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This study is focused on the high-temperature corrosion evaluation of selected thermally sprayed coatings. NiCoCrAlYHfSi, NiCoCrAlY, NiCoCrAlTaReY, and CoCrAlYTaCSi coatings were sprayed on the base material 1.4923. This material is used as a cost-efficient construction material for components of power equipment. All evaluated coatings were sprayed using HP/HVOF (High-Pressure/High-Velocity Oxygen Fuel) technology. High-temperature corrosion testing was performed in a molten salt environment typical for coal-fired boilers. All coatings were exposed to the environment of 75% Na2SO4 and 25% NaCl at the temperature of 800 °C under cyclic conditions. Each cycle consisted of 1 h heating in a silicon carbide tube furnace followed by 20 min of cooling. The weight change measurement was performed after each cycle to establish the corrosion kinetics. Optical microscopy (OM), scanning electron microscopy (SEM), and elemental analysis (EDS) were used to analyze the corrosion mechanism. The CoCrAlYTaCSi coating showed the best corrosion resistance of all the evaluated coatings, followed by NiCoCrAlTaReY and NiCoCrAlY. All the evaluated coatings performed better in this environment than the reference P91 and H800 steels.

Yttrium oxide was sprayed by a plasma torch using a coarse thermal spray powder, which must be in size range of tens of micrometers to ensure good penetration into the plasma stream. Thick coatings on steel substrates were produced with two sprays systems facilitating gas stabilized plasma (GSP) and hybrid water-argon stabilized plasma (WSP–H) techniques. Additionally, an ultra-fine yttrium oxide powder was sprayed from a suspension. Hybrid water-argon stabilized plasma system was used for this purpose. Markedly thinner compact coatings were produced this way. All three sorts of plasma sprayed deposits were studied by the same methods. Dielectric properties were studied in a broad range of frequencies and temperatures. The microstructure aspects as well as crystallite size were analyzed and discussed in relation to electrical properties. All coatings exhibited stable dielectric parameters versus changing frequency and temperature, comparable with literature values for various samples. Concerning sintered bulks, and especially their thermal stability of capacitance, the plasma sprayed coatings were slightly worse. However due to shape and size variability of the plasma spraying are yttria coatings prospective for technical applications.

Calcium titanate (CaTiO3) powder was compacted by spark plasma sintering (SPS). The resulting products were subjected to the phase stability study and dielectric characterization. The change in temperature of SPS between 1100 °C and 1250 °C had a clear and straightforward effect on density, porosity, relative permittivity, loss tangent, and DC resistivity. Since the SPS itself introduces certain oxygen deficiency into Ti-perovskites, all samples were annealed after SPS. However, this post-processing did not mask the effects of the SPS regime. Optical reflectance measurements were completed to compare and quantify the sample coloration and support the dielectric results with corresponding optical band gap estimations. Subtle changes in the CaTiO3 crystal lattice arrangement, completed between 1150 °C and 1250 °C and documented in the literature for conventionally sintered samples, could not be confirmed for SPS-prepared calcium titanate. The novelty of this research work is in producing very stable dielectric ceramics and an indication of the SPS processing parameters suitable for this. The best sample showed at 1 MHz frequency the combination of relative permittivity 370, loss tangent 0.008, and DC resistivity 3 × 1012 Ωm.

