This work is an attempt to evaluate the influence of critical operational parameters on the high temperature erosion of a 1Cr½Mo boiler tube steel. Erosion testing has been carried out in a specially designed and developed unique laboratory apparatus capable of simulating the conditions of temperature, particle velocity and flux as found in the economiser region of pulverised fuel boiler combustors in electricity generation power plants. The work has encompassed the effects of particle type, size, velocity and flux on the erosive wear rates of the 1Cr½Mo boiler tube steel at temperatures of up to 600°C. The response of the target to impacting erodent particles has been analysed using scanning electron and optical microscopy, transmission electron microscopy (TEM) as well as conducting cross-sectional microhardness tests. The change in the mechanical properties of the steel was determined by conducting tensile tests over a range of temperatures from 20°C to 565°C.

Two alloys, Pd 11.1 at.% Cu and Pd 11.1 at.% Nb, predicted to form the A8B ordered structure, were investigated. Prior deformation with systematic heat treatments was used to promote ordering, hardness tests were used to detect changes in the microstructure, which might result from ordering. The Pd-Cu alloy and Pd-Nb alloy did not exhibit any significant hardness changes when heat treated. Transmission Electron Microscopy (TEM) was used to aid detection of any A8B ordered phase in the Pd-Cu alloy. It was concluded that no ordering had occurred and any initial hardness variation was anomalous. The Pd-Nb alloy was further characterised using Differential Scanning Calorimetry, but no transformation was observed. The Pd-Cu alloy was predicted by other workers (after commencement of this project) to have a very low ordering temperature, which probably accounts for the lack of ordering at the temperatures reported here. The Pd-Nb alloy is concluded to be extremely slow in atomic rearrangement, so that unfavourable thermodynamics prevented ordering of the alloy during this project.

A series of four ultrafine WC-Co alloys of varying cobalt contents has been sintered from powder produced through the spray conversion process. The materials have been characterised and subjected to slurry erosion and cavitation erosion. A further twelve WC-Co alloys of varying grain sizes and cobalt contents have been produced through conventional processes and subjected to the same tests in order to provide data for comparison. The erosion resistance of all the grades tested was found to increase with decreasing grain size, both under cavitation erosion and slurry erosion conditions. Furthermore, a transition from a localised material removal mechanism to a bulk material removal mechanism was observed in both erosive systems as the WC grain size of the material decreased below about lμm. The erosion resistance of sub-micron materials was found to be considerably more sensitive to bulk deformation parameters than that of coarser materials. As a result, ultrafine grades subjected to slurry erosion or cavitation erosion were found to exhibit lifetimes up to seven times greater than those of the best-performing materials with grain sizes above 1 μm. This increase in erosion resistance was achieved without any significant drop in fracture toupness. Significant differences were observed between the response of WC-Co to the two erosive systems, particularly in those materials exhibiting a localised erosion response. Under slurry erosion conditions, these materials displayed increasing erosion resistance with decreasing cobalt content, and both the cobalt and WC phases responded to erosive attack. Under cavitation erosion conditions, however, the opposite trend was observed, and only the cobalt phase responded to erosive attack. Materials exhibiting a bulk erosion response responded in a similar fashion to both forms of erosive attack, although cavitation erosion produced damage to a greater depth. The effect of defects on material performance was found to depend critically on the erosive system.

A study has been made concerning the tribological behaviour of ultrahigh molecular weight polyethylene (UHMWPE) during water-lubricated reciprocating sliding wear. The experimental work has been extended to study also the effect of molecular weight, fillers, lubrication, counterface roughness and sliding configuration on the polymer's transfer characteristics. The wear behaviour of polytetrafluoroethylene (PTFE) has been included for comparative studies. The worn material was studied using stylus profilometry, optical microscopy, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), Transmission electron microscopy (TEM), X-ray fluorescence (XRF), X-ray diffraction (XRD), differential scanning calorimetry (DSC), infrared spectroscopy (IR) and mass spectrometry. The effect of two fillers, namely glass beads and a titanium-based inorganic filler on the friction and wear behaviour of UHMWPE has been investigated as a function of counterface roughness (Rₐ). It was found that the filled material exhibited lower wear rates than the unfilled material on the rougher counterface. The filled material was also found to be more sensitive to a change in Rₐ and showed higher wear rates than the unfilled polymer on the smooth counterface. A uniform and coherent transfer film is found on the rougher counterface but the transfer film for the titanium-based filler was patchy on the smooth counterface. No coherent transfer film was found when sliding was conducted parallel to the grinding direction on the steel counterface, resulting in relatively high wear rates. Polymer transfer was patchy, the amount increasing as the sliding distance increased. The observed phenomena are explained in terms of mechanical interlocking and chemical bonding of the polymeric material with the metal counterface. An increase in molecular weight did not significantly improve the wear resistance of the UHMWPE. Small variations in counterface roughness values (Rₐ) were found to have a much greater effect on the wear rates than changes in molecular weight. The steady-state wear rate of the polymer was furthermore found to be more dependent on an adherent transfer film rather than a change in bulk morphology. Although PTFE exhibited low friction coefficients, the high wear rates obtained by this polymer is explained by the polymer's inability to form a transfer film under water lubrication, while any film that forms under dry sliding wear is easily peeled off the surface. Significant improvements in wear are found when fillers are added to the polymer. The wear rates for PTFE under dry sliding are similar to those obtained for UHMWPE under water lubrication. Transfet of UHMWPE material to the metal counterface during sliding wear involves interlamellar shear of the polymer and results in the development of a highly oriented transfer film. Significant differences have been found in the degree of crystallinity, crystallite size and orientation in the deformed surface layers of the polymer and debris compared with those of the bulk polymer. The worn surface of the polymer shows slightly increased crystallinity but the crystallinity of the debris is much higher than that of the bulk whilst the crystallite size is much reduced.

