The paper presents the results of the mechanical, electrical, CCSEM and XRD measurements of hard coal, conducted in simulated conditions of sintering in atmospheres of O2/CO2,. The changes of the coal ash resistivity are correlated with the content of the oxides and with the sintering temperature determined by the mechanical test and Leitz method. The SEM-EDS analysis was conducted for deposits on the probe. The changes of the measured ash samples, observed during sintering process in O2/CO2 atmosphere, were discussed in the ash microstructure point of view.
Using the available analytical methods, including the determination of chemical composition using wavelength-dispersive X-ray
fluorescent spectroscopy technique and phase composition determined using X-ray diffraction, microstructural observations in a highresolution
scanning microscope equipped with an X-ray microanalysis system as well as determination of characteristic softening and
sintering temperatures using high-temperature microscope, the properties of particular chromite sands were defined. For the study has been
typed reference sand with chemical properties, physical and thermal, treated as standard, and the sands of the regeneration process and the
grinding process. Using these kinds of sand in foundries resulted in the occurrence of the phenomenon of the molding mass sintering.
Impurities were identified and causes of sintering of a moulding sand based on chromite sand were characterized. Next, research methods
enabling a quick evaluation of chromite sand suitability for use in the preparation of moulding sands were selected.
The results of structure and mechanical properties investigations of tungsten heavy alloy (THA) after cyclic sintering are presented. The
material for study was prepared using liquid phase sintering of mixed and compacted powders in hydrogen atmosphere. The specimens in
shape of rods were subjected to different number of sintering cycles according to the heating schemes given in the main part of the paper
From the specimens the samples for mechanical testing and structure investigations were prepared. It follows from the results of the
mechanical studies, that increasing of sintering cycles lead to decrease of tensile strength and elongation of THA with either small or no
influence on yield strength. In opposite to that, the microstructure observations showed that the size of tungsten grain increases with
number of sintering cycles. Moreover, scanning electron microscope (SEM) observations revealed distinctly more trans-granular cleavage
mode of fracture in specimens subjected to large number of sintering cycles compared with that after one or two cycles only.
Currently is the biggest problem of metallurgical companies the increase of fossil fuel prices and strict environmental regulations. As a result of this, companies must look for alternatives that would reduce the amount of fossil fuels and reduce emissions. Wood sawdust has huge energy potential, which can be used in the process of agglomerate production. This type of energy is locally available, has some similar properties as fossil fuels and is economically advantageous. For these reasons, experimental study using laboratory agglomeration pan was realized to study the possibility of agglomerate production with a mixed fuel. Experimental results show the viability of mixed fuel use in the agglomeration process, but also show significant possibility for improvement. The maximum acceptable substitution ratio, which corresponds to qualitatively suitable agglomerate is 20% of pine sawdust. Based on the realized experiments and the obtained results we have acceded to the intensification of the agglomeration process with an objective to increase the amount of added substitution fuel while maintaining the required quality of agglomerate.
In this paper the development and method of production of modern, Ni-free sintered structural steels containing Cr, Mn and Mo, enabling the production of structural sintered steels in industrial conditions, using safe, with low H2-content, sintering atmospheres is presented. For this purpose, the analysis of microstructure and mechanical properties of these sintered structural steels produced in different processing conditions and also the connections between the microstructure of sintered material and its mechanical properties, was presented. Following the investigations, the appropriate chemical composition of sintered Ni-free steels with properties which are comparable or even better than those of sintered structural steels containing rich and carcinogenic nickel was choosen. Additionally, in the paper the properties of electrolitically coated carbon steels were presented, as the beginning of investigation for improving the mechanical properties of alloyed, structural sintered steels.
The paper presents the results of research on the production and application of sintered copper matrix composite reinforced with titaniumcopper intermetallic phases. Cu- Ti composites were fabricated by powder metallurgy. The starting materials for obtaining the sintered composites were commercial powders of copper and titanium. Experiments were carried out on specimens containing 2.5, 5, 7.5 and 10 % of titanium by weight. Finished powders mixtures containing appropriate quantities of titanium were subjected to single pressing with a hydraulic press at a compaction pressure of 620 MPa. Obtained samples were subjected to sintering process at 880 °C in an atmosphere of dissociated ammonia. The sintering time was 6 hours. The introduction of titanium into copper resulted in the formation of many particles containing intermetallic phases. The obtained sinters were subjected to hardness, density and electrical conductivity measurements. Observations of the microstructure on metallographic specimens made from the sintered compacts were also performed using a optical microscope. An analysis of the chemical composition (EDS) of the obtained composites was also performed using a scanning electron microscope. Microstructural investigations by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that after 6 hours of sintering at 880°C intermetallic compounds: TiCu, TiCu2, TiCu4, Ti2Cu3, Ti3Cu4 were formed. The hardness increased in comparison with a sample made of pure copper whereas density and electrical conductivity decreased. The aim of this work was to fabricate copper matrix composites reinforced with titanium particles containing copper- titanium intermetallic phases using powder metallurgy technology and determine the influence of the titanium particles on the properties of the sintered compacts and, finally, analyse the potentials application for friction materials or electric motors brushes.
