Advanced Materials Research Vol. 1172

Abstract: Among other parts made of brass there are also the blades and the rotors of the hydraulic machines, respectively ship propellers, which during operation are degraded by cavitation erosion. As a result, most of the researches, including the most recent ones, are focused on the morphological analysis of structures eroded under the impact of micro-jets and shock waves, produced by cavitation hydrodynamics. The goal is to create new materials, but also to use new treatment technologies to increase cavitation resistance. As the literature is quite poor in studies related to the materials resistance to cavitation erosion, respectively treatments and technological procedures of it’s improvement, this paper presents the research results on the behavior of vibration cavitation erosion, carried out on three sets of CuZn39Pb3 brass samples, subjected to volumetric heat treatments of hardening for putting in solution at 800°C, followed by tempering at 250°C, 400°C and 600°C. The characterization of the behavior and the cavitation resistance of the structures resulting from the applied heat treatments is performed based on macroscopic images, taken at different representative periods, SEM images at the end of the test duration and values ​​of specific parameters recommended by ASTM G32-2016. The analysis highlights the differences caused by the change in structure by varying the temperature, but also the hardness of the surface exposed to the cavity. Thus, of the three treatments, it is found that the best resistance to cavitation is conferred by the structure resulting from hardening at 800°C, with tempering at 250°C.

Abstract: The present paper analyzes the differences in behavior and resistance to erosion through vibrating cavitation, between the bronze structures CuSn-12C resulting from two volumetric thermal treatments of hardening and tempering. The analysis was performed on the basis of macro and microscopic images, as well as on the basis of the histogram in which the values ​​of the reference parameters used in the laboratory custom and prescribed by the international norms ASTM G32-2016 are compared. This shows the dependence of the degree of erosion as a function of the temperature of tempering heat treatment, after hardening, as a result of microstructural changes and the hardness of the surface attacked by cavitation. The experimental research is performed on the standard vibrating device within the Cavitation Erosion Research Laboratory of the Politehnica University of Timișoara.

Abstract: Friction stir welding (FSW) is an important research direction within ISIM Timisoara. Also within ISIM Timisoara, in addition to the classic FSW welding, processes and methods derived from FSW were also approached. Those processes and methods include friction stir processing (FSP), coatings with functional layers by friction, conventional friction riveting and friction riveting with hybrid effect, hybrid welding methods: TIG assisted friction stir welding FSW-TIG and ultrasonic assisted friction stir welding FSW-US. Recent research were focused on a new method of applying the FSW process, namely friction stir welding in inert gas environment (FSW-IG). Results obtained by ISIM in the field of FSW-IG welding are presented: data / information on solutions for applying inert gas in the welding area, as well as experimental results obtained for FSW-IG welding of DD13 steel, Cu99 copper and AZ31B magnesium alloy respectively. The solutions for providing shielding gas in the welding area were analyzed, verified and validated by experiment. The experimental welding programs generated the necessary data for the development of the FSW-IG welding technologies for the approached materials. By applying FSW-IG welding there was an improvement in the aspect of the welded joints and for some of mechanical characteristics (as the case may be) compared to the application of classic FSW welding. The use of shielding gas also had beneficial effects on the service life of FSW tools.

Abstract: Welding tools are a determining factor in obtaining welded joints with desired characteristics. The international community pays great attention to research aimed at establishing the optimal characteristics of friction stir welding (FSW) tools. With the development of the FSW welding process with its own contributions, ISIM Timisoara has developed complex research resulting in the conception and design of (innovative) FSW welding tool solutions. A very important factor especially when welding high hardness materials is the durability / lifespan of FSW welding tools. The paper presents general considerations regarding the qualities that FSW welding tools must meet in general, but also ISIM achievements in the field of design and operation of welding tools. Studies regarding operating behavior of welding tools made of sintered tungsten carbide P20S, in terms of service life (wear), both in the case of applying the classical FSW welding process and the method of friction stir welding in inert gas environment (FSW-IG), when joining steels with wide industrial use (304L stainless steel, respectively DD13 steel), are also presented. Concrete data is presented with values of the degree of wear of the tools in the unit of time, in their critical areas: tools made of X38CrMoV5 steel alloy used for welding aluminum alloys with different characteristics, respectively tools made of sintered tungsten carbide P20S used for welding S 235 JR + N steel and 304L stainless steels.

Abstract: Due to its characteristics, DD13 steel is recommended for various applications in the automotive field (including in the manufacture of components for car bodies). The paper presents solutions proposed by ISIM Timisoara for welding of DD13 steel, as alternative solutions to conventional welding processes. One solution that has proven to be viable for joining DD13 steel is the friction stir welding process (FSW). In terms of the quality of the welded joints obtained by applying the classic FSW welding process, these welds were excellent. In an attempt to obtain other benefits, mainly related to the efficiency of the welding process, ISIM Timisoara has developed research programs for the study and application of other methods based on the FSW process principle, namely: - hybrid friction stir welding ultrasonic assisted FSW-US; - friction stir welding in inert gas environment FSW – IG. The important effects due to the application of these methods are: improving (as appropriate) the degree of plasticization of the materials to be joined and increasing the degree of mixing of the materials as result of ultrasonic assistance of the FSW welding process; improvement of the welding process by reducing the pressing forces of the tool during welding, with an effect on increasing the service life of welding tool; respectively improving the aspect of the weld and some mechanical characteristics of the welded joints (at tensile tests, respectively static bending test). The obtained results showed that the two methods derived from the classical FSW welding process, can be used in industrial applications, with important benefits.

