INTERNATIONAL STANDARD ISO 8401 Second edition 2017-02 Metallic coatings — Review of methods of measurement of ductility Revêtements métalliques — Vue d’ensemble sur les méthodes de mesurage de la ductilité Reference number ISO 8401:2017(E) © ISO 2017 ISO 8401:2017(E) COPYRIGHT PROTECTED DOCUMENT © ISO 2017, Published in Switzerland All rights reserved Unless otherwise specified, no part o f this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission Permission can be requested from either ISO at the address below or ISO’s member body in the country o f the requester ISO copyright o ffice Ch de Blandonnet • CP 401 CH-1214 Vernier, Geneva, Switzerland Tel +41 22 749 01 11 Fax +41 22 749 09 47 copyright@iso.org www.iso.org ii © ISO 2017 – All rights reserved ISO 8401:2017(E) Page Contents Foreword v Scope Normative references Terms and definitions Principle Tests on unsupported foils 5.1 5.2 5.3 5.4 5 5.6 General Tensile testing 5.2.1 Principle 5.2.2 Apparatus 5.2.3 Preparation of test pieces 5.2.4 Procedure 5.2.5 Expression of results 5.2.6 Notes on procedure Bending (micrometer bend test) 5.3.1 General 5.3.2 Apparatus 5.3.3 Preparation of test pieces 5.3.4 Procedure 5.3.5 Expression of results Folding (vice-bend test) 10 5.4.1 General 10 5.4.2 Apparatus 10 5.4.3 Preparation of test pieces 10 5.4.4 Procedure 10 5.4.5 Results 10 11 5.5.1 General 11 5.5.2 Principle 11 5.5.3 Apparatus 11 5.5.4 Procedure 12 5.5.5 Expression of results 13 5.5.6 Notes on procedure 13 Mechanical bulging 13 5.6.1 General 13 5.6.2 Apparatus 14 5.6.3 Procedure 14 5.6.4 Expression of results 15 5.6.5 Special cases 15 H ydraulic b ulging Tests on coatings on substrates 17 6.1 6.2 6.3 6.4 General 17 Tensile testing 18 6.2.1 Apparatus 18 6.2.2 Preparation of test pieces 18 6.2.3 Procedure 18 Three-point bending[10] 19 6.3.1 Principle 19 6.3.2 Apparatus 19 6.3.3 Procedure 19 6.3.4 Expression of results 20 Four-point bending[11] 21 6.4.1 General 21 © ISO 2017 – All rights reserved iii ISO 8401:2017(E) 6.4.2 Expression of results 21 22 6.5.1 Principle 22 6.5.2 Apparatus 22 6.5.3 Preparation of test pieces 23 6.5.4 Procedure 23 6.5.5 Expression of results 23 6.5.6 Notes on procedure 23 6.6 Spiral mandrel bending 23 6.6.1 Principle 23 6.6.2 Apparatus 24 6.6.3 Procedure 24 6.6.4 Expression of results 24 6.7 Conical mandrel bending 25 6.7.1 Principle 25 6.7.2 Apparatus 25 6.7.3 Procedure 25 6.7.4 Expression of results 25 6.7.5 Special cases 26 6.8 Mechanical bulging 26 6.8.1 Apparatus 26 6.8.2 Preparation of test pieces 26 6.8.3 Procedure 26 6.8.4 Expression of results 26 Selection of test method 27 Test report 28 Annex A (informative) Methods of producing foils 29 Annex B (informative) Calculation of ductility when increasing the surface area of a foil (bulging) 31 Annex C (informative) Calculation of ductility and tensile strength in the hydraulic bulge test 34 Annex D (informative) Calculation of ductility in the mechanical bulge test 37 Bibliography 38 6.5 iv Cylindrical mandrel b ending © ISO 2017 – All rights reserved ISO 8401:2017(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) The work o f preparing International Standards is normally carried out through ISO technical committees Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters o f electrotechnical standardization The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part In particular the different approval criteria needed for the di fferent types o f ISO documents should be noted This document was dra fted in accordance with the editorial rules of the ISO/IEC Directives, Part (see www.iso org/directives) Attention is drawn to the possibility that some o f the elements o f this document may be the subject o f patent rights ISO shall not be held responsible for identi fying any or all such patent rights Details o f any patent rights identified during the development o f the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso org/patents) Any trade name used in this document is in formation given for the convenience o f users and does not constitute an endorsement For an explanation on the meaning o f ISO specific terms and expressions