Ageing behaviour of spray-deposited 18Ni(250) maraging steel + 10 vol.% Al2O3 particulate-reinforced metal matrix composites

The ageing behaviour of spray-deposited 18Ni(250) maraging steel+10 vol.% Al2O3 particulate-reinforced metal matrix composites (MMCs) was investigated by microhardness and nanoindentation techniques. Compared to the control steel, the composite material showed an accelerated ageing kinetics. Nanoindentation investigation revealed observable gradient distribution of elastic modulus and hardness around Al2O3 particulates inside the plastic zone in the matrix. Around a reinforcement particulate, the gradient distribution of the properties is steeper at the sharp corner than that at the flat interface. Theoretical Avrami-type precipitation model was successfully modified to calculate the distribution of precipitates around an Al2O3 particulate. The calculation results showed a gradient distribution of precipitates similar to the experimentally measured distribution of elastic modulus and hardness, which can attributed to the gradient distribution of dislocations within the plastic zones around the reinforcements.