Modelling investigation of morphology for Ag-C powders mixtures created by mechanical alloying process

Jedną z głównych przeszkód w skutecznym zastosowaniu cząstek węgla do umocnienia kompozytów na osnowie metali jest ich niedostateczna dyspersja w samej osnowie. Szczególne trudności dyspersyjne obserwuje się w kompozytach na osnowie srebra stosowanych na nakładki stykowe w łącznikach niskonapięciowych, ponieważ srebro i węgiel nie reagują ze sobą. W artykule przedstawiono badania struktury proszków otrzymanych podczas procesu mechanicznej syntezy (MS) czystego Ag o różnych kształtach oraz mieszaniny Ag z dodatkami 0,1 % wag. i 3 % wag. węgla. Stwierdzono, że proces formowania cząstek w wyniku zgrzewania na zimno, dzięki wysokiej energii zderzeń pomiędzy kulami i cząstkami srebra, ma różny przebieg i zależy od kształtu proszku wyjściowego. W wyniku procesu MS mieszaniny sferycznego proszku Ag i C zaobserwowano zmniejszenie wielkości cząstek oraz zmianę ich kształtu. Ponadto, badania przeprowadzone na mikroskopie skaningowym wykazały, że już po 30 minutach procesu w przypadku obu rodzajów proszków Ag i kulistego proszku C tworzy się proszek kompozytowy Ag-C. Badania potwierdziły istotną zależność pomiędzy energią procesu MS a strukturą proszków kompozytowych. Otrzymane rezultaty są spójne z wnioskami zaprezentowanymi przez autorów w publikacji [11]. Uważamy, że zastosowanie procesu mechanicznej syntezy do otrzymywania kompozytów Ag-C stosowanych na styki w łącznikach niskonapięciowych może być w przyszłości dobrym rozwiązaniem.One of the major obstacles to the effective use of carbon particles as reinforcements in metal matrix composites is their poor dispersion within metallic matrix. Especially, within silver matrix using on low voltage electrical contact tips for reason that no nuclear phases for Ag and C elements. This paper studies the milling structures of pure, different in shape silver powders and mixtures 0,1% wt. and 3% wt. C in it, formatted during mechanical alloying (MA) processes. It was found that high energy collisions between balls and pure Ag powders cold welded particles together in different ways depending to particles shapes. Two effects: size decreasing and shape particles changing were observed for spherical powders Ag-C3 mixture, MA processes after. Moreover, SEM investigations appeared composite Ag-C structure for both shapes Ag and spherical C in powders milling 30 minutes only. The strongly compositing effects were observed for Ag flat in shape and round C particles. The investigations confirmed essential relation between MA energy and structure of composite powders. Our results and conclusions are convergent to suggestions expressed by Morsi K. and Esawi A. in publication [11]. Authors hope so mechanical alloying is good way to get Ag-C material for low voltage electrical contact tips, in the future

The role of particle size in the process of forming the structure of a composite powder by mechanical alloying

Publikacja stanowi podsumowanie prac teoretycznych i doświadczalnych związanych z prognozowaniem struktury i otrzymywaniem materiałów kompozytowych z osnową srebrową i kruchymi fazami wzmacniającymi. Dwa modele geometryczne: model pokrycia powierzchniowego (MPP) i model gęstego upakowania (MGU) cząstek sferycznych w i na cząstce kulistej zostały zespolone z podstawowym równaniem procentu objętościowego faz wzmacniających w osnowie. W ten sposób uzyskano przestrzeń, w której kierując się zasadami dynamiki można przewidzieć strukturę kompozytów otrzymywanych metodą syntezy mechanicznej (MS). Prognozowanie modelowe zweryfikowano na dziewięciu zaplanowanych materiałach kompozytowych stosowanych na styki elektryczne, ograniczając się do układów kompozytowych złożonych z osnowy plastycznej i kruchych faz wzmacniających.This publication provides a summary of theoretical and experimental research related to forecasting the structure and obtaining composite materials with a silver matrix and fragile reinforcing phases. Two geometrical models, i.e. a model of the surface coating (MSC) and high-density model (MHD) of spherical particles in and on a spherical particle have been combined with a basic equation of the volumetric percentage of the reinforcing phase in the matrix. This has provided a space where the structure of the composites obtained by mechanical alloying (MA) can be predicted when guided by the principles of dynamics. The model forecasting has been verified using nine previously selected composite materials applied in electrical contacts, limited to systems composed of a plastic composite matrix and brittle reinforcement phases

Copper-Carbon Nanoforms Composites - Processing, Microstructure and Thermal Properties

The main current of publication is focused around the issues and problems associated with the formation of composite materials with Cu matrix and reinforcing phases in the various carbon nanoforms. The core of the research has been focused on thermal conductivity of these composites types. This parameter globally reflects the state of the structure, quality of raw materials and the technology used during the formation of composite materials. Vanishingly low affinity of copper for carbon, multilayered forms of graphene, the existence of critical values of graphene volume in the composite are not conducive to the classic procedures of composites designing. As a result, the expected, significant increase in thermal conductivity of composites is not greater than for pure copper matrix. Present paper especially includes: (i) data of obtaining procedure of copper/graphene mixtures, (ii) data of sintering process, (iii) the results of structure investigations and of thermal properties. Structural analysis revealed the homogenous distribution of graphene in copper matrix, the thermal analysis indicate the existence of carbon phase critical concentration, where improvement of thermal diffusivity to pure copper can occur