The sliding wear behaviour of ultrahigh molecular weight polyethylene (UHMWPE) sliding against partially stabilised zirconia (PSZ) and alumina ceramic counterfaces in various lubricating media was investigated. Wear tests were conducted in order to investigate the effect that the addition of proteins to the lubricating solutions had on the wear behaviour of the UHMWPE against a smooth counterface of PSZ . The lubricants selected were physiological saline solution, distilled water and physiological saline solution containing small additions of synovial fluid and up to 15'% by volume of albumen solution. The effect of the addition of proteins to the lubricating solutions on the production of wear debris was also studied. ii The effect of changing the counterface roughness from Ra of 0.01 μm to 0.06μm was also investigated. The wear behaviour of UHMWPE against alumina ceramics in distilled water was compared to that of UHMWPE against PSZ in similar conditions.

Bibliography: leaves 170-179. / Polypropylene is an extremely versatile polymer because its properties can be modified to meet specific requirements. The use of polypropylene in domestic and automobile applications has initiated research focused on the tribological behaviour of the material. In the present study, polypropylene grades have been subjected to both mild and severe abrasive wear conditions with specific emphasis on the surface property of scratch resistance. The experimental work has covered the effect of polymer crystallinity, mineral fillers, and the nature of the abrasive counterface on the wear behaviour of polypropylene. The wear behaviours of polymethylmethacrylate, polycarbonate, acrylonitrile-butadiene-styrene, and high density polyethylene have been determined for comparative purposes. The abrasive wear rates have been measured and the material deformation and removal mechanisms have been identified and characterised in terms of the physical properties of the polymer and the individual fillers, and in terms of the macroscopic mechanical behaviour of the filled composite materials. Investigative techniques used in this study included mechanical testing, optical and scanning electron microscopy, surface profilometry, and differential scanning calorimetry. Under two-body abrasive wear conditions, the unfilled and modified polypropylene materials exhibit a ductile mode of material deformation and removal.

AISI 430 ferritic stainless steel (FSS) is the most widely used FSS alloy due to good resistance to stress corrosion cracking. Owing to the chemical composition range, AISI 430 alloys undergo a partial phase transformation of ferrite to austenite when subjected to hot rolling temperatures. Consequently, the alloys consist of ferrite and austenite during processing. The presence of austenite and ferrite influences the microstructure evolution and texture development during hot rolling and subsequent annealing heat treatments. Two AISI 430 FSS heats of varying austenite volume fraction were used in this study. The two AISI 430 FSS heats were deformed using the first three passes of the Steckel mill hot rolling process. Post deformation heat treatments namely: continuous phase transformation and martensite tempering heat treatments were performed after three successive simulated Steckel mill passes. Microstructure analyses were performed using light microscopy and Electron Backscattered Diffraction (EBSD). The microstructure analyses were performed in order to determine microstructure evolution and texture development during hot deformation and post deformation heat treatments. The difference in austenite volume fraction in the respective heats A and B has profound influence on the possibilities for microstructure and texture evolution. For the higher austenite volume fraction heat A, the post-deformation path for austenite decomposition can lead to two very different textures in the prior austenite regions. During continuous diffusional transformation from austenite to ferrite the final texture is influenced by expected variant selection as well as growth selection during the prolonged isothermal heat treatment. The result is relatively strong {001}<110> texture and comparably very weak γ-fiber texture. In the case of the martensite tempering process the γ-fiber texture that is inherited from the austenite to martensite diffusionless transformation is maintained in the prior austenite regions. The mode of post-deformation heat treatment does not significantly impact on texture development in heat B where the texture is dominated by recovery and growth in the primary ferrite phase.

