Mechanical properties of Si3N4 – graphene composites sintered by SPS method

Silicon nitride powder with a small addition of magnesium oxide and yttria stabilized tetragonal zirconia fine particles was used as a starting material. Multilayer graphene nanoplatelets were used as filler for silicon nitride based composites. Graphene content in the mixtures was 0‒2 wt. %. The composites were obtained by the Spark Plasma Sintering method at 1650°C under 35 MPa of uniaxial pressure. Separation of the agglomerated graphene platelets in the matrix was observed for these materials. Insufficient dispersity of graphene slightly decreased the mechanical properties of Si₃N₄ ceramics. The SEM and TEM microstructural analysis of sintered materials show that the applied pressure during the sintering process leads to the orientation of the graphene phase and in consequence causes anisotropy of properties. The differences of friction coefficients were examined with the Ball-on-Disc method for the two directions (parallel and perpendicular to the pressing axis). Also the specific wear rate of the ball for the direction parallel to pressing axis differ significantly in comparison to the wear for the direction perpendicular to the pressing direction.

Keywords: silicon nitride, graphene, Young’s modulus, hardness, coefficient of friction, wear rate,

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Nanocomposite chromium coatings on aluminum alloys

Chromium coatings modified with nanodiamond particles were deposited on aluminum alloys. The concentration of the nanodiamond particles in the chrome plating electrolyte was from 5 to 25 g/l. The thickness of the layer varied between 30 and 70 μm. The layers were prepared with the same electrolytic conditions and were measured with a metallographic microscope. The maximum microhardness of the coating was 840 kg/mm². X-ray diffraction analysis was performed with a Siemens D500 apparatus using the Bragg-Brentano technique. The distribution of Cr, Al and O in the cross section was studied by SEM-EDS. It was found that the layers were homogenous - only consisted of chromium. The coatings were also studied for non-destructivity by X-ray 3D computed tomography. It was found that the coatings were intact and continuous along the section. In order to obtain the maximum yield of chromium and maximum thickness of the layer, the optimum nanodiamond particle concentration was 10 g/l.

Keywords: chromium coating, aluminum, nanodiamond particles, electrochemical plating,

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Investigation of mechanical properties and coefficients of sound insulation of innovative silicone composite material

A new non-combustible, non-flammable, waterproof, long-lasting, heat-insulating composite material was made of glass foam granules (derived from glass waste) and a hydraulic inorganic binder in the form of a white Portland cement solution (CEM I 52.5 N), zeolite, airborne agent and water. The resulting composite is resistant to climatic temperature fluctuations, characterized by a coefficient of thermal conductivity of λ = 0.047 W/mK and is potentially applicable for the production of sound and heat insulating panels for non-bearing partition walls and external insulation of buildings. The technology for obtaining the product is in line with the current tendencies for the development of ecological productions through the utilization of waste materials and provides the opportunity to produce various standard monolith products suitable for direct use or further processing. Experimental studies of the acoustic and mechanical performance of standard experimental samples made from the developed composite material were carried out. The average sound insulation value is 30 dB. An average tensile strength of 0.036 MPa and an average compressive strength of 0.55 MPa were found.

Keywords: composites, sound insulation, soundproofing materials, heat insulating materials,

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Technological solutions to extend the operating cycle of tools and industrial machinery

One of the most significant problems that engineers and researchers face is the development of technological solutions to extend the exploitation cycle of tools and industrial machinery. The research shows there are a few possibilities to solve this problem:
1. Development of new materials of enhanced working characteristics compared to those currently used. An example of this is the introduction of new metals and alloys in the automotive industry, the mining industry, etc.

2. Preventive processing of assemblies and parts prior to their use consisting mainly in overlay welding with wear resistant layers or thermo-chemical surface treatment of the parts.

3. Recovering assemblies and parts after their resource has been depleted. This is mainly applied in the mining industry, road construction, etc. Worn-out tools are overlay welded and reused. It has been proven that the price of the recovered details is 2 to 20 times lower than that of the new ones. Moreover, it should be pointed out that the recovery saves energy and ore resources
and thus a significant environmental impact is achieved.

This study presents some technological solutions to extend the operating cycle of tools and industrial machines, and namely new types of steel, overlay welding with specially developed electrodes with nanomodifier containing coating, and thermo-chemical treatment.

