A dissertation submitted to the University of the Witwatersrand in fulfilment of the requirements for the degree of Master of Science in Engineering (Metallurgy & Materials) 2016 / The surfaces of AISI 316L stainless steel plate were laser alloyed with ruthenium powder as well as a mixture of ruthenium and nickel powders using a Nd:YAG laser set at fixed operating parameters. The microstructure, elemental composition, and corrosion characteristics of the alloyed zone were analysed using optical and scanning electron microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and corrosion potential measurements. EDS analysis of the alloyed specimen showed that through the laser surface alloying, 2 mm surface layers with 12.5wt % Ru and 5.2wt% Ru were produced on an AISI 316L stainless steel. Similar microstructures which were dendritic and columnar grains, typical of weld beads under non-equilibrium cooling conditions were observed for all samples. Hardness profile measurements showed a significant increase from 160 HV for the substrate to a maximum of 247 HV for the alloyed layer. Using an Autolab potentiostat, the corrosion behaviour and resistance of the laser alloyed layers, substrate AISI 316L, and Hastelloy© C-276 were evaluated and compared in sulphuric acid solution of different concentration and temperatures. The Hastelloy© C-276, followed by the 12.5wt% Ru presented the most noble corrosion potential (Ecorr) and the lowest corrosion current density (icorr). However, in 60wt% H2SO4 and 40oC, the 5.22 wt% Ru alloys exhibited slightly better anticorrosive properties than 12.5wt% Ru. The observed corrosion potential, Ecorr, for untreated AISI 316L stainless steel sample in 40wt% sulphuric acid solution at 40oC was -277 mV. The 5.22 wt% Ru and 12.5wt% Ru alloyed stainless steel samples presented -240 mV, and 61 mV respectively in the same solution. Besides showing comparable performance to 5.2wt%Ru sample within specific short potential ranges, Hastelloy© C-276 was generally superior in all solutions. In addition it was found that the stability of the passive layer was improved with additions of Ru. Based on the developed costing equation the cost of 5 mm AISI 316L stainless steel plate with surface area (A = 1 m2) surface alloyed with 5.2wt% Ru to a depth of 2 mm using Nd: YAG laser is estimated at R15 989, and it is less than the cost of a Hastelloy© C-276 plate of similar size which is estimated at R19 900. As the material thickness increases, the cost benefit of laser surface treatment increases and vice versa. Reduction of the Ru additions to levels below 5.2wt% would improve cost competition without detracting from performance. / MT2017

A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 1993 / The formation of VC, NbC, and Cr-carbide coatings on steels immersed in molten borax baths containing carbide-forming constituents has been known for some time. A study was made of the formation of carbide coating on steel specimens treated in molten borax cont.ad.Lnr.q ferro-vanadium and V20S as bath additives. The prevalence of oxidizing or reducing conditions in the bath was found to playa decisive role in the formation of the VC layer. The influence of treatment factors such as time, temperature, and bath composition on the thickness of the coating was investigated. A detailed investigation into the behaviour of baths containing V205 and Al was carried out in this regard. Microstructural examination of coated specimens was performed using optical and electron microscopy. Microhardness tests, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analyses were carried out in order to characterise the layers produced. The corrosion behaviour of the vanadf.um carbide coating was evaluated by accelerated electrochemical means. Samples of mild steel and EN9(O.5% C) steel were treated for various lengths of time in order to obtain coatings of various thicknesses. The corrosion resLst.ance of the carbide coating was found to be superior to that of the untreated base alloys. Five diffet"ent tool steel materials were a.lso treated. Microscopy examination and hardness testing of the VC coated tool steels was performed in order to assess the effects of treatment by this process on the bas~ material. The austenitizing temperature and the nature of the carbides in the matrix of the tool steels was found to play an important role in this respect. / MT2017

A dissertation submitted to the faculty of engineering, University of the Witwatersrand, Johannesburg in fulfillment of the requirements for the degree of master of science / Steel 3CR12 is a 12 chromium, titanium stabilized, corrosion resisting steel which was developed in South Africa in the recent past (Abbreviation abstract) / AC2017

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / Ph.D.

