1、Designation: B975 15Standard Test Method forMeasurement of Internal Stress of Metallic Coatings by SplitStrip Evaluation (Deposit Stress Analyzer Method)1This standard is issued under the fixed designation B975; the number immediately following the designation indicates the year oforiginal adoption
2、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.INTRODUCTIONThe deposit stress analyzer method provides a rapid, accurate, and economical
3、 means for thedetermination of the internal tensile and compressive stress in metallic and nonmetallic coatings.Internal stress is expressed in pounds per square inch or megapascals. This procedure for measuringinternal stress offers the advantages of test specimens that are pre-calibrated by the ma
4、nufacturer, asmall test specimen coating surface area, and rapid determination of the internal stress in the appliedcoating.1. Scope1.1 This test method for determining the internal tensile orcompressive stress in applied coatings is quantitative. It isapplicable to metallic layers that are applied
5、by the processesof electroplating or chemical deposition that exhibit internaltensile or compressive stress values from 500 to 145 000 psi(3.45 to 1000 MPa).1.2 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI unit
6、s that are provided for information onlyand are not considered standard.1.3 This standard does not purport to address all of thesafety concerns, 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 t
7、he applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B636 Test Method for Measurement of Internal Stress ofPlated Metallic Coatings with the Spiral ContractometerE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for
8、Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 IEC Standard:3IEC 61010 Safety Requirements for Electrical Equipmentfor Measurement, Control, and Laboratory Use3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 average deposit thickness, naverage
9、 deposit thick-ness equals the deposit weight in grams divided by the specificgravity of the deposit in grams per cubic centimetre multipliedby the plated deposit surface area per test strip (see Eq 3).3.1.2 constant K, nthis certifiable calibrated number isdetermined experimentally for each lot of
10、test strips manufac-tured to enable simple mathematical calculation of the internaldeposit stress while factoring the influence of percent elonga-tion difference between the deposit and the substrate withoutthe use of complicated bent strip formulas. See Note 4.3.1.3 helix, nmetal strip approximatel
11、y 0.01 to 0.013 in.(0.025 to 0.033 cm) thick formed as a helix approximately 0.9in. (2.3 cm) in diameter and 0.61 in. (15.5 cm) long with orwithout a polytetrafluoroethylene (PTFE) coating on the insidesurface.3.1.4 internal stress, nstress in a given layer of coatingcan result from foreign atoms or
12、 materials in the layer thatstress the natural structure of the deposit as the coating is beingformed from sources independent of foreign atoms such asmisfit dislocations and the result of additional processing.3.1.4.1 DiscussionStress that develops in a given layer of1This test method is under the
13、jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 onTest Methods.Current edition approved Nov. 1, 2015. Published December 2015. DOI:10.1520/B975-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orconta
14、ct ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from International Electrotechnical Commission (IEC), 3, rue deVaremb, P.O. Box 131, 1211 Geneva 20, Switzerland, http:/www.iec
15、.ch.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1material is measured as pounds per square inch or megapascalswhere 1 MPa = 145 psi.3.1.5 measuring stand, nthis stand supports the test stripabove a logarithmic scale that enables de
16、termination of thetotal number of increments spread between the test strip legtips.3.1.6 modulus of elasticity, nstress required to produceunit strain, which may be a change in length (Youngsmodulus), a twist of shear (modulus of rigidity or modulus oftorsion), or a change in volume (bulk modulus).3
17、.1.7 on site specimen holder, nthis device holds a teststrip during the application of a coating.3.1.7.1 DiscussionAnodes are located external to thespecimen holder.3.1.8 power supply, nrectifier to supply amperage forplating.3.1.9 self-contained plating cell, nthis cell contains twoanodes within th
18、e cell at an equal distance from the test stripthat are suspended in electrolyte for deposition to occur. Asection for a heating coil and a pump for solution agitation isan option.3.1.10 test strip, nmetal strip formed from flat stock thatreceives the coating of material being evaluated for internal
