1、BS ISO28079:2009ICS 77.040.10; 77.160NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDHardmetals Palmqvist toughnesstestThis British Standardwas published under theauthority of the StandardsPolicy and StrategyCommittee on 31 August2009 BSI 2009ISBN 978 0 580 6175
2、5 3Amendments/corrigenda issued since publicationDate CommentsBS ISO 28079:2009National forewordThis British Standard is the UK implementation of ISO 28079:2009.The UK participation in its preparation was entrusted to TechnicalCommittee ISE/65, Sintered metal components.A list of organizations repre
3、sented on this committee can be obtained onrequest to its secretary.This publication does not purport to include all the necessary provisionsof a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunityfrom legal obligations.BS ISO 28079:2
4、009Reference numberISO 28079:2009(E)ISO 2009INTERNATIONAL STANDARD ISO28079First edition2009-07-15Hardmetals Palmqvist toughness test Mtaux durs Mthode dessai de duret de Palmqvist BS ISO 28079:2009ISO 28079:2009(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adob
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9、e 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2009 All rights reservedBS ISO 28079:2009ISO 28079:2009(E) ISO 2009 All rights reserved iiiContents Page Foreword iv Introduction v 1 Scope . 1 2 Normative refe
10、rences . 1 3 Symbols and units 1 4 Test pieces and sample preparation. 2 4.1 Test piece size and sampling 2 4.2 Surface preparation 2 4.3 Surface condition 2 5 Apparatus 3 5.1 General. 3 5.2 Indentation. 3 5.3 Indentation and crack measurement 3 6 Procedure and conditions of testing 3 6.1 Indentatio
11、ns. 3 6.2 Indentation and crack length measurement 3 6.3 Test validity . 5 7 Analysis . 6 7.1 Vickers hardness 6 7.2 Toughness. 6 8 Measurement uncertainty 6 9 Test report . 7 Annex A (informative) Report pro forma Palmqvist toughness measurements on hardmetals . 8 Bibliography . 10 BS ISO 28079:200
12、9ISO 28079:2009(E) iv ISO 2009 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each
13、 member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the Internationa
14、l Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards
15、 adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of
16、 patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 28079 was prepared by Technical Committee ISO/TC 119, Powder metallurgy, Subcommittee SC 4, Sampling and testing methods for hardmetals. BS ISO 28079:2009ISO 28079:2009(E) ISO 2009 All rights reserve
17、d vIntroduction Good test methods are those which enable a user or manufacturer to clearly discriminate between different materials. Fracture toughness values are required for three reasons: a) for product design and performance assessment; b) for selection of materials; c) for quality control. A sp
18、ecific International Standard for the toughness of hardmetals 1)has not been developed to date, primarily because of the difficulty of introducing stable precracks into these tough but hard materials. However, Palmqvist tests for toughness are widely used because of their perceived apparent simplici
19、ty. Cracks are formed at the corners of Vickers hardness indentations and these can be used to calculate a nominal surface toughness value. This value is sensitive to the method of measurement and to the method of surface preparation of the sample. This International Standard outlines good practice
20、to minimize uncertainties due to these issues. There are several possible methods for the measurement of the fracture toughness of hardmetals. The results can be expressed either as a stress intensity factor, in MNm3/2, or as a fracture surface energy, in Jm2. The range of values for typical WC/Co h
21、ardmetals is from 7 MNm3/2to 25 MNm3/2. There is a general inverse trend of hardness against fracture toughness (see 1 and 2 in the Bibliography). When applied unqualified to hardmetals, “toughness” can have several meanings. a) Plane-strain fracture toughness, KIc, in MNm3/2, is a value obtained fr
22、om tests on specimens with appropriate geometries for plane-strain conditions and containing a well-defined geometry of crack. There is no standard method for hardmetals and different organizations use different test methods for introducing the precrack. b) Strain-energy release rate (or work of fra
23、cture), G, is an alternative expression for toughness, often obtained by converting plane-strain toughness, K, to G i.e. G = K2/E(1 2), where E is Youngs modulus and is Poissons ratio. G has units of Jm2. Again, there is no standard method. c) Palmqvist toughness, W, is a value obtained by measuring
24、 the total length of cracks emanating from the four corners of a Vickers hardness indentation. For a given indentation load, the shorter the crack, the tougher the hardmetal. d) Finally, toughness is also widely used, in a loose sense, to describe the empirical relation between perceived resistance
25、to dynamic impacts. This is neither standardized nor quantified, but is clearly important for many industrial applications of hard materials. Also, principally for hardmetals, it can be more realistically assessed through either fatigue tests or high-rate strength tests, rather than a conventional f
26、racture toughness test. 1) Terminology There is a range of terms used for this type of material, especially including cemented carbides and/or cermets, as well as hardmetals. The word “hardmetals” has been used in this document. It includes all hard materials based on carbides that are bonded with a
27、 metal. In ISO 3252 terminology, “hardmetal” is stated to be “a sintered material characterized by high strength and wear resistance, comprising carbides of refractory metals as the main component together with a metallic binder phase”. “Cemented carbide” is synonymous with “hardmetal”. A “cermet” i
28、s defined as “a sintered material containing at least one metallic phase and at least one non-metallic phase, generally of a ceramic nature”. BS ISO 28079:2009ISO 28079:2009(E) vi ISO 2009 All rights reservedThere is a considerable body of published information on Palmqvist toughness tests for hardm
