THE ENGINEERING PROPERTIES OF ELECTRO LESS …

1 , ,thecoatingisdepositedontoapart' ,electrolessnickelcoatingsareuniform,har d,relativelybrittle,lubrious, , ,andhowtheyrelatetotheuseofthecoat-ing, ,commercialcoatingsmaycontain5to12percen tphosphorusdissolvedinnickel, ~percent, ~percentphosphorusconsistonlyofaphasenic kel-phosphorusandarenormallyamorphousto ' 2 ' 3 .Electrondiffractionstudies ofdepositshaveconfirmedtheirlackofcrysta lstructureatmagnifica-tionsupto150,0004 ---~~-~~--Thecontinuityofelectrolessnick elcoatingsalsodependsupon~' ~ ,andespeciallythoseappliedfrombathsstabi lizedorbrightenedwithheavymetalsorsulfur compounds, 'sproper-t:i;ces:YLespecia, ~eXampleo~thistypeofdepositisshowninFigu re21' 2 ' 5 ' 6 .F'IGUREIC rosssectionalviewofa 75llmthickElectrolessNickel;"d~posit.

2 ,',,400 Xmagnification.',Etchedin2%nital.~-"~Cr6 essectionalviE;!wofa 25llm'' ,c'---" , ,eliminatethesevariationsandproducethemo rehomogeneousstructureshowninFigure12, 4 , 5 , 7 .FIGURE3 Crosssectionalviewofalaminar15~ , C(420 to500 F)structuralchangesbegintooccur;First,co herentandthendistinctparticlesofnickelph osphite(Ni3P) C(600oF) , , ,coatingisshowninFigure41, 2 , 5 ,7, , 4 Crosssectionalviewofa 25~mthick,coatingafterheattreat-mentat40 0 ,anickel-ironintermetalliclayerbetweenth ecoatingandthesubstratecanbeproducedby4h ourheattreatmentsattemp-eraturesabove650 C(1200oF).Thislayerprovidesaverywearresi stantsurface,andinsomeenvironmentswillin creasethecorrosionresistanceofthecoating 2,5,7, ' , ,however,tensilestressesof15to45 MPa (2to6ksi) ~FIGURE ".

3 "5 5za:w 10I-z 155678910111213 PHOSPHORUSCONTENT,PERCENTT hestructuralchangesduringheattreatmentat temperaturesabove220 C(420 F), ,8, ,orbythe~resenceofexcesscomplexingagents intheplatingsolution9, ,theadditionofonly5mg/lofbismuthandantim onytomostbathswillcausethedepositstresst oincreasetoasmuchas350 MPa(50ksi) ~ofinteralstressalsoreducethecoating'sdu ctilityandincreaseitsporosity2, ,thicknesscanvarysignificantlydependingu ponthepart' , ~ ,slots,blindholes, , ,oftentheoverallfinishingcostofapartwill belesswithelectrolessnickelthanwithelect ro-platedcoatings, ,thesubstitutionofelectrolessnickelforha rdchromiumonmanyofthecylindersandrollsus edintheprintingandtextileindustrieshasno tonlyreducedthecostofplatingby40percent, butalsohasallowed55percentofthegrindingt imetobesaved1 2 ------------------~--~~~~--------,Withel ectrolessnickel, ~~m( )arecommonlyappliedforelectroniccomponen ts,whilethoseasthickas75to125~m(3to5mils ) ~m(10mils)

4 ,whichoccurswithcatalyticmetals,together withtheassociatedabilityofthebathstoremo vesubmicroscopicsoils, (60ksi) ,butusuallyexceeds300 MPa(40ksi)2,5,7:Withnon-catalyticorpassi vemetals,suchasstainlesssteel, ,however,thebondstrengthofthecoatingnorm allyisatleast140 MPa(20ksi)2,5, (40and50ksi) +200 C(270 to400 F) ,bakingwillhaveonlyaminimaleffectuponbon dstrength2,5, , ~Jlom-t:PIf!J(}'0I'II11/SZ''0\\Salm~k~"~ "'0'~-'~-:;;;-;;;:'"'tl~+~fl15''\~.ffltJ ''0 Iifill>'\SC/JI1;elre\,III~\i_'Of--~'j,\l !1IJ'18/"'"688tJ'I00110<J-"c:000Ni .. '' ' "1"'-"1' (1620DP),whichistheeutectictemperaturefo rnickelphosphide(Ni3P).Thetemperatureatw hichthecoatingiscompletelyliquid,however ,increaseswithde-creasingphosphorusconte ntfromaboutBBODC(1620Dp)at11percent--the eutecticpoint--toapproximately1450 C(2640DP) , (1620DF).)

