1、Designation: B877 96 (Reapproved 2018)Standard Test Method forGross Defects and Mechanical Damage in Metallic Coatingsby the Phosphomolybdic Acid (PMA) Method1This standard is issued under the fixed designation B877; the number immediately following the designation indicates the year oforiginal adop
2、tion 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. Scope1.1 This test standard covers equipment and methods forusing phosphomolybdic
3、 acid (PMA) to detect gross defects andmechanical damage including wear through in metallic coat-ings of gold, silver, or palladium. These metals comprise thetopmost metallic layers over substrates of nickel, copper, orcopper alloys.1.2 Recent reviews of porosity testing, which include thosefor gros
4、s defects, and testing methods can be found in theliterature.2,3An ASTM guide to the selection of porosity andgross defect tests for electrodeposits and related metalliccoatings is available as Guide B765. Other related porosity andgross defects test standards are Test Methods B735, B741,B798, B799,
5、 B809, and B866, Specifications B488, B679,andB689.1.3 The values stated in SI units are the preferred units.Those in parentheses are for information only.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of
6、this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the D
7、ecision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:4B374 Terminology Relating to ElectroplatingB488 Specification for Electrodepos
8、ited Coatings of Goldfor Engineering UsesB542 Terminology Relating to Electrical Contacts and TheirUseB679 Specification for Electrodeposited Coatings of Palla-dium for Engineering UseB689 Specification for Electroplated Engineering NickelCoatingsB735 Test Method for Porosity in Gold Coatings on Met
9、alSubstrates by Nitric Acid VaporB741 Test Method for Porosity In Gold Coatings On MetalSubstrates By Paper Electrography (Withdrawn 2005)5B765 Guide for Selection of Porosity and Gross Defect Testsfor Electrodeposits and Related Metallic CoatingsB798 Test Method for Porosity in Gold or Palladium Co
10、at-ings on Metal Substrates by Gel-Bulk ElectrographyB799 Test Method for Porosity in Gold and PalladiumCoatings by Sulfurous Acid/Sulfur-Dioxide VaporB809 Test Method for Porosity in Metallic Coatings byHumid Sulfur Vapor (“Flowers-of-Sulfur”)B866 Test Method for Gross Defects and Mechanical Dam-ag
11、e in Metallic Coatings by Polysulfide Immersion3. Terminology3.1 DefinitionsMany terms in this test method are definedin Terminology B374 or B5423.2 Definitions of Terms Specific to This Standard:1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and i
12、s the direct responsibility of Subcommittee B08.10 onTest Methods.Current edition approved Aug. 1, 2018. Published August 2018. Originallyapproved in 1996. Last previous edition approved in 2013 as B877 96(2013). DOI:10.1520/B0877-96R18.2Clarke, M., “Porosity and Porosity Tests,” Properties of Elect
13、rodeposits, ed. bySand, Leidheiser, and Ogburn, The Electrochemical Society, 1975, p. 122.3Krumbein, S. J., “Porosity Testing of Contact Platings,” Trans. Connectors andInterconnection Technology Symposium, Philadelphia, PA, October 1987, p. 47.4For referenced ASTM standards, visit the ASTM website,
14、 www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.5The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 10
15、0 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and R
16、ecommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.1 base metal, nany metal other than gold, silver,platinum, palladium, iridium, or rhodium. Typical base metalsused as underplates or substrates are copper, nickel, tin, lead,and their alloys.3.2.2
17、defect indications, ncolored droplets resulting fromthe reaction between the PMA reagent and the underlyingmetal.3.2.3 gross defects, nthose breaks in the coating thatexpose relatively large areas of underlying metal to theenvironment. Gross defects include those produced by me-chanical damage and w
18、ear, as well as as-plated large pores withdiameters an order of magnitude greater than intrinsic porosityand networks of microcracks.NOTE 1Large pores and microcrack networks indicate serious devia-tions from acceptable coating practice (dirty substrates and contaminatedor out-of-balance plating bat
19、hs).3.2.4 intrinsic porosity, nthe normal porosity that ispresent, to some degree, in all commercial thin electrodeposits(precious metal coatings for engineering purposes) that willgenerally follow an inverse relationship with thickness.NOTE 2Intrinsic porosity is due to small deviations from ideal