Metakaolinite was obtained by thermal treatment of natural kaolinite. Both of them, kaolinite with structurally bonded water and metakaolinite without it, were, after sieving to acceptable size fraction, plasma sprayed. The coatings were rather lightweight and composed predominantly of amorphous material. Stainless steel was used for producing self standing deposits, whereas other materials like carbon steel or ceramic tiles formed a permanent substrate-coating system. Metakaolinite coating was less porous, harder and its thermal behavior was simpler compared to kaolinite. Crystallization and formation of secondary phases was monitored after annealing with and without dust particles known in the barrier coatings field as CMAS. Resumen: La metacaolinita se obtuvo por tratamiento térmico de caolinita natural. Ambos, caolinita con agua ligada estructuralmente y metacaolinita sin ella, después de tamizar a una fracción de tamaño aceptable, se proyectó mediante un plasma. Los revestimientos eran bastante porosos y estaban compuestos predominantemente de material amorfo. El acero inoxidable se usó para realizar depósitos independientes, mientras que otros materiales como el acero al carbono o las baldosas cerámicas formaron un sistema permanente de revestimiento de sustrato. El recubrimiento de metacaolinita fue menos poroso, más duro y su comportamiento térmico fue más simple en comparación con la caolinita. La cristalización y la formación de fases secundarias se controlaron después del recocido con y sin partículas de polvo conocidas en el campo de las barreras térmicas como CMAS.

A mixture of kaolin (92 wt.% of kaolinite) and laboratory-grade CaCO3 was used for anorthite preparation using the spark plasma sintering (SPS) technique. The powder was heated up to the maximum temperature (850 °C–1100 °C with a step of 50 °C, heating rate 50 °C/min) using the SPS device. The as-prepared samples were compared with a reference sample produced by dry pressing and conventional firing. Rietveld refinement performed on the X-ray diffraction data revealed that before anorthite formation, gehlenite and Ca-feldspar appeared, which gradually transformed into anorthite with increasing temperature. The sample prepared by SPS at 1100 °C contained 90 wt.% of anorthite, while the anorthite content in the reference sample reached only 47 wt.%. The porosity of the samples prepared by SPS reached significantly lower values compared to that of the reference sample. Therefore, SPS can be considered as a promising technique in the preparation of anorthite ceramics at lower temperatures.

ZnO:Eu thin film fabricated by pulsed laser deposition was treated by pulsed UV laser. The effect of laser fluence from 70 to 125 mJ cm−2 on film properties was investigated. The results showed that the surface morphology was clearly modified and the film treated at laser fluence of 70 mJ cm−2 was more densified compared to the other annealed films. Laser treatment led to a reduction of carbon content and to a stoichiometric ZnO:Eu composition on the surface. Refractive index significantly decreased and extinction coefficient was blue shifted for higher laser fluences. Strong characteristic Eu3+ transitions were obtained using excitation at 266 nm. The highest photoluminescence intensity was observed for the annealed film at a laser fluence of 70 mJ cm−2. The influence of ambient composition (N2 and O2) and temperature (room temperature and 150 °C) to photoluminescence response was examined for optical gas sensor application. The laser-untreated film showed higher sensitivity to the presence of oxygen at both temperatures compared to the treated film. The stability of photoluminescence intensity at elevated temperature was improved for laser-treated areas.

Titanium dioxide (TiO2) was plasma sprayed using a high feed-rate spray system with hybrid water–argon stabilization torch (WSP-H). TiO2 powder agglomerated from nanometric particles was used as the feedstock. The produced coating had thickness over 4 mm, to be comparable with bulk ceramic bodies. The deposit was removed from the substrate and annealed in air to reoxidize the oxygen deficient as-sprayed titania and to obtain material with a proper dielectric behavior. Besides the microstructure studies, radiofrequency dielectric spectroscopy and microwave dielectric spectroscopy were in the focus of investigation. The approach to annealing of an extremely thick coating is studied: The significance of annealing of a large-area thick coating is discussed, as the role of grain interior and grain boundaries in the charge transport is influenced. Relative permittivity er 94 and the Q*f product 12,800 GHz were reached at frequency 4 GHz, whereas the frequency response under 1 MHz was mapped continuously and the values (i.e., low and stable loss tangent) confirmed that a sprayed and air-annealed TiO2 is able to approach or also overperform dielectric parameters typical for TiO2 sintered bulk.

