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Abstract:
The interest in the Spark Plasma Sintering (SPS) technique has continuously increased over the last few years. This article shows the possibility of the development of an SPS device used for material processing and synthesis in both scientific and industrial applications and aims to present manufacturing methods and the versatility of an SPS device, presenting examples of processing Arc-Melted- (half-Heusler, cobalt triantimonide) and Self-propagating High-temperature Synthesis (SHS)-synthesized semiconductor (bismuth telluride) materials. The SPS system functionality development is presented, the purpose of which was to broaden the knowledge of the nature of SPS processes. This approach enabled the precise design of material sintering processes and also contributed to increasing the repeatability and accuracy of sintering conditions.

Keywords:
spark plasma sintering, arc melting, semiconductor materials, half-Heusler, bismuth telluride, cobalt triantimonide, SHS, SPS

Abstract:
The presented paper concerns the technological aspects of the interface evolution in the nickel-silicon carbide composite during the sintering process. The goal of our investigation was to analyse the material changes occurring due to the violent reaction between nickel and silicon carbide at elevated temperatures. The nickel matrix composite with 20 vol pct SiC particles as the reinforcing phase was fabricated by the spark plasma sintering technique. The sintering tests were conducted with variable process conditions (temperature, time, and pressure). It was revealed that the strong interaction between the individual components and the scale of the observed changes depends on the sintering parameters. To identify the microstructural evolution, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy were used. The silicon carbide decomposition process progresses with the extension of the sintering time. As the final product of the observed reaction, new phases from the Ni-Si system and free carbon were detected. The step-by-step materials evolution allowed us to reveal the course of the reaction and the creation of the new structure, especially in the reaction zone. The detailed analysis of the SiC decomposition and formation of new components was the main achievement of the presented paper.

Abstract:
A novel metal matrix composites (MMC) with Mg matrix reinforced with natural filler in the form of Didymosphenia geminata frustules (algae with distinctive siliceous shells) are presented in this work. Pulse plasma sintering (PPS) was used to manufacture Mg-based composites with 1, 5 and 10 vol.% ceramic filler. As a reference, pure Mg was sintered. The results show that the addition of 1 vol.% Didymosphenia geminata frustules to the Mg matrix increases its corrosion resistance by supporting passivation reactions, and do not affect the morphology of L929 fibroblasts. Addition of 5 vol.% the filler does not cause cytotoxic effects, but it supports microgalvanic reactions leading to the greater corrosion rate. Higher content than 5 vol.% the filler causes significant microgalvanic corrosion, as well as increases cytotoxicity due to the greater micro-galvanic effect of the composites containing 10 and 15 vol.% diatoms. The results of contact angle measurements show the hydrophilic character of the investigated materials, with slightly increase in numerical values with addition of amount of ceramic reinforcement. The addition of Didymosphenia geminata frustules causes changes in a thermo-elastic properties such as mean apparent value of coefficient of thermal expansion (CTE) and thermal conductivity (λ). The addition of siliceous reinforcement resulted in a linear decrease of CTE and reduction in thermal conductivity over the entire temperature range. With the increasing addition of Didymosphenia geminata frustules, an increase in strength with a decrease in compressive strain is observed. In all composites an increase in microhardness was attained.
The results clearly indicate that filler in the form of Didymosphenia geminata frustules may significantly change the most important properties of pure Mg, indicating its wide potential in the application of Mg-based composites with a special focus on biomedical use.

Keywords:
Metal-matrix composites (MMCs),Pulse plasma sintering (PPS),Ceramic filler,Microstructure,Properties

Abstract:
This article discusses the morphology and thermomechanical properties of graphene oxide (GO) paper sheets and GO paper composites reinforced with carbon fibers. GO paper was fabricated using GO paste obtained by the condensation of GO aqueous solution synthesized using the Hummers' method. Carbon fibers were implemented to improve the mechanical properties of the pristine GO paper. All the investigated papers were subjected to thermal treatment to check thermo-related morphological and mechanical properties. The results presented in this study allowed for the deeper insight into morphological, structural, and mechanical volume and surface-related properties of pristine GO and GO-based composite materials reinforced with carbon fibers. We showed that there are two important factors that should be taken into consideration for the design and fabrication of GO-based papers. These factors were the concentration of the reinforcing agent and the thermal reduction of the papers. Both factors have influenced the final properties of the resulting GO-based papers. For the first time, it was revealed how the addition of the reinforcing material affects the GO paper thermal expansion coefficient.

