| || || Powder metallurgy|
| || || 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.
Subject: Powder metallurgy, Isostatic pressing
Call No.: Pac TN 695 .N272 2011
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.