The most commonly used material in the automotive industry is steel. Steel used in making Body-In-White (BIW) for cars are broadly classified as Advanced High Strength Steels (AHSS). These AHSS are produced by a well-defined alloying and specific annealing procedure. However, external oxidation of the constituent alloying elements from the steel is observed the annealing step . This selective oxidation of alloying elements on the steel surface affects the adhesion of the Zinc to the steel which is essential for corrosion protection. The main goals of this research work were to define the optimal parametric windows for the Electrolytic Plasma Cleaning technique to form a plasma capable of cleaning a steel surface by removing external oxides formed during the annealing process. Electrolytic Plasma Cleaning uses the traditional electrochemical cell that consists of an anode, a cathode, an external potential and an electrolyte but at higher input potentials. An experimental setup was developed with the aim of finding the ideal working parameters, establishing the groundwork for future large-scale experimentation.

Coating deposition by Physical Vapour Deposition (PVD) on high strength steels is an important research project at TATA Steel - IJmuiden. The research is aimed at replacing the conventional hot-dip galvanisation process to obtain a defect-free coating without affecting their well-engineered properties. However, the annealing treatment of the steel, performed to obtain these properties, affects the coating adhesion properties. This is a result of the selective oxidation process, which forms external oxides of alloying elements at the surface. Therefore, a pre-treatment process is required to remove these surface oxides from the steel strips before they are coated. Plasma sputtering is currently being
used for the pre-treatment to remove any contaminants and surface oxides from the steel. To obtain a good coating adhesion, a relatively large amount of surface oxides needs to be removed by sputtering. Also, the removed material is known to contaminate the vacuum chamber in the PVD deposition line, for which frequent maintenance of the chamber might be necessary. Thus, an additional
surface pre-treatment step was investigated in this study to reduce the sputtering process inside the vacuum as much as possible. In the present work, the effect of both direct current electrolytic alkaline cleaning and sulphuric acid etching on the surface of DP800 steel was investigated. Two different baths were considered for this purpose; a 27 g/L NaOH bath with some additive at 60°C and a 50 g/L H₂SO₄ bath at 25°C and 50°C. A current density of 1.5 A/dm² was applied during the electrolytic cleaning for which both cathodic and anodic polarisation methods were investigated. Also, a range of acid etching times (10s to 120s) was investigated for the given concentration and temperatures of the acid bath to study its effect on the surface. The effect of adding a corrosion inhibitor into the acid bath on the rest of the coating deposition process was also investigated. Various surface characterisation techniques and wettability tests were performed to study the changes in morphology and composition of the surface and their effect on the coating adhesion properties of the treated samples. Finally, coating adhesion tests were performed after zinc deposition to investigate the adhesion performance of the steel after the pre-treatment steps. Initial surface analysis during electrolytic alkaline cleaning showed that the anodic polarisation was more effective than cathodic polarisation of the sample, as the latter tends to reduce the surface wettability by additional deposits of iron fines over the surface. A subsequent acid etching provided a reduction in the minimum required sputter intensity to obtain a good adhesion from 2300 kJ/m² to about 800 kJ/m². A further reduction was achieved to a sputter intensity of only 214 kJ/m² after retarding the effects of surface reoxidation by vacuum sealing the samples. Acid etching at 25°C provided bad coating adhesion at lower etching times, attributed to the partial dissolution of surface oxides and absence of an initial grain roughening. Good coating adhesion was either obtained at higher etching times or by increasing the temperature of the acid bath to 50°C. Addition of a corrosion inhibitor was considered impractical as high sputter intensities (> 321 kJ/m²) was required to remove the adsorbed inhibitor molecules from the surface. Thus, a reduction in the required sputter intensity was achieved by more than a factor of 10 after acid etching, only if the effects of surface reoxidation during the transfer time between acid etching and entering the PVD installation can be minimized.