19、stress.4. Summary of Test Method4.1 The first attempt to measure stress values in appliedcoatings was the bent strip method, wherein a coating ofknown thickness was applied to a strip of flat stock materialhaving a known modulus of elasticity, length, width, andthickness. In the test, one end of the
20、 strip was held in a fixedposition and one end could bend. The degree of bend experi-enced by the test strip was then measured. Equations wereproposed by Stoney, Barklie and Davies, Houssner, Balden andMorse, Brenner and Senderoff for this method of measurementto calculate the internal deposit stres
21、s that was sufficient tocause deflection of the flat stock material.4.2 Later methods include the use of flat stock materialformed into a helix that contracts or expands as a stressedcoating is applied to the base material (spiral contractometer asdescribed in United States Patent 4,086,154) and a d
22、isk formedfrom flat stock material that bows outward or inward as astressed coating is applied to the base material (stress meter).4.3 The deposit stress analyzer method for determining theinternal stress value of a given coating uses bent strip technol-ogy and the formulas devised for calculation o
23、f results appli-cable to this approach. A specific test piece comprises aselected metallic material that exhibits spring-like propertieswith specified dimensions that define an end area split to giveFIG. 1 Test Strip Parameters1in.=2.54cmB975 152two legs (see Fig. 1). These test strips are coated wi
24、th a resist,to prevent deposition, on the front of one leg and the back sideof the other leg and on both sides above where the legs divide,leaving a space uncoated at the top for the purpose of makingelectrical contact to the test piece during the plating process.Asa test piece is plated, the legs b
25、end to relieve the stress that isinduced as deposition occurs. Tensile stress bends the test striplegs with the plated deposit on the outside, while compressivestress bends the test strip legs with the resist on the outside. SeeFig. 2. Each test is performed at specific operating conditionsthat are
26、usually selected to approximate the conditions for partsbeing processed in production mode.4.3.1 The internal deposit stress is calculated based on thetotal number of increments deflection observed from tip to tipafter plating. This value is determined as the test strip issuspended above a measuring
27、 stand. See Fig. 3. Results arecalculated by use of a simple deposit stress analyzer formulaexpressed in pounds per square inch. See Eq 2 and Eq 3.5. Significance and Use5.1 Internal stress in applied coatings exhibits potential tocause a breakdown of resistance to corrosion and erosion as aresult o
28、f the formation of fractures from micro-cracking andmacro-cracking within the applied coating. This phenomenoncan also cause blistering, peeling, reduction of fatigue strength,and loss. The resulting stress can be tensile in nature, causingthe deposit to contract, or compressive in nature, causing t
29、hedeposit to expand.5.2 To maintain quality assurance by the bent strip method,it is necessary to monitor production processes for acceptablelevels of internal deposit stress in applied coatings. Note thatthe highest value of the internal deposit stress as obtained on astress-versus-coating-thicknes
30、s curve is usually the truest valueof the internal deposit stress. Most low values are false. Initialvalues tend to be lower than the actual value because of theeffect of stock material edge burrs and the resistance of thestock material to bending. Excessive deposit thickness causeslower-than-true v
31、alues since the coating overpowers andchanges the initial modulus of elasticity of the test piece, whichbecomes more difficult to bend as the coating continues tobuild upon it. This phenomenon can be corrected considerablyby use of a formula that compensates for modulus of elasticitydifferences betw
32、een the deposit and the substrate materials, butit does remain a factor. See Eq 2.6. Apparatus6.1 Deposit Stress Analyzer Measuring StandThis standhas a scale over which a test strip is suspended to determine theincrements of spread as the value of U between the test strip legtips caused by the indu
33、ced deposit stress. See Fig. 2. See Eq 1and Eq 2.6.2 On site Plating Device for In-Tank or Laboratory BenchPlating (External Anodes)This device does not hold a platingbath. It is a 1 in. diameter, cylindrical tube that is designed withan adjustable bracket to enable placement of the cell in aworking
34、 tank as a permanently mounted fixture. It is alsoamenable to laboratory studies where small solution volumesare advantageous. See Fig. 4. This device supports a single teststrip during the deposition process. To electroplate a test strip,the existing tank anodes may be used for the test if they are
