1、Designation: D7187 15Standard Test Method forMeasuring Mechanistic Aspects of Scratch/Mar Behavior ofPaint Coatings by Nanoscratching1This standard is issued under the fixed designation D7187; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、revision, the year of last 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 nanoscratch method fordetermining the resistance of paint coatings o
3、n smooth flatsurfaces to scratch/mar.1.2 Previous methods used in scratch/mar evaluation firstphysically scratch or mar a samples surface with multiplecontact cutting, and then use visual inspection to assign aranking. It has been recognized that loss of appearance ismainly due to surface damages cr
4、eated. The philosophy of thismethod is to quantitatively and objectively measure scratch/mar behavior by making the evaluation process two steps withemphasis on surface damages. Step one is to find the relation-ship between damage shape and size and external input (suchas forces, contact geometry, a
5、nd deformation). Step two is torelate damage shape and size to visual loss of luster. The firststep is covered by this method; in addition, a survey in theappendix provides an example of an experiment to relate thedamage to the change in luster.1.3 There are three elementary deformation mechanisms:e
6、lastic deformation, plastic deformation and fracture; only thelatter two both contribute significantly to mar. This methodevaluates scratch/mar based on the latter two damage mecha-nisms.1.4 Although this standard was developed for paintcoatings, it can also be applied to other types of similarpolym
7、er-based coatings, for example, lacquers, varnishes,glazes and other decorative and protective layers deposited onhard substrates.1.5 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.6 This standard does not purport to address
8、 all of thesafety problems, 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:2D609 Practice for
9、 Preparation of Cold-Rolled Steel Panelsfor Testing Paint, Varnish, Conversion Coatings, andRelated Coating ProductsD823 Practices for Producing Films of Uniform Thicknessof Paint, Varnish, and Related Products on Test PanelsD1005 Test Method for Measurement of Dry-Film Thick-ness of Organic Coating
10、s Using MicrometersD1044 Test Method for Resistance of Transparent Plastics toSurface AbrasionD3363 Test Method for Film Hardness by Pencil TestD3924 Specification for Environment for Conditioning andTesting Paint, Varnish, Lacquer, and Related MaterialsD5178 Test Method for Mar Resistance of Organi
11、c CoatingsD6037 Test Methods for Dry Abrasion Mar Resistance ofHigh Gloss CoatingsD6279 Test Method for Rub Abrasion Mar Resistance ofHigh Gloss CoatingsD7091 Practice for Nondestructive Measurement of DryFilm Thickness of Nonmagnetic Coatings Applied toFerrous Metals and Nonmagnetic, Nonconductive
12、Coat-ings Applied to Non-Ferrous MetalsG171 Test Method for Scratch Hardness of Materials Usinga Diamond Stylus3. Summary of Test Method3.1 This test method is based on representative samples ofthe paint film being scratched using a nanoscratch instrument.From information received during a scratch t
13、est, values forplastic resistance and fracture resistance can be determined.3.2 From these values of plastic resistance and fractureresistance, the mechanistic aspects of scratch/mar behavior ofthe coating can be subsequently compared.1This test method is under the jurisdiction of ASTM Committee D01
14、 on Paintand Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.23 on Physical Properties of Applied Paint Films.Current edition approved Feb. 1, 2015. Published April 2015. Originallyapproved in 2005. Last previous edition approved in 2010 as D7187 10.
