Study On The Mechanism Of Brittleductile Transition For KDP Crystal Based On Nanoindentation/Nanoscratching

KDP crystal(potassium dihydrogen phosphate)is a kind of uniaxial negative and nonlinear optical crystal material which has excellent optical and electrical properties.This crystal has higher laser induced damage threshold and lager nonlinear optical coefficient,which play a an important role in the laser devices of Inertial Confinement Fusion(ICF).However,KDP crystal's practical laser induced damage threshold is far away from the theoretical value,it reduce the performance of KDP crystal.It is necessary to study the mechanism of brittle-ductile transition and deformation for KDP crystal.In this dissertation,depending on the dislocation theory,brittle-ductile transition model of KDP crystal in nanoindentation and nanoscratching condition with permanent load has been established firstly.Using the aforementioned model,to calculate the the threshold load of brittleductile transition based on the law of conservation of energy,to prediction the position of subsurface damages,and to analyz the influence of shape of indenters and anisotropy on brittleductile transition of KDP crystal.KDP crystal(0 0 1)surface used for the nanoindentation and nanoscratching experimens conducted on a Triboindenter,which obtains the mechanical properties such as hardness and elasticity modulus,and tribological property.Combined the anisotropy and sliping system,through experimental results,for instance graphs of tests,load-displacement curves and variation of friction coefficient,analyzing the effect of load and shape of indenters on threshold load of brittle-ductile transition and mechanism of deformation of KDP crystal.The results of the experiment have been analyzed and used to prove the rationality of the previous brittle-ductile transition model of KDP crystal.The threshold load of brittle-ductile transition of KDP crystal under different processing condition can be predicted by the brittle-ductile transition model which built in this paper.And analyzing the impact of processing parameters on threshold load,which provides the basis of processing parameters optimizing,to realize the none/low sub-surface damages of KDP crystal in ultra-precision machining.