Keywords: operational lifetime, new materials, overlay welding, thermo-chemical treatment,

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Development of a technology for the production of ceramic moulds with reduced thermal conductivity to control the solidification of thin-walled castings

During the project a technology of making ceramic moulds using aluminosilicate microspheres was developed. According to the developed technology, ceramic samples were used to determine thermal conductivity in the temperature range of 500°C to 850°C. In this temperature range, thermal conductivity is about 0.5 W/mK. Strength measurements were conducted using a four-point bending technique. The strength of the developed ceramics and typical ceramics made from molochite materials is similar. Computer simulations facilitated the design of experimental moulds. The recording of Al alloy cooling curves in rectangular insulated and non-insulated moulds allowed for comparison of the thermal parameters of both types of moulds (i.e. ceramics). There was also a castability test performed using the moulds with a "grille" model with 1.5 × 1.5 mm channels, which determined the effect of increased material insulation on the number of properly filled mesh of the mould.

Keywords: ceramic moulds, aluminium alloys, thermal conductivity, thin-walled castings, microspheres,

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XRD phase investigations of steam oxidized Fe and Ni rich Cr alloys

The aim of this work was to summarise XRD investigations performed after the tests carried out in steam oxidation conditions in the temperature range 700‒800°C for 3000 hours. In this work, two solid-solution strengthened alloys; Haynes® 230®, 617 alloy and two (γ’) gamma-prime strengthened alloys; 263 and Haynes® 282® and high alloyed steels rich in Cr: 309S, 310S and HR3C were exposed. The phase analyses were carried out using two techniques; Bragg-Brentano (BB) geometry and geometry of constant angle called grazing incidence α = 1° and α = 3°.

Keywords: austenitic steel, Ni based alloys, high temperature, steam, XRD,

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High temperature corrosion of metallic materials in coal fired power plant boilers

The aim of this work was to perform high temperature tests in steam conditions at 700‒800°C for 3000 hours. In this work seven alloys were studied: Cr rich austenitic steels 309S, 310S, HR3C, and two solid-solution strengthened Ni based alloys; Haynes^® 230^®, 617 alloy and two (γ’) gamma-prime strengthened Ni based alloys; 263 and Haynes^® 282^®. The obtained results suggest that the exposed materials show high corrosion resistance under steam oxidation conditions where predominantly Cr₂O₃ and MnCr₂O₄ compounds developed. The materials showed no chromia evaporation process and no exfoliation of the external oxide scale. However, two (γ’) gamma-prime strengthened Ni based alloys showed a high degree of internal oxidation that increased with temperature.

Keywords: steam oxidation, high temperature, austenitic steel, Ni based alloy,

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Cermet composite material based on aluminothermy

A new method for synthesis of cermet composite materials was developed based on aluminothermy. Employing this method a cermet composite material with a high content of AlN crystal phase was synthesized. Fine powders of aluminum and silica glass were mixed and heated in a corundum crucible for 6 hours at 1100°C in air. The X-ray diffraction analysis showed that the composite material thus synthesized contains a high concentration of AlN particles (about 33 vol. %) embedded in an aluminum silicon alloy. A small amount of Al2O3 particles (about 8 vol. %) was also found.
The method proposed can also be used for synthesis of aluminum matrix composite materials containing, besides AlN, other ceramic reinforcement phases. The properties of these composite materials can be tailored by choosing an appropriate composition of the initial powder mixture for aluminothermic synthesis.

Keywords: aluminum matrix composite, aluminum nitride, aluminothermy,

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The evaluation of microporosity and mechanical properties in high strength aluminum alloys with the use of numerical analysis and computed tomography

One of the aspects of sustainable development is the reduction of the concentration of CO₂ in the atmosphere. This could be achieved for example by the reduction of fuel consumption. That is why the research for the new construction and material solutions regarding the reduction of the weight of vehicles is so important. Alongside weight reduction of different kinds of vehicles, there is also the possibility of the application of alternative propulsion systems. The lower total vehicle weight allows to extend the lifetime of the batteries with the reduction of recharge cycles. The use of the aluminum base AlZnMgCu as cast alloy which is known as 7xxx series plastic forming alloy, allows to significantly reduce the weight of the components manufactured as cast structures, ensuring high strength properties. The wide range of the solidification temperature, which is more than 150°C, characterizes this alloy with a high tendency to create micro and macro porosity. The study presents the relationship between the cooling rate and the area of occurrence and percentage of microporosity. Obtained results were linked to the local tensile strength predicted in the simulation analysis. The evaluation of the microporosity was performed on the basis of the CT (computed tomography) and the analysis of the alloy microstructure. The microstructure analysis was carried out on a test specimen obtained from the varying wall thickness of the experimental casting. The evaluation of the mechanical properties was conducted on the basis of the static tensile test.

