Adhesion strength and wear resistance of a Al2O3 films deposited on 440C stainless steel

Surface and Coatings Technology 182(2004)242–2500257-8972/04/$-see front matter ᮊ2003Elsevier B.V .All rights reserved.doi:10.1016/S0257-8972(03)00862-4Characterization of electrolytic ZrO y Al O double layer coatings on223AISI 440C stainless steelC.C.Chang,S.K.Yen*Department of Materials Engineering,National Chung Hsing University,Taichung 40254,Taiwan,ROCReceived 18April 2003;accepted in revised form11July 2003AbstractElectrolytic ZrO y Al O double layer deposition was conducted on AISI 440C stainless steel in ZrO (NO )and subsequently 22332in Al (NO )aqueous solutions.After drying and annealing,the ZrO y Al O coated specimens were evaluated by X-ray diffraction 33223analysis,SEM,AES component depth profiling,hardness tests,wear tests,scratch tests,and dynamic polarization ing poly-etheretherketone (PEEK )as a pin,weight loss of the coated specimen was only 1y 4of the uncoated materials.The scratch tests indicated that the adhesion strength of the coating was greater than the yield stress of the metal substrate.Electrochemical polarization tests of the coated specimen and optical photograph or SEM observation revealed 10times more corrosion resistance than the uncoated in 1M HCOOH and 3.5%NaCl aqueous solutions.ᮊ2003Elsevier B.V .All rights reserved.Keywords:Electrolytic deposition;ZrO y Al O double layer coating;AISI 440C stainless steel2231.IntroductionAISI 440C stainless steel,one of the martensitic stainless steels,is capable of being age hardened with the tensile strengths of 1970MPa.In addition to corro-sion resistance,it exhibits the highest hardness of har-denable stainless steels.It has been widely used for ball bearings and molds w 1,2x .The nominal chemical com-positions in wt.%of AISI 440C stainless steel are 17.0Cr,1.0Si,1.0Mn,0.75Mo,1.1C,0.03S and 0.04P .Die materials used for plastic injection molding appli-cations are generally subjected to severe abrasive wear fromfibrous fillers and corrosion fromepoxy resin.Due to the high precision requirement on the semiconductor integrated circuit (IC )chip packaging,wear and y or corrosion are always the major problems of die molds.Therefore,some surface modification technologies are used to reduce these problems.Currently,most of packaging dies are coated with hard chrome to reduce wear and corrosion problems.However,the environment contamination is getting serious,and the less contami-native coating technologies are required to replace hard*Corresponding author.Tel.:q 886-4-22852953;fax:q 886-4-22857017.E-mail address:skyen@.tw (S.K.Yen ).chrome.Also,as IC lead frame design becomes more sophisticated,the thickness of hard chrome is too large to be compatible.Recently,electrolytic Al O and ZrO coatings on 232metal have been verified to improve the corrosion resistance w 3–7x and wear resistance w 6,7x of implant alloys.This method has several potential advantages,including the cheap deposition technology,low prepa-ration temperature,high purity of deposits,the ability to cover complex shapes of various materials and the application of multi-component oxides w 8,9x .Especially,the filmthickness can be controlled under 3m mwhich is required for the sophisticated IC packing molds.Electrolytic deposition is achieved via hydrolysis of metal ions or complexes by electrogenerated base to formhydroxide or peroxide deposits on cathode sub-strates.Hydroxide and peroxide deposits can be con-verted to corresponding oxides by thermal treatment w 3,5,8x .In this study,the electrolytic ZrO y Al O double 223layers coating has been deposited on AISI 440C in ZrO (NO )and Al (NO )aqueous solutions,respective-3233ly.The characteristics of the coating have been exam-ined,including crystal structures,hardness,adhesion,wear and corrosion resistance.243C.C.Chang,S.K.Yen /Surface and Coatings Technology 182(2004)242–250Fig.1.SEM observations of (a )ZrO coated,(b )Al O coated and 223(c )ZrO y Al O double layer coated