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|  | Aluminium metal matrix composite under the influence of high strength carbide particles addition
Author: Narayan, Sumesh
Institution: University of the South Pacific.
Award: Ph.D.
Subject: Metallic composites, Aluminum alloys
Date: 2016
Call No.: Pac TA 481 .N37 2016
BRN: 1208307
Copyright:10-20% of this thesis may be copied without the authors written permission
Abstract: The purpose of this thesis is to investigate the workability behavior of aluminium metal matrix composites prepared by powder metallurgy manufacturing route. The performance of carbide reinforced aluminium metal matrix composites (MMC’s) is studied in this investigation. The selected carbides in this study are titanium carbide, iron carbide, molybdenum carbide and tungsten carbide. Powder metallurgy manufacturing process is more ecological than many other industries, as it does not releases harmful gasses and pollutants in the atmosphere and uses re-cycled materials. However, one of the main concerns of this manufacturing route is the porosity left after the sintering process seriously affecting the strength of the material. Complete experimental study on the densification, workability behavior and forming limit of powder metallurgy preforms of pure aluminium, Al-1TiC, Al-2TiC, Al-3TiC, Al- 4TiC, Al-1Fe3C, Al-2Fe3C, Al-4Fe3C, Al-6Fe3C, Al-1Mo2C, Al-2Mo2C, Al-3Mo2C, Al- 4Mo2C, Al-1WC, Al-2WC, Al-3WC and Al-4WC were carried out. Powder preforms having initial relative densities of 0.82 and 0.86, with three height-to-diameter ratios (aspect ratios) were prepared using a suitable die–set assembly on a 1 MN capacity hydraulic press. Sintering operation was carried in an electric muffle furnace at the temperature of 594 oC for a holding period of one hour. Three aspect ratios of 0.2, 0.4 and 0.6 were chosen for this research and the above mentioned powder metallurgy sintered aluminium preforms were machined to respective height-to-diameter ratio. Hot upsetting was carried out at the sintering temperature immediately after the sintering process and the forming process was stopped once visible cracks were seen on the free surface. Flat dies on the upper and lower surface were employed under dry friction conditions during hot upsetting. The hot densification mechanism in forming of aluminium metal matrix composites is developed. The effect of carbide, its concentrations, preform geometry and initial relative density on the aluminium metal matrix composite’s densification during hot deformation is evaluated and presented in this work. iv Workability characteristics of the aforementioned sintered powder metallurgy aluminium composites is established by studying under triaxial stress state condition the behaviour of densification, axial stress, hoop stress, hydrostatic stress, effective stress and formability stress index against axial strain. Further, attained density is considered to establish formability stress index and various stress ratio parameters behavior. Further, the influence of preform geometry and initial relative density on the workability behavior was analyzed and presented in this research work. It was found that the amount of carbide particles in the composite material shows significant effect on the relative density, respective stresses, workability and the formability stress index. An efficient way to find the workability limit for powder metallurgy parts has been suggested. Oyane’s fracture principle was used to develop a theory to study powder metallurgy compacts. A least square technique was used to determine the constants in fracture criteria and these equations finally used to find workability limit. It is found that the projected technique was well in agreement with the experimental values. Further, the hot formability behavior of aluminium metal matrix composites using two key strain hardening parameters are studied to determining the failure zone. Further, a galvanostatic pulse technique was used to determine the corrosion behavior of sinter-forged aluminium composites alongside microstructure studies to expose corrosion dynamics and presented in this report. It is strongly noted that this technique can be successfully used for such studies.
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