The influence of cold rolling on thermal and mechanical properties together with microstructure observation of cast AlZnMgCu(ScZr) alloys has been investigated. Differential scanning calorimetry measurements and microhardness were compared to microstructure that was observed by microscopy (scanning electron and transmission), electron backscatter and X-ray diffractions. Microstructure observation of all studied alloys proved eutectic phase at (sub)grain boundaries. The eutectic phase at grain boundary in the AlZnMgCuScZr has a disordered quasicrystalline structure (known as the T phase or Mg32(Al,Cu,Zn)49). In the AlZnMgCu alloy, the eutectic phase consists of two phases—predominant MgZn2 phase and minor quasicrystalline T phase. During casting and subsequent cooling, multilayer primary Al3(Sc,Zr) particles also precipitated in the alloy with Sc,Zr addition. Solute clusters and/or Guinier–Preston zones were dissolved during the annealing up to ~ 170 °C in the alloys. The highest hardening is caused by particle formation of metastable η′ and stable η phase in AlZnMgCu system observed at ~ 200 °C. Precipitation of the secondary Al3(Sc,Zr) particles is probably the reason of hardening after annealing above 300 °C in the Sc,Zr-containing alloys. Melting of eutectic phases was observed in DSC curves at temperatures ~ 481 and ~ 493 °C in the studied alloys. Activation energies of the Guinier–Preston zones dissolution and/or solute clusters were calculated using Kissinger and Starink method as QA ≈ 100 kJ mol−1 and the formation of the particles of Al–Zn–Mg–Cu system as QB ≈ 150 kJ mol−1. No significant effect on the calculation of activation energy values of thermal processes was observed in deformed alloys. Sc,Zr addition in the alloys stabilizes grains, and there is no recrystallization in the AlZnMgCuScZr alloy at temperature 450 °C/10 h.

NiCrAlY deposited by different thermal spraying methods is commonly used as the bond coat material in thermal barrier coatings (TBCs). In the present study, two experimental coatings were deposited by hybrid water stabilized plasma (WSP-H) and radio frequency inductively coupled plasma (RF-ICP) using the same feedstock powder. Spark plasma sintering (SPS) was used to manufacture a compact NiCrAlY from the same feedstock powder as a reference material. Microstructure, internal oxidation, phase characterization and quantification of the mechanical behaviour in terms of microhardness were studied. The investigations clearly showed microstructural and mechanical differences between the NiCrAlY samples manufactured by different plasma technologies. The results confirmed that SPS and RF-ICP provide dense structures with no oxides due to the fabrication under protective atmosphere and similar mechanical properties. Thus, RF-ICP may be used for deposition of very dense coatings with microstructure and hardness comparable to compacted materials prepared by SPS.

Hybrid water-stabilized plasma (WSP-H) torches provide high-enthalpy plasma which may be utilized for high-throughput and yet economical spraying of coatings from powders, suspensions, and solutions. It was previously demonstrated that microstructures and functional properties of the WSP-H coatings may be tailored to a wide extent for new applications, namely those requiring high coating thickness and/or coating of large components. In this study, applicability potential of WSP-H technology for spraying of novel thermal barrier coatings (TBCs) is demonstrated. WSP-H technology was used for spraying of yttria-stabilized zirconia (YSZ) top-coats from powder, suspension, and solution. Yttria content in the top-coat feedstock was 7-8 wt.%. In addition, gadolinium zirconate (Gd2Zr2O7-GZO) was sprayed from suspension for comparison. NiCrAlY bond-coat was also deposited by WSP-H, and Hastelloy-X alloy was used as substrate material. Microstructure, phase composition, and endurance of the deposited coatings in thermal cycling fatigue (TCF) test and during high-temperature short-term annealing were evaluated. All coatings showed excellent high-temperature stability and TCF resistance withstanding more than 650 cycles, surpassing some of the currently commercially used TBCs. Lifetime of the TBC with columnar top-coat deposited from YSZ suspension exceeded even more than 900 cycles.

