Les analyses de surface et l adhésion

Les analyses de surface et l adhésion X. Vanden Eynde Centre de Recherches Métallurgiques (CRM) BELGIUM CoRI, 26/1/6

Un lien fort entre la propriété macroscopique d adhérence et les mécanismes locaux d adhésion good bad bad Les outils pour caractériser le défaut dépendront : du substrat de la taille du mécanisme d adhésion du type de défaut de l origine supposée du défaut ( organique ou inorganique)

L adhésion entre deux matériaux nécessite un assemblage de plusieurs couches Adhésif/revêtement interphase Couche atmosphérique Oxyde/primaire Ecrouissage substrat Les proportions relatives des différentes couches dépendent des pré-traitements et du système (substrat/revêtement) utilisé

Une combination intéressante d outils analytiques pour la caractérisation physico-chimique des surfaces XPS Surface (2-3nm) Depth Profiles SEM/SAM ToF-SIMS Depth Profiles GDOES Elements B< B< All All Bonding states No Sensitivity Quantification Imaging (~1µm) (~.1µm) (~.15µm) No Other techniques like IR spectroscopy, EDX analysis, C and S surface combustion, atomic force microscopy (AFM), Contact angle (static and dynamic)

Les traitements de surface Modifications de surface d acier et l adhérence (effet du stockage) La préparation de surface pour la galvanisation en continu Cas où le mouillage et l adhérence ne sont pas désirés Préparation de surfaces galvanisées en milieu liquide

Tools to investigate steel surface modification during storage and adherence modification X. Vanden Eynde, B. Schmitz, H. De Deurwaerder, Centre de Recherches Métallurgiques (CRM) Coating Research Institute (CoRI) BELGIUM CoRI, 26/1/6

Tools for tuning surface after continuous annealing lines Temperature ( C) 9 8 7 6 5 4 3 2 1 T Echantillon Cde Regul Water quench or... 1 15 2 25 3 35 Rinsing or not Time (sec) Soaking N 2-5%H 2 DP-3 C

The surface microstructure is made of small oxalate crystals IF without treatment IF treated with Oxalic ac.

The surface composition is directly observed by XPS : iron oxalate Fe2p3 c/s 9 8 7 6 5 4 3 74 Fe sat ~2+ 72 BE (ev) Fe Ox Fe 7 C1s c/s 6 55 5 45 4 35 3 25 2 15 1 3 O-C=O 29 BE (ev) C-(C,H) 28 at.% O1s c/s 25 2 15 1 5 545 Bidentate iron-carboxylate 535 BE (ev) Ratios Theoretical Fe C O Fe/O Fe/C Iron Carbonate FeCO 3 2 2 6.33.33 Ferrous Oxalate 2 + Fe(C 2 O 4 ) 14 29 57.25.51 Ferric Oxalate 3 + Fe 2 (C 2 O 4 ) 3 1 3 6.17.5 Measurements IF-Ti treated with Oxalic acid 13.7 29.7 53.1.26.56 IF-Ti treated with Oxalic acid (corrected) 13.7 26.5 53.1.26.5 Simulation performed with specific HOWAQ or POTC simulators O-Fe 525

Although the oxalate are still present after storage test, tarnishing is obvious IF treated with Oxalic ac. IF treated with Oxalic ac. after HC 32 days 63.5 mm 26.5 mm In climatic chamber with internal regulation of air at 4 C and 95 % relative humidity Fe2p3 15 c/s 13 11 9 7 5 3 74 Fe sat ~3+ 72 BE (ev) 7 Oxalic ac. Oxalic ac. + H2 Oxalic ac.+hc Oxalic ac. +HC+H2O C1s c/s 6 55 5 45 4 35 3 25 2 15 1 Oxalate removes by rinsing before storage 292 O-C=O 287 BE (ev) 282

The oxalate crystal morphology slightly affected by storage conditions IF treated witout treatment IF treated with Oxalic ac. IF treated with Oxalic ac. after storage corrosion test

The acrylic acid treatment removes small selective oxides from the surface without any crystal formation IF without treatment IF treated with Acrylic ac.

