Changes in the mechanical properties of irradiated MgO(1 0 0) crystals investigated by nanoindentation and computer simulation

This paper presents a nanoindentation study of MgO(1 0 0) crystals by experiment and molecular dynamics simulations. The MgO crystals are Ar+ irradiated up to a fluence of 1020 Ar+/m2. The materials are compared both before and after irradiation by nanoindentation confirming an increase in hardness but not in the indentation modulus with increasing dose. The experimental and simulation results also indicate that radiation induced defect pinning decreases the dislocation mobility to increase hardness and to cause the material to become less brittle. Molecular dynamic simulation studies confirm the experimental observation for non-irradiated magnesia of pop-in events and slip occurring in the (1 1 0) planes which can result in pile up patterns after indentation which are dependent on crystal orientation. The slip systems can cause the injection of half planes into the upper layers, that often retract after tip removal. This feature can be attributed to the formation and partial recombination of nanocracks.