specimens annealed at 4508C 223for 3h.Fig.2.SEM Cross-sectional observation of ZrO y Al O coated spec-223imen annealed at 4508C for 3h.Fig.3.XRD diagrams of ZrO as coated specimen,and annealed at 24508C for 3h.2.ExperimentalSample preparation —AISI 440C stainless steel was cut into sheets with 55=40=1mm.All specimens were polished to a mirror finish (R a s 0.059m m )with Al O powder,then degreased by detergent and further23ultrasonically cleaned in deionized water and acetone,then dried by N gas.2Electrolytic deposition —The electrolytic ZrO y 2Al O double layers coating was deposited on AISI 23440C stainless steel in 0.03125M ZrO (NO )and 32subsequently in 0.01M Al (NO )aqueous solution at 33voltage y 1.0to y 1.2V for 500to 700s at room temperature,using an EG&G M273A Potentiostat and M352software.The sample was the cathode,graphite bars (f s 5m m ,l s 55mm )were the anode and satu-rated Ag y AgCl was the reference electrode.The coated specimens were then naturally dried in air and annealed for 3h at 300,350,400,450,500and 5508C,respectively.The thickness of coatings was measured using surface profilometer (Dek tak,USA ).3SEM,XRD and AES —The surface morphology of coated specimens was observed by scanning electron microscopy (SEM,JEOL,JSM-5400,Japan ).The crys-tal structure of ZrO y Al O coated specimen was ana-223lyzed grazing incident X-ray diffraction (GI-XRD )using a MAC MO3X-HF diffractometer,with Cu K a radiation244 C.C.Chang,S.K.Yen /Surface and Coatings Technology 182(2004)242–250Fig.4.XRD diagrams of ZrO y Al O as coated specimen,annealed 223at 350,400and 4508C,respectively,for 3h.Fig.5.AES component depth profiles of ZrO y Al O coated specimen annealed at 4508C for 3h.223(l s 15.418nm ),the range of 2u from10to 708and incident angle of 0.58,at a scanning rate of 18min ,a y 1voltage of 40kV ,and a current of 30mA.The component depth profiles were plotted using an auger electron spectroscopy (AES Fison VG Microlab 310D ).Specimens were sputtered by 5keV Ar with a beam q current of 0.05A,and a sputtering rate of 1nms .y 1Hardness,wear and scratch tests —Hardness meas-urements were made on all specimens using a Vickers microhardness tester (Mitutoyo MVK-GB )with a load of 25g.Wear test was carried out by a pin-on-disc systemwith poly-etheretherketone (PEEK )pin (c s 2mm ),and the coated specimen disc,at a load of 8.28MPa,sliding speed of 0.12ms and a total sliding y 1distance of 10000m.PEEK is a new generation of engineering plastics for plastic packaging in microelec-tronics that has high T value and can stand temperature g up to 2508C for long period of time w 10x .PEEK is the high-performance engineering plastic,with high thermal stability ()2508C ),excellent chemical resistance and superior mechanical,such as the hardness of 108HRB,and the tension strength of 110MPa at RT,and 48MPa at 1508C w 10,11x .The wear loss was measured by the disc weight difference before and after each test.To study the adhesion of the coating on substrate,the ZrO y Al O coated specimens annealed at 4508C were 223tested by scratch (TEER-200,UK ),using diamond indenter as the pin with an initial load 2N,scratch speed 10mm min ,loading rate 50N min and the y 1y 1end load 100N.The friction force between the specimen and diamond indenter was monitored by a load cell attached to the working table,as shown in the previous paper w 7x .Surface energy and work of adhesion —Surface energy measurement were made on the uncoated,ZrO 2coated,and Al O coated specimens using the three-23liquid (water,formamide and ethyleneglycol )procedure by the dynamic contact angle analyzer research model(FTA200,First Ten Angstroms,USA ).When two unlike ˚phases i and j are brought together reversibly,the surface free energy change equals to the free energy of adhesion or the negative of adhesion work w 12,13x .In other a D G ij words,it can be presented by the following equation,a aD G s g y g y g sy W (1)ij ij i j ijwhere g is the interface energy of i y j ,g and g the ij i j surface