1、Designation: C1326 081C1326 13Standard 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 last revis
2、ion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1 NOTEAdded research report footnote to Section 14.6.1 editorially in September 2008.1. Scope1.1 This test method covers the determination o
3、f the Knoop indentation hardness of advanced ceramics. In this test, a pointed,rhombic base, pyramidal diamond indenter of prescribed shape is pressed into the surface of a ceramic with a predetermined forceto produce a relatively small, permanent indentation. The surface projection of the long diag
4、onal of the permanent indentation ismeasured using a light microscope. The length of the long diagonal and the applied force are used to calculate the Knoop hardnesswhich represents the materials resistance to penetration by the Knoop indenter.1.2 The values stated in SI units are to be regarded as
5、standard. No other units of measurement are included in this standard.1.3 UnitsWhen Knoop and Vickers hardness tests were developed, the force levels were specified in units of grams-force (gf)and kilograms-force (kgf). This standard specifies the units of force and length in the International Syste
6、m of Units (SI); that is,force in newtons (N) and length in mm or m. However, because of the historical precedent and continued common usage, forcevalues in gf and kgf units are occasionally provided for information. This test method specifies that Knoop hardness be reportedeither in units of GPa or
7、 as a dimensionless Knoop hardness number.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
8、limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C730 Test Method for Knoop Indentation Hardness of GlassC849 Test Method for Knoop Indentation Hardness of Ceramic WhitewaresE4 Practices for Force Verification of Testing MachinesE177 Practice for Use of the Terms Precision and Bia
9、s in ASTM Test MethodsE384 Test Method for Knoop and Vickers Hardness of MaterialsE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodIEEE/ASTM SI 10 Standard for Use of the International System of Units (SI) (The Modern Metric System)2.2 European Standar
10、d:CEN ENV 843-4 Advanced Technical Ceramics, Monolithic Ceramics, Mechanical Properties at Room Temperature, Part 4:Vickers, Knoop, and Rockwell Superficial Hardness Tests32.3 ISO Standard:ISO 9385 Glass and Glass CeramicsKnoop Hardness Test43. Terminology3.1 Definitions:1 This test method is under
11、the jurisdiction of ASTM Committee C28 on Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on MechanicalProperties and Performance.Current edition approved Aug. 1, 2008Aug. 1, 2013. Published September 2008October 2013. Originally approved in 1996. Last previous edition appr
12、oved in 20032008as C1326 03.C1326 081. DOI: 10.1520/C1326-08E01.10.1520/C1326-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. ForAnnual Book ofASTM Standardsvolume information, refer to the standards Document Summary page on
13、 the ASTM website.3 Available from European Committee for Standardization (CEN), 36 rue de Stassart, B-1050, Brussels, Belgium, http:/www.cenorm.be.4 Available from International Organization for Standardization (ISO), 1, ch. de la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http:
14、/www.iso.ch.This document is not an ASTM standard and is intended only to provide the user of an ASTM 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 consu
15、lt prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.1 Knoop hardness number (HK), na
16、n expression of hardness obtained by dividing the force applied to the Knoop indenterby the projected area of the permanent impression made by the indenter.3.1.2 Knoop indenter, na rhombic-based pyramidal-shaped diamond indenter with edge angles of 172 30 and 130 00.4. Summary of Test Method4.1 This
17、 test method describes an indentation hardness test using a calibrated machine to force a pointed, rhombic base,pyramidal diamond indenter having specified face angles, under a predetermined load,force, into the surface of the material undertest and measures the surface projection of the long diagon
18、al of the resulting impression after removal of the load.NOTE 1A general description of the Knoop indentation hardness test is given in Test Method E384. The present test method differs from thisdescription only in areas required by the special nature of advanced ceramics.NOTE 2This test method is s
19、imilar to Test Methods C730 and C849, but differs primarily in the choice of loadforce and the rate of loading. forceapplication. In addition, the length correction factor for the resolution limits of optical microscopes is not utilized.5. Significance and Use5.1 For advanced ceramics, Knoop indente
