Investigation on the properties of iron powder subjected to an explosive pressing using emulsion explosive (Emulex)

Powder metallurgy method is one of the important techniques used in industry to compacted a powder to a solid metal. To achieve the maximum density and hardness by using powder metallurgy technique, some additive such as nickel and aluminium powder or lubricant are used to increases the compressibility and reduces the release force, so it is difficult to reach high density and high hardness in powder metallurgy using only one type of powder without any addictive of lubricant or other material. The main problem of the compaction of powder is the formation of crack on the surface of specimen. Thus, an alternative method is by using explosive pressing. The aim of this research is to investigate the properties of iron powder subjected to an explosive pressing method using emulsion explosive (Emulex). The type of explosive used is emulsion explosive (Emulex) with charge weight of 100 g, 250 g, 500 g, 750 g, 1000 g and 1250 g with a mass ratio of explosive to mass of plunger add mass of powder of 0.11, 0.27, 0.55, 0.82, 1.10 and 1.38 respectively. The explosive is molded into shape charge to give more pressing energy. The underground explosion is conducted since confined space can give more blast energy. Iron powder without any addictive of lubricant or other material is used in this research. Green compact is sintered at 1000℃ to strengthen the bonding between particles. The density of iron compact is calculated before the sintering process. Analysis of compact powder microstructure is performed using scanning electron microscope (SEM). Then, hardness of compact powder is tested using Rockwell Digital Hardness. The result shows that, the iron compact is fully compact and there is no formation of crack. There is no formation of crack on green compact is due to non-added of any addictive such as lubricant or other material in the iron powder. The improper material composition was one of the causes of formation of crack. Besides, the used of emulsion explosive (Emulex) with 4500 𝑚⁄𝑠 detonation velocity had reduced the formation of crack because low detonation velocity is used. The highest pressing force obtained from this experiment is 357.308k Tonne. The theoretical maximum density result for iron compact without any addictive of lubricant or other material using explosive pressing method is 94.40%, while the theoretical maximum density result for addition of aluminium and iron powder using powder metallurgy method is 94.55%. The highest hardness obtained for iron compact is 50.3 HRA. Microstructure results show lesser porosity and there are a presence of cold welding and mechanical interlocking phenomena at surface of specimens since the grain boundaries is less visible. This research shows that it is possible to produce high density and high hardness of compact powder using explosive pressing method. It shows that, as the explosive ratio increased, the pressing force increased which caused to high hardness and high density of specimen. The density of specimen increased with decrease of pores and growth of cold welding and mechanical properties effects. Thus, specimen gain strength with enhanced resistance to deformation after the pressing force was applied.