Research On Diamond Enhanced Tungsten Carbide Composite Button And Its Bits

At the present, the cutters used in button bits, rock bits and roller bits are mainly cobalt tungsten carbide in our country. Because of their low abrasive resistance, the bit service life and drilling efficiency were very low when the hard and extremely hard formations were being drilled. Owing to its high abrasive resistance, the diamond composite material is widely used in drilling operations. However, its toughness against impact is too low to be used in percussion drilling, only can it be used in rotary drilling. Drilling in the gravel formation is the problem that drilling engineers want to overcome, complex formations make bit endure not only wearing and tearing of rocks but also impacting of rocks. Other drilling methods are not good for this kind of formation, and common tungsten carbide button bit is fit for ordinary gravel formation, but when encountering big rock whose diameter is bigger than diameter of drill hole, cutting button can't penetrate. In order to solve the problems encountered by DTH hammer in hard rock drilling and gravel formations, make bit life longer, increase rate of penetration and decrease drilling cost, it is necessary and urgent to develop a new type composite material with high abrasive resistance and high toughness against impact. Although there are a lot of studies on diamond and cubic boron nitride enhanced tungsten carbide composite button, and some productions are achieved, but there are some problems such as: Firstly, how to solve the heat corrosion of diamond during the process of sintering at high temperature and pressure; Secondly, studying on matrix of substituting cheap iron for costly cobalt; Thirdly, how to solve material and structure designing of sintering mould, in order to reduce machining cost of composite button and improve mechanical performance of composite button; Fourthly, adding modes & quantity of minim element and rare earth, and its effecting mechanism. This paper summarizes and analyzes the making methods of diamond, cubic boron nitride sintering body, and on basis of these theories and tutor's right guidance, it solves the problems of structure, directions and making techniques, by the sintering method of low temperature activation hot-pressing, diamond and cubic boron nitride enhanced tungsten carbide composite button is successfully made. By coating on diamond and cubic boron nitride, it solves the problem of heat corrosion of diamond, combined problem of diamond, cubic boron nitride and matrix, in the same time, by reasonable adding mode and quantity of rare earth, it solves technical problems of substitute iron for cobalt composite button. As diamond and cubic boron nitride are non-metal and there are very high boundary energy between diamond and cubic boron nitride and matrix or ally, so diamond and cubic boron nitride surface can't be sintered by low melting point metal or alloy, with bad bonding between diamond and cubic boron nitride and metal matrix. Because the sintering temperature of diamond and cubic boron nitride enhanced tungsten carbide composite button is about 1050℃, ordinary diamond will suffer serious heating corrosion, then affecting performance of composite button. This paper uses coating technology of diamond and cubic boron nitride such as vacuum metal deposition, chemical coating Ni-W-B, Ni-W-P to solve these problems, and makes performance composite button assure and improve. By optimized designing on structure and material of super-hard composite button, it reduces making cost of composite button, and improves the performance of composite button, then is in favor for optimize sintering parameters such as sintering pressure, sintering temperature and time of keeping pressure and temperature. Life-span of ceramic sintering pressing rod is more 100 times than Life-span of graphite sintering pressing rod, and the mould cost of composite button reduces 600%, bending strength, wear ratio, toughness against impact improve greatly, then it is in favor for realizing rare earth and substitute iron for cobalt of composite button. Because of lack of cobalt resource, it is very important to substitute iron for cobalt. Rare earth that is called industrial monosodium glutamate has been applied successfully in improving material performance. But rare earth is seldom applied in heat-pressing diamond tools or diamond composite materials. The main reason is that rare earth is very easily oxidized during the process of ball grinding, in the same time adding quantity of rare earth is very little, it is very difficult to assure rare earth evenly dispersed, technology repeating and stability. So, expect rare earth middle alloy powder, adding modes of rare earth oxide, carbide, chloride, hydride, nitride and etc. are washed out. But directly adding mode of rare earth middle alloy powder has good effect, such as the patent of RE-Cobalt middle alloy powder is applied successfully in producing tungsten carbide was reported. Rare earth middle alloy powder solves the problem that rare earth is evenly dispersed in metal felting materials. The cost of producing rare earth middle alloy powder is very high, and the price of common middle alloy powder is about 2000yuan/Kg, other middle alloy powders need be made specially, then it is the main factor that restricts rare earth middle alloy powder