15、 DOI:10.1520/D7187-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For ASTM Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Ha
16、rbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Significance and Use4.1 This test attempts to address two major drawbacks inexisting mar tests such as Test Methods D1044, D3363, D5178,D6037, and D6279, namely:4.1.1 Measured damage is caused by hundreds of contactswith dif
17、fering contact geometries making it difficult or impos-sible for mechanical quantities (force, displacement) at thecontact points to be reliably determined.4.1.2 The damage is evaluated using subjective visualassessments, which provide only a qualitative sense of wearwith little information about ma
18、r mechanisms.4.2 This test provides a quantitative assessment of a paintcoatings mechanistic aspects of scratch/mar behavior in vari-ous conditions. The ability to control testing variables such asrate and temperature allow the study of the scratch/marbehavior in a variety of environments.4.3 This t
19、est method is particularly suitable for measure-ment of paint coatings on laboratory test panels.4.4 The accuracy and precision of scratch/mar performancemay be significantly influenced by surface nonuniformity andirregularities.4.5 A correlation has been observed between good marresistance in field
20、 studies and a combination of high PlasticResistance and high Fracture Resistance (terms are definedbelow). When coatings have had either high Plastic Resistanceand low Fracture Resistance, or low Plastic Resistance andhigh Fracture Resistance, there have been contradictory resultsin field studies.4
21、.6 Mar resistance characterizes the ability of the coating toresist light damage. The difference between mar and scratchresistance is that mar is related to only the relatively finesurface scratches which spoil the appearance of the coating.The mechanistic aspects of mar resistance depend on acomple
22、x interplay between visco-elastic and thermal recovery,yield or plastic flow, and micro-fracture. Polymers are chal-lenging because they exhibit a range of mechanical propertiesfrom near liquid through rubber materials to brittle solids. Themechanical properties are rate and temperature dependent an
23、dvisco-elastic recovery can cause scratches to change with time.4.7 Since this method measures mechanical qualities, suchas forces and displacements (deformations) during the damagemaking process, rate dependence, temperature dependence,and visco-elastic-plastic recovery can be further investigateda
24、nd visual impacts of damage can be related to deformationmechanisms.5. Apparatus5.1 Paint Application Equipment, as described in PracticesD609 and D823.5.2 Nanoscratch Instrument, consisting of an instrumentwith a well-defined indenter, which translates perpendicular tothe coating surface and has th
25、e capacity to produce aninstrumented scratch of controlled and variable normal forceand continuously measured displacement during testing. Thenormal force must be feedback controlled, in order to quicklyrespond to variations in surface morphology. The force of theinstrument should have a maximum nor
26、mal force of at least 50mN (mN should be read as milli-Newtons) with a resolution ofat least 0.1 mN. The maximum tangential force, if measured,should be at least 50 mN with a resolution of at least 0.5 mN.The range of the displacement sensors should be at least 50 mwith a resolution of at least 20 n
27、m. Displacement and tangen-tial force response of the coating should be measured with ahigh data acquisition rate, such as a maximum of five mbetween data points.5.3 Suggested Range for Testing Parameters:5.3.1 Indenter size should range from 1 to 100 microns andshould be spherical in geometry. Inde
28、nter material should bediamond.5.3.2 The scratch should be applied at a rate of 0.5 to 10millimetres per minute.5.3.3 The loading rate of the normal force should be appliedat 5 to 200 mN per minute.5.3.4 The scanning preload should be conducted with anapplied force of 0.1 to 1 mN.5.4 The following i
29、s an example of one particular applica-tion of the test ranges. This example is based on automotiveclear coats on a metal substrate.5.4.1 Indenter size of 2 microns.5.4.2 Scratch rate of 3 millimetres per minute.5.4.3 Loading rate of 40 mN per minute.5.4.4 Scanning preload of 0.2 mN.5.4.5 Data acqui
30、sition rate of 3 m between data points.NOTE 1To optimize test parameters for a particular coating, it shouldbe remembered that different combinations of applied load and indenterradius will cause differing damage in polymeric coatings. A smallerindenter radius (sharper tip) will tend to cut the coat
31、ing and apply a highercontact pressure, whereas a larger indenter radius (blunter tip) will tend totear the coating and apply a lower contact pressure.6. Test Specimen6.1 The substrate for the paint coating should be a smooth,plane, rigid surface, such as those specified in Practices D609and D823.6.