Rare-earth doped complex oxide materials have a number of interesting applications in the clean energy economy. By tailoring the materials composition, the electronic, thermal, and ionic transport properties can be tuned for the intended application. In this study, three examples of such applications are considered. First, a crystal structure known as sodium super ionic conductors (Na1+3xZr2(P1-xSixO4)3 ) was modified to synthesize a cerium super ion conductor [Ce.1Zr.9)40/39Nb(PO4)3]. Tuning the composition resulted in a complex oxide that has been shown to have selective cerium ion conductivity, making it a candidate as a solid electrolyte in a real time rare earth ion sensor. These sensors were successfully applied to demonstrate real time monitoring of cerium concentrations in aqueous solutions and could potentially be modified to detect other rare earth elements, eliminating the time intensive chemical assay testing currently used in rare earth recycling and refining. Another application of complex oxides includes the use of lanthanum doped strontium manganese oxide (La.8Sr.2MnO3) as an electronically conductive diffusion barrier. This material was applied to 2205 stainless steel to test its potential as an interconnect in solid oxide fuel cells (SOFCs). These barrier layers can reduce high temperature oxidation and spallation in SOFCs interconnects, potentially increasing the lifetime of SOFC stacks, and allowing for cheaper ferrous alloys to be used in operating conditions up to 800°C, further lowering the overall cost of SOFCs. Lastly, gadolinium doped strontium titanate (Gd.08Sr.92TiO3) is considered as a thermoelectric material. Specifically the addition of a second phase of gadolinium doped cerium oxide (Gd.2Ce.8O3-δ) was used to achieve enhancements in the thermoelectric properties. / 2016-10-27T00:00:00Z

OBJECTIVES: To investigate the effect of various finishing procedures and repeated firings on color stability and translucency of different ceramics. Also, to examine the mechanical properties after finishing procedures. MATERIALS & METHODS: Four glass-ceramics were investigated; IPS e.max CAD, IPS e.max Press, Celtra Duo, and Celtra Press. For each material 87 disc-shaped specimens, 2 mm in thickness and 12 mm in diameter were fabricated. Specimens were divided into 3 groups (n=29) as no treatment, polishing, and glazing group. Five samples from each group were submitted to 1, 3, and 5 simulated “stain” firings using a ceramic furnace according to the manufacturer’s instructions. Color coordinates were recorded in the CIE L*a*b* system using an X-rite Ci7600 spectrophotometer and Vita EasyShade. Color differences relative to the control and translucency by contrast ratio were recorded. The 3-point flexural strength test was performed using an Instron universal testing machine. Hardness test was performed using Vickers microhardness and surface roughness was measured using a contact profilometer. Data were analyzed using multiple ANOVA (α=0.05). RESULTS: In general, glazed materials showed higher flexural strength than polished and no treatment groups. Celtra Duo showed the highest mean Vickers hardness followed by e.max CAD, e.max Press then Celtra Press. Surface roughness is lowered significantly when the glaze was applied to all materials. The contrast ratio of Celtra Duo is significantly lower than e.max CAD, e.max Press, and Celtra Press. Firing cycles displayed a significant effect in lowering the translucency of e.max CAD, and in raising the translucency of Celtra Duo and Celtra press, but no significant effect on Emax press. Surface treatment showed a non-significant effect on contrast ratio in all materials tested. Repeated firing cycles significantly affected color change for all materials tested, except for Celtra Duo. Also, polishing and glazing significantly affected color change for all tested materials. CONCLUSION: Type of material, surface treatments and firing cycles have a significant effect on color change and translucency. Surface treatment have a significant effect on the mechanical properties of glass ceramics; glazing can improve the flexural strength and reduce surface roughness of the ceramic materials.

archives@tulane.edu / Metal whisker formation has been an unwanted byproduct in electronics for the past 70 years. However, in that period, no one has come up with one mechanism that can explain all the collected data. This dissertation focuses on copper whisker formation in the presence of a sulfur-containing compound. Pulsed laser deposition is used to create a molybdenum disulfide thin film, and the resulting whiskers are analyzed with scanning electron microscopy and x-ray photoelectron spectroscopy. The copper whiskers are proven to be pure copper and can be several millimeters in length. The collected data supports a recrystallization-based mechanism, where the copper vapor on the surface recrystallizes at the base of the copper whisker, therefore, adding to the length of the whisker. / 1 / Megan Elizabeth Woods