Research On Performances Of Polycrystalline Diamond Compact Reinforced With Nano-materials

Polycrystalline diamond compact(PDC)are widely used in the manufacturing of petroleum and natural gas drilling bits,and bearings for downhole drilling tools.Given the current complex international environment and geopolitical situation,China’s high dependence on foreign oil and gas energy poses a serious threat to the country’s energy security.Therefore,the development of onshore-,and offshore-deep oil and gas resources has become a top priority.However,traditional PDC face challenges when drilling in formations characterized by high temperature,high pressure,hardness,strong abrasiveness,and uneven soft-hard formation.They exhibit issues such as low rate of penetration,short lifespan,and the need for frequent bit changes during drilling,leading to increased non-drilling time and engineering costs,as well as potential risks of borehole instability.The initial size of diamond grains determines the phase composition,spatial distribution,content of cobalt-based binder phase in the polycrystalline diamond layer,and the failure mechanisms of the polycrystalline diamond layer.Thus,the diamond particle size has a significant impact on the performances of the polycrystalline diamond compact.It is well-known that cobalt removal can improve the wear resistance of PDC,the lower cobalt content may correspond to higher wear resistance.However,the combined effects of cobalt content and diamond grain size on the wear resistance of PDC while cutting dense granite still need further investigation.Therefore,this study investigated the influences of performances and micro characteristics of polycrystalline diamond compact on wear resistance.Based on the results of the research,we preliminarily determined the formula of PDC with balanced performances.Experiments of nano-materials reinforced PDC were conducted to study the effects of nano-material types and contents on the performances of polycrystalline diamond compact,elucidating the mechanisms of their impacts on the performances of PDC.The research findings are as follows:(1)For polycrystalline diamond compact with grain sizes of 5,10,20,and 28 μm,the thermal stability of initial diamond powders,the fracture toughness,and impact resistance of PDC increased with the increase of diamond grain size,while the hardness and density of the polycrystalline diamond layer showed a decreasing trend.The thermal stability and wear resistance of the PDC both exhibited a trend of initially increasing and then decreasing.(2)The diamond grain size affected the wear resistance by influencing the phase types and distribution of cobalt-tungsten binders,rather than just the cobalt content.For coarse-grained polycrystalline diamond compact,the rapid failure of the composite was attributed to crack propagation within the diamond and alone the interfaces between diamond and binders caused by the thermal mismatch,the oxidation of the binders,the graphitization of diamond,the rapid wear and large-scale shedding of well-connected cobalt-tungsten binders and diamond.The coarse-grained diamond from polycrystalline diamond layers were difficult to degrade under high temperatures and cleaned up,promoting the wear of coarse-grained PDC.These reasons collectively contributed to the rapid failure of coarse-grained PDC,leading to poor wear resistance.Polycrystalline diamond compact with the grain size of 10 μm exhibited more balanced performances and higher wear resistance.(3)With the increase of nano-Ta C content,the room-temperature impact resistance,high-temperature impact resistance,and hardness of polycrystalline diamond compact all significantly improved,while the increase in fracture toughness was limited.In addition,the addition of nano-Ta C also helped to increase the starting expansion temperature(thermal stability)of the polycrystalline diamond layer and reduce the maximum expansion of the polycrystalline layer at high temperatures.(4)Nano-Ta C in the polycrystalline diamond layer could enhance the performances of cobalt-based binders through dispersion strengthening and solid solution strengthening,thereby improving the hardness and fracture toughness of the PDC.Due to the higher thermal stability of Ta C and its shielding effect on the contact between diamond and cobalt-based binders,the graphitization of the polycrystalline diamond layer at high temperatures was effectively alleviated,resulting in significantly improved thermal stability of the polycrystalline diamond layer.The increased hardness,thermal stability,impact resistance,and reduced abnormal grain growth at the interface collectively contributed to the improved wear resistance of the polycrystalline diamond compact.Therefore,polycrystalline diamond compact with 0.3 wt% nano-Ta C exhibited the lowest wear area and less shedding of the polycrystalline layer in different wear stages.Additionally,the addition of nano-Ta C was beneficial for increasing the cobalt removal rate of PDC.(5)The addition of nano-diamond could reduce the cobalt content in the polycrystalline diamond layer by filling the gaps between diamond powders,increase the content of D-D bonds and the grain boundary density in the polycrystalline diamond layer,and ultimately improved the hardness and impact resistance of polycrystalline diamond compact.However,due to the lower thermal stability of nano-diamond,the improvement in the thermal stability of the PDC was not significant.Therefore,in the cutting process of granite with low cycle times(when thermal damage was not severe),wear resistance was significantly improved due to the increase in hardness and impact resistance.However,with the increase in cutting cycles,the thermal damage to polycrystalline diamond compact intensified,and the improvement in wear resistance became limited.Therefore,the optimal content of nano-diamond was 0.5 wt%.This paper systematically investigates the effects and rules of different grain sizes of polycrystalline diamond compact and nano-material contents on the performance of polycrystalline diamond compact,revealing the wear mechanism of polycrystalline diamond compact with different grain sizes when cutting granite,as well as the effects of different physical and mechanical properties and thermal properties on wear resistance of the PDC.Through nano-Ta C and nano-diamond modification experiments,the paper studies the effects and mechanisms of their contents on the performance of polycrystalline diamond compact,providing a theoretical basis and guidance for improving the efficiency and lifespan of PDC in petroleum and natural gas drilling.