29、etals (see 5 to 29 in the Bibliography). Palmqvist toughness, W, is a toughness value obtained by measuring the crack lengths at the corners of a Vickers indentation. It can be evaluated by making indentations either at a single load, usually 30 kgf, or from the inverse of the slope of a plot of cra
30、ck length against load for a range of applied loads. For hardmetals, the crack depth profile is normally of the Palmqvist type, i.e. independent shallow arcs emanating from each indentation corner. The measurement of surface crack length is, however, open to operator error. It is widely recognized t
31、hat test surfaces are carefully prepared to remove the effects of residual surface stresses (see 8 in the Bibliography). The test also has a poor fracture-mechanics pedigree because of the uncertainties associated with residual stresses introduced by the indentation. One advantage of the Palmqvist m
32、ethod is that parallel measurements are made of sample hardness, which is required for quality-control purposes. The crack length, and thus toughness measurements, do not therefore require much more effort and can yield equally useful material characterization data, provided the measurements are obt
33、ained carefully in line with the methods proposed in this International Standard. This International Standard is based on a “Good Practice Guide for the Measurement of Palmqvist Toughness” published by the UK National Physical Laboratory in 1998. This International Standard recommends good practice
34、to minimize levels of uncertainty in the measurement process. The procedure has been validated through underpinning technical work within the VAMAS 2)framework (see 29 in the Bibliography). An interlaboratory exercise was conducted to generate underpinning technical information on toughness tests fo
35、r hardmetals. More than ten industrial organizations participated, either by correspondence, supply of materials or by conducting tests. Eight organizations were able to complete Palmqvist tests. Good statistics were obtained on the Palmqvist data that enabled a quantitative assessment of uncertaint
36、ies to be performed for this relatively simple test. Single-edge precracked beam data was thought to be closest to the “true” value, and the mean values from the Palmqvist test data compared reasonably well with these results. However, care was needed in test piece preparation to ensure a good corre
37、lation between data from the Palmqvist tests and the single-edge precracked beam results. 2) VAMAS, Versailles Project on Advanced Materials and Standards, supports trade in high technology products through international collaborative projects aimed at providing the technical basis for drafting code
38、s of practice and specifications for advanced materials. The scope of the collaboration embraces all agreed aspects of enabling science and technology, i.e. databases, test methods, design methods, and materials technology, which are required as a precursor to the drafting of standards for advanced
39、materials. VAMAS activity emphasises collaboration on pre-standards measurement research, intercomparison of test results, and consolidation of existing views on priorities for standardization action. Through this activity, VAMAS fosters the development of internationally acceptable standards for ad
40、vanced materials by the various existing standards agencies. BS ISO 28079:2009INTERNATIONAL STANDARD ISO 28079:2009(E) ISO 2009 All rights reserved 1Hardmetals Palmqvist toughness test 1 Scope This International Standard specifies a method for measuring the Palmqvist toughness of hardmetals and cerm
41、ets at room temperature by an indentation method. This International Standard applies to a measurement of toughness, called Palmqvist toughness, calculated from the total length of cracks emanating from the corners of a Vickers hardness indentation, and it is intended for use with metal-bonded carbi
42、des and carbonitrides (normally called hardmetals, cermets or cemented carbides). The test procedures proposed in this International Standard are intended for use at ambient temperatures, but can be extended to higher or lower temperatures by agreement. The test procedures proposed in this Internati
43、onal Standard are also intended for use in a normal laboratory-air environment. They are not intended for use in corrosive environments, such as strong acids or seawater. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated refer
44、ences, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 3878, Hardmetals Vickers hardness test 3 Symbols and units For the purposes of this document, the following symbols and units apply. Symbol Designation
45、 Unit A Constant of value 0,002 8 d Indentation-diagonal mean value mm d1, d2Indentation-diagonal individual values mm E Youngs modulus Nmm2F Indentation load (toughness calculations) N G Strain-energy release rate Jm2H Hardness kgfmm2HV(P) Vickers hardness at load P (kgf) kgfmm2KlcPlane-strain frac
46、ture toughness MNm3/2AnCrack length at indent corner mm P Indentation load (Vickers hardness method) kgf BS ISO 28079:2009ISO 28079:2009(E) 2 ISO 2009 All rights reservedSymbol Designation Unit T Total crack length mm tnTip-to-tip crack length mm WGPalmqvist toughness Nmm1or Jm2; 1 Nmm1= 1 000 Jm2WK
47、Palmqvist fracture toughness MNm3/2 Poissons ratio 4 Test pieces and sample preparation 4.1 Test piece size and sampling Any test piece shape can be used, provided that it can be prepared with a flat surface and a flat opposing face for making the indentation. Hot mounting in a press gives flat and
48、parallel faces. Cold mounting does not give flat and parallel faces. Diamond slicing or electrospark discharge machines are convenient to use for this purpose. However, the surfaces shall then be polished. It is recommended that 0,2 mm of material be removed before the final polish to ensure that ma
49、terial typical of the bulk is tested. For example, the ISO Vickers hardness test for hardmetals (see ISO 3878) specifies the removal of 0,2 mm. NOTE It has also been suggested, in a dissertation by M. Heinonen (UMIST) 19, that the test piece should be at least as thick as ten times the crack length. Thinner test pieces might not give representative results because the stress state will be dependent on the amount of material supporting the indentation and its associated cracks.