The steel surface is much less affected by storgae conditions, no tarnishing IF treated with Acrylic ac. IF treated with Acrylic ac. after HC 32 days 63.5 mm 26.5 mm In climatic chamber with internal regulation of air at 4 C and 95 % relative humidity Fe2p3 C1s 75 1 Acrylic ac. 65 O-C=O c/s 75 Acrylic ac. +H2O Acrylic ac.+hc c/s 55 45 5 Acrylic ac.+hc+h2o 35 25 25 74 73 72 BE (ev) 71 7 Impossible to remove acrylates by water rinsing 15 3 295 29 BE (ev) 285 28

The acrylic acid treatment removes small selective oxides from the surface and creates a film onto the steel surface, which is affected by storage conditions IF treated with Acrylic ac.

The surface treatment can affect the storage behaviours but also the adherence properties. Waterborne (MPa) Reference 8X9 2. Adhesive AF = Formic 5.2 Cohesive GL = Aminoacetic 4.9 ±.9 Cohesive AG = Glycolic 3.8 ± 1.3 Cohesive AA = Acrylic 4.5 ±.8 Cohesive AO = Oxalic 1.5 ±.4 Cohesive 2-K water based epoxy AF : very clean surface GL, AG, AA : reactive surface AO : reactive surface but with some remaining free AO at the surface

The surface treatment can affect the storage behaviours but also the adherence properties. Water based Not-rinsed Rinsed GL 4.9 ±.9 Coh 3.8 ± 1. Coh AG** 3.8 ± 1.3 Coh 2.8 ±.7 Adh/Coh AA 4.5 ±.8 Coh 4.1 ±.3 Coh AO* 1.5 ±.4 Coh 3.9 ±.6 Coh For GL, AG, AO : active species removed by rinsing but very clean surfaces With AA, the active species remain insoluble films and react with the paint components 2-K water based epoxy Rinsed after storage in plastic bags under vacuum

Fast evolution of selective oxides at the steel surface under storage There is a complete re-organisation of the manganese oxides due to the thin water layer naturally present in humid air IF-Mn-Si treated without treatment AREA 1 h 48h 184h AREA 2

The surface treatment can affect the storage behaviours and also the adherence properties With XPS, it is possible to follow the chemical species along the process and how these species are linked to the surface. Surface treatment can help by adding specific bonds or by getting a very clean surface The electronic microscopy and the corrosion experiments are necessary to characterize the changes in surface morphologies (even for quite small features).

Surface preparation for hot-dip galvanising X. Vanden Eynde, L. Bordignon,, Centre de Recherches Métallurgiques (CRM) BELGIUM Johann Strutzenberger, Alexander Jarosik, Josef Faderl voestalpine Stahl GmbH AUSTRIA CoRI, 26/1/6

Zinc dewetting on an IF-B steel grade (1-3 wt.%) Industrial problem C Mn Si P Al Ti B 2 15 11 5.8 4 68 1.5 SCWE Bulk microstructure by SIMS, O 2 +, BO 2 - image (FoV:15µm) Sometimes, Zn dewetting appears at the edges, the head and the queue of the coils The coating adherence is drastically affected in dewetted regions 5µm SAM-FEG image LOM 3-D imaging

The XPS is equipped with an in-situ preparation chamber in order to characterise surfaces after simulated processes 1 Laboratory facitilities 8 T ( C) 6 4 Heat Treatments 2 Controlled atmosphere 5 1 15 2 25 Tim e (s) XPS UHV Main advantage : Analysis of real surface states before galvanisation ex-situ or in-situ Controlled atmosphere : UHV, HNX, CO, NH 3,... and Dew Point (H 2 O) Scanning Auger Microscope ex-situ Secondary Ion Mass Spectrometry

at.% 35 3 25 2 15 1 5 N 2-5%H 2 at 8 C for 6sec Cold-rolled XPS surface analyses -6-1 7 6 5 4 3 2 1 at.% (Fe, O) Mn Al B O Fe Laboratory study Annealing in N 2-5%H 2 at 8 C for 6sec induces B and Mn external oxidation with a max at DP=-3 C and no B oxide at DP= 1 C Dew point ( C) DP= -3 C SAM-FEG electron image 1µm AREA B1 O1 Mn1 Fe3 PT1 12.3 47.2 15.4 25.1 PT2 17.3 5. 18.2 14.4 AREA3. 69.2. 3.8 nodules and needles at grain boundaries smaller nodules at the ferrite grain surface both are composed of Mn-B oxides

