This work presents an energy-efficient, cheap, and rapid production method of a metal–ceramic preform with open porosity suitable for liquid metal infiltration and filtration applications. It is based on cold isostatic pressing of a mixture of relatively hard Ni and Al2O3 powders with the addition of small amount of Al powders, acting as a binding agent. Open porosity is primarily controlled by Al2O3 particles partially separating Ni particles from mutual contacts. Cold isostatic pressed green compacts were subjected to thermal oxidation by heating in air to 600 °C, 700 °C, and 800 °C. The weight gain and open porosity of oxidized compacts were examined. The chemical composition and microstructure were analyzed by SEM-EDS and XRD techniques. The stability of preforms and the effect of thermal cycling on the open porosity were tested by thermal cycling in an inert Ar atmosphere in the temperature range up to 800 °C. It appeared that, in addition to NiO being an expected product of oxidation, Ni aluminides and spinel particles also played an important role in inter-particle bonding formation. Ni-NiO porous composites resist chemical corrosion and exhibit structural and chemical stability at higher temperatures and admixed Al2O3 particles do not deteriorate them. After subsequent infiltration with Al, it can offer a lower density than other materials, which could result in lower energy consumption, which is highly needed in industries such as the automotive industry.

The performance of attractive Ni-based composites can be affected by changing their microstructures, e.g., introducing pores. Here, we report a novel, relatively low-cost process to fabricate Ni/Al2O3 composites with open porosity modified by the size of Al2O3 particles. The mixture of powders was subjected to thermal oxidation twice in air after a maximal temperature of 800 °C was reached in a stepwise manner and maintained for 120 min. The oxidation kinetics were determined thermogravimetrically. The open porosity was evaluated by an Archimedes’ principle-based method. Localization and quantification of NiO, newly formed on the Ni particle surface and acting as a mechanical bonding agent, were explored by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffractometry. Larger ceramic particles prevented merging of NiO layers on adjacent Ni particles more efficiently; therefore, the open porosity increased from 21% to 24.2% when the Al2O3 particle diameter was increased from 5–20 µm to 32–45 µm. Because both Ni/Al2O3 composites exhibited similar flexural strength, the composite with larger Al2O3 particles and the higher open porosity could be a better candidate for infiltration by molten metal, or it can be directly used in a variety of filtration applications.

In the present study, the different approach of metal reinforcement particles addition was studied. Aluminum matrix composite (AMC) with 5 % alumina (alpha-Al2O3) reinforcement was prepared via stir casting method, using various casting temperature, stirring speed, and stirring time. As a source of reinforcement, alumina master alloy with a high concentration of alumina particles (50 %) prepared through gas pressure assisted infiltration (GPAI) was distributed during stirring. Distribution of the particles and structural characterization dependence on processing parameters were examined Electron microscopy (SEM, TEM) was used for complex visual investigation of the distribution of dispersed particles and to quantify the degree of disintegration of the alumina master alloy after the casting process. To show the effect of the uniformity of the particle distribution on mechanical properties, uniaxial tests were performed after extrusion. Results show an increase in strength of the stir cast composites is in agreement with the particle distribution measurement (cluster size). The highest UTS values are achieved for composites with the lowest values of the remaining clusters.

Cu/ZrB2 and CuCr1Zr/ZrB2 composites were prepared by gas pressure infiltration technology.The ZrB2 powder was used as reinforcement.No interfacial reaction took place for Cu, or CuCr1Zr matrix as confirmed by transmission electron microscopy (TEM).The thermal stability of composites was very good, i.e. without any indication of possible disintegration.Composites exhibit high structural stability when subjected to 5 consecutive heating/cooling cycles to 800 • C. Maximums of relative elongations recorded for particular heating/cooling cycles slightly increased for Cu/ZrB2 composite and slightly decreased for CuCr1Zr/ZrB2 composite.However, the differences are negligible.K e y w o r d s: Cu-ZrB2