20、platingand surface preparation conditions. Scanning electron microscope (SEM)studies have shown the diameter of such pores at the plating surface is 1to 2 m so only small areas of underlying metal are exposed to theenvironment.3.2.5 measurement area, nthat portion or portions of thesurface that is e
21、xamined for the presence of gross defects ormechanical damage and wear through. The measurement areashall be indicated on the drawings of the parts or by theprovision of suitably marked samples.3.2.6 metallic coatings, ninclude electrodeposits,claddings, or other metallic layers applied to the subst
22、rate. Thecoating can comprise a single metallic layer or a combinationof metallic layers (gold over palladium).3.2.7 porosity (general), nthe presence of any hole, crack,or other defect that exposes the underlying metal to theenvironment.3.2.8 underplate, na metallic coating layer between thesubstra
23、te and the topmost metallic coating. The thickness of anunderplate is usually greater than 1 m, in contrast to a strikeor flash, which is usually thinner.3.2.9 wear through, nthe exposure of underplate or sub-strate as a direct result of wear. Wear through is an observablephenomenon.3.2.10 wear trac
24、k, na mark that indicates the path alongwhich physical contact has been made during a sliding process(the mating and unmating of an electrical contact).4. Summary of Test Method4.1 This test method involves the use of a solution ofphosphomolybdic acid (PMA), which is a solid complex ofmolybdenum tri
25、oxide, Mo2O3, and phosphoric acid, H3PO4.Inthis state, molybdenum is very reactive with many free metalsand may be used to detect exposed underplates and substratemetals. The part is exposed briefly to fumes of hydrochloricacid to remove oxides in the defect region. A small drop of theaqueous PMA so
26、lution is applied to the spot in question usingan applicator. If it contacts base metals from exposed under-plate or substrate, the Mo2O3will immediately be reduced tolower oxides, forming the intensely colored, molybdenum bluecomplex (heteropoly blue).64.2 This test may not be suitable for some pre
27、cious metalalloy coatings that contain significant concentrations of non-precious metals (base metals) like nickel or copper. (See .)4.3 The reagents in this test also react with tin, lead, andtin-lead solder.5. Significance and Use5.1 The primary purpose of the PMAtest is to determine thepresence o
28、f mechanical damage, wear through, and other grossdefects in the coating. Most metallic coatings are intended tobe protective, and the presence of gross defects indicates aserious reduction of such protection.5.2 The protection afforded by well applied coatings may bediminished by improper handling
29、following plating or as aresult of wear or mechanical damage during testing or while inservice. The PMA test can serve to indicate the existence ofsuch damage.5.3 This test is used to detect underplate and substrate metalexposed through normal wear during relative motions (matingof electrical contac
30、ts) or through mechanical damage.As such,it is a sensitive pass/fail test and, if properly performed, willrapidly detect wear through to base metals or scratches thatenter the base metal layers.5.4 This test is relatively insensitive to small pores. It is notdesigned to be a general porosity test an
31、d shall not be used assuch. The detection of pores will depend upon their sizes andthe length of time that the reagent remains a liquid.5.5 This test cannot distinguish degrees of wear through orwhether the wear through is to nickel or copper. Once basemetal is exposed, the colored molybdenum comple
32、x is formed.While relatively small area defects (compared to the area of thedroplet) may be seen at the bottom of the drop as tiny coloredregions immediately after applying the PMA, any larger areasof exposed base metal will cause the entire droplet to turn darkinstantly.5.6 The PMA test also detect
33、s mechanical damage thatexposes underplate and substrate metal. Such damage mayoccur in any postplating operation or even at the end of theplating operation. It can often occur in assembly operationswhere plated parts are assembled into larger units by mechani-cal equipment.5.7 The PMA test identifi
34、es the locations of exposed basemetal. The extent and location of these exposed areas may ormay not be detrimental to performance. The PMA test is notrecommended for predictions of product performance, nor is itintended to simulate field failure mechanisms. For such contactperformance evaluations, a
35、n environmental test known tosimulate actual failure mechanisms should be used.6Van Wazer, J. P., Phosphorous and Its Compounds, Interscience Publishers,New York, 1961.B877 96 (2018)25.8 The PMAtest is primarily intended for the evaluation ofindividual samples rather than large sample lots, since ev
