Powder Metallurgy and Advanced Materials最新文献

{"title":"Influence of the palladium coating on the hydrogen embrittlement of Ni61Nb33Zr6 amorphous tapes obtained by melt spinning","authors":"G. Thalmaier, I. Vida-Simiti, N. Sechel","doi":"10.21741/9781945291999-10","DOIUrl":"https://doi.org/10.21741/9781945291999-10","url":null,"abstract":"The current work is focused towards the properties of Ni61Nb33Zr6 amorphous alloy for use in hydrogen-related energy applications. The master alloys were prepared by arc melting using high purity metals in a Ti-gettered argon atmosphere. The alloys were melted several times to improve homogeneity. The ingots were induction-melted under a argon atmosphere in a quartz tube and a graphite crucible, injected through a nozzle onto a Cu wheel to produce rapidly solidified amorphous ribbons. The characterization of the amorphous ribbons was done by X-ray diffraction, DSC analysis and hardness tests. The hydrogen charging was done electrochemically for low temperature tests and by heating in a hydrogen atmosphere at different temperatures in the case of the high temperature tests. It was found that the palladium plating reduces the hydrogen embrittlement limit by 50 °C. Introduction The amorphous alloys have been proposed for hydrogen separation membranes, because amorphous alloys absorb generally hydrogen without forming metallic hydride and show good mechanical properties. However, since amorphous alloys are thermally unstable, using them as dense, hydrogen permeation membrane at elevated temperatures is very hard. Maintaining an amorphous alloy close to its glass transition temperature will trigger crystallization, decrease of the hydrogen permeability and ultimately its mechanical failure. From this point of view it at utmost importance to have a Tg as high as possible. Generally, Ni-Nb amorphous alloys have high Tx [1] and according to Inoue [2] it could be further improved by adding more elements to the alloy. Zirconium on the other hand has excellent hydrogen permeability and in general improves the glass forming ability of the alloys [3]. On the other hand, increasing the zirconium content will lead to the reduction of the Tg, so, an optimal balance of these two issues must be found. Different nickel niobium alloys are studied [4, 5] which could be used as a separation membrane. The studied alloy has a supercooled liquid region of ~ 50K, which would allow it to be shaped by hot-pressing in this temperature range. The purpose of this paper is to evaluate hydrogel embrittlement behavior of the amorphous Ni61Nb33Zr6 alloy and identifying a temperature range in which the alloy could be used as the hydrogen separation membrane from this point of view. Experimental The master alloy (Ni61Nb33Zr6 ) was prepared by arc melting using high purity materials in a Tigettered argon atmosphere. The alloys were melted several times in order to improve homogeneity. The alloy ingot was induction-melted under a high-purity argon atmosphere in a quartz crucible and injected through a nozzle onto a rotating Cu wheel to produce amorphous Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 89-94 doi: http://dx.doi.org/10.21741/9781945291999-10 90 tapes. The obtained tapes were 4 mm wide and approxi","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77654789","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fe2O3 hematite quantity increase in quartz sand by heat treatments","authors":"F. Popa, T. Marinca, A. Cotai","doi":"10.21741/9781945291999-12","DOIUrl":"https://doi.org/10.21741/9781945291999-12","url":null,"abstract":"Heat treatments were performed on the quartz sand to increase the quantity of Fe2O3 hematite phase. The heat treatments were performed on the as-received sand samples. The heating temperatures were chosen in the range of 120-600 C and the time durations in the range of 1-24 h. The sand phases evolution on the temperature was followed by differential scanning calorimetry (DSC). Identification of the phases was realized by X-ray diffraction. The modifications of the iron quantity and distribution in the sand particles were identified by Energy Dispersive X-ray Spectroscopy (EDX) analyses. An optimum temperature/time for the annealing was identified, leading to highest Fe2O3 content. Testes for magnetic separation were performed to validate the method. Introduction At present, there is a steady increase in demand for high purity quartz worldwide [1]. Quartz is used frequently in glass, ceramic and even in nano-industries [2]. Quartz sand is the most common type of sand in the nature [3]. It is used all over the world in different applications because of distinct physical characteristics, like hardness, chemical and heat resistance, also low cost [4]. Depending on the training mode and where it is found, it appears in different shapes