M.Tech. (Operations Management) / Total Quality Management is a management philosophy embracing all activities through which the needs and requirements of customers and the objectives of the organisation are satisfied in a cost effective way through a drive for continuous improvement. Kaizen is a Japanese philosophy and is defined as a process of continuous improvement. It reflects a common-sense, low-cost approach to managing an organisation. A literature review was undertaken on the subjects of Total Quality Management (TQM)principles and Kaizen philosophy and a TQM model was developed for the cellhouse at Manganese Metal Company basedon information from literature review. The cellhouse is part of an organisation that has ISO 9002 accreditation and produces electrolytic manganese metal for customers world-wide. The quality assurance system defines guidelines for producing a quality product, on time and conforming to the required product specifications. The model is designed to complement current quality control philosophy and provide guidance for maintaining and improving the quality assurance programme. All cellhouse employees will be actively involved in participating in a process of improvement on an ongoing basis.

Plasma electrolytic Polishing (PeP) is a non-conventional technology for the surface treatment of electrically conductive materials. It is an effective machining technique for cleaning and polishing of metals and considered as a more environmentally friendly alternative to the electropolishing process. The electropolishing process uses aggressive media such as acids, whereas in PeP, acids or toxicants are replaced by low concentrated water solutions of various salts. In PeP, high DC voltage is applied to the electrodes in the aqueous electrolyte solution, which establishes a thin steam-gas layer around the surface of the work piece resulting in the generation of plasma. From the previous research, it is found that the formation of stable plasma generally takes place between 180-370 volts, where it results in better surface conditions. The aim of this study is to analyse the behaviour of current according to different voltages and their effects on surface roughness and material removal rate (MRR) of stainless steel in Plasma electrolytic Polishing process.

Les alliages de titane sont utilisés dans de nombreux domaines tels que l’aéronautique et l’aérospatial, l’industrie automobile, les plateformes offshore et d’autres applications telles que le biomédical et l’environnement marin. Le choix d’utiliser des alliages de titane repose sur le fait que ces alliages disposent d’un excellent ratio entre la résistance mécanique et la densité ainsi qu’une excellente résistance à la corrosion. Afin d’être employés pour une application marine telle que celle d’un winch innovant, nous avons choisi de travailler sur trois nuances d’alliages de titane β-métastables que sont les alliages Ti-6.8Mo-4.5Fe- 1.5Al, Ti-15Mo-2.7Nb-3Al-0.2Si et Ti-5Al-5Mo-5V-3Cr. Le milieu marin est une atmosphère qui expose les matériaux à des conditions telles qu’elles peuvent générer leur destruction. Divers moyens de dégradation existent. Il était donc intéressant d’évaluer la résistance à la corrosion de ces alliages et de chercher à les protéger contre la corrosion. Le coeur de cette étude repose sur la sélection des alliages de titane susceptibles de répondre au cahier des charges du winch innovant. Des traitements thermomécaniques ont d’abord été définis, puis les alliages ont été caractérisés métallurgiquement et mécaniquement. Ces caractérisations ont permis de connaître les propriétés mécaniques des alliages et de sélectionner les alliages potentiellement employables au sein du winch. Puis des essais de corrosion galvaniques ont été menés via la mesure de différences de potentiel entre les alliages de titane traités et d’autres matériaux susceptibles d’être employé au sein du winch tels que des aciers inoxydables, des alliages d’aluminium et des laitons au plomb. Puis, afin d’évaluer le comportement en corrosion marine du film passif des alliages de titane, des essais de corrosion électrochimiques ont été faits à l’aide d’un dispositif à trois électrodes dans des électrolytes de type chlorure de sodium et eau de mer naturelle. Ainsi des mesures de potentiel libre et de voltammétrie cyclique ont été menées. Le point faible des alliages de titane est le comportement en frottement. Dans ce cas, afin de réduire le coefficient de frottement de ces alliages, il est souvent nécessaire d’effectuer un traitement de surface. Dans cette étude, un traitement thermochimique de nitruration gazeuse a donc été fait sur l’alliage de titane le plus récemment développé parmi les nuances étudiées à savoir le Ti-5Al-5Mo-5V-3Cr. Cet alliage ainsi traité a été caractérisé de façon identique aux alliages traités thermomécaniquement. L’ensemble des essais menés au cours de cette thèse ont permis de déterminer quels alliages de titane parmi ceux étudiés seraient les plus susceptibles d’être employés au sein du winch innovant. / Titanium alloys are used in numerous fields as aerospace industry, automotive industry, off-shore industry, and, in several applications such as medical and marine applications. This is due to their good properties like high mechanical strength, low density and excellent corrosion resistance. In order to be used for an innovating winch and so in a marine environment, we have chosen to study three β-metastable titanium alloys which are Ti-6.8Mo-4.5Fe-1.5Al, Ti-15Mo-2.7Nb-3Al-0.2Si and Ti-5Al-5Mo-5V-3Cr. In marine environment, materials are exposed to tough conditions which can generate their destruction. Several modes of degradation exist. It is so interesting to evaluate the corrosion resistance of these alloys and to search their best corrosion protection. So, the heart of the study is to select titanium alloys to meet the specifications of the innovating winch. At first, we defined thermomechanical treatments for those titanium alloys and then these materials were characterized to know their mechanical and metallurgical properties. These tests allowed us to have a well knowledge of mechanical properties of these alloys and to choose which alloys can be employed in a winch. Then, galvanic corrosion tests were made in nitric acid, sodium chloride and sodium hydroxide. We measured potential differences between our treated titanium alloys and other materials which may be used in a winch such as stainless steels, aluminum alloys and leaded brass. Then, in order to evaluate the behavior of the passive film in marine environment of titanium alloys, electrochemical corrosion tests were conducted using a three-electrode method in sodium chloride and natural seawater electrolytes. So, free potential and cyclic voltammetry measurements were conducted. The flaw of titanium alloys is their low friction coefficient. So in order to improve the coefficient of friction of titanium alloys it is useful to do a surface treatment. In this study, a gaseous nitriding thermochemical treatment was done for the most recent developed alloy among the three studied nuances, which is Ti-5Al-5Mo-5V-3Cr. Then this treated alloy was characterized too similarly to the three thermomechanical treated titanium alloys. All of tests we led allowed us to know which titanium alloys with which thermomechanical and surface treatments may be used for the innovating winch.