5 Forexample,at900DC(1650DF)coatingscontai ning5,Band10~percentphosphorousare46, , , ~percentphosphorus2,7,15,16, ~ ''\.6-,.4~2-,.0-:a.~6,'"7 FIGURE ,"{, ~~ ( )respectivelylB, , ,however, , ~~ , ~-------FIGURE 9111 DPhosphoruscontent,%, '<,10<,.., ~ , , ,however, , C(500 F)improvethemagneticresponseofallelectro lessnickelsandcanprovidecoercitiesofabou t100to300oersteds20, , (100ksi). 2 0000 ,/0V00,J00010302070 BOO" ,% ~percent(aselongation).Whilethisislessth anthatofmostengineeringmaterials, , ,however, , ,orwithdepositscontainingmetallicorsulfu rimpurities,ductilityisgreatlyreducedand mayapproachzero5, (4200F)causea 80to90percentreductioninstrengthandcande stroyductility, ,whichshowstheeffectofdifferentonehourhe attreat-mentsontheelongationatfractureof brasspanelscoatedwitha 6percentphosphoruselectrolessnicke12 0 Becauseoftheirhighphosphoruscontentandhi ~hpurity, C(SOO F) ,of14001000600200a2"'\It1I.}

6 JaEffectofheattreatmentontheductilityofa ,DCThemodulusofelasticityofnon-heattreat edelectrolessnickelcoatingscontaining10t o11percentphosphorusisabout200 GPa(28XI06psi)andisverysimilartothatofst ee12, (18xl06psi) (4000F)causestheirmodulusofelas-ticityto increasesignificantly2, , , 5 ---------------------------------------- -FIGURE12 Temperature,of70012006001110050060040060 0300400200200"000,I''\0i,I\II""1'-0-0~0 ",'">~~. ,OCForsomeapplications, , , C(650 F)for4to6hoursandat290 C(550 F) C(500 F)arealsooccasionallyused, C(450 F)andbelow, , :--<:..00-c(750'F}0/"~02C(55 SoF\I0/~I~//7"310"c(590" '--"0"c1500i"-:0(/230o~(445'Fl/'0f(200 C1390 Ff/'0090so6040110100 , (7500F) , , ,OFTesttemperature. ,':<::'treated"400'C(750' \,Asdeposited'"-<,Chromium~~-,"0"<,~".)) )))))

7 , ;:::"010010080402011100 Effectoftemperatureontheelevatedtemperat urehardnessofa ,electrolessnickelcoatingshaveexcellentr esistancetowearandabrasion, ,whichshowstheresultsoftypicalTaberAbras erWeartestsofelectrolessnickelcoatings,a ndcomparesthemtoelectroplatednickelandch romium26 ,27, THETABERABRASERRESISTANCEOFDIFFERENTENGI NEERINGCOATINGSCOATINJHEATTREA'lMENTTWI, mg/1000 Cycles(1)WattsNickelNone25 ElectrolessNi-9%PNone17 ElectrolessNi-9%P300oC/lhr10 ElectrolessNi-9%P500oC/lhr6 ElectrolessNi-9%P650oC/lhr4 ElectrolessNi-5%BNone9 ElectrolessNi-5%B400oC/lhr3 HardChromiumNone3(1)TaberWearIndex,CS-IO abraserwheels,1000gramload, , 2 COMPARISONOF THE FALEXWEARRESISTANCEOFCHROMIUMANDELECTROL ESS NICKEL COATINGSCOATII'GPLATEDV-BLOCKSUNPLATEDST EELPINSHeatHardness,WearWear,mg(1)Treatm ent"lHNmg (1) (1) (400lb) ,highphosphorusdepositslikeipro-videtheb estresistancetoadhesivewear29,30.