Illitic clays are the commonly used material in building ceramics. Zeolites are microporous, hydrated crystalline aluminosilicates, they are widely used due to their structure and absorption properties. In this study, illitic clay (Füzérradvány, Hungary) was mixed with natural zeolite (Nižný Hrabovec, Slovakia) with up to 50 wt.% of zeolite content. The samples were submitted to thermal analyses, such as differential thermal analysis, differential scanning calorimetry, thermogravimetry, and dilatometry. In addition, the evolution of thermal diffusivity, thermal conductivity, and specific heat capacity in the heating stage of firing were measured and discussed. The amount of the physically bound water in the samples increased along with the amount of zeolite. The temperature of the illite dehydroxylation (peak temperature) was slightly shifted to lower temperatures, from 609 °C to 575 °C (for sample IZ50). On the other hand, the mass loss and the shrinkage of the samples significantly increased with the zeolite content in the samples. Sample IZ50 reached 10.8% shrinkage, while the sample prepared only from the illitic clay contracted by 5.8%. Nevertheless, the temperature of the beginning of the sintering (taken from the dilatometric curves) decreased from 1021 °C (for illitic clay) to 1005 °C (for IZ50). The thermal diffusivity and thermal conductivity values decreased as the amount of zeolite increased in the samples, thus showing promising thermal insulating properties.

In order to extend the life of boilers by applying an anti-corrosion coating without the need to dismantle them, it is advisable to find coatings that can be applied using cheaper and portable techniques, such as Twin Wire Arc Spray technology (TWAS). In this study, we compare selected NiCr-based coatings and two uncoated steel substrates (steel 1.7715 and 1.4903). Two coatings, Cr3C2 - 25% NiCr and Hastelloy C-276 are deposited using High velocity oxygen-fuel technology (HVOF) and three coatings, NiCrTi, NiCrMo, and Inconel 625, are deposited using TWAS. In addition to the corrosion weight gain during 50 cycles of loading in an 18% Na2SO4 and 82% Fe2(SO4)3 salt environment at 690 °C evaluated using the gravimetric method, the microstructure and phase composition of the coatings were analyzed on the samples after the exposure in order to compare the properties and gain a deeper understanding of the corrosion kinetics. Coating cross-sections and free-surfaces were observed with a scanning electron microscope (SEM) with an energy-dispersive (EDX) system. The phase composition was investigated using X-ray diffraction (XRD) and Raman spectroscopy. No significant differences were observed between the TWAS and HVOF coating methods for the coatings compared. Due to the similar corrosion products found on all coatings, a very effective corrosion protective layer was formed on the surface, forming a barrier between the corrosive environment and the coating regardless of the used deposition technology. Therefore, for industrial use on the inner surface of coal-fired boilers we recommend NiCrTi, NiCrMo, or Inconel coatings prepared with the more cost-effective and portable TWAS technology.

In this paper, we examined the dielectric properties of CaCu3Ti4O12 (CCTO) ceramics fabricated by various routes and discussed the most important conditions affecting their dielectric behavior. We prepared feedstock powder using a molten salt route and compared it with a commercial powder. Both powders were sintered using SPS. For some samples, annealing was applied after sintering. Other samples were obtained by high-pressure forming and conventional sintering, using both powders. Phase composition, porosity and microhardness were evaluated in comparison with the literature. The results showed that a sintering temperature just below or equal to 1000 °C should be set for the SPS process. However, the best dielectric characteristics were obtained in samples prepared by high-pressure forming and conventional sintering, which showed a relative permittivity of 22,000 and a loss tangent of 0.13 at 1 MHz.

Solution precursor plasma spraying (SPPS) presents a modern route to deposit coatings directly from liquid feedstock. In this study, unique ability of SPPS to intermix different precursors on the atomic scale was employed to deposit pure and Cr-doped Al2O3 (technically, synthetic ruby) from several mixtures of aluminum and chromium nitrates. Highly porous coatings (> 60% porosity) were deposited by high-enthalpy WSP-H torch. Homogeneous distribution of Cr atoms in Al2O3 resulted in coatings color ranging from pink to grayish-green correlated with increasing Cr content and change of lattice parameters as observed by x-ray diffraction. High content of over 80 wt.% of α-alumina phase was reached for all coatings. For the Cr-doped Al2O3 coatings, distinct and fully reversible thermochromic behavior was observed by temperature-resolved colorimetry. Further increase in α-phase content (up to 95 wt.%) and coating densification were achieved by additional surface remelting by plasma torch.