Please read the abstract in the section 00front of this document / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2005. / Materials Science and Metallurgical Engineering / unrestricted

Strengthening, resistant and shielding properties, to name a few, can be achieved by implementing a surface material coating onto an engineering component. Various elements of these compounded parts can augment the functionality of the part, such as, increased life time and more interactive surfaces. Tungsten has proven to be a challenge to plate with other metals, but if done correctly, the results can allow for the cold spray of tungsten. Cold spraying tungsten particles alone provides a challenge because the powder is too hard and instead of adhering, it erodes the surface it is attempting to plate. Coating tungsten in a softer metal, like copper, will allow for the particles to adhere to the surface and create a strengthened and radiation shielded component. It also yields a better surface to electroplate onto in the future, as tungsten itself is hard to plate onto, so the copper layer provides the ability to easily plate other metals. The purpose of this thesis project is to encapsulate tungsten powder within copper, then scale up the process to produce bulk amounts of the material in a batch process. The particles will be encased using an electroplating method, that has been vi turned into a semi-autonomous process for the ease of producing bulk powder. While electroless deposition has previously shown positive results for attaining a uniform coating, making it a semi-batch process for bulk material would have an extreme cost in comparison to electrolytic deposition. The tungsten particles have been successfully enclosed in copper by electrolytic deposition in this set of experimentation using an HF electro-etch pretreatment and ultrasonic agitation during electroplating. Further experimentation will include improved methods of stirring and transferring powder, as the transfer takes too long between the etch and the onset of plating and the stirring method is bulky and reduces the area that can be efficiently plated on.