and colors [1]. The silicon dioxide that is used to manufacture glass is extracted almost all from quartz sand, which must have over 97 % SiO2 [5]. Usually, the quartz is colorless or white, but the presence of the impurities can change the color. The iron oxide – hematite phase (Fe2O3) is one of the most frequent impurity and depending of the composition concentration, the quartz can alter the color up to yellow [3]. The quality of the sand is as better as the quantity of the iron oxide is smaller. Despite the importance of the sand, the utilization is limited by the quality of the material which contains harmful mineral inclusions. The presence of the impurities, especially iron oxide, limit the sand utilization for high quality glass manufacturing [5]. A big part of the impurities released can be reduced or eliminated by physical operations, such as size separation, spiral concentration, magnetic separation, etc. [6]. The iron oxide from the sand can be reduced also by physicochemical method [4]. The most ecological method to improve the quality of the sand is the magnetic separation method. The magnetic separation is used to decrease and stabilize the iron content [7]. If the method is not effective enough, efficiency can be increased by a thermic treatment, mechanical milling or a specific granulometric class removal. The experiments presented in reference [5], shows that magnetic separation method removes about 80,49 % of iron oxide from sand and decrease the Fe2O3 content from 0,41 % down to 0,08%. Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 105-114 doi: http://dx.doi.org/10.21741/9781945291999-12 106 A big part of the impurities pre","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73217648","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Wear behavior and microhardness of some W/Cu functionally graded materials obtained by spark plasma sintering","authors":"C. Nicolicescu, V. Nicoară, F. Popa, T. Marinca","doi":"10.21741/9781945291999-21","DOIUrl":"https://doi.org/10.21741/9781945291999-21","url":null,"abstract":"This paper is focused on the elaboration of some W/Cu functionally graded materials (FGM) by spark plasma sintering (SPS) process, as well as on their characterization, from the wear behavior and microhardness point of view function of composition and sintering temperature. The raw materials used for the research were W/Cu mechanically alloyed powders for 20 hours, which were subjected to consolidation in three layers of compositions W100-xCux, where x is 25, 30 and 40 % wt. by SPS. The evolution of tribological parameters and microhardness function of the chemical composition and SPS temperature were investigated. Microhardness is influenced by the SPS temperature and composition of the layers namely, the highest value was attained for the sample sintered at 950 C and layer 1 which consists in W75Cu25. The wear behavior is influenced by the composition of the layers and by ball testing material (100Cr6 and alumina). Introduction Copper alloys are frequently used in applications that require high electrical and thermal conductivity. In some applications that require strength and wear resistance it is necessary to alloy copper with others metals. Alloys based on copper and tungsten attract the attention due to the combination of properties such as low thermal expansion coefficient, high melting point, high strength and wear resistance conferred by tungsten with a high electrical and thermal characteristics conferred by copper [1-6]. The researches in the field of W/Cu alloys are focused on the controlling the microstructure by optimizing the composition or processing techniques [7-11]. Due to their insolubility and high differences between densities and melting points it’s very difficult to produce W/Cu composite. There are different methods to produce W/Cu composite/nanocomposite namely: copper infiltration and liquid phase sintering [10, 12] which are considered classical methods, respectively new methods as mechanical alloying (MA), mechano-chemical processes (MCP) [13], mechanothermochemical processing (MTP) [14], the thermo-mechanical method [15], wet-chemical methods [16] and spray drying [17]. Functional graded materials (FGM) based on W/Cu represent a new category of materials consisting in two or more layers, in which the microstructure and the composition vary from the Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 182-191 doi: http://dx.doi.org/10.21741/9781945291999-21 183 top layer to the bottom layer and vice versa. This class of materials presents some advantages comparative to the single layer materials, namely: the properties are different in each layer, residual and thermal stresses are reduced and the fracture strength is optimized [18-20]. The main fields of applications of W/Cu FGM are: electrical contacts, plasma