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View the PDF document 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.
View the PDF document Development of densification mechanism and forming limit for sintered powder metallurgy steel under powder preform forging
Author:Narayan, Sumesh
Institution: University of the South Pacific.
Award: M.Sc.
Subject: Powder metallurgy, Isostatic pressing
Date: 2011.
Call No.: pac TN 695 .N272 2011
BRN: 1184360
Copyright:10-20% of this thesis may be copied without the authors written permission

Abstract: The purpose of this thesis is to investigate the deformation and densification behaviour of sintered plain carbon steels prepared by powder metallurgy manufacturing route. The deformation process is one of the best ways used to increase the density of the powder metallurgy materials and increasing the density of the powder metallurgy material enhances the strength and workability or formability of the material so that it can be used commercially in an efficient manner. These analyses are very important in designing of dies and part geometries. Complete experimental study on the densification, forming limit, strain hardening and workability behaviour of powder metallurgy preforms of pure iron, Fe-0.35%C, Fe-0.75%C and Fe-1.1%C were carried out. Powder preforms having initial theoretical density value of 84%, with two different 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 12000C for a holding period of 1.5 hours. In order to avoid oxidation during sintering and cooling, the entire surface of the compacts were indigenously formed ceramic coated. Two different aspect ratio of 0.4 and 0.6 were chosen for this research and the above mentioned powder metallurgy sintered steel preforms were machined to respective height-to-diameter ratio (aspect ratio). Each sintered compact was subjected to incremental compressive loading of 0.05 MN under three different lubricant conditions (frictional constraints) till a visible crack appeared at the free surface. Three different frictional constraints were chosen for this research which included dry, unlubricated dies called nil/no lubricant condition and lubrication consisting of graphite paste (i.e. graphite with acetone) called graphite lubricant condition and zinc stearate powder called zinc stearate lubricant condition.
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