Composite materials based on Cu matrix have a wide range of applications because of their extraordinary features such as high thermal conductivity and high mechanical strength. The preparation of Cu-ZrB2 and CuCr1Zr-ZrB2 composites via gas pressure infiltration technology is described in this work. In contrast to most ceramic materials, ZrB2 is electrically and thermally conductive. All tested samples, i.e. prepared from the ZrB2 porous preform with a porosity of 40% were infiltrated with molten Cu or CuCr1Zr alloy. Microstructure and homogeneity after infiltration were examined by SEM-EDS microscopy. The interface between the Cu matrix and ZrB2 ceramics was explored by TEM microscopy. As-infiltrated composites were thermally cycled up to 800 degrees C with heating and cooling rates of 3 degrees C min(-1) in an argon atmosphere.

The Ni-NiO skeleton seems to be a good candidate for various applications in industry such as corrosion-proof filters or components in refrigerating systems and as preforms for reactive infiltration with molten metals.The present work was focused on preparation of Ni-NiO composite with higher, controlled porosity. Sintering of pure Ni powder always leads to a substantial closed porosity in almost whole sample volume [1,2]. To eliminate this, we added Al 2 O 3 particles with diameter of-32 +20 μm into the Ni powder (-75 +45 μm diameters) and sintered this loose powder mixture (Ni + 25 vol. % Al 2 O 3 ) in air by progressive heating up to 800 °C followed by 2 hours isothermal exposure. As a control, pure Ni powder was sintered under the same conditions. Thermal oxidation of loose powder samples performed in alumina crucible indicates that the strongest oxidation occurred in the top part of sample, while the bottom part was the least oxidized. Therefore, it was necessary to run the thermal oxidation once more, but out of the crucible, to ensure the sufficient diffusion of oxygen to the whole volume of sample.

Cu/ZrB2 composite was prepared by gas pressure infiltration of molten metal into ceramic preform. Microstructure and erosion resistance of composite was investigated. The microstructure was analysed by light microscopy and scanning electron microscopy. The chemical compositions were analysed using energy dispersive X-ray spectroscopy. Good penetration of copper along the grain boundaries of the 60% porosity sintered ceramics was analysed in the whole volume of composite. The interfacial morphology shows the regular interfaces without any macroscopic reactions [1]. Cu/ZrB2 composite was subjected to 60 spark discharges to investigate the ablation resistance. Linear dependence of the amount of loss material on the number of electrical discharge analytical cycles for Cu/ZrB2 composite was determined.

Two types of aluminium metal matrix composites (Al-MMCs) were prepared by cold spray process. The first Al-MMC was reinforced with granite rock and the second was reinforced with limestone rock particles. Al powder and rock powders (granite or limestone) were mixed to homogeneous mixtures and sprayed onto the Al substrate. The microstructure of as-sprayed composites was compared with microstructure of MMCs reinforced with commercially available Al2O3. The microstructures of Al-MMCs reinforced with granite and limestone were affected by hardness of rocks, particle sizes and compositions of the mixture. The coating is formed through high velocity impact of solid powders. The diameter of Al powder was about 30 μm and diameters of rock powders were from 5 to100 μm. Rock particles are distributed uniformly through the coating, maintaining their irregular morphologies. However, some large sized particles cracked and fragmented. The powder porosity was approximately 2.3 % for both types of Al-MMCs. Porous microstructure leads to lower critical velocity. The results indicate that, introducing irregular morphologies and/or pores into the feedstock. High quality metallic coatings can be more easily deposited by cold spray.

Pressure-assisted reactive infiltration of Mo wire preforms with molten silicon was tested in order to prepare compact and void-free Mo/Mo suicide composite. It appears that when Mo silicides were formed in a stressed condition, the porosity and extensive cracking could be suppressed. Relatively compact samples were prepared. The cumulative failure mode was recorded during bending tests, and the excellent oxidation resistance had been confirmed by TO measurements.

