Investigation on multi-layerd aluminium-aluminium oxide functionally graded materials prepared through powder metallurgy and pressureless sintering / Maziyana Binti Marzuki

Faculty of Manufacturing and Mechatronic Engineering Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang – 2024

Includes bibliographical references

Functional Graded Materials (FGMs) refer to the class of advanced composite materials that are specifically designed to solve the problems of integrating different materials with different properties and solving the problems between particles by reducing the concentration of stress between adjacent layers. In this research, the combination of metallic phase which are aluminium (Al), and the ceramic phase are aluminium oxide (Al2O3) in Al-Al2O3 graded composite materials are investigated because of the mismatch of their thermal properties. The main objectives of this research is to investigate the defects and failure such as decohesion, delamination and crack that might occur during processing influenced by sintering parameters on radial shrinkage, micro-hardness and microstructure of Al-Al2O3 graded structure. The multilayered of AluminiumAluminium Oxide (Al-Al2O3) samples were designed and fabricated through powder metallurgy and pressure-less. The seven graded interlayers, with respect to the Al wt. % are 100, 95, 90, 85, 80, 75 and 70 wt. % respectively for seven layers and for five graded interlayers, with respect to the Al wt. % are 100, 95, 90, 85 and 80 wt. % respectively for five layers. For each FGMs sample, the sintering time were varied 4 hours and 5 hours to compare the physical properties and microstructural evolution of the fabricated samples. The Al-Al2O3 FGMs have been analyzed to find out the effect of sintering condition on shrinkage, micro-hardness, and microstructure. From the result of experimental study hardness of Al-Al2O3 FGM increasing as the sintering time, it give most significant roles during processing. Meanwhile, the shrinkage behavior in all samples increased as the composition of ceramic Al2O3 increase. So, the shrinkage of sample structure and hardness of Al-Al2O3 FGMs depending upon the sintering time. From the microstructural analysis of Al-Al2O3 FGMs, it was found that uniform distribution of Al2O3 ceramic particle in the Al matrix in seven layers and also for five layers mixed composition with minimum agglomeration. Meanwhile, the distribution of Al-Al2O3 in each layer as well as parallel interface showed that proper blending and pressing process had been done. The uniformities structure of FGMs sample were supported by the Energy Dispersive XRay Spectroscopy (EDS) analyses. Micrograph of Field Emission Scanning Electron Microscopy (FESEM) further prove the analyses presences of micro pores and micro cracks especially in Al2O3 rich structure. It can be concluded that all the chosen conditions such as temperature, time and profile play a major role as the micrograph shows the improvement in the distribution, size of the pores and the interface layer with almost straight and parallel lines instead of wavy lines. As for the hardness values, the experimental results indicate that a three-step sintering profile with a duration of 5 hours yields higher hardness values in the samples. Specifically, samples with 5 layers achieved a hardness of 41.7 HV, while those with 7 layers reached 51.4 HV. Meanwhile, a twostep sintering profile maintained for 4 hours resulted in hardness values of 38 HV for 5- layered samples and 45.35 HV for 7-layered samples. In a three-step profile sintering, the good distribution of particle can be seen with less pores and less agglomeration than twostep sintering profile