related to formity assessment, as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL: www.iso org/iso/foreword.html This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings This second edition cancels and replaces the first edition (ISO 8401:1986), o f which it constitutes a minor revision The following changes have been made: — Formula (C.10) has been corrected; — changes have been made in line with the 2016 edition of the ISO/IEC Directives, Part © ISO 2017 – All rights reserved v INTERNATIONAL STANDARD ISO 8401:2017(E) Metallic coatings — Review of methods of measurement of ductility Scope T h i s c u ment s p e c i fie s genera l me tho d s for me as u ri ng the duc ti l ity o f me ta l l ic co ati ngs o f th ickne s s b elow 0 μm prep are d by ele c troplati ng , auto c ata lytic dep o s ition or o ther pro ce s s e s It is applicable to the following methods: — tests on unsupported foils (separated from the substrate); — tests of coatings on substrates I t e s no t apply to I nternationa l Standard s that i nclude s p e ci fic me tho d s o f te s ti ng for i nd ividua l co ati ngs I n the s e c a s e s , the me tho d s s p e c i fie d a re us e d i n pre ference to the me tho d s de s c rib e d i n th i s c u ment a nd are agre e d up on b e foreha nd by the s uppl ier and the pu rcha s er Normative references There are no normative references in this document Terms and definitions For the pu r p o s e s o f th i s c u ment, the fol lowi ng term s and defi n ition s apply ISO and IEC maintain terminological databases for use in standardization at the following addresses: — IEC Electropedia: available at http://www.electropedia org/ — ISO Online browsing platform: available at http://www.iso org/obp 3.1 ductility f f f or cracking 3.2 linear elongation f , of the test piece abi l ity o ratio o a me ta l l ic or o ther co ati ng to u ndergo pl as tic or ela s tic de ormation, or b o th , without rac ture the elongation, Δ l, to a defi n ite i n itia l leng th, l N o te to entr y: T h i s i s ta ken a s a me a s u re o f duc ti l ity N o te to entr y: O ften , th i s ratio i s e xp re s s e d a s a p ercentage Figure of the test piece, i.e the plating, is elongated In bulge tests, however, the surface of the foil is enlarged, requiring calculation of linear elongation from the reduction in the thickness Using the component of deformation f f f Figure b)] In those cases, the thinning of the foil, as calculated from the increase in the surface area, is a better measure of the f Annex B) N o te to entr y: N or m a l l y, the te s t p ie ce s a re elon gate d [s e e (s tre tch i ng) i n on l y one a xi s wou ld give duc ti l ity o a) ] With s ome b end i n g te s ts , the outer l ayer a l s e i n o r m ation ab out the duc ti l ity o the m ateri a l [s e e the m ater ia l (s e e © ISO 2017 – All rights reserved ISO 8401:2017(E) ( d ) ( y − dy ) ( z + dz ) xyz = x − x d d d xyz = xyz + xy z − xz y − yz x dz = dy + dx z y x dz > dy z d l l y t t = d z z a) Tensile test b) Cupping test Figure — Tensile and cupping tests Principle In the testing of unsupported foils separated from the substrate (see Figure ), the foils may consist o f one or more metallic layers There fore, it is possible to measure the ductility o f composites and to determine the influence o f individual layers on overall ductility Methods o f testing o f unsupported foils 4.1 are described in Clause Methods of producing foils for testing are discussed in Annex A In the testing of coatings on substrates (see Figure ), it is especially important to determine the exact point o f crack initiation o f the top layer Attention is drawn to di fferent methods o f discerning this point, by normal or corrected-to-normal vision or with a lens See the guidance in the individual methods 4.2 © ISO 2017 – All rights reserved ISO 8401:2017(E) These methods can also be used to detect embrittlement o f the substrate that may have resulted from the coating process Methods of testing of coatings on substrates are described in Clause Key metal foil substrate Figure — Foil, which can be separated from the substrate Key