The aim of the work is to study interface formation between Al2O3 particles and Al(Ca) matrix in dependence of Ca content. Aluminium matrix composites (AMC) subjected to investigation were prepared by gas pressure assisted infiltration of alumina beds with aluminium-calcium alloys. It is shown that alumina particles in the AMC are covered with a monocalcium aluminates layer whose coherence increases with increasing amounts of Ca in the aluminium-calcium alloys. Moreover, Al4Ca intermetallic phases are formed with increasing Ca content and interconnect alumina particles. XRD confirms the presence of both CaAl2O4 and CaAl4O7 ternary phases. However, HRTEM analysis confirmed CaAl2O4 with a rather complex structure containing a high density of stacking faults. It appeared that annealing at 735°C does improve consistency of interface for Al 2wt.%Ca/Al2O3 AMC, but do not affect the thickness of the interface in dependence on annealing time.

The ablation resistance of Cu and Cu/Al2O3 subjected to 200 spark discharges was compared in this work. It appears that the volume lost in the course of sparking was 6 times higher for Cu than for Cu/Al2O3 composite. Linear dependences of the amount of loss material on the number of electrical discharge analytical cycles for Cu/Al2O3 composite material and pure copper were determined. Cu/Al2O3 composite failure mode includes the evaporation as well as melting of constituents. The interaction of spark with the substrate is quite a discrete process strongly affected by local chemistry (composition). It results in irregular phases with respect to morphology as well as composition. K e y w o r d s: ablation resistance, copper matrix, alumina preform

The interface and thermal expansion behaviour of magnesium matrix composite (Mg-2Al) unidirectionally reinforced with continuous high modulus and high thermal conductivity carbon fibres Thornel K1100 prepared by gas pressure infiltration technique was studied. The structure of the fibre-matrix interface was analysed using light microscopy, SEM, EDS, and TEM. Composite samples were subsequently thermally cycled at the heating/cooling rate of 3 degrees C min(-1) in the temperature range of 30 to 350 degrees C in an argon atmosphere to reveal their thermal expansion behaviour.

The work is focused to prepare Al based master-alloy pellet with 50 vol.% of Al2O3 for subsequent manufacturing of aluminum matrix composites with desired amount of reinforcement (5-20%). Since master-alloy is manufactured via pressure infiltration and proper interface between particles and melt is required for uniform particle distribution within the melt, fundamental correlation between parameters of pressure infiltration and quality of the Al/Al2O3 interface is revealed in this study. Standard observation techniques as 3-D computed tomography (CT), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) are used for structural characterization. Drop test was used to estimate effect of time, temperature, annealing of Al2O3 and its type on the wettability of Al2O3 with Al. Differential scanning calorimetry (DSC) and thermogravimetry (TG) were used to study changes within the Al2O3 prior infiltration. Stir casting was used to prepare the final composite and dynamical mechanical analysis (DMA) was used to estimate the Young's modulus of as-cast composite. The proper infiltration parameters was defined in this work and it were shown that the infiltration temperature and pressure have direct correlation on the interface between particle and aluminum. (C) 2014 Elsevier Ltd. All rights reserved.

Mg and Mg-Li matrix composites were prepared by the melt infiltration of fibrous preform consisting of Saffil alumina fibers and the silica binder. During this process there has occurred decomposition of silica binder and/or surface silica film by displacement redox reactions and the reaction products were characterized using SEM, TEM, SAED, FTIR and XPS techniques. The only reaction products found in Mg infiltrated Saffil preform were MgO and Mg2Si. In Mg-Li melt infiltrated Saffil preform there was found besides MgO and Mg2Si also the non-crystalline phase that appears to be the lithium silicate xLi(2)O center dot ySiO(2). Binary lithium silicides and ternary magnesium-lithium silicides were not detected.

