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Streszczenie:
Functionally Graded Materials (FGMs) are characterized by their gradual spatial variation in composition and properties, which lead to enhanced performance under various operating conditions. Thermal conductivity plays a crucial role in the design of engineering systems where temperature regulation is crucial. This study examines the thermal conductivity of AlSi12 matrix FGMs reinforced with two types of ceramics: silicon carbide (SiC) and aluminum oxide (Al2O3). The powder metallurgy route employing two consolidation techniques (hot pressing, HP and spark plasma sintering, SPS) was utilized to produce ungraded composites and three-layer FGMs with ceramic content of 10, 20, and 30 vol%. The influence of reinforcement type and processing method (HP vs. SPS) on the thermal conductivity was analyzed from room temperature up to 300 °C. It was found that, in composites with a lower ceramic content the aluminum matrix predominantly governs the overall thermal conductivity. In contrast, porosity and interfacial compounds become the controlling factors at higher ceramic contents, particularly in the AlSi12-SiC system. Processing techniques played a crucial role in the evolution of the matrix microstructure in the considered temperature range. For AlSi12-Al2O3 composites and FGMs, HP samples exhibited higher thermal conductivity than SPS samples, due to Al grain growth and lower porosity. For AlSi12-SiC composites produced by HP and SPS, TEM analysis revealed interfacial oxide layer formation around the Al and SiC grains. These oxide layers contributed to a significant decrease in thermal conductivity of AlSi12-SiC composites at elevated temperatures. Samples fabricated via HP had higher relative densities than those produced by SPS. This is an unusual result, as the opposite is typically reported in the literature. The pivotal role of ceramic particle type and interfacial characteristics in shaping the thermal performance of AlSi matrix FGMs was confirmed.

Słowa kluczowe:
sintering, composites, thermal conductivity, Al2O3, SiC

Streszczenie:
Functionally graded metal matrix composites have attracted the attention of various industries as materials with tailorable properties due to spatially varying composition of constituents. This research work was inspired by an application, such as automotive brake disks, which requires advanced materials with improved wear resistance on the outer surface as combined with effective heat flux dissipation of the graded system. To this end, graded AlSi12/Al2O3 composites (FGMs) with a stepwise gradient in the volume fraction of alumina reinforcement were produced by hot pressing and spark plasma sintering techniques. The thermal conductivities of the individual composite layers and the FGMs were evaluated experimentally and simulated numerically using 3D finite element (FE) models based on micro-computed X-ray tomography (micro-XCT) images of actual AlSi12/Al2O3 microstructures. The numerical models incorporated the effects of porosity of the fabricated AlSi12/Al2O3 composites, thermal resistance, and imperfect interfaces between the AlSi12 matrix and the alumina particles. The obtained experimental data and the results of the numerical models are in good agreement, the relative error being in the range of 4 to 6 pct for different compositions and FGMstructure. The predictive capability of the proposed micro-XCT-based FE model suggests that this model can be applied to similar types of composites and different composition gradients.

Streszczenie:
This research on aluminum matrix FGMs was driven by an application to brake disks, which require advanced materials with improved wear resistance on the outer surface and effective heat dissipation of the graded disk. The AlSi12/Al2O3 composite layers with a stepwise gradient in the volume fraction of alumina reinforcement were prepared by hot pressing (HP) and spark plasma sintering (SPS) techniques. The thermal conductivities of the individual composite layers and the FGM specimens were evaluated experimentally and by numerical simulations using finite element models based on micro-computed X-ray tomography (micro-XCT) images of actual AlSi12/Al2O3 microstructures. An incongruity was identified between the thermal conductivity of the pure AlSi12 samples consolidated by hot pressing and spark plasma sintering. The primary reason for the disparity in thermal conductivity between the SPS and HP samples was ascertained to be the difference in grain size, as revealed by SEM analysis. The micro-XCT-based FEM simulations incorporated the effects of porosity, thermal resistance, and imperfect interfaces between the AlSi12 matrix and the alumina particles. The simulation results align well with the experimental data for various compositions and FGM structures.

Słowa kluczowe:
Aluminum-Alumina FGMs, Powder Metallurgy, Thermal Conductivity, Micro-XCT, Finite Element Analysis