Materials Science Forum Vols. 587-588

Abstract: In the present work a new testing method for assessing the wear resistance of matrix materials employed in the manufacture of diamond tools is presented and discussed. The method allows assessing the wear behaviour of different metallic matrices by simulating a circular cutting action of a tool where, instead of a normal abrasive element (matrix impregnated with diamond) only the matrix material is tested. This method has originated a preliminary model of continuum abrasive contact layer between a rotating circular element made of a metal matrix and a glass material. The model allows the determination of the matrix wear rate at different applied forces. To validate the methodology used, different matrix materials (with different mechanical properties) have been analysed in relation to the experimental wear rate.

Abstract: The main objective of this work was to study the influence of the wear properties of two commercial alloys (CK45 and Al7175) on their fretting fatigue behavior. It is verified the effect of material local degradation by wear on a fatigue strength reduction factor, namely the stress concentration factor, and on the overall fretting fatigue life of these materials. The fretting fatigue phenomenon is a synergetic effect between wear and fatigue. It is dependent on both the fatigue and the wear properties of the materials. Material properties promoting an increase in wear resistance should enhance fretting fatigue life.

Abstract: The Friction Stir Welding (FSW) process has a large industrial potential in the field of joining lightweight alloys. Due to the increasing industrial use of aluminium alloys the benefits provided by this technology are very appealing. However, this potential has not, until this time, become a reality due to the lack of relevant available information concerning the process. The lack of information is especially serious in regards to the welding tools. This component, whose importance in the FSW process cannot be overstated, has not been the subject of extensive published research due mainly to the difficulties related to the modelling of the FSW process, which means that all of the development in this field has to be conducted through a trial and error approach. This approach entails significant costs and success risks, thus reducing the capability of R&D institutions to carry out extensive research. The objective behind the work detailed in this paper is the assessment of the effects of the welding tool geometry and features in the weld quality and process productivity. The work was carried out via an experimental procedure, which consisted of carrying out several welds using different pin lengths, pin diameter, pin geometry and shoulder diameter. The geometries that were used are based on known geometries from literature and new concepts. Due to practical limitations the study was conducted using a 3mm thick AA 6082-T6 butt joint configuration. The quality of the welds was assessed through destructive and non destructive testing, namely a visual inspection, an x-ray and a macrographic examination. These results can then be used to correlate the effects of the different tool geometries with the weld quality and productivity. The process productivity can be, according to [1], directly related to the welding speed, this is due to the near absence of welding consumables in the FSW process, leading to the predominance of fixed costs. The results pertaining to this work enable a better comprehension of the manner by which the tool geometry influences the weld quality and the process productivity, thus providing a stepping stone in the ongoing task of optimizing and modelling of the FSW process. The results presented in this paper may also be useful when extrapolated to other materials and thicknesses.

Abstract: An analysis of the microstructure of several modified bitumen shown by phase detection Atomic Force Microscopy (AFM) is presented here. The phase detection and topographic AFM images, displayed three different types of microstructure: the so-called catana phase domains (beelike structures) dispersed in the peri-phase are present in most of the cases; para-phase domains are also observed in the neighbourhood of both catana and peri-phases. These results are consistent with the picture of bitumen as a heterogeneous mixture, as one should expect. The proportions of all these phases display a rather strong dependence on the nature of the modified bitumen considered, on the concentration of the modifier, as well as on the amount of aging of the mix.

Abstract: The paper presents results of a partial experimental programme carried out within the project EUREKA E! 2462 TRUS, which aim is to demonstrate a novel form of hybrid electric drive line without the need for overhead lines. The zero emissions public transport vehicle is based on a hybrid electric drive line with novel, strongly innovative features. The concept includes the use of a small on-board energy storage unit (flywheel) to store the energy that would otherwise be lost on braking. Results of an experimental complex programme of an evaluation of static mechanical and fatigue properties of long glass-fibre reinforced polyester composite material with biaxial or multiaxial structures, respectively, to be used for a manufacture of the flywheel hub disc are presented in the paper. It was shown that results of interlaminar shear fatigue strength of the disc mostly almost correspond to those obtained on basic material – biaxial GRP plates and are close to results obtained on a similar uniaxial GRP used for railways springs. Some ascertained differences are discussed.

