Hardness indentation size effect of KDP crystals for ultra-precision machining surface

Potassium Dihydrogen Phosphate (KDP) is a non-linear optical material used for laser frequency conversion and electrooptic modulators. KDP has several weak points such as soft, brittle and deliquescent from the machining point of view, it is typically diamond machined. In this paper, the near-surface mechanical properties have been investigated in detail, Vickers Hardness of KDP crystals on (001) and (100) plane is also examined under different loads, then the influence of the indentation load on Vickers hardness and crack length are analyzed systematically, the Vickers hardness measurement of KDP crystals shows the indentation size effect, according to which the hardness increases as the indenting load is diminished.