Microhardness and Indentation Fracture of Potassium Dihydrogen Phosphate (KDP) |
| |
Authors: | Tong Fang John C Lambropoulos |
| |
Affiliation: | Crystal Technologies, Palo Alto, California 94303;Department of Mechanical Engineering, Materials Science Program, Center for Optics Manufacturing, and Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14627 |
| |
Abstract: | Potassium dihydrogen phosphate (KDP) is an important electrooptic tetragonal crystal, often used in third harmonic generation in laser systems. We have used microindentation to measure the Vickers and Knoop hardness of KDP and the resulting cracking on (100) and (001) faces. Hardness anisotropy on the (001) face, or among the (100) and (001) faces, was small (∼20%). We observed an indentation size effect for both Vickers and Knoop hardness, for indenting loads in the range 0.24–1.96 N. The large-load Vickers hardness was estimated as 1.4 ± 0.1 GPa. We observed anisotropy in the crack sizes on (100) and (001) faces. Cracks were longer on (100) faces than on (001) faces. Assuming elastic and plastic isotropy, crack sizes were analyzed, and fracture toughness, Kc , was extracted. We present here an approximate model for analyzing crack-load microindentation data in tetragonal crystals. The model uses the minimum elastic modulus of the material. The effect of the isotropic assumption on the extracted fracture toughness is estimated at ∼33%, with a 23% contribution resulting from elastic anisotropy and 10% from the slip-system plastic anisotropy. |
| |
Keywords: | fracture hardness optical materials/properties potassium/potassium compounds |
|
|