coating substrate Figure — Coating on the substrate Although ductility is a property o f the material and independent o f the dimensions o f the test piece, thickness o f the coating may have an influence on the value o f linear elongation (Δ l/l0 ) 4.3 4.3.1 Very thin layers have di fferent properties as the build-up o f the initial layers will be influenced by the properties o f the substrate (epitaxy) High internal stresses may be incorporated into the initial layers and these may affect ductility 4.3.2 It is essential that the test piece has uniform thickness, as thinner spots will give rise to premature cracking Also, the current density is lower at thinner parts and higher at thicker parts o f electroplated test pieces; in this way, current density di fferences may result in di fferent ductilities The current density applied should be maintained as uniform as possible over the test piece, and its value reported 5.1 Tests on unsupported foils General These techniques involve measurement of a foil which has been separated from the substrate (see Figure ) In this case, the foil to be tested can also consist of several layers so as to allow measurement o f the influence o f undercoats on the ductility o f the foil sandwich Examples are gold flash on gold/copper alloys and chromium-plated nickel deposits Methods o f producing unsupported foils are given in Annex A Five methods are described: tensile testing (5.2), bending (micrometer bend test) (5.3), folding (vicebend test) (5.4), hydraulic bulging (5.5) and mechanical bulging (5.6) © ISO 2017 – All rights reserved ISO 8401:2017(E) 5.2 5.2.1 Tensile testing Principle Determination o f the linear elongation o f a foil, which is clamped into the jaws o f a tensile testing machine In this type o f stressing, the foil is lengthened, but both the width and the thickness o f the foil diminish 5.2.2 Apparatus This method may utilize conventional mechanical testing equipment, available commercially and in many metallurgical laboratories [1] For some applications, tensile testing equipment adapted to microscopic inspection during the test may be used 5.2.3 Preparation of test pieces Test pieces may be machined, chipped, punched or cut from the metallic foil or prepared by photoprinting with the help of light-sensitive lacquers or light-sensitive foils which are pressed onto a suitable substrate A fter developing the pattern o f the test piece, it is plated into the final form A similar method uses chemical or electrochemical milling of the desired shape from a foil on which has been applied a suitable resist by silk screen printing or by applying a photosensitive resist These last methods are widely used in the printed circuit industry The test pieces are usually rectangular in shape (see Table for recommended dimensions), but can be widened at both ends to avoid breaking in the clamping jaws (see Figure 4) Table — Possible dimensions of tensile test pieces [1] Gauge length (mm) Width (mm) 200 40 50 12,5 25 6,25 Some methods o f preparing the test pieces may cause microcracking at the edges that results in premature failure and erratic results Test piece preparation involving photoprinting or electroforming is preferred to avoid edge defects Test pieces plated into the final form may have thicker edges unless shielding and other techniques are used to ensure uniform current distribution (see Figure 5) Make equidistant marks on the surface of the test piece as illustrated in Figure a) Determine the distance between the marks before testing © ISO 2017 – All rights reserved ISO 8401:2017(E) 6.7.5 Special cases A variation of this test involves winding electroplated or coated copper wire around a cone (see Figure 26) Key electroplated copper wire 100× microscope cracks Figure 26 — Special case of conical mandrel bending 6.8 Mechanical bulging 6.8.1 Apparatus See 5.6.2 6.8.2 Preparation of test pieces Us i ng ver y duc ti le copp er plate s ,1 m m th ick a s the s ub s trate give s s ati s fac tor y re s u lts 6.8.3 Procedure See 5.6.3 E n s u re th at the d ia me ter o f the hole i s s uch th at the field o f view o f the m ic ro s cop