Subsurface Damage in Scratch Testing of Potassium Dihydrogen Phosphate Crystal

摘要

Potassium dihydrogen phosphate(KDP) is an important electro-optic crystal, often used for frequency conversion and Pockels cells in large aperture laser systems.To investigate the influence of anisotropy to the depth of subsurface damage and the profiles of cracks in subsurface of KDP crystal, an experimental study was made to obtain the form of subsurface damage produced by scratches on KDP crystal in 100, 120 and 110 crystal directions on(001) crystal plane.The results indicated that there were great differences between depth and crack shape in different directions.For many slip planes in KDP, the plastic deformation and cracks generated under pressure in the subsurface were complex.Fluctuations of subsurface damage depth at transition point were attributed to the deformation of the surface which consumed more energy when the surface deformation changed from the mixed region of brittle and plastic to the complete brittle region along the scratch.Also, the process of subsurface damage from shallow to deep, from dislocation to big crack in KDP crystal with the increase of radial force and etch pit on different crystal plane were obtained.Because crystallographic orientation and processing orientation was different, etching pits on(100) crystal plane were quadrilateral while on(110) plane and(120) plane were trapezoidal and triangular, respectively.