Study On Graphene Nanosheets Modified PDC Composites And Their Properties

The high hardness and abrasion resistance of Polycrystalline diamond compact(PDC)composite tools have been recognized as the key contributor to improve the economics of oil and gas drilling and the quality of mechanical cutting.However,these tools still present a high susceptibility to fractures due to low fracture toughness.These tools are prone to breakage and failure during use.In addition,due to the presence of the bonding metal phase cobalt,the heat-resistant temperature of the PDC composite is reduced.In particular,in recent years,drilling geological conditions have become increasingly harsh and a large number of difficult-to-machine materials such as high-silicon aluminum alloys have emerged.The above-mentioned problems are more prominent and pose new challenges for PDC composite tools.Therefore,PDC composites with excellent comprehensive properties such as high strength,high wear resistance,high impact toughness,and high thermal stability are developed,and the performance improvement methods and mechanisms are theoretically studied.They are of great significance to solve the problem of low fracture toughness and thermal stability of traditional PDC composite materials,extend the service life of tools,improve efficiency and accuracy,and expand the application range of PDC composite tools.Aiming at the problems of low fracture toughness and low heat-resistant temperature of the current PDC composites,the topic"Graphene nanosheets tough PDC composites and their properties"is selected.The experimental scheme and performance test methods are described.The effects of high-pressure sintering process of sheet-toughened PDC composites,graphene nanosheets,and the addition amount on the microstructure and physical and mechanical properties have been thoroughly studied.In addition,in order to solve the problems of uniform and high-quality sintering of large-diameter PDC tool composites,low yield and quality stability between batches,based on optimized design of assembly structure and precise control of sintering process,a?62mm PDC tool composite was developed.The main research contents and conclusions are as follows:1.Study on high-pressure sintering process of graphene nanosheets toughened PDC composites.Graphene nanosheets have unique structures and properties and are considered to be effective tougheners for composites.However,there is no successful experience in toughening PDC composites.Therefore,Therefore,it is necessary to study the sintering process of PDC composites after the addition of graphene nanosheets.Adding 0.1wt%of graphene nanosheets to the raw material powder,the effects of sintering pressure,sintering temperature,and sintering time on the structure and properties of graphene nanosheets tough PDC composites were investigated using orthogonal experiments.The experimental results show that the normal sintering of PDC composites can be achieved after adding 0.1wt%graphene nanosheets.PDC composites sintered under the conditions of sintering pressure of 6.0 GPa,sintering temperature of 1500°C,and sintering time of 720s,obtained the best comprehensive performance.The results of verification experiments show that:under the conditions of the sintering process,the obtained samples are sintered uniformly and densely,without cracks,and the diamond grains are closely arranged,and the direct bonding between adjacent diamond particles is realized;The average microhardness of the obtained sample was 7211 kgf/mm~2,the average wear resistance was 21.97×10~4,the average heat resistance temperature was725?,and the impact energy was 1740J.Excellent comprehensive performance was obtained.2.Effect of graphene nanosheet content on the properties of PDC compositesGraphene nanosheets as additives used in sintering PDC composites can improve impact toughness and improve comprehensive performance,but the amount added should meet the following basic principles:It is enough for a uniform distribution of graphene nanoplates on the surface of all diamond grains,but do not exceed the level required for the filling of the pores between the diamond particles,otherwise excessive addition will lead to a decrease of the strength of grain boundaries during the PDC composite process.Therefore,based on the optimized sintering process,the effect of the amount of graphene nanoplatelets on the properties of PDC composites was further studied.The experimental results show that the best comprehensive performance is obtained by adding 0.2wt%graphene nanosheets sintered PDC composites.Compared with PDC composites without graphene nanosheets,the impact toughness of PDC composites obtained under these conditions was improved by 29.78%,and the heat resistance temperature was increased by 34.5?.The hardness and wear resistance of the samples were basically the same as The samples of PDC composites with graphene nanosheets remained flat and did not