e (at 10 ×) i nclude s the area where cracks are expected An mm diameter hole and a mm diameter ball give reproducible results 6.8.4 Expression of results 6.8.4.1 Calculation See Annex D 26 © ISO 2017 – All rights reserved ISO 8401:2017(E) 6.8.4.2 Precision The precision of the method depends on the freedom from scratches of the substrate as these scratches initiate cracks at a lower height o f bulge as would be consistent with the ductility o f the coating Selection of test method 7.1 It is not possible to recommend one method o f measuring the ductility o f coatings that is applicable to all materials and applications The guidelines given in Table may be help ful The results obtained with different methods are seldom comparable Table — Comparison between the respective test methods Suitability for different coatings Test methods Unsupported foils Coatings on substrates Tensile (5.2) Bending (5.3) Folding (5.4) Hydraulic bulge (5.5) Mechanical bulge (5.6) Tensile (6.2) Three-point bending (6.3) Four-point bending (6.4) Cylindrical mandrel bending (6.5) Spiral mandrel bending (6.6) Conical mandrel bending (6.7) Mechanical bulge (6.8) Ductile 1 2 1 Brittle 2 3 3 4 3 Perception of cracks 5 4 3 2 Accuracy 3 2 Sampling efforta 3 5 3 3 Key a acceptable only i f no alternative method available acceptable i f justified by other factors satis factory for most purposes very satis factory, i f not ideal best possible Sampling effort is to be understood as the time devoted to preparing the test piece to be tested 7.2 Coatings less than 10 µm thick should be tested on a suitable substrate For brittle deposits, the 7.3 Coatings thicker than 10 µm can be tested in the form o f foils Ductile foils can be tested by hydraulic 7.4 Brittle and/or highly stressed coatings even when thicker than 10 µm may have to be tested when tensile testing method is preferred but the bending tests (6.5 and 6.6) should be satis factory For ductile deposits, the bending test (6.4) is preferred bulging (5.5) or tensile testing (5.2 ) Brittle foils can be tested by the micrometer bend test (5.3 ) or by mechanical bulging (5.6) applied to a suitable, ductile substrate, in which case tensile testing (6.2) is preferred, although the cylindrical mandrel bending (6.5) or spiral mandrel bending (6.6) tests can be used © ISO 2017 – All rights reserved 27 ISO 8401:2017(E) Test report The test report shall include the following information: a) a reference to the method used; b) the results and the method of expression used; c) details of the preparation of the test piece 28 © ISO 2017 – All rights reserved ISO 8401:2017(E) Annex A (informative) Methods of producing foils A.1 General Metal foils can be prepared by using a substrate from which the electrodeposit can be readily separated Several methods can be used (see A.2 and A.3) A.2 Plating onto a soluble substrate The substrate is dissolved a fter applying to it the coating to be tested This is a method which can be used i f the foil to be tested will not be a ffected by the dissolving solution Even i f the attack is only visible by a diminution in gloss, it would be possible that an embrittlement o f the sur face would enhance the beginning o f cracking throughout the whole layer For gold layers on copper substrates, dissolution of the copper with nitric acid solution is often used In the case of plated plastic, it is possible to dissolve the plastic material into an organic solvent without a ffecting the quality o f the test foil A.3 Plating onto a non-adherent substrate A.3.1 General Plating is carried out on a metal substrate to which the plating will not adhere; the foil is then peeled from the substrate A.3.2 Plating on stainless steel Care shall be taken in this case that the surface of the stainless steel is free from scratches as these will be copied in the plated foil and will start the propagation o f premature cracks The stainless steel may require anodic cleaning for 15 s in a hot alkaline cleaner A.3.3 Plating on copper or bronze sheets A.3.3.1 In the case o f copper or bronze sheets, it is easy to polish the surface before passivating Also, after the