Electrochemical Cr coatings doped with diamond nanoparticles were deposited on sintered steels with different carbon contents (0.2-0.8 wt.-%). The mechanical properties of surfaces as hardness and wear resistance increase as compared to the steel substrate. Microcutting and microgridding mechanisms were observed after tribological tests, but also adhesive wear in some areas was observed. X-ray examination indicated that the layer was textured, with the exception of the sample with the highest concentration of diamond nanoparticles in the electrolyte (42 g/l). The intensity ratio ICr110/ICr200 was calculated and compared with the indices for a standard sample. The greatest differences in the intensity ratio occurred for the samples with low carbon content (0.2%C). On the other hand, more the material is textured the greater the difference.
One of the ways to decrease thermal conductivity is nano structurization. Cobalt triantimonide (CoSb3) samples with added indium or tellurium were prepared by the direct fusion technique from high purity elements. Ingots were pulverized and re-compacted to form electrodes. Then, the pulsed plasma in liquid (PPL) method was applied. All materials were consolidated using rapid spark plasma sintering (SPS). For the analysis, methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) with a laser flash apparatus (LFA) were used. For density measurement, the Archimedes’ method was used. Electrical conductivity was measured using a standard four-wire method. The Seebeck coefficient was calculated to form measured Seebeck voltage in the sample placed in a temperature gradient. The preparation method allowed for obtaining CoSb3 nanomaterial with significantly lower thermal conductivity (10 Wm–1K–1 for pure CoSb3 and 3 Wm–1K–1 for the nanostructured sample in room temperature (RT)). The size of crystallites (from SEM observations) in the powders prepared was about 20 nm, joined into larger agglomerates. The Seebeck coefficient, α, was about –200 µVK–1 in the case of both dopants, In and Te, in microsized material and about –400 µVK–1 for the nanomaterial at RT. For pure CoSb3, α was about 150 µVK–1 and it stood at –50 µVK–1 for nanomaterial at RT. In bulk nanomaterial samples, due to a decrease in electrical conductivity and inversion of the Seebeck coefficient, there was no increase in ZT values and the ZT for the nanosized material was below 0.02 in the measured temperature range, while for microsized In-doped sample it reached maximum ZT = 0.7 in (600K).
Tungsten heavy alloys comprising tungsten, nickel and ferrous were modified, where molybdenum was added in varying weight proportions keeping the ratio of Ni: Fe (8:2) constant. The powders were mixed in a high-energy ball mill and were further fabricated using the spark plasma sintering (SPS) method at a peak temperature of 1000°C with heating rate of 100°C/min. The details of the microstructure and mechanical properties of these various alloy compositions were studied. With the increasing weight composition of the Mo in the alloy, the relative density of the alloy increased with a significant improvement in all the mechanical properties. The yield strength (YS), ultimate tensile strength (UTS) and hardness improved significantly with increase in the proportion of Mo; however, a reduction in elongation percentage was observed. The maximum strength of 1250 MPa UTS was observed in the alloy with a Mo proportion of 24%. The heavy alloy unmixed with Mo has shown distinct white and grey regions, where white (W) grain is due to tungsten and grey region is a combinatorial effect of Ni and Fe. Upon addition of Mo, the white and gray phase differences started to minimize resulting in deep gray and black ‘C’-phase structures because of homogenization of the alloy. The main fracture mode found during this investigation in the alloys was inter-granular mode.
The paper refers to pulverization and sintering of the (Fe80Nb6B14)0.88Tb0.12 high coercive alloy. The powder was sintered using the ultra-fast current aided method. It turned out that too long discharge time leads to appearing of a soft magnetic phase and simultaneously, decrease in coercivity of the compacted powder. Nevertheless, it was possible to establish preference technology parameters, preserving magnetic hardness of the alloy. As a final test, an impact of Co-powder addition on magnetic properties was studied. The introduced soft magnetic phase (about 20 wt. %) caused about 30% increase of magnetic remanence, which is a result of direct exchange interactions between the two phases.