Keywords: AlZnMgCu alloy, microporosity, mechanical properties, computed tomography,

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Wettability, reactivity and interfaces in the Gd/TiO2 system

High-temperature interaction of liquid Gd in contact with dense, polycrystalline TiO₂ substrate, was investigated. Wettability and reactivity tests were carried out at two different temperatures (1362°C and 1412°C) in flowing gas (Ar, 850-900 hPa) using the sessile drop method and classical contact heating of the examined couple of materials. The procedure was combined with a drop pushing procedure. During high temperature studies, images of the Gd/TiO₂ couple were continuously recorded by a high-resolution CCD camera. The results of wettability tests of liquid gadolinium on titanium dioxide substrate show that the Gd/TiO₂ system is non-wettable at both test temperatures (in either case the final contact angle was 100°). The results of structure examinations on the cross-sectioned samples show the dissolution of the TiO₂ substrate in liquid Gd and the presence of two sublayers at the drop/substrate interface: Gd₂TiO₅ (from the drop side) and Gd₂Ti₂O₇ (from the substrate side).

Keywords: Gd, TiO2, sessile drop, wettability, reactivity, interfaces,

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Influence of TiN nanoparticles on the microstructure and hardness of arc overlaid welding layers

Electrodes for manual arc overlay welding with coating containing nanomodifier TiN in concentrations between 0.2% and 1.5% were developed and manufactured. Samples of welded overlay layers with electrodes were both examined by electron microscopy and X-ray microanalysis. Some samples were subjected to heat treatment consisting of annealing and subsequent hardening in water and oil. The Vickers hardness HV_15/15 of the samples in the prepared state, and both after annealing and hardening were measured. It was found that growth of the hardness of nanomodified layers were up to 180 percent compared to the reference sample.

Keywords: arc overlay welding, nanomodifiers, nanosized TiN, nanopowders, heat treatment, Vickers hardness,

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Investigation of the interaction between the CuZn38Pb2 matrix and the Fe reinforcement phase during the production of the complex relief MMCs

The present paper is relevant to the investigation of the interaction between the copper alloy metal matrix (CuZn38Pb2) and the reinforcement phase (Fe) during the production of "hybrid" complex relief MMCs. An innovative production method is used for the creation of composites that have been brought to the application of different space vacuum schemes for composite synthesis of vacuuming the space by using the notion of "capillary forming". In this method, the metal matrix (copper alloy melt) was forcedly infiltrated in the space between the reinforcement phase (Fe) particles as opposed to the classical method to obtain MMCs, uses a mechanism of insertion of the reinforcement phase into the ready for use melt, followed by homogenization of the composite structure. In this paper is presented a cost-effective production processes for metal-matrix composites by using single blanks implementing conventional methods for mould production (in expendable cement mould).
Studies were also carried out metallographic and X-ray diffraction phase analysis to clarify the phase composition and the ongoing diffusion processes due to the high temperature process of production of complex relief MMC. Microhardness of the composite phase was also measured.

Keywords: MMCs, copper alloy CuZn38Pb2, Fe reinforcement particles,

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Wetting behavior of Si-13.5B alloy on polycrystalline h-BN-based substrates

In this work, for the first time the results of an experimental evaluation of the high temperature behavior of molten Si-B alloy in contact with refractory materials at temperatures up to 1750°C, under static argon atmosphere (p = 850-900 mbar), is shown. The material investigated, having a nominal chemical composition of Si-13.5B (at. %), was fabricated by using the crucible-less electric arc-melting process assisted by the levitation drop method. The wettability of the molten alloy in contact with commercial hexagonal boron nitride (h-BN) substrates was evaluated by means of especially developed sessile drop technique combined with a contact heating procedure. It was found that both couples show a lack of wettability in the whole tested temperature range (the measured contact angle was θ > 130°). The more stable behavior in contact with molten Si-13.B alloy, evidenced by higher θ values and a lack of drop vibration during the high temperature exposition, was observed for the h-BN based composite substrate.