36、alu-ations are normally carried out one at a time under themicroscope (see Section 10).5.9 This test is destructive. Any parts exposed to the PMAtest shall not be placed in service.6. Apparatus6.1 In addition to the normal equipment (beakers, weighingbalances, funnels, etc.) that are a part of every
37、 chemicallaboratory.6.2 Microscope, Optical, Stereo, 10 to 30 It is preferredthat one eyepiece contain a graduated reticle for measuring thedefect location. The reticle shall be calibrated for the magni-fication at which the microscope is to be used, preferably 10.76.3 Light source (illuminator) for
38、 microscope, incandescent.6.4 Glass volumetric flask, 10 mL.6.5 Glass bottle of a stable shape and with glass stopper.Thebottle opening shall be 2.5 cm (1 in) minimum. An example isa 50-mL low-form weighing bottle or a flask-shaped weighingbottle.6.6 Applicators (see 9.2)Platinum wire, 32 AWG, ordis
39、posable glass micropipets, 1 or 0.5 L size.7. Reagents and Materials7.1 Phosphomolybdic Acid (PMA)Crystalline, ACS certi-fied grade.7.2 Concentrated Hydrochloric Acid ACS analytical re-agent (AR) grade or better.8. Specific Safety and Health Precautions8.1 All the normal precautions shall be observe
40、d in handlingthe materials required for this test. This shall include, but is notlimited to, procuring and reviewing Material Safety DataSheets that meet the minimum requirements of the OSHAHazard Communication Standard for all chemicals used incleaning and testing and observing the recommendationsg
41、iven.9. Preparations9.1 Preparation of solutions:9.1.1 Two types of PMA solutions can be used with thismethod.9.1.1.1 Method A, the preferred method, uses a dilute 8 %solution of PMA in water.9.1.1.2 Method B, uses a saturated solution of PMA inwater.NOTE 3The dilute solution is preferred because it
42、 works well withsilver, gold, and palladium coatings, while the saturated solution reactswith silver to give false indications. In addition, the saturated solution hasa tendency to dry up quickly on the test surface before proper evaluationscan be made.9.1.2 Dilute (8 %) PMA solution (for Method A):
43、9.1.2.1 Place a small, clean, and dry glass funnel in the neckof a clean, dry 10 mL volumetric flask.9.1.2.2 Tare out the weight of the funnel and flask on abalance.9.1.2.3 Weigh 0.8 (60.1) g PMA into the flask, using aplastic or glass spatula.9.1.2.4 Rinse the funnel with distilled or deionized wat
44、er todrain any adhering PMA into the flask.9.1.2.5 Dilute to mark with deionized water.9.1.2.6 Place stopper in flask and mix thoroughly. Cloudysolution will clear after standing 10 to 15 min.9.1.2.7 Pour clear solution into a clean glass bottle and sealwith glass stopper. Label bottle with PMA conc
45、entration anddate of preparation.9.1.2.8 Store bottle in refrigerator. Solution may be used forone week.9.1.3 Saturated PMA solution (for Method B):9.1.3.1 Prepare solution in accordance with 9.1.2.1 9.1.2.6, except use approximately5gofPMAinstead of 0.8 g.(Filter out sediment, if necessary.)9.1.3.2
46、 Mix thoroughly for at least 10 min.NOTE 4There shall be a small excess of PMA, seen as a sediment inthe bottom of the flask. This indicates saturation.9.1.3.3 Pour into a clean bottle and label bottle withcontents and preparation date.9.1.3.4 Solution may be used for one week. Store inrefrigerator
47、when not in use.9.1.4 Hydrochloric acid (for both methods):9.1.4.1 Fill the special glass bottle (see 6.4) to approxi-mately halfway from the top.9.1.4.2 Label glass bottle with contents.9.1.4.3 Keep stoppered and under a fume hood when not inuse.9.2 Preparation of applicators:9.2.1 The applicator s
48、hall not react with the PMA solution.Examples are as follows:9.2.1.1 PlatinumMake a small loop using a 32 AWGplatinum wire and an appropriate size mandrel (such as aneedle). Leave a small gap to facilitate release of the PMAdroplet (see Fig. 1). Attach loop to a wooden or plastic handle.9.2.1.2 Plat
49、inum inoculating loops with handles may bepurchased. Cut the loop with a knife to create a small gap (Fig.1), which will facilitate the release of the PMA droplet.9.2.1.3 Glass capillary micropipets in the 1-L size orsmaller.9.2.2 If a platinum loop is used as the applicator, the loopdiameter shall preferably be 1 mm and shall not exceed 2 mm.The loop diameter is kept small for the following reasons:7Magnification standards suitable for calibrating optical microscopes may bepurchased from U.S. National Institute of Standards and Technology, Office ofStanda