Usually porous metals are known as relatively excellent characteristic such as large surface area, light, lower heat capacity, high toughness and permeability for exhaust gas filter, hydrogen reformer catalyst support. The Ni alloys have high corrosion resistance, heat resistance and chemical stability for high temperature applications. In this study, the Ni-based porous metals have been developed with Hastelloy powder by gas atomization and water atomization in order to find the effects of powder shape on porous metal. Each Hastelloy powder is pressed on disk shape of 2 mm thickness with 12 tons using uniaxial press machine. The specimens are sintered at various temperatures in high vacuum condition. The pore properties were evaluated using Porometer and microstructures were observed with SEM.
439L stainless steel composites blended with fifteen micron SiC particles were prepared by uniaxial pressing of raw powders at 100 MPa and conventional sintering at 1350oC for 2 h. Based on the results of X-ray diffraction analysis, dissolution of SiC particles were apparent. The 5 vol% SiC specimen demonstrated maximal densification (91.5%) among prepared specimens (0-10 vol% SiC); the relative density was higher than the specimens in the literature (80-84%) prepared by a similar process but at a higher forming pressure (700 MPa). The stress-strain curve and yield strength were also maximal at the 5 vol% of SiC, indicating that densification is the most important parameter determining the mechanical property. The added SiC particles in this study did not serve as the reinforcement phase for the 439L steel matrix but as a liquid-phase-sintering agent for facilitating densification, which eventually improved the mechanical property of the sintered product.
The mechanical behavior and the change of retained austenite of nanocrystalline Fe-Ni alloy have been investigated by considering the effect of various Ni addition amount. The nanocrystalline Fe-Ni alloy samples were rapidly fabricated by spark plasma sintering (SPS). The SPS is a well-known effective sintering process with an extremely short densification time not only to reach a theoretical density value but also to prevent a grain growth, which could result in a nanocrystalline structures. The effect of Ni addition on the compressive stress-strain behavior was analyzed. The variation of the volume fraction of retained austenite due to deformation was quantitatively measured by means of x-ray diffraction and microscope analyses. The strain-induced martensite transformation was observed in Fe-Ni alloy. The different amount of Ni influenced the rate of the strain-induced martensite transformation kinetics and resulted in the change of the work hardening during the compressive deformation.
Krajowa baza zasobowa dolomitów jest duża. Ich łączne zasoby bilansowe, udokumentowane w 62 złożach - wykazywanych w aktualnych statystykach zasobów kopalin - wynoszą 1 500 mln t. Mimo tego występuje deficyt wysokiej jakości tzw. dolomitów konwertorowych, które mają zastosowanie do produkcji materiałów ogniotrwałych. Dla tego celu wykorzystywane są od wielu lat dolomity triasowe ze złóż Brudzowice i Ząbkowice Śląskie I, z regionu śląsko-krakowskiego. Do innych potencjalnie interesujących złóż tego regionu, ze względu na charakter i właściwości dolomitów, należy złoże Libiąż. Wątpliwa, choć niewykluczona wydaje się możliwość wykorzystania dolomitów ze złóż Nowa Wioska i Stare Gliny. Wymaga to jednak przeprowadzenia bardziej dokładnych badań ich składu chemicznego i podatności do spiekania. Jak dotąd bowiem, dolomity z tych złóż są rozpoznane i aktualnie eksploatowane na znaczną skalę przede wszystkim dla potrzeb drogownictwa i budownictwa. Niestety, pogarszająca się jakość dolomitów zalegających w innym, dużym i udostępnionym złożu tego regionu - Żelatowa - była przyczyną zaniechania wykorzystania tej kopaliny do produkcji materiałów ogniotrwałych. Spośród złóż rezerwowych najkorzystniejszymi właściwościami wyróżniają się cztery: Chruszczobród, Chruszczobród I, Chruszczobród 2 i Libiąż Wielki. Przeprowadzona analiza wskazuje także na możliwość wykorzystania dla celów przemysłu materiałów ogniotrwałych kopalin ze złóż Winna i - w mniejszym stopniu - Radkowice-Podwole. Wymaga to jednak przeprowadzenia bardziej szczegółowych badań ich składu chemicznego i struktury, a zwłaszcza określenia wielkości ziaren. Odrębne zagadnienie stanowi kwestia wykorzystania marmurów dolomitowych ze złóż regionu dolnośląskiego. Tradycyjnie uważa się, że są one nieprzydatne do produkcji materiałów ogniotrwałych z uwagi na grube uziarnienie. Kopalina ta występuje jednak w kilku odmianach, reprezentując również struktury drobno i średniokrystaliczne. Najczystsze i najbardziej drobnoziarniste odmiany mogą być interesujące do produkcji materiałów ogniotrwałych. Wymaga to jednak prowadzenia selektywnej ich eksploatacji.