Precipitation reactions of the cast Al–3.4 at%Mg–2.7 at%Zn–0.80 at%Cu–0.10 at%Fe–0.05 at%Si alloy with and without addition of 0.14 at%Sc and 0.06 at%Zr were characterized by electrical resistometry, electron microscopy, X-ray diffraction, thermal analysis, microhardness testing, and positron annihilation. The AlMgZnCuScZr alloy contains a grain boundary T-phase (Mg32(Al,Cu,Zn)49) with a cubic and/or quasicrystalline structure. The AlMgZnCu alloy contains a mixture of MgZn2- and the T-phase. Primary multilayer Al3(Sc,Zr) particles precipitated during casting and subsequent cooling. The particles have a layered Al3(Sc,Zr) + α-Al + Al3(Sc,Zr) structure, i.e. consist of regions enriched with both Sc and Zr. Small atomic Mg,Zn(,Cu)-rich clusters coherent with the matrix were formed during the cooling of both alloys and/or in the course of their storage at ambient temperature. Their dissolution enables precipitation of the transient η′- and/or stable η-phases of the AlZnMgCu system in both investigated alloys. The effective activation energy for the dissolution of the clusters was calculated as ~ 103 kJ/mol. Annealing of the AlMgZnCuScZr alloy above 300 °C leads to a formation of the secondary Al3(Sc,Zr) particles which cause precipitation hardening and guarantee thermal stability of mechanical properties. Addition of Sc and Zr micro alloying elements resulted in a substantial grain refinement. The grain size remains unchanged up to isochronal annealing at 390 °C.

The equiatomic CoCrFeMnNi alloy is currently one of the most studied high-entropy alloys. In our previous work, a new grade of CoCrFeMnNi high-entropy alloy with yttria-based particle dispersion was introduced showing improved mechanical properties, especially high-temperature strength and creep rate. In this study, a detailed analysis of room to high-temperature thermal properties was performed, as it is important for defining the future application of the alloy and opening the discussion on tailoring the thermal response. Thermal properties are not well known for the original CoCrFeMnNi alloy or for CoCrFeMnNi with yttria dispersion. As a result of the analysis, thermal properties of both alloys and the effect of the oxide dispersion are discussed. Most of the thermal properties remain unchanged. However, it was found that the presence of 0.3% yttria influences the oxidation rate of CoCrFeMnNi alloy at the initial and intermediate oxidation times. The onset of the oxidation is described in detail. Yttria nano-oxide dispersion and related grain refinement also reduce the microstructural degradation caused by the formation of voids due to outward Mn diffusion.

The novel method of hybrid suspension plasma spraying of dry coarse aluminum oxide powder with chromium oxide suspension using hybrid water/argon-stabilized (WSP-H 500) plasma torch was utilized for the deposition of coatings with very high α-phase content reaching up to 90%. The deposition mechanism and phase composition were compared with those of coatings deposited from i) intermixed alumina-chromia suspension and ii) alumina suspension doped with chromium nitrate nonahydrate solution. All deposition routes showed alternative ways of preparation of novel multimaterial coatings. It was demonstrated that the chromia addition and the deposition route play the crucial role in the pronounced formation of the thermodynamically stable α-phase.