8 ~'~'"5;">~..0E~.e~,'0> :.deposited- I2ilr-,--r-1186250 c{480of}for1h_ "::<,2400"c(750of)for1~11,6 <, "E~o.~.'" ~ ~ ~ ~ , ,one-halfofthatofsteel, , 2 6 , 3 0 .SOLDERABILITYANDWELDABILITYE lectrolessnickelcoatingscanbeeasilysolde redandarecommonlyusedinelectronicapplica tionstofacilitatesolderingoflightmetals, ,mildlyactivatedrosin(RMA) to110 C(2100to230 F) ,suchasthoseresultingfromsteamaging,acti vatedrosin(RA)fluxisusuallyrequiredtoobt ainwettingofthecoating2, 3 1 CORROSIONRESISTANCEE lectrolessnickelisabarriercoating,itprot ectsitssubstratebysealingitofffromtheenv ironment, ,however, ,becauseoftheirfreedomfromgrainorphasebo undaries, ,ElectrolessNickelisalmosttotallyresista nttoalkalies,tosaltsolutionsandbrines,to chemicalandpetroleumen"'-~nments, ,toorganicacids, ,9, (andcorrosionresistance)

9 ,however, , ,whichcomparesthecorrosionexperiencedbye lectrolessnickelcoatingscontainingSto10~ percentphosphorusinaerated,6percentcitri cacidatSOoC(120 F) 1210 540,;----;-~;---;--~----:--;--7.;---":-- ~PHOSPHORUSCONTENT,WT. PERCENTCORROSIONOFTABLE3 ELECTROLESS NICKEL INVARIOUSENVIRONMENTSEN\lI:ROtMENTTEMPER ATURECORROSIONRATE cIlm/ ympyAceticAcid, ,27% ,25% ,20% , ,3~%Salt, ,3'>%Salt,H2 SSaturated95 NilNilCalciumChloride,42% , ,5% ,1% ,88% ,5% ,2% ,85% ,36% ,1% ,10% ,90% ,85% ,50%20 NilNilSodiumCarbonate, ,45%20 NilNilSodiumHydroxide,50% ,10% ,65% ,AcidMine, ,Distilled,N2deaerated100 NilNilWater,Distilled,O2 Saturated95 NilNilWater,Sea(3'>%Salt)95 NilNilInthesetests, , ,tin, ' ,whichshowstheresultsofcorrosiontestswit h6differentelectrolessnickeldepositsinC0 2saturated,3~percentsaltbrineat9 SoC(2000F) 4 EFFECTOF COMPOSITIONONCORROSIONRESISTANCEOF ELECTROLESSNICKELINCO2 SATURATED,3~PERCENTSALT BRINE AT9 SoCDEPOSITPHOSPHORLSOTHERCORROSIONRATECO NTENT,%ELEMENTS,% ( )forto660umz'y(26mpy)

10 ,buttheirbaths' , , to260 C(420 to500 F)nickelphosphideparticlesbegintoform, ' $,furthercontributingtothedeposit' ,whichshowstheresultsoftestswithdeposits , , C(7500F)isshowninFigure79 FIGURE 17 Crosssectionalviewofa75romthick_electrol essnickelde-positafterheattreat-mentat40 0 5 THEEFFECTOF HEATTREATMENTONTHECORROSION OFELECTROLESSNICKELIN10%HClHEATTREATMENT DEPOSITCORROSIONRATEHARDNESS,u mz' C(375 E)for11, C(550 F)for6hours900190075290 C(550 E)for10hours970140055340 C(650 E)for4hours97090035400 C(750 F)for1hour1050120047 Bakingat190 C(375 F),likethatusedforhydrogenembrittle-ment relief, ,however,causedthecoating'scorrosionrate toincreasefrom15).Im/y( )tomorethan900).Im/y(35mpy) ,hardenedcoatingsshouldnotbeused9 SUMMARYOFTHEPROPERTIESOFELECTROLESSNICKE LCOMPOSITIONSTRUCTUREINTERNALSTRESSDENSI TYMELTINGPOINTELECTRICALRESISTIVITYTHERM ALCONDUCTIVITYMAGNETICSUSCEPTABILITYTENS ILESTRENGTHDUCTILITYMODULASOFELASTICITYC OEFFICIENTOFTHERMALEXPANSIONADHESIONSTRE NGTHHARDNESS,ASDEPOSITEDIMRDNESS,HEATTRE ATED(400 C/lhr) ,ASDEPOSITEDTABERWEARRESISTANCEHEATTREAT ED(400 C/lhr)CORROSIONRESISTANCERND.