1、Designation: D7187 10Standard 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 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for info
7、rmationonly.1.5 This standard does not purport to address 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.
8、Referenced Documents2.1 ASTM Standards:2D609 Practice for 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
9、for Measurement of Dry-Film Thick-ness of Organic Coatings Using MicrometersD1044 Test Method for Resistance of Transparent Plasticsto Surface AbrasionD1186 Test Methods for Nondestructive Measurement ofDry Film Thickness of Nonmagnetic Coatings Applied toa Ferrous Base3D1400 Test Method for Nondest
10、ructive Measurement ofDry Film Thickness of Nonconductive CoatingsApplied toa Nonferrous Metal Base3D3363 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
11、Organic Coat-ingsD6037 Test Methods for Dry Abrasion Mar Resistance ofHigh Gloss CoatingsD6279 Test Method for Rub Abrasion Mar Resistance ofHigh Gloss CoatingsG171 Test Method for Scratch Hardness of Materials Usinga Diamond Stylus3. Summary of Test Method3.1 This test method is based on representa
12、tive samples ofthe paint film being scratched using a nanoscratch instrument.From information received during a scratch test, values forplastic resistance and fracture resistance can be determined.1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings, Materia
13、ls, and Applications and is the direct responsibility ofSubcommittee D01.23 on Physical Properties of Applied Paint Films.Current edition approved Dec. 1, 2010. Published December 2010. Originallyapproved in 2005. Last previous edition approved in 2005 as D7187 - 05. DOI:10.1520/D7187-10.2For refere
14、nced 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.3Withdrawn. The last approved version of this historical standard is refer
15、encedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2 From these values of plastic resistance and fractureresistance, the mechanistic aspects of scratch/mar behavior ofthe coating can be subsequently compared.4. Si
16、gnificance 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 differing contact geometries making it difficult or impos-sible for mechanical qu
17、antities (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 mar mechanisms.4.2 This test provides a quantitative assessment of a paintcoatin
18、gs 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 test method is particularly suitable for measure-ment of paint coatings on labo
19、ratory 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 studies and a combination of high PlasticResistance and high Fracture Resista
20、nce (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.4.6 Mar resistance characterizes the ability of the coating toresist light dama
21、ge. 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 acomplex interplay between visco-elastic and thermal recovery,yield or plastic flow,
22、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 andvisco-elastic recovery can cause scratches to change with time.4.7 Since this
23、 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 investigatedand visual impacts of damage can be related to deformationmechanisms.5. Apparat
24、us5.1 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 the capacity to produce aninstrumented scratch of controlled and variable normal
25、 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 normal force of at least 50mN (mN should be read as milli-Newtons) with a resolut
26、ion 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 nm. Displacement and tangen-tial force response of the coating should be measur
27、ed 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. Indenter material should bediamond.5.3.2 The scratch should be applied at a rate o
28、f 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 is an example of one particular applica-tion of the test ranges. This example i
29、s 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 acquisition rate of 3 m between data points.NOTE 1To optimize test parameters for a
30、 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 coating and apply a highercontact pressure, whereas a larger indenter radius (blun
31、ter 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 D823.6.2 The thickness of the coating being tested, determined inaccordance with eith
32、er Test Methods D1005, D1186,orD1400,should be uniform within 500 nm. In order to minimize theeffect of the substrate for maximum accuracy, the penetrationdepth should not exceed one-half the coating thickness.6.3 At least three scratches should be performed on each testspecimen.6.4 The surface of t
33、he specimens should be free of any dirtand oils.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 recommended that substrates with similar c
34、ompliances beused when comparing different coatings.7. 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.D7187 1027.2 Condition and test the test specimens at 23 6 2C (73.5
35、6 3.5F) and a relative humidity of 50 6 5 % for at least 24h,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 on theinstrument with the surface to be mea
36、sured 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 surface.8.3 The complete scratch test consist
37、s 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 5.48.3.1 Perform a prescan to measure the topography of theundamaged coating. Apply the lowest load that the instrumentcan apply but t
38、hat 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 controlled rate. At the end ofthe scratch, r
39、eturn 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 theinstrument can apply.NOTE 4Prescan and postsc
40、an 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 Typical results of a nanoscratch test are pre
41、sented inFig. 1.4The 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 unscratchedsurface along the scratch path. It is a
42、 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 vertical displacement of theindenter tip during
43、 a low (;0.2 mN) constant load scanthrough the completed scratch.4The boldface numbers in parentheses refer to the list of references at the end ofthis test method.NOTEThe unit “mN” is meant to be read as mili-Newton.FIG. 1 Typical Data from a Nanoscratch Experiment C1 Vertical Displacement of the I
44、ndenter During the Pre-scan C2 VerticalDisplacement During Post-scan C3 Vertical Displacement During Scratch . C4 Tangential Force C5 Applied Normal Force (1)D7187 1038.5.3 Curve 3 shows the vertical displacement of the in-denter tip during the scratching process.8.5.4 Curve 4 shows the tangential f
45、orce 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 quantitiesrelating to the mechanical behavior of the
46、coating vs. scratchdistance 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 the scratch, Curve 3.PD 5 C32C1where PD means Pe
47、netration Depth, and C3and C1correspondto 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, Curve 1, from the topography after the scratch,
48、Curve2.RD 5 C22C19.1.3 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 C32C29.1.4 The ratio of tangential force, Curve 4, to the normalforce, Curve 5, is a form of the friction
49、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 done to accuratelymeasure recovery aspects since these aspects will vary with time.9.2 Plastic resistance (PR) at a particular normal force canbe calculated by dividing the normal force by the magnitude ofthe permanent damage at that normal force before fractureoccurs. Selecting the spot for measurement to be at a higherapplied normal force results in