Biomedical Ti-6Al-7Nb alloy was prepared by a dedicated thermal treatment followed by equal-channel angular pressing (ECAP) and extrusion. Ultra-fine grained duplex microstructure consisting of deformed primary α-grains and fragmented α + β region was achieved. Microstructural changes during heating with the rate of 5 °C/min were studied by in-situ electrical resistance. Microstructure after deformation and also after subsequent heating was thoroughly characterized by scanning electron microscopy, X-ray diffraction, and positron annihilation spectroscopy (PAS). X-ray diffraction and positron annihilation spectroscopy proved a very high dislocation density and the presence of high concentration of vacancy clusters in deformed material. The ultra-fine grained microstructure of Ti-6Al-7Nb alloy is stable up to 440 °C, while upon heating to 550 °C and to 660 °C, the dislocation density decreases and vacancy clusters disappear. Enhanced microhardness can be achieved by ECAP followed by aging at 500 °C. Upon heating to 660 °C, the microhardness decreases due to ongoing recovery and recrystallization. Coincidence Doppler broadening (CDB), a special method of PAS, proved that dislocation cores are preferentially occupied by Al atoms that are known to cause substitutional solid solution strengthening.

Tungsten is a refractory metal, suitable for a broad range of high-temperature applications, due to its high melting point and high-temperature strength. Recently, tungsten alloys became of great interest in thermonuclear fusion research. The alloys maintain low sputtering yield and high melting point, but greatly improve some drawback properties comparing to pure tungsten. These alloys are commonly prepared by mechanical alloying and compacted using Spark Plasma Sintering/Field Assisted Sintering. Powder in a graphite die is consolidated by applying pulsed electric current and pressure. Graphite foil is commonly placed between the die and the powder, to prevent adhesion. However, for number of applications it is necessary to avoid carbon contamination. In the present study we have examined carbon contamination mechanism of W - 10 wt.%Cr - 1 wt.%Hf alloy during Field Assisted Sintering along with the alloy's properties. The experiments have shown that the graphite foil leads to significant dealloying via mechanism of liquid phase sintering. As a result, tailored properties of the material are deteriorated after several minutes of the consolidation process. Therefore, application of carbon diffusion barrier was proposed, examined and compared with the alloy sintered with graphite foil.

In suspension spraying, two most frequently used solvents are water and ethanol. In this study, we test the potential of using alternative, high molecular weight solvent and demonstrate the associated advantages. For that, two organic solvents are directly compared: ethanol (serving as a benchmark, suspension formulated at 10 wt.% solid load) and di-propylene glycol methyl ether (two suspensions at 10 wt.% and 20 wt.% solid load). As a model material, $$\hbox {Al}_{2}\hbox {O}_3$$ is selected, a frequently sprayed ceramics employed in many industrial sectors. Sub-micron 100% alpha-alumina powder is used to formulate the suspensions. Identical spray conditions are then used to deposit the coatings using hybrid water-stabilized plasma torch. Shadowgraphy monitoring of the suspension fragmentation as well as in situ measurement of the particle in-flight properties is employed, showing no significant differences between the three series. Further, it is shown that the ethanol- and ether-based-feedstock coatings are fully comparable in terms of their microstructure, porosity content, surface roughness as well as hardness and adhesion to the substrates. Importantly, the ether-based coatings exhibit slightly higher levels of $$\alpha$$ - $$\hbox {Al}_{2}\hbox {O}_3$$ phase when compared to their ethanol-based counterpart (17 wt.% vs. 6 wt.%). The use of 20 wt.% solid load in the ether solvent leads to twofold increase in the deposition rate while (as opposed to ethanol) successfully retaining a dense microstructure. Lastly, the ether is significantly cheaper and safer to handle than ethanol.

Hybrid plasma spraying is emerging as the next potential technology leap in thermal spraying. The combination of high throughput and deposition rates of coatings sprayed from powders with the tailored functionality of liquid-feedstock sprayed coatings appears highly promising for a wide range of applications. Moreover, possible refined mixtures of different materials come readily with the utilization of multiple feedstocks with varying particle sizes. However, the practical aspects of hybrid coatings production are accompanied with several peculiarities not encountered when using distinct feedstocks. To deepen the understanding of this novel route, this paper presents fundamental hybrid coating formation principles and the effect of selected deposition parameters using multiple case-study material systems, such as Al2O3-YSZ, Al2O3-Cr2O3, and Al2O3-TiO2.