Keywords:
Flake graphene, Graphene oxide, Graphene oxide paper, Carbon fibers, Mechanical properties

Abstract:
Additive manufacturing (AM) has seen remarkable development in recent years due to relatively high efficiency of the process. Cold spraying (CS) is a particular method of AM, in which titanium and titanium alloy powders are used. CS is a very competitive technology enabling the deposition of coatings, repairing machine parts, and manufacturing new components. For specific applications, the surface of cold-sprayed materials may require further processing. This paper reports an attempt to employ laser surface treatment (LST) of cold-sprayed coatings on an aluminium alloy substrate. The influence of laser beam interaction time on the coatings’ properties was analysed. The microstructure was investigated and observed employing scanning electron microscopy (SEM). To evaluate residual stress after CS and LST, the sin2ψ technique was used. Investigations were also performed on Vickers hardness, contact angle, and surface roughness. Significant changes in the surface morphology of the coatings and elevated residual stress levels dependent on the laser beam interaction time were observed. Increased Vickers hardness was recorded for titanium alloy Ti6Al4V. LST also led to increased surface hydrophilicity of the modified materials Ti and Ti6Al4V.

Keywords:
cold spray, laser surface treatment, titanium coating, Ti6Al4V, residual stresses

Abstract:
Doping is one of the possible ways to significantly increase the thermoelectric properties of many different materials. It has been confirmed that by introducing bismuth atoms into Mg sites in the Mg2Si compound, it is possible to increase career concentration and intensify the effect of phonon scattering, which results in remarkable enhancement in the figure of merit (ZT) value. Magnesium silicide has gained scientists’ attention due to its nontoxicity, low density, and inexpensiveness. This paper reports on our latest attempt to employ ultrafast selfpropagating high-temperature synthesis (SHS) followed by the spark plasma sintering (SPS) as a synthesis process of doped Mg2Si. Materials with varied bismuth doping were fabricated and then thoroughly analyzed with the laser flash method (LFA), X-ray diffraction (XRD), scanning electron microscopy (SEM) with an integrated energy-dispersive spectrometer (EDS). For density measurement, the Archimedes method was used. The electrical conductivity was measured using a standard four-probe method. The Seebeck coefficient was calculated from measured Seebeck voltage in the sample subjected to a temperature gradient. The structural analyses showed the Mg2Si phase as dominant and Bi2Mg3 located at grain boundaries. Bismuth doping enhanced ZT for every dopant concentration. ZT = 0:44 and ZT=0.38 were obtained for 3wt% and 2wt% at 770 K, respectively.

Keywords:
thermoelectric materials, magnesium silicide, bismuth doping, SHS, spark plasma sintering

Abstract:
In the presented paper a coating of SiC particles with a metallic layer were used to prepare copper matrix composite materials. The role of the layer was to protect the silicon carbide from decomposition and dissolution of silicon in the copper matrix during the sintering process. The SiC particles were covered by chromium, tungsten and titanium using Plasma Vapour Deposition method. After powder mixing of components, the final densification process via Spark Plasma Sintering (SPS) method at temperature 950C was provided. The almost fully dense materials were obtained (> 97.5%). The microstructure of obtained composites was studied using scanning electron microscopy as well as transmission electron microscopy. The microstructural analysis of composites confirmed that regardless of the type of deposited material, there is no evidence for decomposition process of silicon carbide in copper. In order to measure the strength of the interface between ceramic particles and the metal matrix, the micro tensile tests have been performed. Furthermore, thermal diffusivity was measured with the use of the laser pulse technique. In the context of performed studies, the tungsten coating seems to be the most promising solution for heat sink application. Compared to pure composites without metallic layer, Cu-SiC with W coating indicate the higher tensile strength and thermal diffusitivy, irrespective of an amount of SiC reinforcement. The improvement of the composite properties is related to advantageous condition of Cu-SiC interface characterized by well homogenity and low porosity, as well as individual properties of the tungsten coating material.