20、rs are used to create indentations. The surface projection of the long diagonal ismeasured with optical microscopes.5.2 The Knoop indentation hardness is one of many properties that is used to characterize advanced ceramics. Attempts havebeen made to relate Knoop indentation hardness to other hardne
21、ss scales, but no generally accepted methods are available. Suchconversions are limited in scope and should be used with caution, except for special cases where a reliable basis for the conversionhas been obtained by comparison tests.5.3 For advanced ceramics, the Knoop indentation is often preferre
22、d to the Vickers indentation since the Knoop long diagonallength is 2.8 times longer than the Vickers diagonal for the same load,force, and cracking is much less of a problem (1).5 On theother hand, the long slender tip of the Knoop indentation is more difficult to precisely discern, especially in m
23、aterials with lowcontrast. The indentation loadsforces chosen in this test method are designed to produce indentations as large as may be possiblewith conventional microhardness equipment, yet not so large as to cause cracking.5.4 The Knoop indentation is shallower than Vickers indentations made at
24、the same load.force. Knoop indents may be usefulin evaluating coating hardnesses.5.5 Knoop hardness is calculated from the ratio of the applied loadforce divided by the projected indentation area on thespecimen surface. It is assumed that the elastic springback of the narrow diagonal is negligible.
25、(Vickers indenters are also usedto measure hardness, but Vickers hardness is calculated from the ratio of applied loadforce to the area of contact of the four facesof the undeformed indenter.)5.6 A full hardness characterization includes measurements over a broad range of indentation loads.forces. K
26、noop hardness ofceramics usually decreases with increasing indentation size or indentation force (load). such as that shown in Fig. 1.6 The trendis known as the indentation size effect (ISE). Hardness approaches a plateau constant hardness at sufficiently large indentation sizeor forces (loads). The
27、 test forces or loads that are needed to achieve a constant hardness vary with the ceramic. The test forcespecified in this standard is intended to be sufficiently large that hardness is either close to or on the plateau, but not so large asto introduce excessive cracking. A comprehensive characteri
28、zation of the ISE is recommended but is beyond the scope of this testmethod which measures hardness at a single, designated load.force.6. Interferences6.1 Cracking from the indentation tips can interfere with interpretation of the exact tip location. The loadsforces chosen for thistest method are su
29、fficiently low that tip cracking, if it occurs, will cause tiny, rather tight cracks at the indentation tips in advancedceramics. Such cracks will have a negligible interference on measurements of the long diagonal length (2) (unlike Vickersindentations in ceramics).6.2 Cracking or spalling from the
30、 sides of the Knoop impression may also occur, possibly in a time-dependent manner (minutesor hours) after the impression is made. Small amounts of such lateral cracking have little or no influence upon measured hardness,provided that the tip impressions are still readable and the tips are not dislo
31、dged (2).6.3 Porosity (either on or just below the surface) may interfere with measuring Knoop hardness, especially if the indentationfalls directly onto a large pore or if the indentation tip falls in a pore.6.4 At higher magnifications in the optical microscope, it may be difficult to obtain a sha
32、rp contrast between the indentation tipand the polished surface of some advanced ceramics. This may be overcome by careful adjustment of the lighting as discussed inTest Method E384 and Refs (2, 3).5 The boldface numbers in parentheses refer to the list of references at the end of this test method.6
33、 Standard Reference Materials Program (NIST) 100 Bureau Drive, Stop 2300 Gaithersburg, MD 20899-2300.C1326 1327. Apparatus7.1 Testing Machines:7.1.1 There are twothree general types of machines available for making this test. One type is a self-contained unit built for thispurpose, and the other pur
34、pose that uses deadweights (masses) on a pan or lever beam to carefully apply force to the test piece.There is no load cell to record the force during the test sequence. The machine has a built-in compound optical microscope formeasuring the indentation sizes. The second type is an accessory availab