Keywords: silicon-boron alloys, hexagonal boron nitride, wettability, interfaces, AMADEUS Project,

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Viscous flow features of amorphous Zr65(Ni,Pd)35 alloy

Viscous flow behavior of amorphous Zr₆₅(Ni,Pd)₃₅ alloy has been studied at a heating rate of 20 K/min. The viscosity experimental results are interpreted on the basis of the free volume model. The values of the model parameters obtained are used for estimation of glass forming ability in terms of the Angell parameter, and the fracture strength of the alloys based on its correlation with the glass transition temperature.
The glass transition temperature is 663 K. The alloy Zr₆₅(Ni,Pd)₃₅ possesses excellent fracture strength of about 2.28 GPa, comparable to that of stainless steels.
The relatively good thermal and excellent mechanical properties make this alloy promising for preparing bulk amorphous samples.

Keywords: metallic glass, viscosity, glass-forming ability,

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Electrolyte coatings of chromium with nanodiamonds on sintered steels

Sintered ferrous components were coated with electrochemical chromium coatings modified with nanodiamond particles. The nanodiamond particles were produced by detonation synthesis with an average grain size 8 nm. The objective of this study was to determine the tribological properties and the corrosion resistance of sintered iron samples coated with an electrochemically deposited chromium layer modified with nanodiamond particles. The thickness of the obtained composite coatings was more than 25 μm. The microstructure and microhardness were determined by metallographic methods. The mechanical and chemical properties of the samples were compared to uncoated samples prepared from the same iron powder. The microhardness was 5 times higher, the wear resistance increased 6 times and the corrosion resistance in 0.1 M NaCl solution was 10 times higher.

Keywords: sintered products, chromium coating, wear resistance, corrosion resistance,

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A comparison of various imaging modes in scanning electron microscopy during evaluation of selected Si/refractory sessile drop couples after wettability tests at ultra-high temperature

In this work, FEI Scios^TM field emission gun scanning electron microscope (FEG SEM) equipped with a unique combination of analytical and imaging detectors was utilized to examine structure and chemistry of selected Si/refractory couples. The couples were obtained in wettability tests performed by the sessile drop method coupled with contact heating of a refractory substrate (h-BN, SiC) at ultra-high temperature (up to 1750°C). The SEM observations were carried out on top-views of the couples, in order to evaluate surface and interfacial phenomena in Si/h-BN and Si/SiC systems. A full range of available detectors (e.g. classical Everhart-Thornley detector (ETD) or advanced in-lens detectors) working under various operation modes (secondary electrons (SE), backscattered electrons (BSE), a mixed mode), were used upon analyses in order to reveal specific features of obtained structures.

Keywords: scanning electron microscopy, sessile drop method, silicon, refractories, in-lens detectors,

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Thermophysical properties of selected vermicular graphite cast iron alloy

The paper presents the results of thermophysical properties of selected vermicular graphite cast iron with nominal chemical composition of 3.70 C; 2.30 Si; 0.44 Mn; 0.054 P; 0.015 S; 0.017 Mg (wt. %). The comparative studies of the alloy were performed using differential scanning calorimetry, dilatometry and laser flash analysis. The calorimetric investigations proved that upon the heating to melting temperature (~1200°C), four endothermic transformations take place:
1) ferromagnetic → paramagnetic at 742°C, 2) pearlite → austenite at 824.2°C, 3) allotropic transformation of bcc ferrite to fcc austenite at 802°C, 4) melting at 1173.1°C. The character of the dilatometric curve shows small deviation at the temperature above 810°C corresponding to the pearlite → austenite transformation. The values of thermal diffusivity and thermal conductivity change throughout the entire examined temperature range. Both curves showed a changeover from negative to positive trends between 700 and 800°C. This effect might be associated with the pearlite → austenite transformation.