facing materials, heat sink materials, etc. [21] In recent decades, Spark Plasma Sintering (SPS) became a popular sintering method which i","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87018487","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New weldability model based on the welding parameters and hardness profile","authors":"M. Bodea","doi":"10.21741/9781945291999-13","DOIUrl":"https://doi.org/10.21741/9781945291999-13","url":null,"abstract":"The weldability of the steels represents a problem of great interest in order to achieve welded structures that satisfy the high requirements on quality, imposed by the nowadays applications. In this paper has been proposed a more advanced model that has considered more factors of weldability influence, thus allowing a more detailed analysis based on the main welding process variables. Introduction Weldability is a general technological property commonly used in engineering, but very difficult to be defined and quantified in an exact manner. The American Welding Society has defined the weldability as being: “The capacity of a metal to be welded under the fabrication conditions imposed with a specific suitability designed structure and to perform satisfactorily in service” [1]. According to DIN 8528, Part 1 the weldability is seen as the output of the interaction of three main group factors, given in Table 1 [2]. Table 1. The weldability’s factors of influence. MATERIAL WELDING SUITABILITY MANUFACTURE WELDING POSSIBILITY DESIGN","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84775738","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The properties of bimetallic multi-layer (C45 and S235JR) and the multi-layer steel made by forging","authors":"D. Frunză, D. Iluțiu-Varvara, I. Toma, I. Sas-Boca","doi":"10.21741/9781945291999-2","DOIUrl":"https://doi.org/10.21741/9781945291999-2","url":null,"abstract":"In this paper are presented the results of the research on properties and behavior of hotforged bimetallic multi-layer material (C45-S235JR) compared to the properties and behavior of hot-forged multi-layer materials C45 and S235JR. The material was layered by successive manual hot forging to form 36-layers of the billets. Thus, it has been attempted to obtain superior materials in terms of properties, to withstand the demands they are subjected to. It has also been tried by stratification, obtaining results particularly relevant for resilience testing, where the different layer breakage occurs at higher strengths and has a high malleability. The microstructure of multi-layered materials was investigated in this paper and the mechanical properties were studied by tensile testing and Charpy impact testing. The Brinell micro-hardness has also been studied. Introduction Hot plastic deformation processes are the most common and used method for generating metallurgical metals [1, 2]. These processes are based on the characteristics of the metals obtained by high-temperature processing. By heating metals, we get less mechanical strength and increased malleability [3, 4]. Thus, raw materials can be processed with low material losses and low energy consumption in a form close to the finished piece. The need to obtain the most effective and safe materials leads to a reorientation of the research to the ancient techniques [5] and technologies applicable to modern areas, such as cycling and, in particular, the acrobatics on the bicycle. The main objective of the paper was to determine the characteristics [6 8] of the layered metal [9 11]. Another approach was to obtain bimetallic layered steel by forging [12]. This type of material combines the advantages of both materials and reduces the major inconvenience of each one taken separately. Often, the outer part of the piece is made of other metallic material to provide outstanding properties, as well as to reduce the cost price. This is possible due to the understanding of the function of the piece because the piece needs a certain mechanical strength [4, 13, 14], which does not mean that the whole piece will be made of that material but only that part inner or the outer part of the piece. The rest of the material can be a cheaper material also, in accordance with the requirements of the finished product. In this work was aimed at making multi-layered steel bars and sandwich bars (C45S235JRC45). The mechanical and microstructural properties were determined as follows: the tensile testings, Brinell hardness measurement, Charpy impact testing and microstructures were performed. Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 11-17 doi: http://dx.doi.org/10.21741/9781945291999-2 12 Material and method The materials used are the C45 band according to SR EN 10083 and the S235JR steel band according to EN 10204/2004. The chemical compositi","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83297704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structural and optical characterization of titanium nitride thin films deposited by magnetron sputtering","authors":"G. Negrea, V. Merie, A. Molea, V. N. Burnete, B. Neamțu","doi":"10.21741/9781945291999-15","DOIUrl":"https://doi.org/10.21741/9781945291999-15","url":null,"abstract":"Titanium nitride applicability covers different industries such as microelectronics, biomedicine and so on. This paper presents the analysis of the structural and optical properties of titanium nitride thin films for different deposition conditions. The samples were deposited by direct current magnetron sputtering on silicon substrates. The deposition was done at room temperature, on substrates preheated at 300 °C or on substrates that were polarized at -40 V and 90 V respectively. The results indicate a dependency of the structural orientation with respect to the deposition process when this takes place at room temperature. When the deposition was done on a preheated substrate there was no structural orientation. A negative polarization of the substrate leads to the formation of small sized crystallites. Regarding the optical properties, the films showed good semiconductor properties and a low reflectivity. Introduction Titanium nitride (TiN) thin films were studied by many researchers due to their excellent properties, especially mechanical and tribological properties, corrosion resistance, wear resistance and thermodynamic stability [1–3]. Due to these properties, titanium nitride thin films can be used in a wide range of applications like: diffusion barriers for micro-electric devices, optical coatings with antireflection and antistatic properties, electrodes, biomedicine and hard coatings for tools and so on [4–9]. The most often used methods to obtain titanium nitride films are: reactive magnetron sputtering, laser ablation, ion beam deposition or plasma assisted chemical vapor deposition and so on [10–14]. The physical-chemical and mechanical/tribological properties of titanium nitride films depend on the deposition parameters. In this regard, different researches present the influence of some deposition parameters such as the deposition rate, deposition time, substrate, the heating or the polarization of the substrate on the topographical, mechanical, tribological, adhesion properties for titanium nitride thin films deposited by DC (direct current) magnetron sputtering. All the results are pointing out a change in these properties with the change in deposition parameters. A possible explanation for this change can be the growth of the deposited films after different preferential orientations. The present paper is a study concerning the deposition of titanium nitride thin films by DC magnetron sputtering on silicon substrates at different deposition parameters (substrate Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 134-142 doi: http://dx.doi.org/10.21741/9781945291999-15 135 temperature, substrate bias voltage, deposition time) and the structural and optical characterization of the obtained thin films. Materials and Methods Deposition of titanium nitride thin films The deposition of titanium nitride films was done by direct current reactive magnetron sputtering","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87672969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Helical structure of linear homopolymers","authors":"S. Bolboacă, L. Jäntschi","doi":"10.21741/9781945291999-5","DOIUrl":"https://doi.org/10.21741/9781945291999-5","url":null,"abstract":". The aim of our research was to conduct a computational study on helical geometries of several homopolymers. Simple helix of polymers with seventeen (poly(lactic acid)) or eighteen (poly(1-chloro-trans-1-butenylene), poly(1-methyl-trans-1-butenylene), poly(1,4,4-trifluoro-trans-1-butenylene), polyacrylonitrile and respectively polychlorotrifluoroethylene) monomers were investigated. The X, Y, and Z coordinates obtained after optimization of the geometry of polymers were used as input data to identify the rotation and translation of the coordinates and respectively the coefficient of the helix. The values of interest were calculated by minimization of residuals using two different protocols. The first protocol investigated the whole polymer by imposing (step a fixed value of the helix by minimization of if the monomer (one or two) from each end of the is or not an outlier of the helical geometry of the","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75218042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study on the particle size reduction by milling of quartz sand for magnetic separation","authors":"N. Sechel, F. Popa, L. Copil, V. Cebotari, B. Neamțu, I. Chicinaș","doi":"10.21741/9781945291999-11","DOIUrl":"https://doi.org/10.21741/9781945291999-11","url":null,"abstract":"For