Iris De Graeve

A Shape-Recovery Polymer Coating for the Corrosion Protection of Metallic Surfaces

Self-healing polymer coatings are a type of smart material aimed for advanced corrosion protection of metals. This paper presents the synthesis and characterization of two new UV-cure self-healing coatings based on acrylated polycaprolactone polyurethanes. On a macroscopic scale, the cured films all show outstanding mechanical properties, combining relatively high Youngs modulus of up to 270 MPa with a strain at break above 350%. After thermal activation the strained films recover up to 97% of their original length. Optical and electron microscopy reveals the self-healing properties of these coatings on hot dip galvanized steel with scratches and microindentations. The temperature-induced closing of such defects restores the corrosion protection and barrier properties of the coating as shown by electrochemical impedance spectroscopy and scanning vibrating electrode technique. Therefore, such coatings are a complementary option for encapsulation-based autonomous corrosion protection systems.

Evaluation of the Yasuda parameter for the atmospheric plasma deposition of allyl methacrylate

This work studies the influence of the proportional change in discharge power and the monomer feed on the morphology and the chemistry of atmospheric plasma deposited films. Atmospheric plasma coatings of allyl methacrylate were deposited using dielectric barrier discharge plasma under different conditions but always under the same ratio between the discharge power and monomer feed (W/FM). It is shown that a constant W/FM does not necessarily provide the same chemistry and the same morphology for atmospheric pressure plasma. This is explained by the higher discharge power of the plasma resulting in an increase of streamers which alter the distribution of energy among the plasma species. On the surface of the deposited coatings, globular-like features were observed, which are suggested to be formed in the volume of the discharge. The deposition rate is also influenced. providing thicker coatings, when high monomer feed/high power are used. Finally, infrared spectra showed a higher retention of the ester functionality at high power/high monomer feed.

A Multiple-Action Self-Healing Coating

This paper describes a self-healing coating for corrosion protection of metals which combines two different types of self-healing mechanisms in one coating with multiple-healing functionality. 2-Mercaptobenzothiazole (MBT) was loaded into layered double hydroxide (LDH) carriers which were mixed into an acrylated polycaprolactone polyurethane based shape recovery coating and applied on Hot Dip Galvanized steel (HDG). The effect of triggered release of MBT on the protection of HDG became visible when samples with manually applied defects in the coating were immersed in 0.05 M NaCl solution (first, autonomous healing mechanism). The shape recovery (second, non-autonomous healing mechanism) was triggered by heating the samples for 2 minutes to 60°C. SEM-EDX and Raman Spectroscopy proved the presence of MBT in the LDH, in the MBT-loaded LDH in the coating and the released MBT on the HDG surface in the damaged area after being in contact with a solution containing corrosive ions. Electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET) demonstrate the corrosion protection effect of MBT in the coating with a defect and the restoration of the barrier properties of the coating after defect closure. This way, the independent mechanisms of this multi-action self-healing coating could be demonstrated.

Development of novel surface treatments for corrosion protection of aluminum: self-repairing coatings

Abstract Two types of self-repairing coatings for the protection of Al and its alloys are reviewed: (1) organic coatings with capsules containing repairing agent and (2) porous anodic oxide films with inhibitor solution stored in the pores of the oxide film. First, polyurethane microcapsules containing liquid surface-repairing agents were synthesized and polyurethane coating with the capsules was painted on Al alloy specimens. After mechanical damage to the coating, self-repairing occurred by the reaction of water vapor in the air with the repairing agents released from the capsules. Second, porous-type anodic oxide films were formed on Al alloys, and the pores of the anodic oxide films were filled with inhibitor solutions, followed by application of a covering polyurethane layer. Inhibitors released from the pores efficiently protected the Al alloy substrate from corrosion arising from induced mechanical damage.