Właściwości elektryczne materiałów stykowych Ag-C i Cu-C

Industrial production of various forms of carbon, including graphene, nanotubes, and fullerenes, expanded the range of composite materials for which they constitute the reinforcing phase of metallic matrices. It was expected that the graphene form (GF) reinforcing phase would improve the electrical, thermal, and mechanical properties of such composites. Composites with Cu and Ag matrices, having a wide range of applications in micro- and optoelectronics, aerospace and automotive industries, proved to be particularly promising. A specific group of these composites is used in a variety of electrical circuits for electrical switches, contactors, circuit breakers, voltage regulators, and arcing tips. Among others, this group includes composites such as Ag-W, Ag-WC, Ag-WC-C, or Cu-W. The presented results of electrical tests performed for the Cu (Ag) /GF composites extend the number of properties of materials used in air and vacuum electrical contacts.Przemysłowe otrzymywanie rozmaitych form węgla – grafenu, nanorurek, fulerenów – rozszerzyło gamę materiałów kompozytowych, w których stanowią one fazę wzmacniającą matryc metalicznych. Oczekiwano, że grafenowa faza wzmacniająca polepszy cechy elektryczne, cieplne i wytrzymałościowe takich kompozytów. Szczególnie obiecującymi są kompozyty z matrycami Cu lub Ag znajdujące zastosowania w mikroelektronice i optoelektronice, przemysłach lotniczym i samochodowym. Specyficzna grupa tych kompozytów stosowana jest w rozmaitych elementach układów elektrycznych jako wyłączniki etc. Do grupy tej należą między innymi kompozyty Ag-W; Ag-WC, Ag-WC-C lub Cu-W. Prezentowane wyniki badań elektrycznych kompozytów Cu(Ag)/GF poszerzają zbiór właściwości materiałów stosowanych w powietrznych i próżniowych stykach elektrycznych

Physical and Electrical Properties of Silver-Matrix Composites Reinforced with Various Forms of Refractory Phases

This paper presents technological trials aimed at producing Ag-W, Ag-WC, Ag-W-C and Ag-WC-C composite contact materials and characterizing their properties. These materials were obtained using two methods, i.e. press-sinter-repress (PSR) at the refractory phase content of less than 30% by weight as well as press-sinter-infiltration (PSI) at the refractory phase content of ≥50% by weight). The results of research into both the physical and electrical properties of the outcome composites were shown. They include the analysis of the influence of the refractory phase content (W or WC) on arc erosion and contact resistance changes for the following current range: 6 kAmax in the case of composites with a low refractory phase content, 10 kAmax in the case of composites with the refractory phase content of ≥50% by weight

The effect of ceramic type reinforcement on structure and properties of Cu-Al2O3 composites

The purpose of this paper is to elaborate on mechanical alloying conditions for a composite powder consisting of copper and brittle aluminium oxides. Detailed analysis of the Cu-Al2O3 powder mixture structure obtained in the mechanical alloying process allows for the study of the homogenization phenomena and for obtaining grains (in composite form) with a high degree of uniformity. The Cu-5vol.%Al2O3 composites were obtained by means of the spark plasma sintering technique. The results presented herein were studied and discussed in terms of the impact of using a different form of aluminium oxide powder and a different shape of copper powder on composite properties. Research methodology included microstructure analysis as well as its relation to the strength of Cu-Al2O3 interfaces. It transpires from the results presented below that the application of electrocorundum as a reinforcement phase in composites decreases porosity in the ceramic phase, thus improving thermal properties and interfacial strength

The CMS Data Acquisition - Architectures for the Phase-2 Upgrade

The upgraded High Luminosity LHC, after the third Long Shutdown (LS3), will provide an instantaneous luminosity of 7.5 × 10 34 cm⁻² s⁻¹ (levelled), at the price of extreme pileup of up to 200 interactions per crossing. In LS3, the CMS Detector will also undergo a major upgrade to prepare for the phase-2 of the LHC physics program, starting around 2025. The upgraded detector will be read out at an unprecedented data rate of up to 50 Tb/s and an event rate of 750 kHz. Complete events will be analysed by software algorithms running on standard processing nodes, and selected events will be stored permanently at a rate of up to 10 kHz for offline processing and analysis. In this paper we discuss the baseline design of the DAQ and HLT systems for the phase-2, taking into account the projected evolution of high speed network fabrics for event building and distribution, and the anticipated performance of general purpose CPU. Implications on hardware and infrastructure requirements for the DAQ "data center" are analysed. Emerging technologies for data reduction are considered. Novel possible approaches to event building and online processing, inspired by trending developments in other areas of computing dealing with large masses of data, are also examined. We conclude by discussing the opportunities offered by reading out and processing parts of the detector, wherever the front-end electronics allows, at the machine clock rate (40 MHz). This idea presents interesting challenges and its physics potential should be studied

New operator assistance features in the CMS Run Control System

During Run-1 of the LHC, many operational procedures have been automated in the run control system of the Compact Muon Solenoid (CMS) experiment. When detector high voltages are ramped up or down or upon certain beam mode changes of the LHC, the DAQ system is automatically partially reconfigured with new parameters. Certain types of errors such as errors caused by single-event upsets may trigger an automatic recovery procedure. Furthermore, the top-level control node continuously performs cross-checks to detect sub-system actions becoming necessary because of changes in configuration keys, changes in the set of included front-end drivers or because of potential clock instabilities. The operator is guided to perform the necessary actions through graphical indicators displayed next to the relevant command buttons in the user interface. Through these indicators, consistent configuration of CMS is ensured. However, manually following the indicators can still be inefficient at times. A new assistant to the operator has therefore been developed that can automatically perform all the necessary actions in a streamlined order. If additional problems arise, the new assistant tries to automatically recover from these. With the new assistant, a run can be started from any state of the sub-systems with a single click. An ongoing run may be recovered with a single click, once the appropriate recovery action has been selected. We review the automation features of CMS Run Control and discuss the new assistant in detail including first operational experience