ics, MonolithicCeramics, Mechanical Properties at Room Temperature,Part 4: Vickers, Knoop, and Rockwell Superficial Hard-ness Tests2.3 ISO Standard:4ISO 9385 Glass and Glass CeramicsKnoop Hardness Test3. Terminology3.1 Definitions:3.1.1 Knoop hardness number (HK), nan expression ofhardness obtained
12、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 172 30 and130 00.4. Summary of Test Method4.1 This test method describes an indentatio
13、n hardness testusing a calibrated machine to force a pointed, rhombic-based,1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.01 onMechanical Properties and Performance.Current edition approved Jan. 1, 2018. Pub
14、lished January 2018. Originallyapproved in 1996. Last previous edition approved in 2013 as C1326 13. DOI:10.1520/C1326-13R18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information,
15、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, ch. dela Voie-Creuse, Case postale
16、56, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in
17、the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1pyramidal diamond indenter having specified face angles,under a predetermined force, into the surface of the materi
18、alunder 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 indentation hardness testis given in Test Method E384. The present test method differs from thisdescription only in areas required by th
19、e special nature of advancedceramics.NOTE 2This test method is similar to Test Methods C730 and C849,but differs primarily in the choice of force and the rate of force application.In addition, the length correction factor for the resolution limits of opticalmicroscopes is not utilized.5. Significanc
20、e 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 Knoop indentation hardness is one of many prop-erties that is used to characterize advanced ceramics. Attemptshave been made to
21、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 caution, except for special cases where a reliable basis forthe conversion has been obtained by comparison tests.5.3 For advanced
22、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 force, and cracking is much less of a problem (1).5On the other hand, the long slender tip of the Knoop indenta-tion is more diff
23、icult to precisely discern, especially in mate-rials with low contrast. The indentation forces chosen in thistest method are designed to produce indentations as large asmay be possible with conventional microhardness equipment,yet not so large as to cause cracking.5.4 The Knoop indentation is shallo
24、wer than Vickers inden-tations made at the same force. Knoop indents may be useful inevaluating coating hardnesses.5.5 Knoop hardness is calculated from the ratio of theapplied force divided by the projected indentation area on thespecimen surface. It is assumed that the elastic springback ofthe nar
25、row diagonal is negligible. (Vickers indenters are alsoused to measure hardness, but Vickers hardness is calculatedfrom the ratio of applied force to the area of contact of the fourfaces of the undeformed indenter.)5.6 A full hardness characterization includes measurementsover a broad range of inden
26、tation forces. Knoop hardness ofceramics usually decreases with increasing indentation size orindentation force such as that shown in Fig. 1.6The trend isknown as the indentation size effect (ISE). Hardness ap-proaches a plateau constant hardness at sufficiently largeindentation size or forces (load
27、s). The test forces that areneeded to achieve a constant hardness vary with the ceramic.The test force specified in this standard is intended to besufficiently large that hardness is either close to or on theplateau, but not so large as to introduce excessive cracking. Acomprehensive characterizatio
28、n of the ISE is recommended butis beyond the scope of this test method which measureshardness at a single, designated force.6. Interferences6.1 Cracking from the indentation tips can interfere withinterpretation of the exact tip location. The forces chosen forthis test method are sufficiently low th
29、at 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 sides of the Knoop
30、impression 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 (2).6.3 Porosity
31、(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 contrast between thein
32、dentation tip and the polished surface of some advanced5The boldface numbers in parentheses refer to the list of references at the end ofthis test method.6Standard Reference Materials Program (NIST) 100 Bureau Drive, Stop 2300Gaithersburg, MD 20899-2300.FIG. 1 A Typical Indentation Size Effect (ISE)
33、 Curve for a Ceramic(The data shown are for NIST SRM 2830 silicon nitride)C1326 13 (2018)2ceramics. This may be overcome by careful adjustment of thelighting as discussed in Test Method E384 and Refs (2, 3).7. Apparatus7.1 Testing Machines:7.1.1 There are three general types of machines available fo
34、rmaking this test. One type is a self-contained unit built for thispurpose that uses deadweights (masses) on a pan or lever beamto carefully apply force to the test piece. There is no load cellto record the force during the test sequence. The machine hasa built-in compound optical microscope for mea
35、suring theindentation sizes. The second type is an accessory to existingcompound optical microscopes. Usually, this second type isfitted on an inverted-stage microscope. The third, more moderntype, is a self-contained unit built for this purpose which has abuilt-in load cell that controls a ram or c
36、rosshead that movesthe indenter into contact with the test piece. The peak force andrate of force application can be controlled by a closed-loopfeedback circuit. The machine has a built-in compound opticalmicroscope for measuring the indentation sizes. Descriptionsof the various machines are availab
37、le (4-6).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.The machine should be designed so that vibrations ind
38、uced 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 or force applica-tion system should be checked monthly or as needed. Inden-tations in standard reference materials may also be used tocheck calibration when needed.7
39、.2 Indenter:7.2.1 The indenter shall meet the specifications for Knoopindenters. See Test Method E384.7.2.2 Fig. 2 shows the indenter and its maximum usabledimensions. The diagonals have an approximate ratio of 7:1,and the depth of the indentation is approximately130 the lengthof the long diagonal.
40、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 morethan 1 % from this value.7
41、.2.4 The offset at the indenter tip shall not exceed 1.0 m.See Test Method E384.7.2.5 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 replaced.NOTE 3This requirement
42、 is from Test Method E384 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 can lead to indenter dam
43、age. 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 microscope with at least500 power, but care should be taken to avoid damaging the micro
44、scopelens.7.3 Measuring Microscope:7.3.1 The measurement system shall be constructed so thatthe length of the diagonals can be determined with errors notexceeding 60.0005 mm.NOTE 4Stage micrometers with uncertainties less than this shall beused to establish calibration constants for the microscope.
45、See TestMethod E384. Ordinary stage micrometers which are used for determiningthe approximate magnification of photographs may be ruled too coarse ormay not have the required accuracy and precision.7.3.2 The numerical aperture (NA) of the objective lensshall be between 0.60 and 0.90.NOTE 5The appare
46、nt 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 100 objective lenses. Thehigher-power lenses may have higher resolution, but the contrast betweenthe indentation tips and the polished surf
47、ace 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 advanced ceramic specimens. In general, theaccuracy of the test will depend on the smoothn
48、ess 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 the specimen is over ten timesas thick as the indentation depth, the test will not be af
49、fected.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 should be less than 0.1 mFIG. 2 Knoop Indenter Showing Maximum Usable DimensionsC1326 13 (2018)3rms. 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 p
