Study On The Influence Of Solid Lubricants On The Properties Of Impregnated Diamond Bit Composite Materials

The fast development of economy and society has put forward new requirements for impregnated diamond bits?IDB?.In fields like building decoration,reconstruction and machining where IDB are often used,the need for site cleanness and personnel health requires less or no cutting fluid,resulting in heat-related problems which shorten IDB's service life.In geological drilling,as conventional resources are being depleted quickly,the drilling industry is striding towards unconventional areas,with high-temperature issues of IDB the main obstacle too.The above problems are in essence the friction and wear issues of IDB surface at micro scales.The self-lubricating composite technique has been widely studied and applied.The technique can reduce coefficient of friction?COF?and wear and increase the service life of units during they work.At a micro scale,the functioning mechanisms of a self-lubricating composite and an IDB can be fairly compatible.Theoretically,the introduction of self-lubricating technique will prolong IDB's service life without hindering its normal cutting performance.At present,research towards self-lubricating IDB is quite limited,with only ones using IDB matrix specimens to analyze and normal low-temperature solid lubricants as lubricant additive.There is a lack of research by whole bits under drilling environment and that specifically focusing on poor heat-dissipation working conditions like dry drilling and vacuum environment.Based on these,this paper conducted research on the influence of solid lubricants on the properties of IDB composite.The main research contents include:1.suitable high-temperature solid lubricant types were determined considering high downhole temperature and the high-temperature environment during bit fabrication;2.using the selected solid lubricants,self-lubricating IDB matrix specimens were produced to investigate the influence of solid lubricant concentration on matrix mechanical and tribological properties;3.self-lubricating micro IDB were produced by best solid lubricant types and concentrations,and drilling experiments were conducted to investigate the influence of solid lubricant concentration on drilling properties;4.through literature on electroless plating,surface modification methods for the best solid lubricant?Ca F₂?were formulated,and the best method was determined through experiments;5.using modified solid lubricant and diamond,the influence of particle modification on the mechanical and drilling properties of self-lubricating IDB composite was investigated;6.by controlling flow rate,the influence of heat dissipation condition on the drilling performance of normal,unoptimized self-lubricating and optimized self-lubricating IDB was studied;7.specimens were analyzed using the abovementioned apparatuses,and micro mechanisms of the experimental phenomena were revealed from the perspectives of material property and micro structure.Through the above research contents,several conclusions can be drawn.This paper first selected middle-temperature solid lubricants Mo S₂and WS₂,high-temperature solid lubricants Ca F₂and h BN to respectively fabricate WC-based matrix specimens for normal drilling conditions and Fe-based matrix specimens for high-temperature conditions.Mechanical experiments proved that with increase in lubricant concentration,the tensile-strength-related mechanical strengths of the matrices generally decreased;the hardness of the matrices behaved differently according to different types of the matrix;the addition of solid lubricants could increase the compactness of the matrix to a certain extent;the compactness of the matrix was positively correlated with its hardness.Tribological experiments showed that COF decreased monotonically with increasing lubricant concentration;some matrices experienced a rise in their abrasion resistance;with increase in surrounding temperature,the lubricating ability of Ca F₂increased.Micro analyses proved that except for h BN group,all groups of specimens experienced a decrease in major wear mechanisms;such improvement was a result of the appearance of a lubricant layer and some new lubricious matters generated by tribological reactions.WS₂and Ca F₂were considered best suited for the subsequent experiments and were used to fabricate WC-based self-lubricating micro IDB,by which drilling experiments were conducted.The results showed that all self-lubricating IDB outperformed normal IDB in terms of ROP;with increase in WS₂concentration,the ROP increased,but the service life decreased drastically;with increase in Ca F₂concentration,service life gradually increased while ROP decreased slightly.Micro analyses proved that the increase in Ca F₂content greatly improved the wear condition of bit surface,while the increase in WS₂content induced more severe wear.Therefore,Ca F₂was selected to produce Fe-based IDB designed for high-temperature conditions,by which same experiments were conducted with similar results obtained.This paper then studied the influence of heat-dissipation condition on the drilling performance of the best-performing self-lubricating IDB,which was compared by normal IDB.The results showed that with the deterioration of heat-dissipation condition,the service life of both self-lubricating and normal IDB presented a downward trend.However,such trend was less rapid for self-lubricating IDB;the service life of self-lubricating IDB was in general higher than that of normal IDB.The technique of plating Ni on Ca F₂surface was researched,with excellent plating quality achieved.Modified particles were used to fabricate matrix and bit specimens to conduct mechanical and drilling experiments.The results showed that the surface modification of Ca F₂and diamond both could increase the tensile-strength-related mechanical properties and thus further prolong the service life of self-lubricating IDB.The service life of optimized self-lubricating IDB was8.03%greater than that of the unoptimized ones and 13.42%greater than that of the normal IDB.However,the optimized IDB had a lower level of diamond protrusion height.Consequently,their ROP was 2.46%lower than that of the unoptimized self-lubricating IDB.The drilling performance of optimized self-lubricating IDB under various heat-dissipating conditions was studied.It was found that the optimized self-lubricating IDB had a generally higher service life and a less decreasing rate of their service life compared with unoptimized ones.This paper has the following innovations:1.whole bit as researching unit has been adopted to study self-lubricating IDB subjects;2.high-temperature solid lubricant type and its concentration suitable for IDB have been determined;3.the relationship between solid lubricant concentration and the properties of IDB composites has been revealed,with micro mechanisms analyzed;4.the self-lubricating IDB fabrication technique has been optimized to improve self-lubricating performance;5.the influence of heat-dissipation condition on the performance of self-lubricating IDB has been revealed,demonstrating the advantage of self-lubricating IDB under high-temperature working environment such as dry drilling condition.This paper is a further attempt to introduce self-lubricating technique into the field of IDB,which put self-lubricating IDB related studies a step forward.The present paper has formulated methodology and principles for high-temperature solid lubricant selection,bit fabrication,research/analysis and optimization of high-temperature self-lubricating IDB.The methods and results of this paper can provide theoretical references for the design and optimization of self-lubricating IDB,and serve as technical reserve for future drilling tasks under unconventional working conditions.