being used in crystal glass industry, the iron content of quartz sand must be under 0.09 %. If the reserve contains a higher quantity, methods for iron reduction must be used. Usually the iron phases are present in large quantity in the small particle size fraction. For reducing the sand grain size, milling was performed on a planetary ball mill. Different ball/powders ratio were studied for determining an optimum particle size vs. milling duration. The particle size was determined for each milling experiment. Using Energy Dispersive X-ray spectroscopy (EDX), the elemental distribution for the particle was quantified. By X-ray diffraction, the phase distribution of the sand was analyzed and correlated with the chemical composition. The phases are changing their ratio versus the grain size. The main phase is SiO2 as quartz, accompanied by minor phases: iron oxides (Fe3O4, Fe2O3, and FeTiO3) and some oxide of Al, Na, Ca, and K. Testes for magnetic separation were performed for validating the method. Introduction The quartz sand is the raw material for glass industry. Unfortunately, as all raw materials, quartz sand purity is the limiting criterion for his usage, since the structure and composition give the properties, the usage and classification criteria for glasses [1]. The most detrimental impurity in the quartz sand is iron, followed by some other metallic oxides (titanium, cobalt, copper, etc.). The effect of metallic impurities in the sand is most commonly observed in color of the resulting glass [2]. The minimum iron quantity in the sand for obtaining a color glass is 0.1 %. The classical way for iron removing is flotation, using toxic reagents as amine, NaOH or H3PO4 [3 5]. A cleaner approach is magnetic separation [6]. In magnetic separation experiments, the content in magnetic phase (iron oxides) and particle size represent a key factor for an efficient removing setup [6]. Also, the different types of magnetic separators are considered [7]. A method of controlling the particle size of the sand is by ball milling [8]. In the milling experiments the particle size modification is realized by collision events between balls and sand particles [8]. For our studies is suitable that a high productivity to be achieved, at small milling time and the powder to be produced in a continuous way [9]. For high productivity, the quantity of sand is analyzed and in the milling experiments can be expressed in the form of ball to powder mass ratio (BPR). A high BPR means less quantity of material for processing and small BPR means high material quantity introduced in milling chamber. One purpose of this study is to determine optimal condition of sand milling considering different BPR and milling times. Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 95-104 doi: http://dx.doi.org/10.21741/9781945291999-11 96 The ball milling was found to be useful in sand purification and particl","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90694518","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Morphology and mechanical characteristics of some TBCs used for internal combustion valves","authors":"M. Benchea, C. Munteanu, D. Chicet, M. Panțuru, O. Mocănița","doi":"10.21741/9781945291999-22","DOIUrl":"https://doi.org/10.21741/9781945291999-22","url":null,"abstract":"Three types of commercial powders have been deposited on the inlet and outlet valve plates in order to increase their lifetime, but especially the temperature in the combustion chamber. The layers were coated by atmospheric plasma spray method. The coatings morphology was analysed using two complementary methods: scanning electron microscopy and X-ray diffraction. The mechanical characteristics analysed were: microhardness, modulus of elasticity and adhesion / cohesion of coatings using scratch tests. Following those tests it was observed that the coatings are physically suited for further tests as thermal barrier coatings (TBC) on the valve discs of internal combustion engines. Introduction The distribution system (especially the intake/evacuation areas) of the internal combustion engine is subjected, during its operation, to a series of very complex loads involving: mechanical impact and high frequency micro-slipping, high temperatures with a very large variation, presence of microparticles, etc. Another very important stress factor is the working pressure, which often in combination with other stresses causes damage to the valve disc and implicitly change the contact geometry of the seat of the valve. Taking into account all this, but also that the new regulations related to the emission of combustion gases will become more and more strict, we come up with the proposal to cover the valves discs with layers as thermal barrier. Thermal barrier coatings have initially