EFFECT OF RARE EARTH MATERIALS ON THE MECHANICAL PROPERTIES OF ALUMINIUM METAL MATRIX COMPOSITES

Abstract

The central objective of this thesis work is to fabricate aluminum metal matrix composite using one of the best processes named as spark plasma sintering and analyze its mechanical and metallurgical characteristics. Powder metallurgy have ever been a popular process for fabricating components of aluminum in aerospace and automobile industries. This is mainly due to its property of being light in weight in addition to sufficient strength, wear resistant, ductility etc. Powders were prepared by milling it in High Energy Ball Milling (HEBM). Six different samples were weighed with six different weight percent (Wt. %) of Nano Yttria reinforced with 2024 AA. Al (2024AA+ x* Yttria) where x= (0, 1, 2, 3, 4, 5). The powders were characterized by x-ray diffraction (XRD) and Scanning Electron Microscope (SEM). Spark plasma sintering has been used for compaction and sintering which is quite advantageous in terms of both properties and time taken. In SPS both compaction and sintering are done on the same place almost simultaneously, which is why it is less time consuming and easy to handle. The consolidation of the powders were done by Spark Plasma Sintering (SPS) with 50 MPa pressure, 450 0c sintering temperature, 500c/min heating rate and 2000c/min cooling rate. Moreover, excellent strength of composites fabricated through it is, attributed to its high heating and cooling rate. Heating is done through joule heating which enables to achieve very high temperature in a very short period of time, thus forms a number of nucleation points. This is again cooled at very high rate thus not allowing the grains grow considerably, which helps in achieving high strength of the composite we get. The matrix used is AA 2024 and the reinforcement used is yttria (Y2O3) which is a rare earth heavy material, having very good strength and plasma resistance. This is supposed to increase the strength as it gets it gets embedded between the grains and restraint them from any dislocation as a result of which its strength increases. For having complete idea about the sample a series of tests are done on samples. These are hardness testing on Vickers’s Hardness testing machine, Ultimate Tensile Strength, Yield Strength and elongation testing on universal testing machine (UTM). Also its metallurgical characterization is done on scanning electron microscope (SEM), Field Emission Scanning Electron Microscope (FE-SEM) and X-Ray diffraction (XRD). After doing all the tests its results are analyzed and reasons for a particular trend is discussed. Hardness increased by almost 30 %, ultimate tensile strength also increased by almost 25 % by addition of yttria. So the purpose of mixing reinforcement is achieved.