decrease significantly.3.Toughening mechanism of graphene nanosheets on PDC compositesAdding an appropriate amount of graphene nanosheets in the sintering process of the PDC composite can significantly improve the impact resistance,improve the heat resistance temperature,and obtain a PDC composite with excellent comprehensive properties.Mainly due to:(1)During the cold-pressing stage of the high-pressure sintering process of PDC composites,since graphene nanosheets are uniformly dispersed among the pores of diamond particles,they slide together when the mixed powder is compressed.The tribological properties can effectively reduce the friction and occlusion between diamond particles,promote the mutual sliding between adjacent diamond particles,rearrange the particles,and fill the pores to obtain a more dense and uniform PDC composite.(2)The graphene nanosheets added in the raw materials,the poor quality or defective part provides a carbon source for the liquid phase sintering of PDC composites,and promotes the formation of strong carbon-carbon bonds between diamond particles;Good graphene nanoplatelets still exist after high pressure and high temperature sintering,and fill the triangular grain boundary voids between diamond grains with the bonding metal.The graphene nanosheets distributed at the triangular grain boundaries on the one hand improve the microstructure of the PDC composite material to make it more uniform and dense;on the other hand,the graphene nanosheets at the triangular grain boundaries are interspersed in the binder cobalt It forms a unique structure of"cobalt-graphene nanosheets",which plays a skeleton role,which can effectively prevent fracture cracks from expanding;and it can also connect adjacent grains and firmly fix them together.This complex structure provides a stronger interfacial cohesion resistance,which can resist the graphene nanosheets being pulled out of the matrix;in addition,the stick-slip effect of graphene also effectively inhibits crack propagation.Therefore,even if the graphene nanosheet content is very low,the fracture toughness of the PDC composite can be significantly improved.(3)Graphene is the carbon material with the highest thermal conductivity and has very good thermal conductivity.It can make the heat generated during the use of PDC composite tools quickly,reduce the surface temperature of PDC composite tools,reduce the high-temperature graphitization and oxidation effects of polycrystalline diamond,and improve heat resistance.Improve the abnormal failure of PDC composite tools and obtain better economic benefits.4.Study on sintering mechanism of graphene nanosheets toughened PDC compositesThe sintering process of PDC composites is a complex multi-phase physicochemical change process.Studying the basic rules of sintering process and bonding mechanism of PDC composites is of great significance for controlling and improving the properties of PDC composites.It is the basic premise and technical guarantee for PDC composites with uniform sintered structure and excellent performance.This paper analyzes the high temperature and high pressure liquid phase sintering process,sintering driving force and sintering mechanism of PDC composites with the participation of graphene nanosheets,and discusses the role of graphene nanosheets in sintering process.5.Graphene nanosheet modified silicon intermediary combined with PCD materialAdding 0.1wt%of graphene nanosheets,polycrystalline diamond without free silicon was prepared under high temperature and high pressure,the wear resistance increased by 16.29%,and the compressive strength increased by 12.58%.6.Synthesis and characterisation of?62mm polycrystalline diamond compactThrough the design of the assembly structure of the HTHP sintering cavity and the precise control of the sintering process,?62mm PDC material was successfully sintered by a 6×55000k N large-volume cubic press at a pressure of 5.8±0.1GPa,a temperature of1500?,sintering time 20 minutes and adding 0.2wt%graphene nanosheets.The sample has no defects such as delamination,cracks,and uneven thickness of the diamond layer.The sample is dense and crack-free,and the diamond grains are closely arranged.Most of the diamond powder has been sintered and joined together,forming direct bonds through diamond–diamond bonds.Physical and mechanical properties tests showed that the Vickers hardness reached86.25GPa,the flexural strength was 1398.6MPa,the interfacial shear strength was 2690.4MPa,the impact energy was 1770J,the wear resistance was 29.8×10~4,and the initial oxidation temperature was 742.8?.The radial test of microhardness and abrasion resistance decreased from the edge to the center point by 9.4%and 8.09%,respectively.This shows that the?62mm PDC composite material developed in this paper not only has high physical and mechanical properties,but also the comprehensive performance is basically uniform,achieving uniform and high-quality sintering.