energies of phase i and j .245C.C.Chang,S.K.Yen /Surface and Coatings Technology 182(2004)242–250Fig.6.Vickers hardness of the uncoated and ZrO y Al O coated specimens annealed at various temperatures and the hardness increased by 223coatings.Polarization test —The corrosion resistance of the ZrO y Al O coated were evaluated by an electrochemi-223cal dynamic polarization tests in 1M HCOOH and 3.5%NaCl aqueous solutions,respectively,also by using a EG&G Model 273A,M352.After the open-circuit potential became steady,the cyclic polarization test was from y 0.2V (vs.open-circuit potential )to 1V (Ag y AgCl ),then back to open-circuit potential at a scanning rate of 0.167mV s .The first oxidation-reduction y 1equilibriumpotential E was derived when current 01density equaled zero during the applied voltage increased (forward cycle ).If oxidation is due to the corrosion of electrode,this potential is also named corrosion potential E ,and the corrosion current den-corr sity i can be calculated at this potential.The second corr oxidation-reduction equilibriumpotential E was 02derived when current density was back to zero again during the applied voltage decreased (backward cycle ).246 C.C.Chang,S.K.Yen /Surface and Coatings Technology 182(2004)242–250Fig.7.Friction force vs.the normal load of the scratch test on ZrO y Al O coated specimen annealed at 4508C for 3h.223Table 1Weight Loss of the uncoated and ZrO y Al O coated specimens annealed at various temperatures,using PEEK as the pin223Uncoated ZrO y Al O coated specimen annealed at various temperatures 223specimen3008C 3508C 4008C 4508C 5008C Weight loss 0.18330.11330.07670.05730.04850.0474(mg )"18.4%"11.9%"7.2%"9.7.%"13.4%"14.2%If the oxidation is decreased abruptly at some passivation potential E ,because of the formation of passivation pass films and corrosion rate falls to very low,and the beginning current density is named the critical passive current density i ,and the stable current density is crit named the passive current density i .If the oxidation pass is increased abruptly at some pitting potential E pit because of the breakdown of passive filmand the localized corrosion of the electrode,the crossover of the backward cycle and the forward cycle on the anodic polarization region will be found because of repassiva-tion and defined as protection potential E .pp 3.Results and discussion 3.1.Surface morphologySEM observations of the ZrO ,Al O and ZrO y 2232Al O coated specimens with the same film thickness 23of 0.7m mare shown in Fig.1.More and larger cracks are found in Fig.1a and b.On the other hand,less and smaller cracks are found in Fig.1c.Obviously,the mud cracks found on the single layer coating,can be reduced by the double layers coating for the same film thickness of 0.7m m.SEM cross sectional observation of the ZrO y Al O coated specimen is shown in Fig.2.The 223thickness of ZrO coating and Al O coating was 223approximately 0.3m mand 0.4m m,respectively.3.2.Crystal structures and component profiles The XRD diagrams of ZrO coated specimens are 2shown in Fig.3.No obvious diffraction peak was found on the patterns of the as coated samples.The (101),(110)and (112)peaks of tetragonal ZrO were found 2on the specimen annealed at 4508C.The XRD diagrams of the ZrO y Al O coated specimens are shown in Fig.2234.The (100),(002)and (200)peaks of aluminum hydroxide hydrate (Al (OH )H O )were found on the 262as-coated.The (020),(110),(130),(111),(140),(221)and (002)peaks of aluminum oxide hydroxide (AlO (OH ))were found on the coated specimens annealed at 350and 4008C.The (102)and (220)peaks of aluminum oxide hydrate (Al O H O )were found 10152at 400and 4508C,and finally,the (111)and (220)peaks of g -Al O were found at 450,500and 5508C.23No obvious ZrO peak was found for double layer 2coating.If the missing of ZrO peak was caused by 2value of X-rays penetration depth at GI-XRD the grazing angle chosen,the peaks of metal substrate should not be found either.However,the (110)and (200)peaks