The thesis deals with the topic of silver coating on the inner surface of the tubes made of aluminum alloy EN AW-6101B. The high affinity of the aluminum for the oxygen, the heterogeneity of the surface and the presence of the hydrogen in the base material, are the properties which hinder the formation of metallic coating on the surface of the aluminum alloy. The saturation of the base material with the hydrogen, e.g. due to the pretreatment of the surface or by the process of creating of coatings, may under certain conditions cause the defects of the silver coating in the form of the bubbles (blisters). Other factors that may affect the quality of the silver coating are the way of creating of the interlayer and the conditions for the electrolytic deposition of the silver.

No description available.

This study aims on characterization of non-metallic inclusions (oxides and sulfides) in steel with and without Calcium treatment. In this paper, the three-dimensional (3-D) investigation method of inclusions on film filter after Electrolytic Extraction (EE) of steel samples is applied on two different steel grades (280, 316L). Image analysis of non-metallic inclusions is carried out on Scanning Electron Microscope (SEM) images following with inclusion characteristic analysis. Steel samples with calcium treatment in the production process and reference samples was investigated and compared in density, size and composition. It shows that higher magnification and larger inclusion size correspond to more accurate result. With restriction of equipment and measurement, 2μm is the smallest size could be measured in ×500 magnification within 5% error. The comparison of distribution of inclusions varies with different zones: center has the largest size with least number of NMI; surface has the smallest size with largest number of NM; middle part has the median properties. In 316L steel, Ca treatment increases the number of oxides inclusions significantly; the content of Ca and Si in oxides inclusions is also increased. Two shapes of oxides inclusions, oval and elongated ones, are found with Ca treatment. In 280 steel, the total amount of NMI decreases slightly with Ca treatment; CaS is found in spherical inclusions; Because of earlier formation of larger size spherical inclusions, higher Ca content is found than that in smaller size spherical inclusions.

No description available.

Platinum-gold and nanoceria-modified platinum-gold electrodes were prepared on a platinum surface via electrochemical reduction of solutions of platinum and gold salts in the dispersion of nanoceria. The molar ratios of Pt and Au were varied in both PtAu and PtAu/CeO₂ electrodes while the total concentration of the metals was maintained at 2 x 10⁻³M and the concentration of nanoceria was maintained constant at 5 x 10⁻³M. The electrodes were characterized by their cyclic voltammetry curves in 0.5M sulfuric acid solution. The electrochemically active area of the electrodes was determined using the copper underpotential deposition method. The linear sweep voltammograms of the PtAu and PtAu/CeO₂ electrodes were plotted from -1V to 0V vs. Ag/AgCl, 3M KCl reference electrode using the rotating disk electrodes for the rotation speeds from 200 to 3600rpm in an oxygen saturated 0.1M sodium hydroxide solution. The values of the kinetic controlled current density were determined from the rotating disk voltammetry. The values of the limiting current density for each rotation speed were used to plot the Koutecky-Levich plots for the electrodes. The rate constants were obtained from the Koutecky-Levich plots for each composition of the electrode. The values of kinetic current density and the rate constants indicated that the addition of Au enhances the ORR rates in both the PtAu and the PtAu/CeO₂ electrodes. The values of the kinetic current densities of the PtAu/CeO₂ were lower than that of the PtAu electrodes owing to the poor electrical conductivity of ceria. The Koutecky-Levich plots for the PtAu and the PtAu/CeO₂ electrodes are linear for the four-electron reduction of oxygen in the alkaline media, which indicates that the overall reaction follows the first order kinetics. The electron transfer rate constants obtained from the Koutecky-Levich plots for the PtAu and the PtAu/CeO₂ electrodes both were found to increase in values with the addition of Au. The Tafel plots were plotted for the PtAu and PtAu/CeO₂ electrodes and the values of Tafel slopes were found to be in a small range for lower amounts of Au which indicated that the ORR rates were enhanced in lower amounts of Au. The values of Tafel slopes were found to be much higher for the ceria-modified PtAu electrodes as compared to the PtAu electrodes, which indicate the lower rates of ORR after the modification with ceria. Also, the ORR rates for the electrodes with smaller amounts of Au in PtAu/CeO₂ were higher than those in the larger amounts of Au.