test, these sheets can be repolished and used again There exist several passivating methods (see A.3.3.2 to A.3.3.4) A.3.3.2 Electroplating the copper or bronze substrate with µm to 15 µm o f bright nickel and subsequent passivation by immersion in a mass fraction o f % to % solution o f chromic acid for 30 s to 60 s Before immersion in the electroplating solution, the test surface should be connected to the negative electrical supply and the current switched on so as to prevent spoiling the passivation (live entry) A.3.3.3 Plating the copper or bronze substrate with arsenic, using as electrolyte 59 g o f arsenic trioxide (As O ) and 21 g o f sodium hydroxide (NaOH) in l o f water Plate for at 0,3 A/dm2 and 18 °C to 30 °C, using as anodes carbon or graphite A.3.3.4 Immersion in a polysulfide solution — 50 g o f sodium polysulfide (Na2 S n ) in l of water © ISO 2017 – All rights reserved 29 ISO 8401:2017(E) A.3.4 Plating on steel A steel panel electroplated with nickel may be used For example, a piece o f cold-rolled steel, o f any convenient size, shall be properly cleaned, acid dipped and electroplated with about 7,5 µm o f nickel After rinsing, the test piece is either passivated (see A.3.3 ) or cleaned anodically for 15 s in a hot alkaline cleaner, acid dipped in 0,5 mol/l sulfuric acid, water rinsed, and placed in the electroplating solution of the metal to be tested An electrodeposit of the desired thickness is electroplated on the prepared surface 30 © ISO 2017 – All rights reserved ISO 8401:2017(E) Annex B (informative) Calculation of ductility when increasing the surface area of a foil (bulging) During the stressing of a material, two strains are observed: a) elastic de formation — in electroplated metals, this part o f the overall de formation is very small as compared with plastic deformation, as shown in Formula (B.1): dl » 2% , l (B.1) This type o f de formation will give rise to a slight diminution o f the volume b) plastic de formation — this part o f the overall de formation can be as high as 42 % The volume o f the material will be constant The tensile test gives the correct elongation in a direction z and shrinking of dimensions in the directions x and y (see Figure a) Let the volume of an infinitesimal test piece be xyz The cupping test (see Figure b) gives correct elongation also in the z direction, but in this case, z is the direction perpendicular to the surface, i.e the diminishing thickness d z has to be taken into account The elongation in the y direction is less because in the plane xy, there will occur elongation in both directions x and y As the direction of flow is contrary to the flow in a tensile test, it is necessary to use Formula (B.2) D= dz z − dz (B.2) to obtain values equivalent to those obtained from the tensile test (see Figures B.1 and B.2) © ISO 2017 – All rights reserved 31 ISO 8401:2017(E) d d d xyz = ( x − x ) ( y − y ) ( z + z ) d l l t t = d z z Key material flow Figure B.1 — Tensile test 32 © ISO 2017 – All rights reserved ISO 8401:2017(E) xy = A + d x ) ( y + d y ) = A + ∆A (x d d d ( ) ( d ) ( x + dx ) ( y + dy ) xyz = ( x + x ) ( y + y ) ( z − z ) ∆l c l c = d z xy = z − z d zA = ( z − z ) ( A + ∆A ) z z z z − dz dz z − dz D = ∆l l = A + ∆A A −1 = = −1 = A + ∆A A A + ∆A A −1 −1 ∆A A Key material flo w Figure B.2 — Cupping test (hydraulic/mechanical) © ISO 2017 – All rights reserved 33 ISO 8401:2017(E) Annex C (informative) Calculation of ductility and tensile strength in the hydraulic bulge test T he volu me o f the dome radius, r forme d du ri ng hyd rau l ic bu lge te s ti ng i s a , o f the b as e o f the dome a nd i s given b y fu nc tion Formula (C.1) (see Figure C.1) o f the height, h , and the Key metal foil Figure C.1 — Calculation of ductility for hydraulic bulge test V = π h3 + π hr 2 (C.1) Solving Formula (C.1) for h h= yield s Formula (C.2): 3V + +r + π π 3V 3 3V − +r π π 3V (C.2) The volume of the test piece remains constant during the test, i.e Formula (C.3) (see Figures B.1 and B.2): ( zA = z − ∆z ) ( A + ∆A ) � (C.3) where z A 34 is the thickness of the foil; is the surface area © ISO 2017 – All rights reserved