be applied directly in heat-pressing diamond composite material. This paper adopts direct adulterating method to do adding rare earth experimentation; in the same time do some experiments of matrix of substituting iron for cobalt composite button, and gains success. Bending strength, wear ratio and toughness against impact of some kind of substituting iron for cobalt composite button achieves and indeed exceeds the performance of common super hard composite button. Testing results on laboratory condition show that its hardness is more than HRA88, equals to conventional tungsten carbide, and that its abrasive resistance is 10~40 times than conventional tungsten carbide, and its most toughness against impact is more than 200 Joules, its least toughness against impact is more than 120 Joules. Therefore, theoretically, this super hard composite body has very high mechanical properties that can meet the need of percussion drilling, and can solve the problems encountered with conventional tungsten carbide button bit and drilling in complex gravel formation. The results during the process of drilling on micro-drilling experiment station, field practical drilling in gravel formation, drilling in drilling hall, drilling on percussion drilling station and field percussion drilling show that compositebuttons and its bits meet drilling needs. During the development, I have optimized the formula and sintering parameters of the super hard composite body. Its optimum sintering temperature is from 1050℃ to 1060℃, the optimum pressure of graphite sintering mould is from 40MPa to 55MPa and the optimum pressure of ceramic sintering mould is from 60MPa to 80MPa, and the optimum sintering time from 3 minutes to 5 minutes. Upon the thorough analysis on diamond & cubic boron nitride enhanced super hard composite button, substituting iron for cobalt super hard composite button, and indoor & field drilling experiments of composite button bits, it shows that: Firstly, using technology of coating on diamond surface, there is crystal abnormity area between diamond and matrix, linking mode of diamond surface and crystal abnormity area is microcosmic inlaid mode, and it has strong resistance to diffusing of carbon element, and then protects diamond very well; in the same time makes diamond and matrix alloy have high combined strength, improves toughness against impact of composite button. Secondly, because of adding boron mode of chemical coating cobalt & boron, it make boron element disperse evenly in super hard composite button, and reacts with carbon in diamond surface to form B4C that enhanced diamond crystal interface. In the other hand, boron can react with cobalt to form chemical compound that reduces the presence of single-phase cobalt in super hard composite body system, and then improves the thermal resistance of the super hard composite body. Thirdly, because of adding phosphor mode of chemical coating cobalt & boron, it make phosphor element disperse evenly in super hard composite button, phosphor, nickel & phosphor alloy adsorbing on the surface of nickel and cobalt grains, the surface energy of these particles is decreased largely, this made it possible to sinter tungsten carbide cobalt hard metal at low temperature; Fourthly, according to powder metallurgy pressing theory, and combining with practical studies of diamond & cubic boron nitride tungsten carbide, this paper designs reasonable sintering mould of composite button, then improves life-span and low making cost of mould, and make composite button density & rigidity be improved. By optimizing sintering mould, it assures that sintering parameters optimization and improving performances of super hard composite button. The ceramic pressing rod can support more than 100 million Pa even if the sintering temperature is at 1100℃, but graphite pressing rod can support 20 to 50 million Pa, resisting intensity of pressure of ceramic pressing rod is very higher than graphite pressing rod; Substituting conventional mould for optimized mould, it assures the performance of composite button and low making cost. Fifthly, substituting iron for cobalt lows the cost of composite button, and solves the practical problems in the strategic altitude. Sixthly, diamond & cubic boron nitride enhanced tungsten carbide and rare earth substituting iron for cobalt composite button bits of reasonable formula can solve drilling problems in gravel formation and skidding formation, the bits have good performance of high penetration and longlife-span. Seventhly, the toughness against impact, wear ratio of diamond & cubic boron nitride enhanced composite button of adding diamond & cubic boron nitride of vacuum coated tungsten is higher than using uncoated diamond & cubic boron nitride. Eighthly, diamond & cubic boron nitride enhanced composite button has good economical and social benefits. In general, this paper combines coating technology of single crystal diamond and cubic boron nitride, substituting iron for cobalt formula, rare earth & microelement adding mode, optimizing designing of sintering mould, optimizing parameters reasonably, then improves the performances of composite button and low the making cost; it studies from theory to practice and gains some practical results. Room and field drilling experiments and analyzing & testing technology show that super hard composite button have predominant performances.