This thesis reports a research of the corrosion mechanism and corrosion rate of steel reinforcement in concrete. Experimental results are presented to compare the corrosion behaviours of steel reinforcement in two blended-cement concretes in seawater. The experimental program included a study of the influence of crack width on macrocell corrosion, an investigation of the procedure for the determination of polarisation curves of steel in concrete and, an evaluation of the corrosion rate of steel in concrete and the influence of crack width as determined by a new polarisation curve analysis. A mechanism is proposed to interpret the different influences, in both the short and long term, of concrete crack width on the macrocell corrosion rate. This mechanism is based on the finding that the corrosion-spread phenomenon is caused by polarisation effects. An oxygen-depletion mechanism is also proposed to explain the much lower macrocell corrosion rate in the slag cement concrete than that in the flyash cement concrete. The procedure for polarisation testing of steel in concrete is found to be critical to obtaining correct polarisation curves. A twotest procedure is verified to be an appropriate procedure and used in this investigation. Experimental polarisation curves of steel in concrete are found to be very different to those expressed by the kinetic Butler-Volmer equation and, this is considered to be a result of the influence of the passive film on the steel surface in concrete. An empirical polarisation formula is developed and its interpretation is based on the postulation of two parallel kinetic processes occurring at the steel/passive-film/concrete interface; one is the active corrosion process and the other is the film growth/dissolution process. The formula is used to model experimental polarisation curves of steel in concrete through curvefitting analyses. Good curve-fitting results are obtained between the polarisation test curves and model curves. The results are used for evaluation of the corrosion rate and Tafel behaviours of steel in the two concretes and for assessment of the influence of crack width on the corrosion rate within the crack zone.

M. Tech. Metallurgical Engineering / Mild steel is vulnerable to corrosion; this behaviour affects the material strength and electrochemical behaviour during industrial application. Mild steel also has poor tribological resistance; its application for the components of machines, however, requires good tribological property. The cost incurred from equipment failures, properties loss and increased production overheads makes is imperative to enhance mild steel's electrochemical and tribological properties. Electroless nickel plating has found extensive use in various industries attesting to its exceptional properties. The effect of bath parameters on the electroless plating process is of importance as this affects the adhesion, morphological behaviour, electrochemical properties and uniformity of coating. The key aim of this research is: To generally improve the understanding of the effect of electroless binary and ternary alloys on the corrosion and wear resistance of mild steel using weight loss method, potential measurement, linear polarization and tribological sliding wear tests. This work studies the effect of temperature, concentration, deposition time and the inclusion of Tin (Sn) as a third addition to the electroless bath. Corrosion and wear behaviour of the electroless plated mild steel was studied.

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This thesis reports a research of the corrosion mechanism and corrosion rate of steel reinforcement in concrete. Experimental results are presented to compare the corrosion behaviours of steel reinforcement in two blended-cement concretes in seawater. The experimental program included a study of the influence of crack width on macrocell corrosion, an investigation of the procedure for the determination of polarisation curves of steel in concrete and, an evaluation of the corrosion rate of steel in concrete and the influence of crack width as determined by a new polarisation curve analysis. A mechanism is proposed to interpret the different influences, in both the short and long term, of concrete crack width on the macrocell corrosion rate. This mechanism is based on the finding that the corrosion-spread phenomenon is caused by polarisation effects. An oxygen-depletion mechanism is also proposed to explain the much lower macrocell corrosion rate in the slag cement concrete than that in the flyash cement concrete. The procedure for polarisation testing of steel in concrete is found to be critical to obtaining correct polarisation curves. A twotest procedure is verified to be an appropriate procedure and used in this investigation. Experimental polarisation curves of steel in concrete are found to be very different to those expressed by the kinetic Butler-Volmer equation and, this is considered to be a result of the influence of the passive film on the steel surface in concrete. An empirical polarisation formula is developed and its interpretation is based on the postulation of two parallel kinetic processes occurring at the steel/passive-film/concrete interface; one is the active corrosion process and the other is the film growth/dissolution process. The formula is used to model experimental polarisation curves of steel in concrete through curvefitting analyses. Good curve-fitting results are obtained between the polarisation test curves and model curves. The results are used for evaluation of the corrosion rate and Tafel behaviours of steel in the two concretes and for assessment of the influence of crack width on the corrosion rate within the crack zone.

Thesis (M.S.)--University of Michigan, 1973.

Thesis (M.S.)--University of Michigan, 1973.