In recent years, Tata Steel Europe has increased their focus on Physical Vapor Deposition (PVD) for the zinc coating application of their steel substrates, as an alternative to Hot Dip Galvanizing (HDG). PVD offers some benefits over HDG like multilayer structures and lower heat impact on the steel.
To achieve sufficient coating adhesion strength of the zinc coating, before deposition the steel substrate is normally cleaned and activated by a plasma sputter unit. As this sputtering takes place in the vacuum chamber, like the deposition, it is prone to precipitation of sputtered material in the vacuum chamber. If the PVD process is scaled up to an industrial coating line, the volumes of sputtered material and precipitated material will become problematic for the service reliability. Therefore it has been investigated whether an acid etching surface pre-treatment step before the vacuum chamber could reduce the needed plasma intensity, and thereby decrease the sputtered volume in the vacuum chamber.
A range of acid etching times and plasma sputtering times were tested, to obtain the range in which the coating adhesion was sufficient. To test the coating adhesion, two (automotive) tests were used. It was found that by pickling, the plasma sputter intensity could not be reduced. So the coating adhesion strength seemed not directly related to the pickling time, for the particular steel used in this project.
After the limits of good adhesion were determined, the characterization started to identify what in the elemental composition or the surface morphology could determine whether there was good adhesion or not. It was found that (even very short) pickling completely removes the surface enrichment of the first 50 nm, while plasma sputtering only lowers the surface enrichments. It was found that plasma sputtering does not influence the morphology, while pickling smoothens the surface out, with increasing pickling. As the oxygen concentration profile did not change significantly as function of pickling time, but its enrichment thickness was about equal to the minimum plasma sputter depth, it is thought that the oxygen concentration is the major influence on good and bad adhesion.

Piezoelectric energy harvesting technology is an alternative source for powering low power electronics. The ability of piezoelectric materials to convert ambient vibrational energy into usable electrical energy is seen as a promising battery-free solution to be used in inhospitable areas to self-power electronics for a longer time with little maintenance. The goal of this research is to maximise the mechanical input: elastic strain energy experienced by a lead zirconium titanate (PZT) bilayer piezoelectric buzzer by introducing four different boundary conditions during loading. Investigation of how mechanical input from each of these boundary condition influences the stored electrical output is carried out. The effect of three different static loads on each of the stored electrical output for four boundary conditions are studied. In order to accurately compare the data, the mechanical input (elastic strain energy) is calculated while the electrical output (stored energy) is measured experimentally. Given the brittle nature of ceramics, the maximum load bearing capacity for the PZT ceramic disc is determined by mechanical tests such as the ball-on-the-ring and uniaxial compression tests. This is to ensure that the experiments do not fracture the sample. Results show that, by inducing a bending mode in the buzzer, mechanical input values almost four orders of magnitude higher can be reached when compared to boundary conditions without bending modes. A similar result was found for the stored electrical energy with values for the bending mode of almost three orders of magnitude higher than when no bending is involved. The comparison between the calculated mechanical input and the measured electrical output shows good agreement in the boundary conditions involving bending. The energy conversion is highly efficient for the full range of applied loads for these boundary conditions. In the case of non-bending boundary conditions, the stored electrical energy is one order of magnitude high than predicted for the mechanical input and thus the model is in poor agreement with experiment.

Selective oxidation behaviour of Fe-Mn-Cr steel alloys annealed at 950°C in Ar plus 5 vol.% H2 atmosphere under different annealing time and dew points was studied. The Fe-Mn-Cr steel alloys are externally oxidized when annealing at dew point of -45 °C, while internally oxidized at dew points of -10 and 10 °C. The internal oxides formed in the Fe-Mn-Cr steel alloys are (Mn, Fe)O and (Cr, Mn, Fe)3O4. The kinetics of internal oxidation of Fe-Mn-Cr alloys at 950 °C is diffusion controlled and follows parabolic growth rate law. The measured kinetics of internal oxidation of Fe-Mn-Cr alloys and the concentration depth profiles of internal oxides are in good agreement with simulation results. Adding Cr to the Fe-Mn steel alloys decreases the kinetics of internal oxidation. The growth rate of internal oxidation zone can be predicted by a modified Wagner’s internal oxidation model. The external oxides formed during annealing of Fe-Mn-Cr steel alloys cannot be reduced by H2. However, an oxide-free steel surface can be obtained by first forming and then reducing a Wüstite scale.