Grinding of transformation-toughened mixed oxide ceramic

During the manufacturing of ceramic components, grinding is an important manufacturing step. It influences the workpiece quality and the operational reliability. Thermomechanical loads during grinding can influence the lifetime and operational reliability of ceramics by modifying their bending strength and subsurface properties. Therefore, it is necessary to consider the influence of the grinding forces and mechanical loads on the strength of the ceramics in order to design a suitable grinding process. In this investigation, a quick-stop device is used to interrupt the grinding process of the newly developed mixed oxide ceramic SHYTZ (strontium hexaaluminate/yttria-toughened zirconia) and the market-established ceramic ATZ (alumina-toughened zirconia). Subsequently, an analysis of the occurring material removal phenomena, the number of active abrasive grains, and the real thermomechanical loads is carried out. It was found that the number of active grains and the material removal phenomena are influenced by the tool specifications. Besides that, the experimentally determined number of active grains was found to be up to 14 times higher than predicted by an analytical model given in literature. Consequently, the calculated single grain chip thickness was found to be up to 12.1% lower than analytically predicted. The investigation of the process forces and thermal loads showed up to 52% higher loads for ATZ than for SHYTZ. The subsequent analysis of the resulting bending strength of the ceramics revealed a lower influence of the grinding process on the strength of SHYTZ than for ATZ. Furthermore, a correlation between the used tool bonding and the resulting thermomechanical loads, bending strength, and residual stresses could be observed. © 2020, The Author(s)

Grain growth in ultrafine-grained Y-TZP ceramics

Grain growth in dense ultrafine-grained (120–600 nm) tetragonal ZrO2-Y2O3 ceramics is studied as a function of temperature. At all temperatures investigated both segregation and phase partitioning occur. It is argued that at temperatures ≤ 1150 °C grain growth is not significantly inhibited by solid solution drag or by phase partitioning. At higher temperatures the grain growth behaviour can be explained by the models of solid solution drag and/or phase partitioning depending on conditions.\u

Development studies of lubricating fluids to accelerate removal of material from silicon nitride

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The superior qualities of ceramics such as high hardness, chemical stability and wear resistance make them promising tribological materials for machine elements, for example, pumps, bearings and heat engines. Ceramics are hard and brittle, therefore, machining such materials is time-consuming, difficult and expensive. A low cost machining process that can remove material rapidly while maintaining a good surface finish is required. The general aim of the studies presented is to find a correlation between the wear mechanisms and surface modifications induced by interactions of tribochemical nature and to identify the most effective combination of parameters involved in producing high material removal rates of ceramics. This study concentrates on silicon nitride, as this material has most potential for use in industry. The influence of lubricant chemistry on the friction and wear of silicon nitride is investigated using a ball-on -plate tribotester and a modified four-ball machine. A wide variety of liquid lubricants and additives supplied by Castrol International are tested to evaluate the role of the chemical characteristics of the lubricant on the friction and wear of silicon nitride. Surface and chemical analysis results reveal that by using different chemistries of liquids, the material removal rate and the surface finish of the silicon nitride can be significantly altered. The highest material removal rate is obtained when using the ester base fluid T80884 + 0.3% triethanol amine. This gives an increase by four fold when compared to the material removal rate obtained with the industrial reference slurry Kemet. The topography of the silicon nitride ball after the grinding test is found to be very smooth indicating that the predominant mechanism of material removal rate could be due to a tribochemical reaction occurring at the contact interface.This study is funded by Castrol International Ltd

Microstructure of (Hf-Ta-Zr-Nb)C high-entropy carbide at micro and nano/atomic level

Support from the projects APVV-15-0469, APVV-15-0621, VEGA 2/0163/16, and VEGA 2/0082/17 is acknowledged. MJR and EGC acknowledge the support of EPSRC grant XMAT (EP/K008749/2)

Microstructures and corrosion of intermediate level wasteforms fabricated using novel thermal techniques

Simulant intermediate level waste materials received from Sellafield, 3 produced using Joule heating techniques, and 3 from plasma furnace methods, were characterised and subjected to leaching tests for up to 14 weeks to assess their potential as a waste matrix. Each wasteform was used to simulate a combination of waste surrogates such as plutonium contaminated material, site ion exchange plant waste, high metal content waste, Magnox sludge, asbestos, or pile fuel cladding. Five samples were characterised as glass composite materials, containing a crystalline and glassy portion, with the sixth being characterised as a glass. XRD and EDX analysis were used to identify the crystalline components, revealing a wide array of phases over the six samples such as pigeonite, anorthite, diopside, Cerium-Lanthanum silicate, proto and clino hypersthene, augite, and two glasses from liquid-liquid phase separation. ICP-OES analysis and pH were used to analyse the leachant, and SEM-EDX surface scans and depth profiles for analysis of the wasteform, post corrosion. Results revealed several of the wasteforms to be more than adequate for safe disposal, showing protective corrosion layers or durable crystalline components. However, not all wasteforms were suitable; in particular glass encapsulated metals should not be used as a waste matrix due to the susceptibility of the metal/metal oxide portion to chemical attack.Open Acces

Heavy vehicle propulsion system materials program: Semiannual progress report, April 1996--September 1996

The purpose of the Heavy Vehicle Propulsion System Materials Program is the development of materials: ceramics, intermetallics, metal alloys, and metal and ceramic coatings, to support the dieselization of class 1-3 trucks to realize a 35% fuel-economy improvement over current gasoline-fueled trucks and to support commercialization of fuel-flexible LE-55 low-emissions, high-efficiency diesel engines for class 7-8 trucks. The Office of Transportation Technologies, Office of Heavy Vehicle Technologies (OTT OHVT) has an active program to develop the technology for advanced LE-55 diesel engines with 55% efficiency and low emissions levels of 2.0 g/bhp-h NO{sub x} and 0.05 g/bhp-h particulates. The goal is also for the LE-55 engine to run on natural gas with efficiency approaching that of diesel fuel. The LE-55 program is being completed in FY 1997 and, after approximately 10 years of effort, has largely met the program goals of 55% efficiency and low emissions. However, the commercialization of the LE-55 technology requires more durable materials than those that have been used to demonstrate the goals. Heavy Vehicle Propulsion System Materials will, in concert with the heavy duty diesel engine companies, develop the durable materials required to commercialize the LE-55 technologies. OTT OHVT also recognizes a significant opportunity for reduction in petroleum consumption by dieselization of pickup trucks, vans, and sport utility vehicles. Application of the diesel engine to class 1, 2, and 3 trucks is expected to yield a 35% increase in fuel economy per vehicle. The foremost barrier to diesel use in this market is emission control. Once an engine is made certifiable, subsequent challenges will be in cost; noise, vibration, and harshness (NVH); and performance. Separate abstracts have been submitted to the database for contributions to this report