been used for gas turbine elements protection applications, in the specialized literature being available multiple studies on this type of use. [1-5] Starting from these studies, the range of applications has been expanded so that over the past 20 years, TBCs have found many other applications, one of which is covering the components of diesel engines in order to improve their thermal efficiency, to reduce weight by removing the cooling system, to increase the efficiency by lowering the amount of energy lost through thermal effect and to improve the durability of components [6,7]. Depending on the working conditions, different mechanisms of wear and destruction of TBCs become dominant. These coatings are in fact complex systems formed of the top layer of TBC, the intermediate layer with bonding function that supports the upper layer and the substrate, so that the properties of the whole system influence its lifetime in operation. By analysing the components, it is observed that in the case of the TBC top layer these properties are the microstructure, density, thickness, distribution of the micro-cracks and cohesion in the layer Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 192-199 doi: http://dx.doi.org/10.21741/9781945291999-22 193 (between splats that form it). In the case of the bonding layer, it is the oxidation resistance, the density of the layer, its thickness and the surface roughness [8]. An equa","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82843641","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Caracterisation of high manganese silicides prepared by mechanical milling","authors":"I. Chicinaș, V. Popescu, T. Marinca, V. Cebotari, F. Popa","doi":"10.21741/9781945291999-9","DOIUrl":"https://doi.org/10.21741/9781945291999-9","url":null,"abstract":"The mechanical milling of manganese and silicon powder in a planetary ball mill up to 18 h was performed. In the X-ray diffraction pattern recorded after 18 hours of milling the MnSi phase and Mn15Si26 compound are detected. The agglomeration of powders after complete reaction of the elements was observed by scanning electron microscopy. Heating up at 1000 °C, an unreacted sample, milled 4 hours, has found to have the effect of completing the reaction of elements, but forms oxides. Handling of the powder during sampling, without protective atmosphere was found to form oxides. The oxidation of the samples was evidenced by FTIR analysis. Introduction The modern society has the tendency to increase the quantity of hydrocarbons which are transformed into energy, with negative effects on the environment. To reduce this impact alternatives are searched. Thermoelectric materials represent a solution to improve the quality of the environment by reducing the combustion product gases. These materials are able to convert the thermal energy directly into electrical energy and vice versa. The quality of a thermoelectric material can be estimated by the figure of merit ZT=SσT/k where: S is the Seebeck coefficient, σ is electrical conductivity, T is temperature and k is thermal conductivity [1]. Thermoelectric materials can convert heat from a different source such as solar heat, geothermal heat or exhaust gases [2]. From the studied thermoelectric materials, those based on silicon, especially High Manganese Silicide (HMS) is friendly with the environment and considered as promising candidates. HMS is chemically stable [3] and are preferred in detriment of those based on Pb-Te which operate in the same range of temperature. The HMS materials are nontoxic as well as their constituent chemical elements [4]. HMS are thermoelectric compounds with p-type conduction, having general formula MnSix where the x value ranges from 1.67 up to 1.87 [5] and with an energy gap of 0.77 [eV] [6]. HMS system contains four compounds, Mn4Si7, Mn11Si19, Mn15Si26, and Mn27Si47, all with the same electronic structure [7]. Crystallographic structure of HMS compounds belongs to Nowotny chimney ladder (NCL) phases, where manganese is located in the corners of tetragon and silicon are arranged inside in the form of a spiral [8]. MnSi1.75 compound presents the largest ZT, while the MnSi1.77 compound has the smallest value. The low value for the figure of merit is the effect of Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 88-88 doi: http://dx.doi.org/10.21741/9781945291999-9 81 a large thermal conductivity [6]. Problem with HMS is that obtaining method influence the final phase. Based on the preparation method it is possible to obtain different compounds: by vacuum levitation melting Mn15Si26 is obtained, Mn4Si7 may obtain by vacuum levitation-induction melting and by dry milling [9-11]. Preparation by melting l","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76114465","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}