Combined EBSD and AFM Study of the Corrosion Behaviour of ETP-Cu

In order to increase the sustainability of metals, a more detailed understanding of the corrosion process is of crucial importance. Current literature often considers corrosion as a purely chemical interaction with a nearly exclusive dependence on compositional effects, while ignoring microstructural and crystallographic properties of the metal surface. Some recent literature data, however, suggest an important effect of microstructural elements such as grain size, crystallographic orientation and grain boundary characteristics. The aim of this work is to obtain a better understanding of the relation between the corrosion behaviour of a metal and its microstructural and crystallographic features. Therefore, warm rolled Electrolytic Tough Pitch (ETP-) Cu was immersed in a 0.1 M NaCl and 0.5M Na2SO4 solution and the combination of Atomic Force Microscope (AFM) and Electron Backscatter Diffraction (EBSD) allowed to identify differences in attack for different crystallographic orientations.

Fatigue Performance of Ti-6Al-4V Additively Manufactured Specimens with Integrated Capillaries of an Embedded Structural Health Monitoring System

Additive manufacturing (AM) of metals offers new possibilities for the production of complex structures. Up to now, investigations on the mechanical response of AM metallic parts show a significant spread and unexpected failures cannot be excluded. In this work, we focus on the detection of fatigue cracks through the integration of a Structural Health Monitoring (SHM) system in Ti-6Al-4V specimens. The working principle of the presented system is based on the integration of small capillaries that are capable of detecting fatigue cracks. Four-point bending fatigue tests have been performed on Ti-6Al-4V specimens with integrated capillaries and compared to the reference specimenswithout capillaries. Specimens were produced by conventional subtractive manufacturing of wrought material and AM, using the laser based Directed Energy Deposition (DED) process. In this study, we investigated the effect of the presence of the capillary on the fatigue strength and fatigue initiation location. Finite element (FEM) simulations were performed to validate the experimental test results. The presence of a drilled capillary in the specimens did not alter the fatigue initiation location. However, the laser based DED production process introduced roughness on the capillary surface that altered the fatigue initiation location to the capillary surface. The fatigue performance was greatly reduced when considering a printed capillary. It is concluded that the surface quality of the integrated capillary is of primary importance in order not to influence the structural integrity of the component to be monitored.

On the Role of the Crystallographic Grain Characteristics in the Corrosion Behavior of Polycrystalline Copper

In order to increase the sustainability of metals, a more detailed understanding of the corrosion phenomenon is of crucial importance. In current literature, corrosion is often considered as a purely chemical interaction with nearly exclusive dependence on compositional effects, whilst ignoring the microstructural features of the metal surface. In the present work, results are presented which illustrate both the role of grain orientation and grain boundaries in the corrosion process. To evaluate the grain orientation dependent electrochemical behavior, polycrystalline Cu, was brought into contact with a corrosive electrolyte. Subsequently, the attack was evaluated by measuring the surface with both Atomic Force Microscopy (AFM) and Electron Backscatter Diffraction (EBSD). It was demonstrated that the grain orientation itself did not significantly influence the corrosion kinetics, but, alternatively, that the orientation of the neighboring grains seemed to play a decisive role in the grain dissolution rate. To increase understanding on the role of grain boundaries, a method was developed based on the electrochemical (galvanic) displacement of gold, which is deposited from an aqueous solution on a pure copper substrate. This technique demonstrated its sensitivity to the grain boundary characteristics as far less gold was deposited on special boundaries, such as coincidence site lattice boundaries, as compared to the random high angle grain boundaries.

Experimental Evaluation and Simulation of Al/Si Diffusion in Hot Dipped Fe-Si Steels

Hot dipping is a coating technique used in industry for galvanizing machine elements and steel profiles for construction or automotive applications. However, an alternative use of this process might be to improve specific properties. For instance, in order to improve the magnetic properties of electrical steels, it may be desirable to increase the Si and/or Al content. A possible and alternative route to realize this is by the application of an Al-Si-rich coating on the steel substrate using a hot dipping process, followed by a diffusion annealing treatment in order to distribute the Al/Si more evenly in the steel. The obtained distribution depends on the annealing parameters and can be both beneficial and detrimental for the magnetic properties. In the present work, Fe-Si substrates were hot dipped in different Al-Si baths. Subsequently, the samples were annealed at 1100°C during 20 minutes and concentration profiles were measured with scanning electron microscope energy dispersive spectroscopy line scans. The experimental results were analyzed using a specifically designed simulation model in order to determine the Al and Si diffusion coefficients. This model uses an inverse algorithm to determine interdiffusion coefficients that arise in a macro ternary diffusion system.