35、le for existing to existing compound optical microscopes.Usually, this second type is fitted on an inverted-stage microscope. The third, more modern type, is a self-contained unit built forthis purpose which has a built-in load cell that controls a ram or crosshead that moves the indenter into conta
36、ct with the test piece.The peak force and rate of force application can be controlled by a closed-loop feedback circuit. The machine has a built-incompound optical microscope for measuring the indentation sizes. Descriptions of the various machines are availableavailable.(46).7.1.2 Design of the mac
37、hine should be such that the loading rate, dwell time, and applied load can be set within the limits setforth in 10.5. It is an advantage to eliminate the human element whenever possible by appropriate machine design. The machineshould be designed so that vibrations induced at the beginning of a tes
38、t will be damped out by the time the indenter touches thesample.7.1.3 The calibration of the balance beam or force application system should be checked monthly or as needed. Indentationsin standard reference materials may also be used to check calibration when needed.7.2 Indenter:7.2.1 The indenter
39、shall meet the specifications for Knoop indenters. See Test Method E384.7.2.2 Fig. 12 shows the indenter and its maximum usable dimensions. The diagonals have an approximate ratio of 7:1, and thedepth of the indentation is approximately 1/30 the length of the long diagonal.Aperfect Knoop indenter ha
40、s the following 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 indenter is 0.07028. The specifications require a variation of not more than1 % from this value.7.2.4 The offset at the i
41、ndenter tip shall not exceed 1.0 m. See Test Method E384.7.2.5 The four faces of the indenter shall meet at sharp edges.7.2.6 The diamond should be examined periodically, and if it is loose in the mounting material, chipped, or cracked, it shall bereplaced.FIG. 1 A typical indentation size effect (I
42、SE) curve for a ceramic. The data shown are for NIST SRM 2830 silicon nitride.C1326 133NOTE 3This requirement is from Test Method E384 and is especially pertinent to diamond indenters that are used to measure hardness of ceramics.In addition, these indenters sometimes are used to precrack advanced c
43、eramic specimens at loads higher than customarily used for hardness testing. Suchusage can lead to indenter damage. The diamond indenter can be examined with a scanning electron microscope, or indents can be made into soft copperto help determine if a chip or crack is present. Indenters may also be
44、inspected with an optical microscope with at least 500X power, but care shouldbe taken to avoid damaging the microscope lens.7.3 Measuring Microscope:7.3.1 The measurement system shall be constructed so that the length of the diagonals can be determined with errors notexceeding6 0.0005 mm.NOTE 4Stag
45、e micrometers with uncertainties less than this shall be used to establish calibration constants for the microscope. See Test Method E384.Ordinary stage micrometers which are used for determining the approximate magnification of photographs may be ruled too coarse or may not have therequired accurac
46、y and precision.7.3.2 The numerical aperture (NA) of the objective lens shall be between 0.60 and 0.90.NOTE 5The apparent length of a Knoop indentation will increase as the resolving power and NA of a lens increases. The range of NA specified bythis test method corresponds to 40 to 100 objective len
47、ses. The higher power lenses may have higher resolution, but the contrast between the indentationtips and the polished surface may be less.7.3.3 A filter may be used to provide monochromatic illumination. Green filters have proved to be useful.8. Test Specimens8.1 The Knoop indentation hardness test
48、 is adaptable to a wide variety of advanced ceramic specimens. In general, the accuracyof the test will depend on the smoothness of the surface and, whenever possible, ground and polished specimens should be used.The back of the specimen shall be fixed so that the specimen cannot rock or shift durin
49、g the test.8.1.1 ThicknessAs long as the specimen is over ten times as thick as the indentation depth, the test will not be affected. Ingeneral, if specimens are at least 0.50 mm thick, the hardness will not be affected by variations in the thickness.8.1.2 Surface FinishSpecimens should have a ground and polished surface. The roughness should be less than 0.1 m rms.However, if one is investigating a surface coating or treatment, one cannot grind and polish the specimen.NOTE 6This requirement is necessary to ensure that the surface is flat and that
