Nanoindentation behaviour of aluminium based hybrid composites with graphite nanofiber/alumina short fiber

Nanoindentation was performed on Al based hybrid composites containing graphite nanofiber/alumina short fiber. Measurement of hardness and elastic modulus were carried out using the continuous stiffness method (CSM) with an indentation depth of about 2000 nm. To find out the hardness and moduli of the composites at various local regions, nanoindentation tests were carried out in different locations of the sample. In all cases, the measured values for hardness and modulus are a mixture of the effects of the presence of the graphite nanofiber (GNF) and alumina short fiber (Al2O3sf) and of the precipitation phases in the Al matrix. Moreover, the large number of dislocations in the plastic zone formed in the indented region of the GNF contributes to an increase in values of both modulus and hardness. The enhancement of indentation properties of the Al matrix is attributed to the possible indentation on the Al4C3 phase or MgAl2O4 precipitate. The hardness values and material pile-up are also shown to depend significantly on the mismatch between the moduli of the Al matrix and reinforcements.