1、Designation:E233806 Designation: E2338 11Standard Practice forCharacterization of Coatings Using Conformable Eddy-Current Sensors without Coating Reference Standards1This standard is issued under the fixed designation E2338; the number immediately following the designation indicates the year oforigi
2、nal adoption or, in the case of 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. Scope*1.1 This practice covers the use of conformable eddy-current sensor
3、s for nondestructive characterization of coatings withoutstandardization on coated reference parts. It includes the following: (1) thickness measurement of a conductive coating on aconductive substrate, (2) detection and characterization of local regions of increased porosity of a conductive coating
4、, and (3)measurement of thickness for nonconductive coatings on a conductive substrate or on a conductive coating. This practice includesonly nonmagnetic coatings on either magnetic ( fi 0) or nonmagnetic ( = 0) substrates. This practice can also be used tomeasure the effective thickness of a proces
5、s-affected zone (for example, shot peened layer for aluminum alloys, alpha case fortitanium alloys). For specific types of coated parts, the user may need a more specific procedure tailored to a specific application.1.2 Specific uses of conventional eddy-current sensors are covered by Practices D709
6、1 and the following test methods issuedby ASTM: Test Methods B244, and E376 and the following test methods issued by ASTM: B244, E1004, and G12.1.3The values stated in SI units are to be regarded as standard. The inch-pound units are provided for information.1.3 The values stated in SI units are to
7、be regarded as standard. The values given in parentheses are mathematical conversionsto inch-pound units that are provided for information only and are not considered standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the respons
8、ibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B244 Test Method for Measurement of Thickness of Anodic Coatings on Aluminum and of Other Noncondu
9、ctive Coatings onNonmagnetic Basis Metals with Eddy-Current InstrumentsD7091 Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metalsand Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous MetalsE376 Practice for Measuring Coating Thickne
10、ss by Magnetic-Field or Eddy-Current (Electromagnetic) Examination MethodsE543 Specification for Agencies Performing Nondestructive TestingE1004 Test Method for Determining Electrical Conductivity Using the Electromagnetic (Eddy-Current) MethodE1316 Terminology for Nondestructive ExaminationsG12 Tes
11、t Method for Nondestructive Measurement of Film Thickness of Pipeline Coatings on Steel2.2 ASNT Documents:3SNT-TC-1A Recommended Practice for Personnel Qualification and Certification In Nondestructive TestingANSI/ASNT-CP-189 Standard for Qualification and Certification of NDT Personnel2.3 AIA Stand
12、ard:NAS 410 Certification and Qualification of Nondestructive Testing Personnel4NOTE 1See Appendix X1.1This practice is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.07 on ElectromagneticMethod.Current edition approved Dec
13、. 1, 2006. Published January 2007. Originally approved in 2004. Last previous edition approved in 2004 as E2338-04. DOI:10.1520/E2338-06.Current edition approved Feb. 15, 2011. Published March 2011. Originally approved in 2004. Last previous edition approved in 2006 as E2338 - 06. DOI:10.1520/E2338-
14、11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3Available from American Society for Nondestructive Test
15、ing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4Available from Aerospace Industries Association of America, Inc. (AIA), 1000 Wilson Blvd., Suite 1700, Arlington, VA 22209-3928, http:/www.aia-aerospace.org.(Replacement standard for MIL-STD-410.)1This docum
16、ent 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 consult prior editions as a
17、ppropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United
18、 States.3. Terminology3.1 DefinitionsDefinitions of terms relating to electromagnetic examination are given in Terminology For definitions of termsrelating to this practice, refer to Terminology E1316. The following definitions are specific to the conformable sensors:3.1.1 conformablerefers to an ab
19、ility of sensors or sensor arrays to conform to nonplanar surfaces without any significanteffects on the measurement results.3.1.2 lift-offnormal distance from the conformable sensor winding plane to the top of the first conducting layer of the partunder examination.3.1.3 model for sensor responsea
20、relation between the response of the sensor (for example, transimpedance magnitude andphase or real and imaginary parts) to properties of interest, for example, electrical conductivity, magnetic permeability, lift-off, andconductive coating thickness, etc. These model responses may be obtained from
21、database tables and may be analysis-based orempirical.3.1.4 depth of sensitivitydepth to which sensor response to features or properties of interest, for example, coating thicknessvariations, exceeds a noise threshold.3.1.5 spatial half-wavelengthspacing between the center of adjacent primary (drive
22、) winding segments with current flow inopposite directions; this spacing affects the depth of sensitivity. Spatial wavelength equals two times this spacing. A single turnconformable circular coil has an approximate spatial wavelength of twice the coil diameter.3.1.6 insulating shimsconformable insul
23、ating foils used to measure effects of small lift-off excursions on sensor response.3.1.7 air standardizationan adjustment of the instrument with the sensor in air, that is, at least one spatial wavelength awayfrom any conductive or magnetic objects, to match the model for the sensor response. Measu
24、rements on conductive materials afterair standardization should provide absolute electrical properties and lift-off values. The performance can be verified on certifiedreference standards over the frequency range of interest.3.1.8 reference substrate standardizationan adjustment of the instrument to
25、 an appropriate reference substrate standard. Theadjustment is to remove offsets between the model for the sensor response and at least two reference substrate measurements (forexample, two measurements with different lift-offs at the same position on the standard). These standards should have a kno
26、wnelectrical conductivity that is essentially uniform with depth and should have essentially the same electrical conductivity andmagnetic permeability as the substrate in the components being characterized.3.1.9 performance verification, uncoated parta measurement of electrical conductivity performe
27、d on a reference part withknown properties to confirm that the electrical conductivity variation with frequency is within specified tolerances for theapplication. When a reference standardization is performed, reference parts used for standardization should not be used forperformance verification. T
