Advanced Engineering Forum Vol. 42

Abstract: Materials consisting of a hard phase, usually WC, and a tough binder, traditionally Co, form the most successful class of composite materials, also known as Hard Metals (HM) or Cemented Carbides. Powder metallurgy routes are employed generally for the production of such [1]. The typical processing route of such materials involves mixing the components, kneading and consolidation. Alcohols, alkanes and alkenes are commonly used to limit any excessive heating and oxidation of powders during mixing the components. In this study, we report the results of milling in a more environmentally friendly aqueous milling media. The obtained results are presented comparatively with milling under a traditional media, such as isohexane and acetone. The characterization of the milled samples has been done from the structural, compositional and morphological point of view. Considering our previous results, an important aspect of the milled powder is the carbon content, which dictates the sintering behavior of such parts. The carbon balance investigation performed on a carbon analyzer has revealed no significant differences upon changing the milling media. This work emphasizes the influence of the milling media on the HM powder. HM powders with similar properties have been obtained both by traditional and aqueous milling. The comparative study has revealed that the substitution of the traditional milling media does not influence the carbon content in the HM powder.

Abstract: Among the various alloying techniques used in powder metallurgy, the masteralloy concept has been known for a long time. However, its use for production of ferrous precision parts has been hampered by several obstacles such as poor output of the useful fine fractions, high tool wear and slow homogenization kinetics of the alloy elements in the matrix. On the other hand, the masteralloy concept is particularly interesting for introducing cost-effective alloy elements such as Cr, Mn and Si since the masteralloy approach at least alleviates the problems caused by the high oxygen affinity of these elements. In the present study it is shown that recent developments have given a boost to this classical concept, one of these developments being powder manufacturing by high pressure water atomization which dramatically increases the yield of fine masteralloy fractions. The other progress is availability of thermodynamic software that enables defining masteralloy compositions with low melting range and thus fast homogenization also at moderate sintering temperatures. Combined, these new developments open the door for implementation of the masteralloy route in large scale PM parts production.

Abstract: Sinter hardening is a powder metallurgy processing route that combines the sintering and the heat treating processes in one step by gas quenching the components immediately after they have left the high temperature zone of the furnace. It is both economically attractive and ecologically beneficial since it renders deoiling processes unnecessary. The slower cooling rates associated with gas compared to oil quenching however requires special alloy concepts different to those known from wrought steels. In the present study it is shown that by admixing atomized masteralloy powders consisting of suitable combinations of Mn, Cr, Si, Fe and C to base iron or pre-alloyed steel powders, sinter hardening PM steel grades can be produced that transform to martensitic microstructure at cooling rates of 2-3 K/s as typical for industrial sinter hardening. This is confirmed by CCT diagrams and hardness measurements. However, metallographic investigations are also necessary because in sintered steels, the cores of the largest base powder particles are alloyed very slowly during sintering and therefore tend to result in soft spots in the sinter hardened microstructure which are mostly not discernible in the CCT diagrams. Here, even slight pre-alloying of the base powder with Mo and/or Cr is helpful, both increasing the hardenability of the steels compared to base plain iron and avoiding soft spots in the microstructure.

Abstract: The paper presents some researches about the dynamic mechanical properties for some green composites made as follows: the reinforcement is made from rush and bulrush and the matrix is from epoxy resin Resoltech 1050 with its hardener Resoltech 1055. The dynamic parameters were determined from the bars free vibrations. In the first part of the paper, there are presented the mathematical calculus formulas used for the dynamic parameters determination based on the experimental recordings for the free vibrations. The next experimental montage was used: the bars were clamped at one end and were left free at the other end. At the free end, a Bruel&Kjaer accelerometer with 0.04 pC/ms^-2 sensitivity was placed in order to record the beams dynamic response. A force was applied at the free end to bend the beams and after bending, the force was cancelled and the beams were left to freely vibrate. The accelerometer was connected to a signal conditioner Nexus and the signal conditioner was connected to a data acquisition system SPIDER 8 made by Hottinger Baldwin Messtec. The acquisition system was connected to a notebook ant the experimental parameters were obtained through CATMAN EASY software. From the free vibrations recording, the following mechanical parameters were determined: the eigenfrequency of the first eigenmode and the damping factors per unit mass. With these values, we have determined some direct calculus formulas for the damping factor per unit mass.

