| In recent years,with the continuous deepening of petroleum exploration and development,shallow and easy-to-develop oil and gas resources have become less and less,and drilling work has developed from shallow,medium and deep.At the same time,the exploration and development of deep oil and gas resources,geothermal resources,and solid mineral resources put forward higher requirements for drilling technology.In order to solve the requirements of high-efficiency and long-life drill bits for complex conditions such as hard rock,strong abrasiveness,high temperature and high pressure in deep formations,it is urgent to develop drill materials with excellent comprehensive performance.Due to the universality of hard rock for polycrystalline diamond composite(PDC)drill bits,the research and development of high-performance PDC materials has become a hot spot at domestic and abroad.Research has found that in hard and highly abrasive formations,the main factors affecting the performance of diamond composite drill bits are the high contact pressure and the high abrasiveness of the rock.The above factors will cause the friction temperature between the polycrystalline diamond layer of the PDC and the rock contact surface to be too high,which will reduce the strength of the diamond polycrystalline layer and accelerate the wear,which will lead to a reduction in the service life of the diamond composite drill bit.In order to solve the above problems,in addition to the need to optimize the structure and drilling parameters of the PDC bit for different formations,it is also necessary to develop a polycrystalline diamond composite sheet with high strength,high wear resistance and high thermal stability.Carry out theoretical research on PDC performance improvement methods and mechanisms.It is extremely important to improve the efficiency and expand the application range of PDC bits.In order to improve the mechanical properties and thermal stability of PDC,it can be studied from multiple perspectives such as the material system,interface structure design,preparation process of the superhard material,including the analysis of the relationship between the microstructure of the superhard material and the macroscopic physical properties of the finished product,analyze the influence of binder content and particle size on the macroscopic physical properties of superhard materials,analyze the influence of diamond powder particle size,coating characteristics,and spatial morphology on the macroscopic physical properties of superhard materials,analyze superhard material formulation research and interface structure optimization design.Since graphene was discovered,due to its excellent mechanical and mechanical properties,it can be used as an ideal reinforcement for composite materials.However,the current research on composite materials with graphene as a reinforcement mainly focuses on polymer matrix and ceramics.Based on composite materials,there is little research on polycrystalline diamond composite materials,and some problems have not been resolved.Diamond has various excellent properties,and is widely used in various fields.However,the chemical and thermal stability of diamond is poor.Cubic boron nitride(c BN)has excellent thermal stability.Its thermal stability can reach about 1100°C in air atmosphere,as well as higher hardness,large elastic modulus,fracture toughness and high melting point.The affinity and covalent bond characteristics of diamond and boron nitride in the structural lattice,diamond and cubic boron nitride can form alloys,which may fill the performance gap.The thermal expansion coefficient of Ti CN binder is more compatible with c BN.At the same time,Ti CN combines the advantages of Ti C and Ti N,with high melting point,high hardness and conductivity.It is used as a c BN intensifier to increase the bending strength and fracture toughness of the material,thereby obtaining a higher red hardness and lower friction coefficient Pc BN.In this paper,aiming at granite and other hard formations,the starting point is to develop polycrystalline diamond composite sheets with high strength,high wear resistance and high thermal stability.Using the reasonable addition amount of graphene and cubic boron nitride,the PDC composite sheet with high wear resistance,high conductivity and high heat resistance was prepared on a domestic six-sided top press,and theoretical research was carried out on the method and mechanism of PDC performance improvement.By studying the temperature field and stress field simulation of different interface structures,combined with indoor drilling experiments,the applicability of PDC bits used in the drilling field is improved,and it provides important theoretical significance and engineering application value for deep hole drilling.The main research work and related conclusions of the paper are as follows:(1)Under the high temperature and high pressure conditions of China-type cubic high-pressure apparatus(5-6.5Gpa,1300-1700°C),polycrystalline diamond composite sheets with sizes of 13mm and 30mm were successfully sintered.Graphene reinforced sintered composite sheet is PDC-Graphene composite sheet,cubic boron nitride reinforced sintered composite sheet is TDBN series composite sheet,PDC sintered with titanium carbonitride as a binder is TDBN-Ti CN composite sheet.The performance of the prepared PDC can meet the needs of hard rock drilling.(2)In the PDC-Graphene series composite sheet,an appropriate amount of graphene can form a lubricating protective film on the diamond surface,reducing the frictional resistance between diamond particles under high pressure conditions,promoting the filling of the fractured diamond gaps,and improving the uniform distribution of the binder,thereby a denser and uniform structure is formed in the polycrystalline diamond layer.Compared with the PDC prepared without graphene,the electrical conductivity,thermal conductivity and mechanical properties of the PDC-Graphene prepared with graphene are improved to a certain extent.(3)Compared with the traditional PDC,the diamond in the TDBN series composite sheet is dissolved and resolved under the action of the Co binder.At the same time,it is accompanied by the delamination of the surface titanium film and reacts with c BN to form new phases such as Ti B2,Ti N,with good wear resistance and thermal stability.On the one hand,it will not affect the formation of D-D bonds between the diamond particles.On the other hand,the ceramic phase generated by the reaction connects the diamonds filled in the gaps of the diamonds by bonding,thereby making the synthesized PDC composite sheet compact and wear-resistant.(4)In the TDBN-Ti CN series composite sheet,the Co in the cemented carbide substrate penetrated into the PCD layer and the binder Ti CN to form a metal-ceramic binder system.It can promote the formation of polycrystalline cubic boron nitride(Pc BN)from cubic boron nitride particles at the grain boundaries,and promote the TDBN-Ti CN series PDC to have the performance of PCD and Pc BN.(5)The non-planar structure of the PDC cemented carbide substrate was modified and designed,and the finite element numerical simulation analysis was carried out.The Abaqus finite element numerical simulation software was used to analyze the residual stress of the new non-planar interface structure PDC.The results showed that the uniformly distributed rectangular protrusions played an effective role in dispersing the stress and significantly reduced the internal residual stress of the PDC after high temperature and high pressure. |
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