Abstract: This paper covers the literature review of the work by author, who have been involved in the subject of machine element repairing from the techno-economical point of view. Positive aspects of repairing, as opposed to purchasing new parts are shown and discussed. All of the examples given as part of the literature review are related to real, practical problems. It was concluded in all cases, that the repairing of damaged parts was the better option, since not only did it cost significantly less, it also noticeably decreased the equipment downtime, as there was no need to wait for the new part to be delivered.

Abstract: Sustainable development requires green energy and low carbon footprint in manufacturing sector of photovoltaic systems. The electrical connections of photovoltaic cells need to have low electrical resistance in order to reduce the electrical losses and therefore to improve the performance of the photovoltaic panels. This paper aims to present researches related to bonding of wires that connect solar cells by using microwave technology. The microwave bonding has the main advantage that offers fast bonding but, in the same time, this technology does not offer stability of the thermal heating. Two different unwanted phenomena like thermal runaway and plasma arc discharge often lead to the damaging of copper and aluminum wires used in electrical connection. The study presented in this paper is focused on simulation of the thermal field developed in copper wires in order to optimize the bonding process and increase the quality of products. The simulation of the thermal field has been done using Fourier equations for conducting heating in copper materials and eutectic alloys. The simulation model has been validated through experimental heating using a 6 kW water-cooled microwave generator controlled by a matching load auto-tuner for best transfer of the power from generator to copper wires. The temperature has been measured in real time using an infrared pyrometer for metals with 2.3 μm spectral range and measurement range between 0o C and 7000 C. The study is finalized with elaboration of mathematical model for microwave-injected power as function for temperature developed in copper wires that can be applied with success in further microwave bonding applications of copper wires. In addition, the electrical resistance of bonded wires was measured in order to collect feedback for improving the microwave bonding process.

Abstract: The manufacture of photovoltaic panels for the production of sustainable energy also involves the stage of electrical connection of the cells in the panel structure. This electrical connection is made by soldering of copper strips on the negative electrode of the cell. During the bonding process, due to the temperature of approximately 220-240°C at which the connecting strip is continuously heated, cracking processes of the upper layer of glass from the cell surface were identified. For this reason, it is necessary either to heat to lower temperatures, a solution that is not viable due to the melting temperature of the solder alloy which usually exceeds 210°C, or a different dosing of the heat flux. The solution proposed in the paper is to create a variable heat flux that allows the melting of the solder alloy, but at the same time to reduce the thermal load of the glass support layer. Through the proposed variant, the energy dosing is done with the help of a heating system consisting of two sources, an ultra-acoustic energy source and a classical resistive source. The resistive source provides an amount of energy to ensure a temperature in the range of 60-140°C, the difference to the melting point of the solder alloy being transferred locally by ultrasonic pulses. Research has highlighted the need to limit the range of values of the pressure of the circular sonotrode, which positively influences the mechanical stress of the photovoltaic cell, but also leads to a reduction in the joining speed. The dosing of the two components of the total energy, the one coming from the resistive source and the one coming from the ultra-acoustic vibration source is decisive for the efficiency of the joining process and for the quality of the soldered joint. Microscopic analyses revealed micro-cracks of the glass surface layer at forces higher than 100 N. Areas with lack of soldering for resistive heating at temperatures lower than 130oC were highlighted, the difference of 90-110°C being achieved by the contribution of ultra-acoustic energy.

Abstract: Gas sensors have been widely implemented to solve concerns of air pollution, monitor human health, and crop yields. Because of its high sensitivity, quick response time, and short recovery time, metal oxide semiconductor (MOS) gas sensors have become a significant topic of research in the field of gas sensing. In the recent decade, many researchers are work on the different types of pure and doped MOS for improve gas sensor response. The present research work deals with the fabrication of p-n heterojunction thin films on alumina substrate by using thermal evaporation technique for reducing gas sensing application. In the current research work, ZnO is used as a functional material and MgO as a dopant. The structural, electrical, and gas sensing properties of fabricated p-n (CuO-ZnO) heterojunction thin films were studied. The resistivity of p-n heterojunction thin films was found to be 23.461Ω/m. The found to be negative to p-n heterojunction thin films. The morphological, elemental and structural characterization of fabricated CuO-ZnO heterojunction thin films were analyzed by using , EDAX and XRD standard tools respectively. By using Scherer’s formula the crystallite size of CuO-ZnO heterojunction thin films was found as 36.83 nm. The fabricated CuO-ZnO heterojunction thin films were exposed to reducing gases such as Liquefied petroleum (LPG), Ammonia (NH₃), Ethanol (C₂H₅OH), and Dichlorofluoromethane (R12) to determine gas response and selectivity. Fabricated CuO-ZnO heterojunction thin films shows maximum response to LPG gas as compare to other gases. The maximum sensitivity has to be found 89.23% to LPG gas of concentration 300 ppm. Fabricated MgO-ZnO thin films also show fast response and recovery time in seconds.