of 440C substrate were found,as shown in Fig.4.There-fore,the factor of grazing angle chosen should be excluded.However,it is more possible that the conden-sation of Zr (OH )and the crystallization of ZrO should 42be delayed by the existence of H O in the top layer.2AES component depth profiles are plotted in Fig.5,It is confirmed that the deposited coating is composed of two layers.The inner layer is ZrO and the out layer 2is Al O .A part of Fe diffused out to ZrO layer and a 232part of O diffused into metal substrates.This result is similar to the oxidation of AISI 430stainless steel where the oxidation rate of Fe is greater than that of Cr at 4508C w 14x .The phenomenon of interdiffusion may be also caused by the vacancy which was formed due to the evaporation of H O during the condensation reaction of 2Zr (OH )w 5x .Such an interdiffusion between ZrO and 42substrate also retard the crystallization of ZrO ,so that 2no obvious diffraction peaks of ZrO was found at 45028C annealing,as shown in Fig.4.3.3.HardnessVickers Hardness of the uncoated and ZrO y Al O 223coated specimens annealed at various temperatures are247C.C.Chang,S.K.Yen /Surface and Coatings Technology 182(2004)242–250Fig.8.SEM observations and EDS mapping of ZrO y Al O coated annealed at 4508C for 3h at the scratch load around (a )22N and (b )100223N.shown in Fig.6a.The temper softening effect during annealing and the secondary hardening effect approxi-mately 4508C were found on the AISI 440C substrate.Increasing annealing temperature enhanced the hardness increase in the coatings.The increased hardness was more obvious at (or above )the annealing temperature of 4508C,due to the formation of g -Al O as shown 23in Figs.4and 6b.3.4.Wear resistanceWith PEEK as the pin,the weight losses of the uncoated and coated specimens are listed in Table 1.The wear of coated specimens decreased with increase in annealing temperature.The increasing wear resistance was resulted fromthe increased hardness of the coatings,which was linked to the phase transformation from248 C.C.Chang,S.K.Yen /Surface and Coatings Technology 182(2004)242–250Table 2Contact angles of water,formamide and ethyleneglycol on the uncoat-ed,ZrO coated and Al O coated,respectively223AISI 440C ZrO coated 2Al O coated 23888Water877083Formamide 605059Ethyleneglycol646363Table 3Surface energies g ,interface energies g ,and adhesion works W a I ij calculated fromcontact angles listed in Table 2by Van Oss m ethod w 12,13xAISI 440CZrO coated 2Al O coated 23Surface energy,70.40694.40867.165g (mJ y m )2I ZrO y 440C 2Al O y 440C 2ZrO y Al O 223Interface energy,16.4160.04113.796g (mJ y m )2ij Adhesion work,148.398137.530147.777W (mJ y m )a 2Fig.9.Polarization curves of the uncoated and ZrO y Al O coated 223specimens in 3.5%NaCl aqueous solution.Table 4List of the first redox potential E (E ),exchange current density i (i ),critical passive current density i ,passive current density i ,01corr corr crit pass pitting potential E ,the second redox potential E and protection potential E of the uncoated and ZrO y Al O -coated specimens,derived form pit 02pp 223the polarization tests in 3.5%NaCl and 1M HCOOH aqueous solutions Test Specimens E (E )01cor i (i )cor i criti passE pit E 02E pp solutions (mV )(m A y cm )2(m A y cm )2(m A y cm )2(mV )(mV )(mV )3.5%Uncoatedy 534231——y 136——NaCl Al O y ZrO y 440C 232y 34125———y 272y 961M Uncoatedy 4869698030———HCOOHAl O y ZrO y 440C232y 457890.9———aluminum hydroxide hydrate (Al (OH )H O )to alumi-262numoxide hydroxide (AlO (OH )),aluminum oxide hydrate (Al O H O )and finally to g -Al O ,as shown 1015223in Figs.4and 6.In contrast,the wear resistance seems to be independent of the tempering softening and sec-ondary hardening effects of the substrate.3.5.AdhesionFig.7shows the friction force vs.the normal load on the stylus during the scratch test.This curve may be divided into two regions.One revealed a slope of 0.13and the other 0.34.The transition point was around the load 22N.The increased slope