Research On Diamond Retention Capacity Of Hot-pressed Impregnated Bit Matrix

The research and development of high-performance diamond bits with high cutting efficiency and long service life play a very important role in improving drilling efficiency and reducing drilling costs in deep drilling engineering.And it is the need for the development of drilling industry.The retention capacity of the matrix on diamonds greatly determines the cutting efficiency and service life of the diamond bit.The adjustment and control of the diamond retention are the key technology to developing high-performance diamond bits.At present,there is neither a corresponding test device nor a unified evaluation method or standard in the research on diamond retention.There are also few quantitative studies on the influence of matrix formulation,preparation technology,diamond parameters,and working temperature on the holding performance of the matrix.In order to solve these problems,this thesis carried out the research on the diamond retention capacity of hot pressing impregnated diamond bits.In this thesis,the existing evaluation methods for the diamond retention performance were summarized by the literature research method,and the advantages and disadvantages of these methods were analyzed and compared.Then,the diamond retention capacity evaluation methods based on thermodynamic theoretical calculation,finite element numerical simulation,and bending strength test were determined to evaluate the mechanical holding performance.Based on the traditional WC-Cu matrix formula,the cooling process of the diamond-containing composite matrix after sintering was analyzed,and the influence laws of the matrix formula,sintering process parameters,diamond parameters,and working temperature on the diamond retention capacity were studied.The main work and research results of this thesis are as follows:(1)Based on the traditional WC-Cu matrix formula,the validity and consistency of evaluating the mechanical holding force based on the thermodynamic theory calculation method and the finite element numerical simulation method were verified.And the finite element method was used to analyze the cooling process of sintered diamond-containing composite matrix.The results show that the local plastic deformation occurs in the WC-Cu matrix around the diamond particles during the cooling process after sintering.(2)The effects of the content change of skeleton material,binder material,and the replacement of binder material by a pre-alloyed powder on the holding property of the WC-Cu matrix were studied by using a mixed regression test design method based on the holding force coefficient as the evaluation index.The results show that the quadratic regression model relationship between the holding force coefficient and WC,663 Cu,and Ni content is significant within the range of test parameters.The addition of the pre-alloyed powder FJT-A3 is helpful to reduce the sintering temperature of the WC-Cu matrix,and can effectively improve the diamond holding property of the matrix.(3)The influences of Young’s modulus,Poisson’s ratio,thermal expansion coefficient,and yield strength of the matrix on the mechanical holding force were analyzed by the thermodynamic model calculations using the residual pressure on the diamond surface and the radius ratio of the plastic yield zone near the diamond particles as indicators.The results show that,within the test parameters,the Poisson’s ratio has little effect on the mechanical holding force,but the yield strength,elastic modulus,and thermal expansion coefficient have significant effects,and there is an interactive effect between these three factors.The relationship between the strength and weakness of the mechanical holding force is yield strength > modulus of elasticity > thermal expansion coefficient > Poisson’s ratio.The mechanical holding property of the matrix to diamonds is enhanced with the increase of the yield strength,and shows a trend of increasing first and then decreasing with the increase of Young’s modulus and the thermal expansion coefficient,and decreases little with the increase of the Poisson’s ratio.(4)The effects of hot pressing process parameters including sintering temperature,sintering pressure,holding time,heating rate,tapping temperature,and cooling mode on the bending strength and the diamond holding property of the WC-Cu matrix were studied utilizing orthogonal test and thermodynamic theoretical analysis.The research results show that within the test range of hot pressing process parameters,the holding time,the heating rate,and the tapping temperature have no significant effect on the strength and holding force.In order to regulate the strength and holding performance of the WC-Cu matrix,the sintering temperature,the sintering pressure,and the cooling mode need to be focused on.The sintering temperature has a significant effect on the bending strength of the matrix,but not on the holding performance.The sintering pressure has a certain effect on the bending strength and a significant effect on the holding performance.With the increase of the sintering pressure,the holding performance tends to increase first and then decrease.The effect of the cooling mode on the bending strength is not significant but has a certain effect on the holding performance.With the cooling speed becoming slower,the holding performance tends to increase.(5)The influences of diamond crystal shape,diamond concentration,diamond particle size,diamond coating,and working temperature of the matrix on the mechanical holding performance were analyzed through numerical simulation,thermodynamic calculation model,and mechanical test.The results show that the change of diamond crystal shape has a significant effect on the mechanical holding performance,and it is suggested that octahedral diamonds and hexahedral diamonds can be preferred in the selection of diamond crystal shape.The increase of the diamond concentration will lead to a decrease in holding force,but it is helpful to improve the cutting efficiency of the drill bit,and the volume concentration of diamond should not exceed 1/3.The diamond particle size does not affect the holding performance,but the appropriate increase of the diamond particle size is beneficial to improve the drilling efficiency of diamond bits.Ti-plated diamond has a certain significance to improve the mechanical holding force,but it cannot significantly improve the force.The working temperature of the matrix has a very significant effect on the holding property.With the increase of the working temperature,the holding property of the matrix to diamond will keep decreasing.