Research On Influence Of Sapphire Growth Process And Crystal Orientation On Crystal Quality And Performance

With the gradual development of the military competition,military weapons require supersonic and ultra-high precision.As one of the core forces of military weapons,supersonic and precision-guided missile weapons are of concern,requiring that the internal components undamaged during their flight,and that reconnaissance and strike capability are in the best performance.Optical properties and optimum mechanical properties of the optical window material is sapphire single crystal.Compared to other traditional infrared,fairing window materials,which have preparation difficulties,high cost,poor mechanical properties and other shortcomings,sapphire crystal stands out,and gradually recognized.At present,the application of sapphire single crystal gradually transits from the military optical window material to the dual-use.The demand for different crystal orientation of sapphire is also increasing.Market demand has developed from the initial single C orientation to C,A,M and R and other crystal orientations.However,due to many available single crystal growth methods in the market,and physical,mechanical and optical properties of their products vary widely,resulting in the quality of product is difficult to unify,which seriously hindered the healthy development of applications of sapphire single crystal.Therefore,this paper studid the KY method and EFG method,different crystal orientation sapphire single crystal,contrasting performance data,analysis of the reasons for the formation of performance differences,the establishment of the system evaluation system,which had a very important theory and practical significance on the development of sapphire single crystal applications.The microscopic defects of sapphire crystal seriously affect the properties of sapphire single crystal.In order to investigate the performance changes of sapphire single crystal resulting from microscopic defects,KY method and EFG method sapphire,A orientation,C orientation and R orientation sapphire specimens were subjected to chemical wet etching.The samples were observed at different corrosive time and different corrosive temperature,in order to get optimum corrosion process.In the optimum corrosion process,the samples were observed at different corrosive time,in order to determine the corrosion rate of the corrosion zone of the sample.When the corrosive temperature was 270? and the corrosive time was 30 min,this work calculated the number of corrosion pits in sapphire per unit area,and compared dislocation density and corrosion pits size of different growth process and crystal orientation of sapphire,and then determined the best growth process and crystal orientation.Sapphire was annealed at 1650 ? 300 min,in order to analyze the change of sapphire dislocation corrosion pit area and quantity.In order to explore the mechanical properties and optical properties of sapphire,there respectively had theoretical elastic modulus and hardness calculation,three-point bending experiment,Vickers hardness test,transmittance test and Raman spectroscopy.This work used Material Studio CASTEP to build Al2O3 crystal model,and the coordination was transformed.The theoretical elastic modulus of Sapphire C surface was 442.85 GPa,and the theoretical elastic modulus of A surface was 424.49 GPa,and the theoretical elastic modulus of sapphire M surface was 429.74 Pa,and the theoretical elastic modulus of Sapphire R surface was 373.00 GPa.Based on the theoretical elastic modulus C surface > M surface> A surface,it was reasonable to explain the reason why the bending strength of the sapphire spline could be increased when the C surface was the end face of the sapphire crystal.The theoretical Vickers hardness of Sapphire was 20.34 GPa.This work tested Vickers hardness of sapphire.Because C surface and A surface prone to slip when therer was an external load on the C surface and A surface,and also C surface spacing is less than the A surface spacing,Vickers hardness of different orientation sapphire had a relationship: R surface> C surface> A surface.This work tested the transmittance of sapphire.Due to amount of microscopic defects of EFG method was significantly greater than the KY method sapphire,resulting in its 200nm-300 nm band,the transmittance value was significantly smaller than the KY method sapphire.With the gradual increase in wavelength,KY method and EFG sapphire transmittance were similar,over 85% transmittance.When the wavelength is greater than 4.5?m,sapphire transmittance began to decline.This work tested the Raman spectroscopy of sapphire.It proved that EFG method sapphire were not as good as KY method.In addition,this work did above experiments on the annealed sapphire.Annealing can improve the mechanical properties of sapphire,and sapphire optical performance changed unobviously.