35、 ofsimilar composition and size and are located equally distantand parallel to the device open ports. Using a rectifier that isseparate from the power supply used to plate the parts, connectthe positive outlet to each of the two selected tank anodes, andthe negative outlet to the top of the test str
36、ip at the crossbar thatextends over the top of the device. The bottom of the device issufficiently closed to prevent the test strip from droppingFIG. 2 Deposit Stress Analyzer Measuring StandFIG. 3 In-site 1 Plating DeviceB975 153through. It is critical that the test strip legs do not pass throughth
37、e side openings as a test strip is placed inside the device.Adjust the test strip into position against the bottom of thedevice and approximately 4 in. (10 cm) below the solutionlevel. A 0-1 to 0-2 amp output constant amperage, constantvoltage power supply is recommended to control the amperageaccur
38、ately. The negative lead from a power supply is thenconnected to the test strip at the crossbar located at the top ofthe device. When using deposition conditions similar to workthat is processed in the work tank, the stress measurementresult will represent the condition of the work being processed.T
39、he device may also be used on a laboratory table in acontainer for a plating bath as small as 400 mL in which twosmall nickel anodes are positioned each across from a cell sideopening. See Fig. 4. This becomes helpful and economicalwhen the plating solution is undergoing laboratory studies inregard
40、to additions of multiple additives, particularly if pre-cious metals are involved. In-tank deposit stress testing yieldssimilar results to those determined on a laboratory bench setupwhen the test parameters are similar. However, the depositstress will vary over a given part, particularly over parts
41、 thatare electroformed where the low-current density area depositsusually exhibit the highest deposit stress. In such cases, thedetermined deposit stress becomes an approximate averagevalue that serves as a quality control procedure.6.3 Cells for In-Tank Plating or Laboratory Bench Plating(Internal
42、Anodes)When agitation and solution temperatureare not needed for tests, a test plating cell that includes twoanodes of similar size and composition at an equal distancefrom the test piece is recommended. When solution agitationand elevated bath temperature are required, a two-section cellcould be us
43、ed where one side has a pump and heater. Cells withopen low side ports would permit immersion into a workingbath allowing the cell to fill as it is being lowered. The test stripmust have its own power supply. In these cells, a test strip issuspended at the center of the cell by clipping it to a stai
44、nlesssteel cross support bar. Two anodes2218 1/8in.(550.3 cm) are positioned along the end of the cell walls whereanode pockets are attached. These cells can be designed to behung directly in a working tank or they could be used in alaboratory setup.6.4 AnodesWhen using the deposit stress analyzer m
45、ethodto evaluate the internal deposit stress by electroplating a givenmetal or metal alloy deposit, two anodes of similar size, shape,and composition are placed at a similar distance from the teststrip in a position parallel to the test strip to allow equalexposure of the test strip to the negative
46、current. The positivelead from the power supply shall be connected to each anode.6.5 ContainerFor tabletop setups, a suitable container canbe used to hold a plating bath selected for evaluation whenusing the in-tank plating cells that have bottom holes forsolution flow.6.6 Test StripsTest strips are
47、 used to receive an appliedcoating that is under investigation for the determination ofinternal deposit stress. Test strips are shaped similar to a tuningfork so that the test strip legs exist in the same planegeometrically. During the application of a stressed coating, thetest strip legs deflect ou
48、tward in opposite directions. They aremade from materials that exhibit spring-like properties so theplated test strip legs will return to the as-plated position ifdeflected or disturbed by minor mishandling before the degreeof deflection is determined. Each test strip is selectivelycovered with an o
49、rganic material that is resistant to attack bymost solutions to which the test strips are exposed.This coatingserves as a mask to define the area to receive metallic depositsfor tests. See Fig. 1.NOTE 1Strong alkaline solutions could dissolve away the resistmaterial that covers the areas that do not receive the deposit. If this occurs,a thin coat of high-solids, air-dry lacquer such as Micro-Shield dilutedwith acetone in a one-to-one ratio is applied by an artist brush over thatspecific area. When dry, the test can proceed. If lacquer is removed duringthe
