CdZnTe wafers were machined by lapping and mechanical polishing processes,and their surface and subsurface damages were investigated.The surface damages are mainly induced by three-body abrasive wear and embedded abrasive wear during lapping process.A new damage type,which is induced by the indentation of embedded abrasives,is found in the subsurface.When a floss pad is used to replace the lapping plate during machining,the surface damage is mainly induced by two-body abrasive and three-body abrasive wear,and the effect of embedded abrasives on the surface is greatly weakened.Moreover,this new damage type nearly disappears on the subsurface.
LI Yan,KANG Renke,GAO Hang,and WU Dongjiang Key Laboratory for Precision and Non-Traditional Machining Technology (Ministry of Education),Dalian University of Technology,Dalian 116024,China
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.
WANG Ben WU Dongjiang GAO Hang KANG Renke GUO Dongming
The nanomechanical behaviors of （110） and （111 ） CdZnTe crystals were investigated by nanoindentation. It was found that the indenter tip was adhered by the removed materials in scanning testing area although the scanning force on the tested surface was very small （1000 nN）, which would affect the testing result of nanoindentation, so the indenter was clean before nanoindentation test. The experimemtal results showed that the hardness and Young＇s modulus decreased with the increase of indentation loads on the same plane. Because of the anisotropy of the CdZnTe crystal, the average hardness of （110） plane is 35% lower than that of （111） plane, and there are about 30% difference of the hardness along different crystallographic directions on the same plane. The hardness in 0° and 120° testing directions was the same due to the threefold symmetry of a Berkovich indenter. And the anisotropy affected the surface quality during machining of CdZnTe crystal.