32、2 The thickness of the coating being tested, determined inaccordance with either Test Methods D1005,orD7091, shouldbe uniform within 500 nm. In order to minimize the effect ofthe substrate for maximum accuracy, the penetration depthshould not exceed one-half the coating thickness.6.3 At least three
33、scratches should be performed on each testspecimen.6.4 The surface of the specimens should be free of any dirtand oils. Care should be taken when cleaning samples: solventsshould not be used as they may modify the surface propertiesof polymer-based coatings. For removing dust, it is recom-mended to
34、blow off particulates with compressed air from aclean source (without oil contamination).6.5 The specimen size should be sufficient to be adequatelysecured to the nanoscratch instrument, but not so small as tointerfere with the movement of the indenter tip or its support-ing cantilever.NOTE 2It is r
35、ecommended that substrates with similar compliances beused when comparing different coatings.D7187 1527. Conditioning7.1 Cure the coated test specimens under conditions agreedupon between the purchaser and seller that reflect the condi-tions of curing of the paint in actual service.7.2 Condition and
36、 test the test specimens at 23 6 2C (73.56 3.5F) and a relative humidity of 50 6 5 % for at least 24 h,unless the purchaser and seller agree on more suitable testcharacteristics, as specified in the Standard Atmosphere ofSpecification D3924.8. Procedure8.1 Secure the specimen to the moveable stage o
37、n theinstrument with the surface to be measured located perpendicu-larly to the indenter tip. Ensure the panel is held rigidly to thestage and cannot be moved by the action of the subsequentscratch test.8.2 Carefully move this area under the indenter and bringthe indenter tip close to the sample sur
38、face.8.3 The complete scratch test consists of three distinct steps.In all three steps, the indenter follows the exact same pathacross the sample surface.NOTE 3A set of sample test parameters can be found in 5.4.8.3.1 Perform a prescan to measure the topography of theundamaged coating. Apply the low
39、est load that the instrumentcan apply but that makes no permanent damage. The prescan,scratch, and postscan should all be performed on the same line.8.3.2 Instruct the instrument to begin making a scratch toproduce damage to the coating. Allow the instrument to rampto the desired normal force at a c
40、ontrolled rate. At the end ofthe scratch, return the indenter tip to its starting position at thebeginning of the scratch.8.3.3 Perform a postscan, where the indenter tip is scannedalong the scratch, measuring the residual topography of thedamaged area. This should be done with the lowest load thein
41、strument can apply.NOTE 4Prescan and postscan should only be used if the instrumenthas force feedback control, otherwise significant error may be incurred.8.4 The complete scratch test should be repeated 2 moretimes at different locations so that there are a total of 3scratches per test panel.8.5 Ty
42、pical results of a nanoscratch test are presented inFig. 1.3The graph consists of five curves labeled 1 through 5.If needed, correct the data by curve fitting so that zero indenterpenetration and residual depth corresponds to zero appliednormal force.8.5.1 Curve 1 shows the topography of the unscrat
43、chedsurface along the scratch path. It is a measure of the verticaldisplacement of the indenter tip during a low (;0.2 mN)constant load prescan.8.5.2 Curve 2 shows the topography of the damaged surfacealong the scratch path immediately after the scratch test wasconcluded. It is a measure of the vert
44、ical displacement of theindenter tip during a low (;0.2 mN) constant load scanthrough the completed scratch.3The boldface numbers in parentheses refer to the list of references at the end ofthis test method.NOTE 1The unit “mN” is meant to be read as mili-Newton.FIG. 1 Typical Data from a Nanoscratch
45、 Experiment C1 Vertical Displacement of the Indenter During the Pre-scan C2 Vertical Dis-placement During Post-scan C3 Vertical Displacement During Scratch C4 Tangential Force C5 Applied Normal Force(1)D7187 1538.5.3 Curve 3 shows the vertical displacement of the in-denter tip during the scratching
46、process.8.5.4 Curve 4 shows the tangential force that arises betweenthe coating and the indenter tip.8.5.5 Curve 5 shows the applied normal force on the coatingsurface.9. Calculations9.1 From analysis of the Force/Displacement versus ScratchDistance plot produced (Fig. 1), plots of various quantitie
47、srelating to the mechanical behavior of the coating versusscratch distance can be generated:9.1.1 The penetration depth (PD) of the indenter under theapplied normal force can be calculated by subtracting thesurface topography measured from the prescan, Curve 1, fromthe displacement measured during t
48、he scratch, Curve 3.PD 5 C32 C1where PD means Penetration Depth, and C3and C1corre-spond to Curves 3 and 1 respectively.9.1.2 The magnitude of residual depth (RD), otherwiseknown as permanent plastic deformation, to the coating can becalculated by subtracting the surface topography before thescratch
49、, Curve 1, from the topography after the scratch, Curve2.RD 5 C22 C19.1.3 The difference between the displacement during thescratch, Curve 3, and the surface topography after the scratch,Curve 2, is the elastic recovery (ER) of the coating.ER 5 C32 C29.1.4 The ratio of tangential force, Curve 4, to the normalforce, Curve 5, is a form of the friction coefficient (Cf).Cf5 C4/C5NOTE 5The prescan and postscan need to be conducted consistently(with the same scanning parameters done within less than 10 minutes)before and after the scratch load is applied. This is
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