FEM Simulation Studies On The Stress Field During The Diamond Growth

As a limiting functional material,diamond is widely used in many fields such as national defense,medical treatment,science and technology,industry,biology and electronics.Its excellent performance for the greater hardness,greater thermal conductivity,smaller compression rate,wider light transmission band,corrosion resistance,radiation resistance and so on.With the increase in the size of diamond,its application areas are becoming more and more extensive.However,the natural diamond mineral resources are very limited,which limits the application of diamond in the above fields.If artificially synthesized large-size high-quality diamond single crystals can replace natural diamonds,the application of diamonds will be greatly expanded.Therefore,the synthesis of large-size diamond single crystals has become an important subject of the diamond research.At present,the theoretical basis for diamond synthesis is based on the temperature gradient method established by G.E.in 1970.Growth of diamonds using this method is very sensitive to pressure.In the temperature gradient method for growing large-size diamonds,the sensitivity to pressure during crystal growth has been greatly reduced.However,pressure still has a great influence on the synthesis effect,and fluctuations in pressure also lead to a decrease in crystal quality.In particular,with the increase in the size of the synthesis chamber for the six-side press,the effect of inhomogeneity pressure distribution in the high pressure chamber on the diamond synthesis becomes even more important.Therefore,grasping the distribution of stress has important practical significance for improving the synthesis process of large cavities.However,under the current ultra high pressure technology,the measurement of pressure is very difficult.The most commonly used method is to conduct pressure calibration by using Bi,Tl,Ba and other materials to undergo phase change under high pressure.However,in the diamond synthesis process,due to the synthesisIV performed under the sealed condition,the internal pressure of the chamber cannot be measured in-situ.Constrained by the ultrahigh pressure environment,the above method can only calibrate the pressure at a certain point in the high-pressure cavity,In other words,it cannot measure the pressure at other locations in the cavity at the same time.Therefore,this method do not contribute to understand the pressure distribution in the cavity.In addition,since the measurement of the pressure depends on the phase change of the pressure material such as Bi,Tl,Ba,etc.,it is impossible to calibrate the pressure range where no phase change occurs.At present,the analysis and judgment of the experiment mainly come from long-term accumulation of experience,there is no theoretical basis,and the finite element method can solve this problem.In this paper,the dynamics method in the finite element method is used to simulate the stress distribution in the cavity.In this paper,the finite element software ABAQUS is used to simulate the pressure field distribution in the diamond synthesis process.According to the simulation results,a more in-depth understanding of the distribution trend of the internal pressure field of the diamond synthesis cavity has guiding significance for cavity optimization and material selection.The specific research content as follows:1.The diamond synthesizing equipment mainly studied in this paper is domestic SPD6×1200 type hinged six-faced top press.According to the six-side top press top hammer design drawing and the high-pressure synthesis device assembly drawing,the geometry was separately performed by Solidworks software.The establishment of the model,using the finite element analysis software ABAQUS to establish the finite element model of the hexahedral top hammer and the synthetic cavity.2.Using finite element analysis software ABAQUS based on the finite element display dynamics method,the pressure field distribution of the solid pyrophyllite block is simulated,and the pressure field distribution and pressure inside the solid pyrophyllite block can be intuitively observed and the internal pressure of the solid block can be directly observed.deformation.Through the analysis of the finite element results,the distribution of the pressure field in the solid block of pyrophyllite is unevenly distributed.The pressure value at the center of the hammer surface is almost equal to the pressure value at the center of the solid block.The pressure field distribution generally shows the pressure outside height and the inside and outside trend.,consistent with our experience in synthetic experiments.It provides a theoretical basis for the finite element simulation of the pressure field during diamondsynthesis.3.Use the dynamic analysis method shown in the finite element method to simulate the distribution of pressure field during the growth of diamond crystals.The simulation results show that under high temperature and high pressure,the stress is unevenly distributed in the high temperature and high pressure synthesis device.In the pyrophyllite assembly block,the stress is mainly distributed in the steel cap,sealing edge,graphite tube,carbon source,and catalyst,while the stress distribution in other parts is relatively small.4.In the diamond growth area,the pressure distribution is relatively large compared to other areas.The diamond growth zone forms a high pressure zone with a pressure of 5.8 GPa.This pressure just provides the proper pressure conditions for crystal growth,consistent with the actual pressure measurement.5.According to the distribution of the strain field in the pyrophyllite assembly block,it is known that in the entire assembly block,except where we know that the sealing edge is a large deformation,the steel cap,sodium chloride tube,graphite tube,dolomite tube Insulation tubes and carbon sources are also more deformed parts.6.According to the simulation results,intuitively see the deformation and pressure values of each material in the synthesis cavity,verify the conclusions and experiments,and change the pressure value of the diamond synthesis cavity and combine it with the experiment by controlling the assembly of the synthesis cavity and the adjustment of the material.The determination of a better synthesis scheme greatly saves the manpower and material resources for the experiment and provides an important theoretical reference for better cavity optimization and material selection.