Densification and plastic deformation under microindentation in silicate glasses and the relation to hardness and crack resistance

To quantify and study the densification and plastic deformation under Vickerʹs indentation we prepared a series of simple soda-lime-silicate glasses with different modifying ion contents and four glasses with constant silica content but potassium and/or barium substituted for sodium and/or calcium. The densification and plastic deformation in these glasses were determined using atomic force microscopy (AFM) by measuring each sample twice, i.e., once immediately following indentation, and once after annealing to relax the densified volume. The results show that the densified volume of the glasses decreases approximately linearly with the bulk modulus, and the plastic deformation volume with silica mole fraction. These results have important implications in the prediction of hardness and crack resistance (i.e. load for crack initiation) from composition.