1、Designation: D 7187 05Standard Test Method forMeasuring Mechanistic Aspects of Scratch/Mar Behavior ofPaint Coatings by Nanoscratching1This standard is issued under the fixed designation D 7187; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 coating
3、s on 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
4、 created. 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
5、, and 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 mechanism
6、s:elastic 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 i
7、nformationonly.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.
8、2. Referenced Documents2.1 ASTM Standards:2D 609 Practice for Preparation of Cold-Rolled Steel Panelsfor Testing Paint, Varnish, Conversion Coatings, andRelated Coating ProductsD 823 Practices for Producing Films of Uniform Thicknessof Paint, Varnish, and Related Products on Test PanelsD 1005 Test M
9、ethod for Measurement of Dry-Film Thick-ness of Organic Coatings Using MicrometersD 1044 Test Method for Resistance of Transparent Plasticsto Surface AbrasionD 1186 Test Methods for Nondestructive Measurement ofDry Film Thickness of Nonmagnetic Coatings Applied toa Ferrous BaseD 1400 Test Method for
10、 Nondestructive Measurement ofDry Film Thickness of Nonconductive CoatingsApplied toa Nonferrous Metal BaseD 3363 Test Method for Film Hardness by Pencil TestD 3924 Specification for Standard Environment for Condi-tioning and Testing Paint, Varnish, Lacquer and RelatedMaterialsD 5178 Test Method for
11、 Mar Resistance of Organic Coat-ingsD 6037 Test Methods for Dry Abrasion Mar Resistance ofHigh Gloss CoatingsD 6279 Test Method for Rub Abrasion Resistance of HighGloss Coatings3. Summary of Test Method3.1 This test method is based on representative samples ofthe paint film being scratched using a n
12、anoscratch instrument.From information received during a scratch test, 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
13、.4. Significance and Use4.1 This test attempts to address two major drawbacks inexisting mar tests such as Test Methods D 1044, D 3363,D 5178, D 6037, and D 6279, namely:1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings, Materials, and Applications and is
14、 the direct responsibility ofSubcommittee D01.23 on Physical Properties of Applied Paint Films.Current edition approved July 1, 2005. Published October 2005.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For ASTM Book of ASTM
15、Standards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.1.1 Measured damage is caused by hundreds of contactswith differing contact geometries ma
16、king 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 mar mechanisms.4.2 This test p
17、rovides 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 test method is particularly s
18、uitable 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 studies and a combination o
19、f 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.4.6 Mar resistance characteri
20、zes 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 acomplex interplay between visco-el
21、astic 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 andvisco-elastic recovery can
22、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 investigatedand visual impacts of damage
23、can be related to deformationmechanisms.5. Apparatus5.1 Paint Application Equipment, as described in PracticesD 609 and D 823.5.2 Nanoscratch Instrument, consisting of an instrumentwith a well-defined indenter, which translates perpendicular tothe coating surface and has the capacity to produce anin
24、strumented 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 normal force of at least 50mN
25、 (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 nm. Displacement and tangen
26、-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.5.3.2 The scratch should be app
27、lied 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 is an example of one particular applica-tion of the test ranges
28、. 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 acquisition rate of 3 m between data points.6. Test Specimen6.1 The
29、 substrate for the paint coating should be a smooth,plane, rigid surface, such as those specified in Practices D 609and D 823.6.2 The thickness of the coating being tested, determined inaccordance with either Test Methods D 1005, D 1186, orD 1400, should be uniform within 500 nm. In order tominimize
30、 the effect of the substrate for maximum accuracy, thepenetration depth should not exceed one-half the coatingthickness.6.3 At least three scratches should be performed on each testspecimen.6.4 The surface of the specimens should be free of any dirtand oils.6.5 The specimen size should be sufficient
31、 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 1It is recommended that substrates with similar compliances beused when comparing different coatings.7. Conditioning7.1 Cure the coated tes
32、t 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 test the test specimens at 23 6 2C (73.56 3.5F) and a relative humidity of 50 6 5 % for at least 24h,unless the purchaser and seller agree
33、on more suitable testcharacteristics, as specified in the Standard Atmosphere ofSpecification D 3924.8. Procedure8.1 Secure the specimen to the moveable stage on theinstrument with the surface to be measured located perpendicu-larly to the indenter tip. Ensure the panel is held rigidly to thestage a
34、nd cannot be moved by the action of the subsequentscratch test.D71870528.2 Carefully move this area under the indenter and bringthe indenter tip close to the sample surface.8.3 The complete scratch test consists of three distinct steps.In all three steps, the indenter follows the exact same pathacro
35、ss the sample surface.NOTE 2A 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 that makes no permanent damage. The prescan,scratch, and postscan should all be performed o
36、n 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, return the indenter tip to its starting position at thebeginning of the scratch.8.3.3 Perfo
37、rm 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 3Prescan and postscan should only be used if the instrumenthas force feedback control, otherwise significant
38、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 presented inFig. 1.3The graph consists of five curves labeled 1 through 5.If needed, correct
39、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 measure of the verticaldisplacement of the indenter tip during a low (;0.2 mN)constant lo
40、ad 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 a low (;0.2 mN) constant load scanthrough the completed scratch.8.5.3 Curve 3 shows the v
41、ertical displacement of the in-denter tip during the scratching 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.3The boldface numbers in parentheses refer to the list of references
42、 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 Indenter During the Pre-scan C2 VerticalDisplacement During Post-scan C3 Vertical Displacement During Scratch . C4 Tangential Force C5
43、 Applied Normal Force (1)D71870539. Calculations9.1 From analysis of the Force/Displacement versus ScratchDistance plot produced (Fig. 1), plots of various quantitiesrelating to the mechanical behavior of the coating vs. scratchdistance can be generated:9.1.1 The penetration depth (PD) of the indent
44、er 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 Penetration Depth, and C3and C1correspondto Curves 3 and 1 respectively.9.1.2 The magnitude o
45、f 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, Curve2.RD 5 C22C19.1.3 The difference between the displacement during thescratch, Curve 3,
46、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 coefficient (Cf).Cf5 C4/C5NOTE 4The prescan and postscan need to be conducted consistently(
47、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
48、 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 values that reflect a more trueplastic resistance. This gives a value for plastic resistance thatis relatively constant that
49、is in units of force per unit of damagedepth, or mN/m.PR 5 FN/RDwhere:PR = plastic resistance,FN= the normal force in mN, andRD = permanent plastic deformation or residual depth inmicronsNOTE 5Only at very low normal force values does the plasticNOTEThe unit “mN” is meant to be read as mili-Newton.FIG. 2 Variation of Plastic Resistance (PR) with Respect to Applied Normal Force. Note that the constant plastic resistance value athigher (greater than 3 mN) applied loads. FR refers to the Fracture resistance, or critical load. (2)D7187054resistance differ radicall