Abstract: Synthesis of single-phase tungsten sub-carbide W2C was attempted by heating pellets made out of a source of carbon (graphite-G) and W powders with G/W atom ratio between 0.35 and 0.50 to two target temperatures, namely 1600°C and 1900°C in an argon atmosphere using a solar furnace at PROMES-CNRS in Odeillo (France). The results showed that synthesis of single-phase W2C phase was difficult at either target temperature yielding the W2C co-existed with free metallic W. It was noted that the thin top surface layer of the solar-synthesised tungsten carbide pellets heated to 1900°C was distinguishable from the rest of the bulk specimen showing localised growth of nano-meter scale WC whiskers over W2C grains. Detailed XRD (X-ray diffraction) results on the effect of both G/W ratio and temperature on W2C lattice parameters are discussed.

Abstract: Based on the annual sales volume, stereolitography (SLA) can be considered a Rapid Prototyping (RP) technology with a promising future. Besides being the pioneering equipment, when RP took the first steps in 1988, this technology has been developed with interesting and fast innovations, and a great activity in patents registration. One can assist to a strong research seeking the enlargement of the system capacity to produce large and micro-size parts, and simultaneously impose the technology as a mass production process that is evolving towards a true Rapid Manufacturing (RM) technology. SLA is an excellent tool to materialize concepts and ideas due to the high-resolution capacity, transparency and fine details of the models and prototypes that can be produced. In this study, the state of art of SLA is analyzed and the recent innovations are presented, and considering that the authors have a considerable experience in supervising design students, from different universities, some of the more emblematic projects that were developed at INEGI – Institute of Mechanical Engineering and Industrial Management, are presented. SLA and direct conversion processes were combined to produce new products in materials such as glass, ceramics and metals, for different industrial sectors.

Abstract: Pre-painted metal sheets (coil-coatings) are widely used in casings of household appliances, roofs and side walls in buildings and body parts for the automotive industry. One of the main problems of this type of material is the difficulty to weld it. In an attempt to overcome this problem weldable organic coatings are being experimented. Primers with heavy loads of zinc powder are being employed with success to spot-weld different components of an article. These primers may also present an anticorrosive effect through the galvanic protection offered by the zinc powder. However in aggressive conditions the zinc containing primers can corrode very fast and be consumed in a short period of time. Work has been undertaken in order to extend the lifetime of these primers but maintaining the welding and anticorrosive capabilities. The approach followed here was the modification of primers by corrosion inhibitors that can provide additional active protective effect. A set of organic and inorganic corrosion inhibitors was tested in order to partially passivate the primer. The inhibition of corrosion of zinc and iron was also investigated. Electrochemical testing was done with Electrochemical Impedance Spectroscopy (EIS) and the Scanning Vibrating Electrode Technique (SVET). Results showed that soluble inorganic salts of Ce(III) and La(III) and organic inhibitors like benzotriazole and mercaptobenzothiazole are good candidates to increase the service life of weldable primers.

Abstract: In this work, the Scanning Reference Electrode Technique (SRET) was used to visualise the pyrite corrosion by atmospheric oxygen and its inhibition by a thymol derivative. SRET has the advantage over the potentiostatic and galvanostatic techniques of enabling in situ operation without imposing any potential or current to the sample under study. SRET revealed that the inhibiting effect is effective only if the sample is oxidised beforehand. It also revealed that pyrite corrosion by oxygen is a localised process whereas that by Fe(III) is not local, thus the oxidation of pyrite by atmospheric oxygen is not only due to the oxidative role of Fe(III). Adsorption of oxygen plays probably a determining role. Studies are now carried on to evidence the intervention of galvanic processes or catalysis phenomena occurring during the corrosion of natural conducting minerals and industrial wastes. Their aim is to better understand the mechanisms and to propose remediation processes.

Abstract: As the first step in the restoration process of a Renaissance bronze statue, a comprehensive study of the metallic product was carried out. This paper reports metallographic features and their possible relation to the casting process. Tensile properties are also discussed as they depend on porosity and lead content, what can be useful in the restoration process.