28、hese variations should be documented in the report (see Section 9). Performance verification is a qualitycontrol procedure recommended prior to or during measurements after standardization.3.1.10 performance verification, coated parta measurement of coating electrical conductivity and/or thickness o
29、n a coatedreference part with known properties to confirm that the coating electrical conductivity and/or thickness are within specifiedtolerances for the application. Performance verification is a quality control procedure that does not represent standardization andshould be documented in the repor
30、t (see Section 9).3.1.11 process-affected zonea region near the surface with depth less than the half wavelength that can be represented by aconductivity that is different than that of the base material, that is, substrate.3.1.12 sensor footprintarea of the sensor face placed against the material un
31、der examination.4. Significance and Use4.1 Conformable Eddy-Current SensorsConformable, eddy-current sensors can be used on both flat and curved surfaces,including fillets, cylindrical surfaces, etc. When used with models for predicting the sensor response and appropriate algorithms,these sensors ca
32、n measure variations in physical properties, such as electrical conductivity and/or magnetic permeability, as wellas thickness of conductive coatings on any substrate and nonconductive coatings on conductive substrates or on a conductingcoating. These property variations can be used to detect and ch
33、aracterize heterogeneous regions within the conductive coatings,for example, regions of locally higher porosity.4.2 Sensors and Sensor ArraysDepending on the application, either a single-sensing element sensor or a sensor array can beused for coating characterization. A sensor array would provide a
34、better capability to map spatial variations in coating thicknessand/or conductivity (reflecting, for example, porosity variations) and provide better throughput for scanning large areas. The sizeof the sensor footprint and the size and number of sensing elements within an array depend on the applica
35、tion requirements andconstraints, and the nonconductive (for example, ceramic) coating thickness.4.3 Coating Thickness RangeThe conductive coating thickness range over which a sensor performs best depends on thedifference between the electrical conductivity of the substrate and conductive coating an
36、d available frequency range. For example,a specific sensor geometry with a specific frequency range for impedance measurements may provide acceptable performance foran MCrAlY coating over a nickel-alloy substrate for a relatively wide range of conductive coating thickness, for example, from75 to 400
37、 m 0.003(0.003 to 0.016 in.in.). Yet, for another conductive coating-substrate combination, this range may be 10 to100 m 0.0004(0.0004 to 0.004 in.in.). The coating characterization performance may also depend on the thickness of anonconductive topcoat. For any coating system, performance verificati
38、on on representative coated specimens is critical toE2338 112establishing the range of optimum performance. For nonconductive, for example, ceramic, coatings the thickness measurementrange increases with an increase of the spatial wavelength of the sensor (for example, thicker coatings can be measur
39、ed with largersensor winding spatial wavelength). For nonconductive coatings, when roughness of the coating may have a significant effect onthe thickness measurement, independent measurements of the nonconductive coating roughness, for example, by profilometry mayprovide a correction for the roughne
40、ss effects.4.4 Process-Affected ZoneFor some processes, for example, shot peening, the process-affected zone can be represented by aneffective layer thickness and conductivity. These values can in turn be used to assess process quality. A strong correlation must bedemonstrated between these “effecti
41、ve coating” properties and process quality.4.5 Three-Unknown AlgorithmUse of multi-frequency impedance measurements and a three-unknown algorithm permitsindependent determination of three unknowns: (1) thickness of conductive nonmagnetic coatings, (2) conductivity of conductivenonmagnetic coatings,
42、and (3) lift-off that provides a measure of the nonconductive coating thickness.4.6 AccuracyDepending on the material properties and frequency range, there is an optimal measurement performance rangefor each coating system. The instrument, its air standardization and/or reference substrate standardi
43、zation, and its operation permitthe coating thickness to be determined within 615 % of its true thickness for coating thickness within the optimal range and within630 % outside the optimal range. Better performance may be required for some applications.5. Interferences5.1 Thickness of CoatingThe pre
44、cision of a measurement can change with coating thickness. The thickness of a coatingshould be less than the maximum depth of sensitivity. Ideally, the depth of sensitivity at the highest frequency should be less thanthe conductive coating thickness, while the depth of sensitivity at the lowest freq
45、uency should be significantly greater than theconductive coating thickness. The number of frequencies used in the selected frequency range should be sufficient to provide areliable representation of the frequency-response shape.5.2 Thickness of SubstrateThe thickness of the substrate should be large
46、r than the depth of sensitivity at the lowest frequency.Otherwise, this thickness must be known and accounted for in the model for the sensor response.5.3 Magnetic Permeability and Electrical Conductivity of Base Metal (Substrate)The magnetic permeability and electricalconductivity of the substrate
47、can affect the measurement and must be known prior to coating characterization unless they can bedetermined independently on a coated part. When the substrate properties vary spatially, this variation must be determined as partof the coating characterization on a noncoated part that preferably has t
48、he same thermal history as the coated parts. Originaluncoated parts may have significantly different microstructure than heat treated coated substrates. Uncoated colder regions ofotherwise coated parts may have different properties than the coated substrate due to changes during coating and heat tre
49、atment,and, thus, may or may not be reasonably representative of the substrate under the coating. In the case these variations are consistentfrom component to component, a reference standard essentially equivalent to the actual substrate must be used. Differencesbetween the actual substrate values at any coating measurement location and the values assumed for property estimation, forexample, in the sensor response model, may produce errors in coating property estimates.5.4 Electrical Conductivity of CoatingThe precision of a measurement can chang
