Instytut Podstawowych Problemów Techniki

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Squeeze casting and powder metallurgy techniques were employed to fabricate AlSi12/Al2O3 composites, which are lightweight structural materials with potential applications in the automotive industry. The impact of the processing route on the material properties was studied. Comparative analyses were conducted for the Vickers hardness, flexural strength, fracture toughness, thermal conductivity, thermal residual stresses, and frictional wear. Our results show that the squeeze cast composite exhibits superior properties to those obtained using powder metallurgy.

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This investigation examines the problem of homogenization in metal matrix composites (MMCs) and the methods of increasing their strength using severe plastic deformation (SPD). In this research MMCs of pure copper and silicon carbide were synthesized by spark plasma sintering (SPS) and then further processed via high-pressure torsion (HPT). The microstructures in the sintered and in the deformed materials were investigated using Scanning Electron Microscopy (SEM) and Scanning Transmission Electron Microscopy (STEM). The mechanical properties were evaluated in microhardness tests and in tensile testing. The thermal conductivity of the composites was measured with the use of a laser pulse technique. Microstructural analysis revealed that HPT processing leads to an improved densification of the SPS-produced composites with significant grain refinement in the copper matrix and with fragmentation of the SiC particles and their homogeneous distribution in the copper matrix. The HPT processing of Cu and the Cu–SiC samples enhanced their mechanical properties at the expense of limiting their plasticity. Processing by HPT also had a major influence on the thermal conductivity of materials. It is demonstrated that the deformed samples exhibit higher thermal conductivity than the initial coarse-grained samples.

Słowa kluczowe:

copper, silicon carbide, high-pressure torsion, spark plasma sintering, thermal conductivity

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Aluminum-alumina composites with interpenetrating network structure are interesting structural materials due to their high resistance to elevated temperature and frictional wear, good heat conductivity, enhanced mechanical strength and fracture toughness. In this paper aluminum-alumina bulk composites and FGMs are manufactured by pressure infiltration of porous alumina preforms with molten aluminium alloy (EN AC-44200). Influence of the interpenetrating microstructure on the macroscopic bending strength, fracture toughness, hardness and heat conduction is examined. Special focus is on processing-induced thermal residual stresses in aluminium-alumina composites due to their potentially detrimental effects on material performance in structural elements under in-service conditions. The residual stresses are measured experimentally in the ceramic phase by neutron diffraction and simulated numerically using a micro-CT based Finite Element model, which takes into account the actual interpenetrating microstructure of the composite. The model predictions for two different volume fractions of alumina agree fairly well with the neutron diffraction measurements

Słowa kluczowe:

A. stress measurements, X-ray analysis, finite element analysis, B. composites, C. casting methods

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This review paper deals with flaws in aluminum–alumina composites and FGMs induced by their manufacturing processes. Aluminum–alumina composites have been studied for many years as potentially interesting materials for applications, for example, in the automotive sector due to their enhanced mechanical strength, wear resistance, good heat conductivity and low specific weight. The focus here is on the interpenetrating phase composites (IPCs) manufactured by infiltration of porous alumina preforms with molten aluminum alloys. The primary objective is to provide an updated overview of research findings on a variety of flaws occurring at different stages of the manufacturing processes. Some precautions on how to avoid processing induced flaws in aluminum–alumina bulk composites and FGMs are mentioned.

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Streszczenie:

In this paper the influence of material microstructure and thermal residual stresses on the macroscopic fracture toughness, Young’s modulus and bending strength of metal-ceramic composites is studied.
The investigated materials were: (1) Cr/Al2O3 composites (MMC and cermets) with various proportions of the starting powders prepared by hot pressing, and (2) Al2O3/Al infiltrated composites with different volume fractions of the aluminium phase. The two groups of composites (particulate vs. infiltrated) were chosen to examine the effect in question because of their significantly different microstructure.
In the case of hot pressed Cr/Al2O3 composites local thermal residual stresses are generated during cooling from the sintering temperature to RT due to number of factors such as (i) differences in the coefficients of thermal expansion of the ceramic and metal phase, (ii) differences in cooling speeds in different parts of the material, and (iii) irregular shapes of pores causing stress concentrations.
The same problem of formation of thermal residual stresses occurs in the infiltrated Al2O3/Al composite with metal and ceramic phases forming spatially continuous networks throughout the structure (also called Interpenetrating Phase Composites, IPCs).
The fracture toughness and bending strength measurements were performed in a four-point bend test on SEVNB specimens. The microstructural characterization and crack growth analysis were done using scanning electron microscopy.
Our results show that the fracture toughness and other mechanical properties investigated in this study strongly depend on such microstructural features like the amount and distribution of metal and ceramic phase and the type of microstructure (particulate vs. infiltrated). On the other hand the stiffness of reinforcement and matrix, the volume fraction and the grain size of the reinforcement, difference in grain sizes between matrix and reinforcement have an effect on thermal residual stresses distribution, which in turn have an effect on the macroscopic fracture parameters and the crack growth path.

Słowa kluczowe:

thermal residual stresses, mechanical properties, powder metallurgy, interpenetrating phase composites

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