Investigation of mechanical properties of granular γ-alumina using experimental nano indentation and nano scratch tests

Abstract

The mechanical properties of ceramic granular γ-alumina, including resistance and stability, are examined using Nano indentation and Nano scratch tests. In so doing, surface morphology, kind of material used, topography, and roughness of the surface of the granular ceramic are evaluated using a scanning electron microscope, energy-dispersive X-ray spectroscopy and atomic force microscopy. To achieve these objectives, the initial step involves the synthesis of granular γ-alumina ceramic nanoparticles with average diameters of 1.7 mm. Moreover, the elasticity modulus and hardness of granular γ-alumina are estimated using a Nanoindentation method under different loads. It is shown that the nanoparticles in this coarse material are about 17 nm on average. Besides, the results demonstrate that the modulus of elasticity and hardness do not follow a particular pattern when the load increases. In other words, the modulus of elasticity increases and then decreases but the hardness decreases and then increases within the load ranges of 200–400 μN. Overall, it is concluded that the modulus of elasticity and hardness of granular γ-alumina are obtained to be equal to 12.6 GPa and 0.433 GPa, respectively. The plasticity index of granular alumina is also examined, and the results show that it is highly plastic with a plasticity index of 0.83. Also, nano scratch tests are performed under two different forces to obtain the scratch resistance of granular γ-alumina. The results reveal that the scratch resistance which is a representative of the friction coefficient, surges from 0.72 to 0.9 by increasing the indenter force. In general, the results indicate that the method of creating the material leads to a doubling of its Young's modulus, which is a measure of its stiffness, and as a result, there is a notable improvement in its overall mechanical strength.