ISO 8401 : 01 7(E) D, i s defi ne d as the ratio o f the de cre as e i n th ickne s s , Δ z, to the thickness of the foil in the T he duc ti l ity, stressed stage, z − ∆z , Formula (C.4): D= ∆z A + ∆A ∆A = −1 = z − ∆z A A (C.4) (see Figures B.1 and B.2) The surface areas given in Formula (C.3) are those of the base of the dome, A , and of the surface of the dome, A + ∆A Formula (C.5): , a nd are given b y A = πr A + ∆A = πRh where R � (C.5) is the radius of the sphere of which the dome is a part (see Figure C.1) Formula (C.4) D= Rh R= −1 r2 The radius, R Formula (C.6): may then b e written a s (C.6) , i s given b y the rel ation sh ip (R − h) + r = R and therefore Formula (C.7): h2 + r2 (C.7) 2h Substituting in Formula (C.6) yield s Formula (C.8): h D= r (C.8) T he duc ti l ity i s the s quare o f the ratio o f the height o f the dome to the rad iu s o f the dome Formula (C.2) may b e combi ne d with Formula (C.8) to yield an expre s s ion for p ercentage, i n term s o f the volu me o f the dome and the rad iu s o f the c yl i nder, 3V 3V + +r π π D= + r 3V 3V − +r π π r duc ti l ity, e xpres s e d as a Formula (C.9): (C.9) Formula (C.9) is plotted in Figure C.2 © ISO 2017 – All rights reserved 35 ISO 8401:2017(E) Key l/l in % V in ml Δ Figure C.2 — Plot of Formula (C.9) The tensile strength, σ , o f the σ =p foi l i s given b y Formula (C.10): R 2z (C.10) where p R z 36 is the pressure which causes the test piece to burst; is the radius of the sphere of which the dome is a part; is the thickness of the test piece © ISO 2017 – All rights reserved ISO 8401:2017(E) Annex D (informative) Calculation of ductility in the mechanical bulge test According to the same underlying principle as used in the calculation o f the hydraulic bulge test (5.5), the ductility will be as shown in Formula (D.1): D= where A max −1 Ao (D.1) A o = πR A max is the surface area of the cone (see Figure D.1) the dome KK′ and the cone-mantle MK − K′M′: A max consists of the sum of the areas of Adome = πr r − r − k A mantle = π R+k (R − k) + h − r − r − k A max = πr r − r − k + π ( R + k ) ( R − k ) + h − r − r − k With a programmable calculator, it is not di fficult to obtain a function D = f (h) Key foil Figure D.1 — Calculation of ductility for mechanical bulge test © ISO 2017 – All rights reserved 37 ISO 8401:2017(E) Bibliography [1] [2] [3] ANSI/ASTM E 8a, Test Methods for Tension Testing of Metallic Materials ASTM B 490, Standard practice for micrometer bend test for ductility of electrodeposits P rater T.A., & Re ad J.H The strength and ductility o f electrodeposited metals: I The hydraulic bulge test Plating 1949, 36 p 1221; II Some data on acid copper deposits Plating 1950, 37 p 830; III Some problems related to specimen preparation Plating 1951, 38 p 142 [4] Re ad H.J., & Wh alen T.J The ductility of plated coatings Tech Proc Am Electroplaters’ Soc 1959, 46 p 318 [5] Rolff R Die Messung der Duktilität mit Hil fe eines hydraulischen Wölbungsgerätes Metalloberfläche 1978, 32 p 537 [6] N akah ara S., O kinaka Y., T urner D.R A simple ductility tester for metal films J Test Eval 1977, p 178 [7] Dahms W., & Rolff R Messmethode zur Bestimmung der Duktilität von galvanisch oder chemisch reduktiv abgeschiedenen Metallschichten Metalloberfläche 1981, 35 pp 402–405 [8] S uch T.E The prevention of cracking in nickel electrodeposits Trans Inst Metal Finishing 1954, 31 p 190 [9] C ashmore S.C., & F ellows R A new method of ductility testing of nickel electrodeposits Trans Inst Metal Finishing 1962, 39 p 70 [10] ASTM E 290, Standard Test Methods for Bend Testing of Material for Ductility [11] L o C.C The four-point bend test for measuring the ductility of brittle coatings J Electrochem Soc 1978, 125 p 400 [12] ASTM B 489, Standard practice for bend test for ductility of electrodeposited and autocatalytically deposited metal coatings on metals [13] E dwards J Spiral bending test for electrodeposited coatings Trans Inst Metal Finishing 1958, 35 p 101 [14] P into N.P J Met 1950, 190 p 1444 38 © ISO 2017 – All rights reserved ISO 8401 : 01 7(E) ICS 25.220.40 Price based on 38 pages © ISO 2017 – All rights reserved