Keywords:
metal matrix composites, silicon carbide, metallic layers deposition, thermal conductovity, interface strength

Abstract:
Antimony telluride (Sb2Te3) is an intermetallic compound crystallizing in a hexagonal lattice with R-3m space group. It creates a c lose packed structure of an ABCABC type. As intrinsic semiconductor characterized by excellent electrical properties, Sb2Te3 is widely used as a low-temperature thermoelectric material. At the same time, due to unusual properties (strictly connected with the structure), antimony telluride exhibits nonlinear optical properties, including saturable absorption. Nanostructurization, elemental doping and possibilities of synthesis Sb2Te3 in various forms (polycrystalline, single crystal or thin film) are the most promising methods for improving thermoelectric properties of Sb2Te3.Applications of Sb2Te3 in optical devices (e.g. nonlinear modulator, in particular saturable absorbers for ultrafast lasers) are also interesting. The antimony telluride in form of bulk polycrystals and layers for thermoelectric and optoelectronic applications respectively were used. For optical applications thin layers of the material were formed and studied. Synthesis and structural characterization of Sb2Te3 were also presented here. The anisotropy (packed structure) and its influence on thermoelectric properties have been performed. Furthermore, preparation and characterization of Sb2Te3 thin films for optical uses have been also made

Keywords:
antimony telluride, thermoelectric materials, thin films, PVD magnetron sputtering, topological insulator

Abstract:
The presented paper investigates the relationship between the microstructure and thermal properties of copper–silicon carbide composites obtained through hot pressing (HP) and spark plasma sintering (SPS) techniques. The microstructural analysis showed a better densification in the case of composites sintered in the SPS process. TEM investigations revealed the presence of silicon in the area of metallic matrix in the region close to metal ceramic boundary. It is the product of silicon dissolving process in copper occurring at an elevated temperature. The Cu-SiC interface is significantly defected in composites obtained through the hot pressing method, which has a major influence on the thermal conductivity of materials.

Keywords:
metal matrix composites, silicon carbide, interface, spark plasma sintering, thermal conductivity

Abstract:
The main aim of this work was to construct and test an apparatus for characterization of high temperature thermoelectric modules to be used in thermoelectric generator (TEGs) applications. The idea of this apparatus is based on very precise measurements of heat fluxes passing through the thermoelectric (TE) module, at both its hot and cold sides. The electrical properties of the module, under different temperature and load conditions, were used to estimate efficiency of energy conversion based on electrical and thermal energy conservation analysis. The temperature of the cold side, Tc, was stabilized by a precise circulating thermostat (≤0.1°C) in a temperature range from 5°C to 90°C. The amount of heat absorbed by a coolant flowing through the heat sink was measured by the calibrated and certified heat flow meter with an accuracy better than 1%. The temperature of the hot side, Th, was forced to assumed temperature (Tmax = 450°C) by an electric heater with known power (Ph = 0–600 W) with ample thermal insulation. The electrical power was used in calculations. The TE module, heaters and cooling plate were placed in an adiabatic vacuum chamber. The load characteristics of the module were evaluated using an electronically controlled current source as a load. The apparatus may be used to determine the essential parameters of TE modules (open circuit voltage, Uoc, short circuit current, Isc, internal electrical resistance, Rint, thermal resistance, Rth, power density, and efficiency, η, as a function of Tc and Th). Several commercially available TE modules based on Bi2Te3 and Sb2Te3 alloys were tested. The measurements confirmed that the constructed apparatus was highly accurate, stable and yielded reproducible results; therefore, it is a reliable tool for the development of thermoelectric generators.

Keywords:
energy conversion efficiency, power generation, thermoelectric modules, performance characterization, heat recovery, renewable energy

Abstract:
Combination of extreme service conditions and complex thermomechanical loadings, e.g., in electronics or power industry, requires using advanced materials with unique properties. Dissipation of heat generated during the operation of high-power electronic elements is crucial from the point of view of their efficiency. Good cooling conditions can be guaranteed, for instance, with materials of very high thermal conductivity and low thermal expansion coefficient, and by designing the heat dissipation system in an accurate manner. Conventional materials such as silver, copper, or their alloys, often fail to meet such severe requirements. This paper discusses the results of investigations connected with Cu-C (multiwall carbon nanotubes (MWNTs), graphene nanopowder (GNP), or thermally reduced graphene oxide (RGO)) composites, produced using the spark plasma sintering technique. The obtained composites are characterized by uniform distribution of a carbon phase and high relative density. Compared with pure copper, developed materials are characterized by similar thermal conductivity and much lower values of thermal expansion coefficient. The most promising materials to use as heat dissipation elements seems to be copper-based composites reinforced by carbon nanotubes (CNTs) and GNP.

Keywords:
copper matrix composites, graphene, spark plasma sintering, thermal properties