Keywords: vermicular cast iron, thermophysical properties, transformation temperatures, melting heat, thermal expansion, thermal expansion coefficient, thermal diffusivity, thermal conductivity,

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Development and manufacturing of casting technology for crawler vehicle suspension used in wetlands

The modern designing techniques and development procedures requires the use of advanced integrated methods. That kind of approach requires the involvement of series of steps which leads to the logical work stream known as Integrated Computational Material Engineering. The steps involve the design and evaluation process in the virtual environment of CAD/CAE and simulation software. The use of simulation software allows for online optimization of the shape and properties of designed part. The publication presents a design and manufacturing process of a component of the larger assembly of the chassis of heavy-duty machine. Established methodology includes the analysis of the initial geometry of the part of the heavy vehicle used in difficult wetland environmental conditions.

Keywords: CAx, computer simulations, Flow3D, Ansys, casting technology, 3D printing, aluminum casting,

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A comparison of the oxygen, nitrogen and hydrogen content in ductile iron castings and their effect on microstructure and mechanical properties

Two different spheroidization methods were compared in terms of the effect they may have on gas content (oxygen, nitrogen and hydrogen) in ductile iron castings and process efficiency.
Two methods of cast iron treatment were investigated, i.e. spheroidization in the foundry mould using a reaction chamber (reactor) developed by the Foundry Research Institute and, as a reference, the method currently used by foundry shops, i.e. spheroidization in the foundry ladle.
The effect of spheroidization process was evaluated on test castings. The results of metallographic examinations and mechanical tests as well as the results of measurements of the oxygen, nitrogen and hydrogen content in cast iron after spheroidizing treatment were presented.

Keywords: ductile iron, oxygen/nitrogen/hydrogen content, methods of spheroidizing treatment, reaction chamber (reactor),

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Tribological characterization of high porosity aluminum based composite materials

The present work aims to study the effect of the reinforcing phase on dynamic coefficient of friction and mass wear of specimen with different compositions under various friction conditions.
Porous materials with different compositions and reinforcing phase are obtained by replication method applying salt (NaCl) space holder. The reinforcing phase is Fly Ash (FA) particles. The microstructure of the obtained materials is observed and the tribological properties such as mass losses and the dynamic coefficient of friction are determined.
A comparison of the tribological properties between nominally nonporous matrix, porous matrix and porous composite are presented in this study.

Keywords: aluminum based composite materials, tribological properties, fly ash, reinforcing phase,

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High porosity fly ash/Ni/P composite produced by electroless deposition

The aim of the present study is to create a composite material possessing useful properties enabling the waste fly ash to be utilized. To obtain the final material, fly ash is subjected to separation by size and density. The innovative approach to making the composite material is the use of chemical nickel deposition by which the free particles are bonded as a solid body. Deposition of nickel was carried out by two stages: first Ni-coating of the particles and second - bonding of the particles by nickel deposition. Structure of this material is near to syntactic foam. Some properties of the obtained material as a porosity, density, and permeability with regard to its application have been investigated.

Keywords: fly ash, porosity, permeability, syntactic foam, electroless deposition,

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High-temperature interaction of molten vermicular graphite cast iron with Al2O3 substrate

The wetting behavior and reactivity between molten cast iron (originally vermicular graphite cast iron, containing in wt. %: 3.70 C, 2.30 Si, 0.44 Mn, 0.054 P, 0.017 Mg, 0.015 S) and commercial polycrystalline alumina (Al₂O₃ substrate of 99.70% purity and less than 3 vol. % porosity) were investigated. The wettability test was performed under an inert flowing gas atmosphere (Ar, 850-900 hPa) at a temperature of 1450°C for 15 min using a sessile drop method combined with classical contact heating procedure.
The high temperature interaction between molten cast iron sample and Al₂O₃ substrate was continuously recorded with a high-speed high-resolution CCD camera. The results showed that the molten cast iron does not wet the Al₂O₃ substrate (θ = 131°).
After wettability test, the cross-sectioned sessile drop couple was examined using scanning electron microscopy coupled with X-ray energy dispersive spectroscopy. It was found that in the solidified cast iron drop, the graphite phase took the shape of flakes having a different dispersion degree, i.e. vermicular precipitates of graphite did not re-grow during solidification of the drop. Moreover, structural characterization of the drop/substrate interface revealed the layer of about 26 μm thick composed mainly of carbon and located at the drop-side interface while at the substrate-side interface, the reaction zone (~70 μm) formed due interaction between Al₂O₃ and molten cast iron was well distinguished.

Keywords: vermicular graphite cast iron, Al2O3, sessile drop method, wetting kinetics, reactivity,

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