Boron profiles vary along the width before annealing Intensity (a.u.) 7 6 5 4 3 2 1 GDOES depth profiles (33nm/s) bulk level 1st edge Axis 2 4 6 8 1 Sputtering time (s) 2nd edge ~2µm SIMS cross-section of axis sample Cu spacer 2µm depleted area SIMS, Cs +, B 2 - image (FoV:15µm) Industrial problem Boron depletion more pronounced at the axis The origin of such depletion could be related to the hot-rolling process parameters and practice

at.% 35 3 25 2 15 1 5 N 2-5%H 2 at 8 C for 6sec Cold-rolled XPS surface analyses 7 6 5 4 3 2 1 at.% (Fe, O) Mn Al B O Fe at.% 35 3 25 2 15 1 5 Laboratory study Polished (3µm) 7 6 5 4 3 2 1 at.% (Fe, O) -6-1 -6-1 Dew point ( C) Dew point ( C) DP= -3 C 1µm 1µm SAM-FEG electron images

at.% 35 3 25 2 15 1 5 N 2-5%H 2 at 8 C for 6sec Cold-rolled XPS surface analyses 7 6 5 4 3 2 1 at.% (Fe, O) Mn Al B O Fe at.% 35 3 25 2 15 1 5 Laboratory study Polished (3µm) 7 6 5 4 3 2 1 at.% (Fe, O) -6-1 -6-1 Dew point ( C) Dew point ( C) DP= -3 C B mappings 1µm 1µm SAM-FEG elemental mappings

Wettability measurements Correlation between surface states and zinc wetting Sample annealed under desired conditions is transferred in-situ to wetting force measurement device Laboratory facilities.8 Dynamic Θ 11 N 2-5%H 2 DP-54 C Liquid bath SAMPLE γ i Θ γ s γ l Wetting force (mn).4. -.4 A F (W) F (meas) Θ 5 1 15 2 25 Time (s) 9 7 5 3 Wetting angle ( ) Θ Static Θ hot dipping at 46 C in Zn-.2wt% Al cos Θ = (γ s - γ i ) / γ l F (meas.) = F (W) - F (A) = P γ l cos Θ - F (A) High Θ bad wetting Low Θ good wetting

N 2-5%H 2 at 8 C with DP=-3 C Polished (3µm) Laboratory study 6 sec 6 sec 6 sec SEM 1µm at.% 35 3 7 6 25 5 2 4 15 3 1 2 5 1 1 1 1 1 time (sec) at.% (Fe,O) Mn Si S B O Fe Static wetting 2s ( ) Soaking:82 C / 5%H 2 / DP-3 C 8 75 12 115 7 Static 11 65 15 6 1 Dynamic 55 95 5 9 45 Polished 3X1 steel grade 85 4 8 1 1 1 Soaking time (s) Dynamic wetting ( ) Morphology Wettability Adherence

Zn coating after oxidation/maturation shows good adherence 1-T bend test (strip thickness 1mm) SEM image of bend part TRIP Si Oxidation N 2-1%Air 65 C, 1 sec Annealing in N 2 with DP C Cooling in N 2-1%H 2 Same after scotch tape test

Zn coating after oxidation/maturation shows good adherence Oxidation N 2-1%Air 65 C, 1 sec Annealing in N 2 with DP C Cooling in N 2-1%H 2 1-T bend test (strip thickness 1mm) SEM image of bend part TRIP Si Before the 1-T bend test bend part

The surface compostion can affect liquid metal wetting and through the interface homogeneity, the adherence With in-situ XPS, it is possible to follow the chemical species along the process and how these species are linked to the surface. Complementary analysis with SIMS and GDOES with their high sensitivity indicates composition variations The electronic microscopy shows the distribution at the surface before treatment or after galvanising treatment Wetting measurements are related to the surface state and to the coating adherence The weak point is not always in the coating or at the interface