Harnessing nuclear fusion is a challenging task, in particular because of the demands put on the used materials. In tokamaks, future energy sources, the inner-most chambers are to be coated with dense coatings of W, or W-Cr-based alloys. So far, the attempts for such coatings formation by other methods failed due to oxidation, high porosity, insufficient adhesion, high specific surface, or even insufficient thickness below 10 &mu, m. Cold spraying seems a promising technology for the task. In our study, we demonstrate the first successful fabrication of thick pure W coatings. W-Cr and W-Cr-Ti coatings were further prepared without oxidation of the metals. All coatings exhibited high hardness levels, good interface quality with three tested substrates and, importantly, a promising potential for formation of stable Cr 2 WO x phases.

Thanks to the low working temperature, less product size limitations and one order of magnitude higher deposition rates compared to the established additive manufacturing techniques, more attention has been brought to the potential of cold spraying for additive manufacturing . As a process dealing with deformation of solid particles possibly leaving non-bonded interfaces and causing work hardening, any optimization should (i) adjust spray parameters to obtain high performance as-sprayed parts and (ii) tune ductility and internal stresses by post-treatments. The present study first deals with strategies to optimize spray parameters for fabrication of high performance steel 316 L deposits. Next, the performances of deposits are further adjusted by various heat treatments. The structural strength of the freestanding samples before and after the heat treatments is evaluated under static and cyclic axial loading and supported by fatigue crack growth rate analysis. The results highlight the feasibility of obtaining high quality steel 316 L deposits using N2 as process gas, rather than the costly He that is commonly suggested. This study demonstrates the potential of cold spraying to be used for deposition of freeform structural components with a static strength comparable to that of bulk and laser-based additive manufactured materials and a fatigue strength similar to that of bulk cast material.

The knowledge about thermal transformations of glass is important, especially if the glass is used as a precursor for glass-ceramic materials. In this study, thermal transformations of glass with composition near to anorthite stoichiometry (2SiO2·Al2O3·CaO) are studied up to 1300 °C. Differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) were used for this purpose. The samples were heat-treated at various temperatures to reveal the nature of the exothermic and endothermic effects on DSC. The change in heat capacity related to glass transition was observed at 722 °C. Besides, one exothermic and one endothermic peak appeared at 957 °C and 1157 °C, respectively. No further thermal effects were observed up to 1300 °C. The peak centered at 957 °C was attributed to the overlapping crystallization of gehlenite (2CaO·Al2O3·SiO), anorthite, and CaO·Al2O3·2SiO polymorph (Ca-feldspar). To explain the endothermic effect, DSC experiments were performed on thermally treated glass. The glass previously heated at 1157 °C showed weak crystallization (exothermic) effect during the second DSC run. Moreover, no decrease in crystalline phase content was detected by XRD. A usual explanation of the second endothermic peak – the dissolution of crystalline phases, was questioned. Conversion of Ca-feldspar and gehlenite to anorthite is suggested as an alternative explanation.

The application of non-equilibrium methods such as Mechanical Alloying and Field Assisted Sintering enables the formation of a single solid solution in immiscible systems, or the ones characterized by a miscibility gap. This work shows that W-Cr solid solution can be used as an intermediate step to produce ultrafine-grained composite alloys with rod-like microstructural features. It is shown that a significant increase in strength can be achieved without an increase in hardness using this top-down material design.

