Materials Science Forum Vols. 539-543

Abstract: Groove pressing (GP) is a severe plastic deformation technique for producing ultra fine grain sized microstructures in metals and alloys. In the present study, groove pressing and a two-step process of groove pressing followed by cold rolling was used to investigate the potential of these processes to produce ultra fine grained copper with significantly enhanced strength. Mechanical and microstructure properties were evaluated after groove pressing and after groove pressing followed by cold rolling. The advantages conferred by groove pressing prior to cold rolling on producing copper with enhanced properties has been investigated.

Abstract: The material characterization on the weak points of the structural systems is essential to evaluate safety accurately. However, general material characterization methods such as uniaxial tensile test and CTOD (crack tip opening displacement) test are destructive, therefore, it cannot be applied to the system in use. To overcome this problem, the material characterization using instrumented indentation technique was developed. However, current researches on instrumented indentation technique focus on the hardness measurement. The evaluation of flow property, residual stress and fracture toughness using instrumented indentation technique is not sufficiently performed. In this paper, we introduce the evaluation method of the flow property, the residual stress near the weldment and the fracture toughness developed from damage mechanics. The algorithm of flow property evaluation, the residual stress evaluation model and the fracture toughness model by using indentation were verified comparing with the experimental results.

Abstract: Due to its outstanding mechanical properties at high temperatures and chemical stability iridium is used for demanding high temperature applications. In order to obtain materials data necessary for the design of high temperature equipment and the numerical simulation of their service performance the stress-rupture strength and creep behaviour have been investigated in a temperature range between 1650°C and 2300°C. The results of metallographic and fracture examinations (SEM) revealed that, in common with other pure metals, unalloyed iridium shows marked grain growth at high temperatures. Under these conditions, the deformation characteristics of iridium may not be entirely uniform and predictable, as will be demonstrated with examples from the creep studies. Both metallographic examination and investigations by means of scanning electron microscopy gave indications of possible causes for a significant anomaly in the creep behaviour. It is therefore advantageous for the mechanical properties if a fine-grained microstructure can be maintained even at the highest service temperatures.

Abstract: The cold expansion technique is often used to introduce beneficial compressive residual stresses at fastener holes that retard cracking in fatigue loaded material. The present investigation emphasizes micro structural changes along the radial section of holes after the holes are subjected to cold working. The experiment was conducted for two different materials, namely Steel85, EN-8D alloy steel with thickness 10mm. The holes are expanded to different percentages by split sleeve method and the microstructures are observed using SEM (Scanning Electron Microscope). It is observed from the micrographs that a zone of plastic deformation close to the hole followed by a zone of elastic compression induced by the split sleeve expansion. A comparative study of microstructure of the hole before and after expansion and also study the pattern after different extent of expansion of holes

Abstract: Neutron scattering using diffraction techniques is now recognised as the most precise and reliable method of mapping sub-surface residual stresses in materials and industrial devices. It was therefore decided to build the dedicated strain scanner KOWARI among the first suite of instruments for the new Australian Replacement Research Reactor OPAL. In order to support the new instrument and familiarize the Australian user community with the technique a „Neutrons for Engineering“ project has been established to provide a fully integrated residual stress service. To make use of the neutrons at Australias HIFAR reactor the existing three-axis spectrometer has been refurbished and modified to allow strain measurements. The Australian Strain Scanner (TASS) will operate until the new strain scanner becomes operational in 2006. Apart from giving an overview about the technique and properties of the new strain scanner we would like to present and discuss two case studies: a) residual-stresses obtained from a break-disc of a car and b) residual-stresses within a flash-butt welded plate cut out of a railway.

Abstract: The goal of this work is to model the temperature distribution, phase transformation and residual stresses induced during the heat treatment of 3 and 5 inches diameter grinding balls. In the first step, the radial distribution of temperature inside the balls was calculated and validated experimentally. During the quenching, the model considers factors such as the heating of the water and the formation of a steam layer that surrounds the balls in the beginning of the treatment. In a second step, with the temperature distribution, the CCT curves of the steel and the Koistinen- Marburger equation, the radial distribution of martensite was determined during the heat treatment. Finally, in the third step, the residual stresses field was modeled considering the temperature distribution, the force equilibrium equations and the constitutive thermo-elastic relationships, where the expansion due to the austenite – martensite transformation was included. In the temperature distribution, a good experimental-theoretical agreement was obtained, with differences at the end of the quenching no higher than 0,5 %. Respect to the residual stresses, the model indicates that the maximum tensile values occur at certain depth below the surface of the balls and the experimental evidence of the behavior of the balls in a mill simulator, as well as the measured residual stresses by means of DRX shows an acceptable agreement with the theoretical predictions.

Abstract: The photocatalytic degradation of organics in aqueous solution is an active research field. Currently, the relatively low degradation efficiency is the key problem to be solved that caused by the simple recombination of the photo-generated electrons and holes. The electrode was prepared by anodic oxidation on titanium thin plate and produced multiporous nano-crystalline titanium dioxide film with anatase structure on titanium substrate. In order to inhibit the simple recombination of the electrons and holes, the electric potential bias was applied to the electrode to drive away the chargers. The change of the photocurrent and the discolouration of the dye solution containing either methylene blue or acid red G with different magnitude of the applied bias were measured. It shows that the photocurrent increased by three orders of magnitude from μA to mA level by the applied bias. Correspondingly, the discolouration rate of the methylene blue in dye solution was increased greatly with the increasing applied bias up to 3.5V. The different kinds of transitional metal ions dopants of Mn2+, Cr3+, Fe3+, and Ni2+ to the electrodes was done by anodic oxidation method. The effects of different types of dopants on the photocatalytic activity were revealed by measuring the degradation of an organics aqueous solution containing a dye using a combination of ultraviolet light energy in the presence of these electrodes. The photocatalytic efficiency, which was remarkably enhanced by the incorporation of Mn2+、 Cr3+.、 Mn2+, showed the largest enhancement. However, Fe3+ changed only slightly, and Ni2+ showed no enhancement. These effects were related to the difference of these transitional metal dopants electron work function values and also to the difference of their ionic radii in respect to that of Ti4+. The configuration of the reactor for water treatment with the rotating electrode and 365nm wavelength UV radiation was described.

Abstract: As one of the oldest manufacturing methods, the plasticity processing still is the basic and important way to produce the components in this period of IT. In the recent years, the plasticity processing has gained more attentions and a further development. At the same time, for the purpose of the sustainable development and the big profit, the environmental friendly methods should be applied into the plasticity processing. Based on the introduction to the development of the precise forging and stamping, this paper described the development trends and the basic needs of the plasticity processing and indicated that it is demanded to speed up the change of plasticity processing from the experimental or trial-and-error types to the scientific analysis and to realize more of precision, more of economy and more of greening (3M strategy) for the processing.