Tungsten as refractory material and high thermal conductive carbon fibres are promising candidates for production of copper matrix composites for high temperature applications. Three types of rod-like samples were prepared by gas pressure infiltration of different carbon/tungsten fibre preforms with copper and/or copper alloy (Cu-0.5Cr) respectively. The fibres are aligned parallel to rod axis and were combined with the tungsten wire cloth. The microstructure of prepared hybrid composites was examined. The samples were thermally cycled 3 times up to 550 °C at a relatively high heating/cooling rate (10 K/min) to touch real condition in applications where high heat is formed during short time. The thermal expansion behaviour in radial direction was also analysed. Results show that a combination of both types of reinforcements in rod-shapes samples insures good protection against composite disintegration during high temperature thermal loading.

Reactions during compaction of Mo/Mo suicide wires with Ni interlayers are qualitatively assessed in this work. It appeared that due to extreme high temperature strength of MoSi2 hot pressing even at 1800 degrees C/60 min/30 MPa in vacuum had not been sufficient to compact the Mo/Mo suicide wires in the absence of any additional interfacial layer. Therefore Ni had been chemically coated on the surface of Mo/Mo suicide wires that were subsequently compacted by hot pressing. Structural analysis revealed the reaction between Ni and MoSi2 resulting in the formation of ternary (MoNiSi) compounds. These established an interfacial bonding with minimal porosity.

The thermal expansion behaviour of Cu-1Cr/C composite subjected to 5 thermal cycles in the temperature range 30 - 1000 °C was investigated. The coefficients of thermal expansions (CTEs) as low as 0.7 x 10-6 K-1 in longitudinal and as large as 24.0 x 10-6 K-1 in transversal direction were obtained. Electron microscopy observations confirmed the high structural stability of the thermally cycled composite as no signs of disintegration were observed within the applied thermal cycling conditions.

The effect of atmosphere on microstructure and formation of new phases during the reaction synthesis in Ni-Al green compacts was studied. The green bodies were prepared by uniaxial double action compression of Ni + 34 vol.% Al powders. The reactions in compacts during their heating to 660 degrees C and isothermal exposure for 8 h at 800 degrees C in air and argon atmospheres were monitored by DTA. Weight increase of oxidized samples determined by TO curves followed parabolic behaviour. This agrees with a diffusive character of thermal oxidation of metals. Heating in argon revealed the strong exothermic reaction represented by a sharp peak in DTA curve close to the melting temperature of Al. The exothermic reaction in the air takes place as well, however, it is spread over a wider temperature interval. Microstructures of samples were analysed by SEM, EDS and XRD. After 8 h of isothermal exposure at 800 degrees C in argon Ni3Al and NiAl intermetallic phases appeared whereas after the thermal treatment in air NiO and NiAl phases were predominantly formed. The unreacted Ni was determined after both types of treatments as well. The analysis of the compacts revealed that the applied thermal treatment in the air significantly improved the interparticle bonding providing thus the required structural integrity of Ni-Al compacts.

Cu-0.2Cr/Granoc composite was prepared by gas pressure infiltration of molten metal alloy into fibre preform in laboratory autoclave. Rod like carbon fibre preform was manufactured from Granoc ® XN-100 high modulus short C fibres with the length of 1 mm via their disintegration and subsequent sedimentation in polyvinylalcohol solution. The fibres were randomly oriented in planes parallel to the x,y directions (in-plane); z-direction is perpendicular to this plane. Thermal diffusivity was measured by means of the flash method and thermal conductivity (TC) was calculated using values of density and specific heat of composite. All measurements were performed at room temperature on disc shaped composite samples with the diameter of 10 mm and the thickness of 5 mm. The TC of composite exhibits anisotropy. TC in z-direction as high as 259.0 Wm -1 K -1 and in-plane as high as 292.0 Wm -1 K -1 were determined. The influence of Cr addition on the TC of four copper alloys (Cu-0.1Cr, Cu-0.2Cr, Cu-0.5Cr and Cu-1Cr) was also determined.