Thesis (Ph. D.)--Columbia University, 1930. / Vita. Bibliography: p. [26].

No description available.

Diss. (sammanfattning) Uppsala : Univ., 2004. / Härtill 4 uppsatser.

The processing of materials has become a specialist field and the industry will continue to grow due to rising costs in labour and raw materials which has forced many automotive industry suppliers to invest heavily in this field. In order to be relevant and competitive in today’s industrial world, companies in South Africa are now forced to dedicate billions of rands in profits to research and development. Metals like titanium are finding favour with automotive and aviation companies in pursuit of savings in fuel consumption. This saving is achieved by reducing weight on aircraft and automobiles yet still meeting acceptable and improved structural integrity. In-depth research into the behaviour of various materials under varying loading conditions is therefore essential. The study on the processing of commercially pure grade 2 titanium alloy plates focuses on the development of process parameters for bending the material using a 4kW Nd: YAG laser to an approximate radius of curvature of 120mm. The resulting mechanical properties of laser formed plates are then compared to those obtained from mechanically formed samples. The titanium parent material was used to benchmark the performance of formed samples. The effect of process parameters on the mechanical properties and structural integrity also formed part of this study. To obtain the bending parameters for laser forming, various combinations of processing speeds and laser powers were used. The line energy is dependent on the power and scanning velocity parameters and these are shown in table 1. The laser power, line energy and scanning velocity were the main parameters controlled in this study and the beam diameter remained unchanged. Residual stress analysis, micro-hardness and fatigue life testing were carried out to analyse mechanical properties and the structural integrity of the plate samples. Microstructural analysis was also done to observe changes in the material as a result of the forming processes. From the results it is evident that laser forming is beneficial to the hardness of titanium but detrimental to the fatigue life at higher line energies. Residual stress analysis showed the amount of stress within the study samples increased with each forming operation. This information was vital in the analysis of the fatigue life of titanium. A fatigue life prediction model was developed from this study and it shed some light on the behaviour of titanium in fatigue testing. The model could be used to predict fatigue life when no fatigue data is available for commercially pure grade 2 titanium alloy plates. In conclusion, this study helped establish parameters that could be used to bend titanium while the analysis of mechanical properties showed the limits of working with this alloy.

The processing of materials has become a specialist field and the industry will continue to grow due to rising costs in labour and raw materials which has forced many automotive industry suppliers to invest heavily in this field. In order to be relevant and competitive in today’s industrial world, companies in South Africa are now forced to dedicate billions of rands in profits to research and development. Metals like titanium are finding favour with automotive and aviation companies in pursuit of savings in fuel consumption. This saving is achieved by reducing weight on aircraft and automobiles yet still meeting acceptable and improved structural integrity. In-depth research into the behaviour of various materials under varying loading conditions is therefore essential. The study on the processing of commercially pure grade 2 titanium alloy plates focuses on the development of process parameters for bending the material using a 4kW Nd: YAG laser to an approximate radius of curvature of 120mm. The resulting mechanical properties of laser formed plates are then compared to those obtained from mechanically formed samples. The titanium parent material was used to benchmark the performance of formed samples. The effect of process parameters on the mechanical properties and structural integrity also formed part of this study. To obtain the bending parameters for laser forming, various combinations of processing speeds and laser powers were used. The line energy is dependent on the power and scanning velocity parameters and these are shown in table 1. The laser power, line energy and scanning velocity were the main parameters controlled in this study and the beam diameter remained unchanged. Residual stress analysis, micro-hardness and fatigue life testing were carried out to analyse mechanical properties and the structural integrity of the plate samples. Microstructural analysis was also done to observe changes in the material as a result of the forming processes. From the results it is evident that laser forming is beneficial to the hardness of titanium but detrimental to the fatigue life at higher line energies. Residual stress analysis showed the amount of stress within the study samples increased with each forming operation. This information was vital in the analysis of the fatigue life of titanium. A fatigue life prediction model was developed from this study and it shed some light on the behaviour of titanium in fatigue testing. The model could be used to predict fatigue life when no fatigue data is available for commercially pure grade 2 titanium alloy plates. In conclusion, this study helped establish parameters that could be used to bend titanium while the analysis of mechanical properties showed the limits of working with this alloy.

No description available.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 250-253). Also available via the Internet.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xvii, 181 p.; also includes graphics (some col.). Includes bibliographical references (p. 168-181). Available online via OhioLINK's ETD Center

Tribocorrosion is a term used to describe the material degradation due to the combination of electrochemical and tribological processes. Due to a synergetic effect, the material loss can be larger than the sum of the losses due to wear and corrosion acting separately. In this thesis, the synergy of wear and corrosion was investigated for different types of material, namely the Ti-6Al-4V alloy, the SS316L stainless steel coated with a thin film of Diamond Like Carbon (DLC), and the SS301 stainless steel coated with a thin film of chromium silicon nitride (CrSiN). / A tribocorrosion apparatus was designed and constructed to conduct wear experiments in corrosive media. Sliding ball-on-plate configuration was used in this design, where the contact between the ball and the specimen is totally immersed in the test electrolyte. The specimen was connected to a potentiostat to control its electrochemical parameters, namely the potential and the current. Electrochemical techniques were used to control the kinetics of corrosion reactions, and therefore it was possible to assess separately the role of corrosion and wear in the total degradation of material, and to evaluate the synergy between them. / For Ti-6Al-4V, it was found that the corrosion and tribocorrosion depend strongly on the structure of the material. The alpha-equiaxed microstructure with fine dispersed beta-phase exhibited the best corrosion resistance. The corrosion resistance was found to decrease when the basal plane was preferentially aligned parallel to the surface, which is attributed to a low resistance to charge transfer in the oxide films formed on this plane. On the other hand, when wear and corrosion were involved simultaneously, the oxide layer protecting the substrate against dissolution was mechanically destroyed leading to a high corrosion rate. It was found that the hardness was the most important factor determining the tribocorrosion behavior of the Ti-6Al-4V alloy; samples with high hardness exhibited less mechanical wear, less wear-enhanced corrosion, and less corrosion-enhanced wear. / For DLC coatings, it was found that interface engineering plays a crucial role in the tribocorrosion behavior of DLC films. DLC films with nitrided interface layer (SS\N3h\DLC) were shown to have very poor tribocorrosion resistance; the DLC film delaminated from the substrate after 50 cycles of sliding wear at 9 N load in Ringer's solution. It should be mentioned that a previous study performed at Ecole Polytechnique de Montreal [4] has shown that the same coating resisted 1800 cycles of dry wear at 22 N without delamination. This demonstrates clearly the effect of corrosion on the wear resistance of DLC films. The use of a-SiN:H bond layer between the SS316L substrate and the DLC film improved significantly the tribocorrosion behavior of the coating. This layer acts as a barrier against corrosion reaction; the polarization resistance was 5.76 GO.cm2 compared to 27.5 MO.cm2 and 1.81 MO.cm2 for the DLC-coated SS316L with nitrided interface layer and the bare substrate, respectively. / For CrSiN coatings, it was also shown that nitriding treatment of the substrate prior to deposition reduces significantly the tribocorosion resistance of the CrSiN-coated SS301 substrates. This is attributed to the peculiar morphology of the nitrided surface prior to deposition. The high relives at the grain boundaries of the substrate may be the reason for the generation, during sliding wear, of defects in the film, which makes the infiltration of the liquid easier, and consequently leads to the destruction of the CrSiN film.

No description available.