Alloying of Mg with rare-earth (RE) elements proved to be beneficial for their in-vitro and in-vivo performance. In this work, a novel WN43 (Mg-4 wt%Y-3 wt%Nd) alloy with a well-defined composition was prepared, where, unlike in the commercial WE43 alloy, the possibly harmful RE mischmetal was substituted by less toxic Nd. A modern spark plasma sintering (SPS) technique was used to effectively produce WN43 samples from atomized powders. Sintering temperatures of 400 °C – 550 °C and holding times of 3 or 10 min were used and well-compacted final materials were successfully prepared. It was shown that a superior combination of corrosion and mechanical properties was attained in the samples sintered at 500 °C and 550 °C, while the effect of sintering time was rather negligible. The performance of this material was exceptional within the group of Mg alloys prepared by powder metallurgy and comparable with conventionally prepared alloys. Moreover, it was shown that a great variety of mechanical and corrosion characteristics can be obtained by altering the SPS parameters so as to fulfill case-specific requirements typical of biomedical materials. Consequently, the novel WN43 alloy prepared by SPS seems to be a particularly suitable material for biomedical use.

The aims of this study were: (1) to produce composite coatings by high velocity oxy fuel (HVOF) spraying with steel matrix reinforced by cermets (a) Cr3C2&ndash, 20%Ni and (b) TiC&ndash, 20%NiMo, manufactured by mechanically activated synthesis (MAS), (2) to synthesize in situ a carbide reinforcement for iron matrix from a mixture of titanium and carbon during HVOF reactive thermal spraying (RTS), (3) to compare the wear resistance of produced coatings. As a reference, HVOF sprayed coatings from commercial Cr3C2&ndash, 25%NiCr (Amperit 588.074) and AISI 316L were utilized. Study of microstructure revealed the inhomogeneity of the Cr-based MAS coating, the Ti-based MAS coating had typical carbide granular structure, and the Ti-based RTS coating possessed elongated structures of TiC. The X-ray diffraction revealed two main phases in the Cr-based MAS coating: Cr3C2 and austenite, and two phases in the Ti-based coatings: TiC and austenite. Among the studied coatings, the Cr-based MAS coating demonstrated the highest low-force hardness (490 HV0.3). During the abrasive rubber wheel test (ASTM G65), the Ti-based MAS coating showed the best wear resistance, followed by Cr3C2&ndash, 25%NiCr and Ti-based RTS coating. In the abrasive&ndash, erosive test (GOST 23.201-78), the Ti-based MAS coating was 44% better than Cr3C2&ndash, 25%NiCr coating. The Ti-based RTS coating was 11% more wear resistant than the reference Cr3C2&ndash, 25%NiCr coating.

Dynamical thermomechanical analysis of 5 illite-based clays from deposits in Slovakia, Estonia, Latvia, and Hungary is presented. The clays consist of illite (37&ndash, 80 mass%), quartz (12&ndash, 48 mass%), K-feldspar (4&ndash, 13 mass%), kaolinite (0&ndash, 18 mass%), and calcite (0&ndash, 3 mass%). Young&rsquo, s modulus is measured during the heating and cooling stages of firing (25 &deg, C &rarr, 1100 &deg, 25 &deg, C). The liberation of the physically bound water increases Young&rsquo, s modulus by &sim, 70% for all studied clays. By increasing the temperature, dehydroxylation and the &alpha, &rarr, &beta, transition of quartz take place without a significant effect on Young&rsquo, s modulus. Sintering, which starts at 800 &deg, C, leads to an intensive increase in Young&rsquo, s modulus up to the highest temperature (1100 &deg, C). The increase remains also in the early stage of cooling (1100 &deg, 800 &deg, C). This increase of Young&rsquo, s modulus is also the result of solidification of the glassy phase, which is finished at &sim, 750 &deg, C. A sharp minimum of Young&rsquo, s modulus is observed at around the &beta, &alpha, transition of quartz. Then, Young&rsquo, s modulus still decreases its value down to the room temperature. The physical processes observed during heating and cooling do not differ in nature for the studied clays. Values of Young&rsquo, s modulus vary at around 8 GPa, up to 800 &deg, C. During sintering, Young&rsquo, s modulus reaches values from 30 GPa to 70 GPa for the studied clays. The microstructure and composition given by the origin of the clay play a cardinal role for the Young&rsquo, s modulus of the final ceramic body.