was caused by the deformation of the metal substrate,which was plastically deformed by the indenter at the load beyond 22N.However,most of the ZrO y Al O coating was found 223at 22and 100N of the scratch test,as shown in Fig.8a and b.This means that the adhesion strength of ZrO y 2Al O and ZrO y 440C was stronger than the yield stress 232of the 440C.Contact angles of water,formamide,and ethylenegly-col on specimens are listed in Table 3.Surface energies,interface energies and adhesion work have been calcu-lated by Van Oss method w 11,12x ,as listed in Table 4.The adhesion work of ZrO y 440C was a little greater 2than that of Al O y 440C.Also,the adhesion work of 23ZrO y Al O was greater than that of Al O y 440C.It is 22323concluded that the better choice of the bottomlayer is ZrO coating and that of the top layer is Al O coating.2233.6.Corrosion resistanceRepresentative polarization curves of the uncoated and coated specimens in 3.5%NaCl and 1M HCOOH aqueous solutions are shown in Figs.9and 10,respec-tively.Fromthe forward curves,E (or E ),i (or 01corr 0i ),E ,i ,i and E were analyzed,and fromthe corr pass crit pass p backward curves E and E were measured,as given 02pp in Table 4.In 3.5%NaCl aqueous solution,the ZrO y 2Al O coated specimens revealed the higher E ,and 23corr lower i .No obvious E ,was found on the coated corr pit samples,but it was found on the uncoated ones at y 136mV .In 1M HCOOH,the coated sample exhibited a lower i and i than the uncoated.After polariza-corr pass tion tests in 3.5%NaCl aqueous solution,a large area penetrated on the uncoated was observed,as shown in Fig.11a,but none on the coated,as shown in Fig.11b.Similar results were found in 1M HCOOH,as shown in Fig.12.These results indicate that the ZrO y Al O film 223was more corrosion resistant or inert than the natural249C.C.Chang,S.K.Yen /Surface and Coatings Technology 182(2004)242–250Fig.10.Polarization curves of the uncoated and ZrO y Al O coated 223specimens in 1M HCOOH aqueoussolution.Fig.11.Optical photograph of (a )the uncoated and (b )ZrO y Al O coated specimens after polarization test in 3.5%NaCl.223Fig.12.SEM observations of (a )the uncoated and (b )ZrO y Al O coated specimens after polarization test in 1M HCOOH.223passivation filmof AISI 440C stainless steel,in both 3.5%NaCl and 1M HCOOH aqueous solutions.Also,the lower i of the coated specimen at the anodic pass polarization region means that the coating film is more stable than the natural passivation filmof the substrate.4.ConclusionsA new electrolytic coating method of ZrO y Al O 223double layers has been successfully applied on an AISI 440C stainless steel to investigate its characteristics.The following conclusions are drawn:1.The single layer deposition of ZrO or Al O revealed 223many large cracks,which can be reduced by the ZrO y Al O double layer coating.2232.The annealing resulted in increase of the hardness of the coatings,but was independent of the temper softening and secondary hardening effect on the 440C substrate.The increasing hardness of the coatings was caused by the series of phase transformations from the as-deposited Al (OH )H O to AlO (OH )at 3502628C,to Al O H O at 4008C,and finally to g -Al O 1015223at 4508C.Wear resistance was increased with increas-ing annealing temperature.Especially,the weight loss of the ZrO y Al O coated specimen annealed at 4502238C is only 1y 4of the uncoated.3.The scratch tests revealed that the adhesion strength of the ZrO y Al O coating filmon the substrate was 223stronger than the yield stress of AISI 440C stainless steel.Also,the surface energy analyses suggested that the better choice of the bottomlayer is the ZrO and 2that of the top layer is the Al O coating.234.The electrochemical polarization tests in 1M HCOOH and 3.5%NaCl aqueous solution revealed that the ZrO y Al O coated specimen was 10times 223more corrosion resistance than the uncoated.AcknowledgmentsThe authors are grateful for the 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