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Abstract:
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.

Abstract:
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.

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