Abstract: In this paper we present some researches about the static mechanical properties for some composites made in this way: the reinforcement is made from two types of felt and the matrix is from epoxy resin Resoltech 1050 with its hardener Resoltech 1055. There are built some plates from felt/epoxy resin and from these plates there are cut some samples. The samples are tensile loaded on an universal testing machine Instron 1000 HDX which is assisted by a BlueHill software. There are determined the next mechanical properties: Young modulus, yield strength, elongation at break and breaking strength. By using an optical microscope, there are presented some images with the breaking sections.

Abstract: This paper aims to present preliminary researches on the influence of the shape and dimensions of composites materials on the stability of microwave heating. The research was focused on cordierite composite material, which is used as ceramic substrate in selective catalytic reaction for reduction of nitrogen oxide emissions from combustion engines. For experimental program were used different shapes for cordierite material, such as cubic, cylindrical, sphere and rectangular. Based on previous researches where it was demonstrated that an injected microwave power between 600 W and 1200 W, the samples were heated in order to establish which shape is more suitable for fast heating, thermal stability in terms of thermal runaway as well as for avoiding the unwanted microwave plasma initiation.

Abstract: In the research activities on the barium monoferrite pyrosynthesis, an important place is occupied by TG and DTA analysis. The effects of different hematite (α-Fe₂O₃) granulations on the BaFe₂O₄ pyrosynthesis temperature were followed. Four types of commercial hematite powders were used, the difference between them being the fineness of the powder granules and the purity. Only one type of commercial barium carbonate (BaCO₃) powder was also used as a barium additive in the BaFe₂O₄ pyrosynthesis. Each of the 4 types of α-Fe₂O₃ with BaCO₃ were subjected to the homogenization process in a planetary mill for a more intimate mixing of the powders in order to obtain error-free results regarding the pyrosynthesis reaction. To determine BaFe₂O₄ pyrosynthesis temperature, a derivatograph device was used. All the data obtained with this thermal device were digitally processed in order to extract the two TG and DTA curves. The protective atmosphere in the furnace was nitrogen. BaFe₂O₄ pyrosynthesis temperatures recorded different values for the four mixtures, depending on the particle size of the α-Fe₂O₃ powders, protective atmosphere from furnace and the mixing conditions. The effects of Fe₂O₃ oxides on the BaFe₂O₄ pyrosynthesis temperature is observed when are used very fine hematite powders in mixtures, obtaining a reduction of pyrosynthesis temperature up to 16% compared to the mixture where the size of the hematite is coarser.

Abstract: The quenching is one of the most used mechanisms for increase the strength of aluminium alloys sheets. The purpose of quenching is to keep the super-saturated solid solution formed during the solution heat treatment as intact by rapid cooling. In order to establish the influence of the addition of polymer in the quenching water on the distortion and residual stresses of the aluminium alloy sheets, several tests were performed with different concentrations of the polymer in demineralized water. The experiments were performed on 6082 aluminium alloy sheets with a thickness of 5 mm. The quenching of the samples was done by immersion in a stainless steel vessel with a capacity of 10 liters. The obtained results show that the addition of polymer in demineralized water positively influences the deformation of aluminium alloy sheets. In this way, a correlation between the polymer concentration and the deformation of the plates was established. Regarding the internal stresses, no correlation was identified with the level of polymer used in demineralized water.

Abstract: The 1.4301 stainless steel is part of the category of austenitic stainless steels, steels which do no undergo heat treatments in general, as they are intended for hot plastic deformation in particular. The aim of the research presented in this paper was to obtain significantly improved characteristics of the resistance properties in relation to the values obtained under classical conditions, by applying heat treatments. Samples taken from the delivery state material underwent annealing, quenching and ageing heat treatments. Subsequently, the samples thus treated were subjected to tests enabling the determination of the correlations between the heat treatment parameters, the structure and the properties.

Abstract: In daily activities, serial numbers represent one way to range finished products of different types of production fields and also tracking those objects during their lifetime – ever since their exit of the production site until their recycling. In this paper are presented several types of imprinting techniques as well as a case study for restoration of a modified serial number.