Preparation, Characterization And Optimization Of Polycrystalline Diamond Compact For Drilling

Sintering process, residual stress measurement, Characterization and Optimization of Polycrystalline Diamond Compact (PDC) for drilling were studied using SEM, EDX, XRD, Raman spectroscopy, DTA-TG and finite element analysis (FEA) method.The distribution of the temperature in high-pressure cell assembly for sintering PDC and factors influencing it were discussed by using FEA method. Based on the XRD patterns of the diamond top surface of PDC sintered at the same temperature and different times, the sintering of PDC was proved to have gone through the graphitization of diamond and the changing pattern of the intensity of WC peak during sintering was discovered. Residual stresses in the diamond layer of PDC were measured using stress-release method, XRD and Raman spectroscopy, respectively. It was confirmed that the three methods could be used to test the residual stress of PDC by comparing the testing values with the results in the FEA model. Characterization of wear-resistant ability, thermostability and toughness of PDC were analyzed, and improving measurements were brought forward. A new kind of PDC with transition layer inside was designed and manufactured by optimizing the technology preparing PDC.Referring to the corresponding researches at home and abroad, there are several points of highlight in this work as follows:a) An expression on the relationship among the critical length (Lk), practical length (Lo) of the pyrophillite cube used for the sintering of PDC and the dimension of the square (a) of cemented carbide anvil was presented:LO/Lk=0.985exp(-a/9.05)+1.135. This makes it possible to calculate the practical length of the pyrophillite cube accurately based on the parameters of the anvil used in the experiment.b) A new cell assembly for sintering PDC was designed; the results of FEA show that the axial temperature difference in the chamber in which PDC is sintered is about 30℃, and the radial temperature difference is about 15℃. This means that the assembly is suitable for manufacturing high quality PDC. The influence of the anvil's temperature and preheating temperature of the cubic assembly on the temperature distribution in the chamber was taken into consideration. The time-history graph of the temperature in the chamber obtained from FEA illuminates that the increase of the heating temperature shortens the time the temperature in the chamber to reach the maximum while it has no influence on the temperature distribution and maximum. The change of the initial temperature in an anvil has no great impact on the temperature distribution in the chamber and the time it took to reach the equilibrium state though it affects the maximum of the temperature to some extent.c) XRD and FEA method were used to measure and simulate the stress in the diamond layer of PDC respectively, the FEA model result was found to correlate well with the measured values. The relations between the residual stress in the top surface of the diamond layer and the thickness of the diamond layer resulted from measuring the stress using XRD residual stress instrument were given:σφcenter=758 h -2294.5,σφedge =253.8h -366. The expression provides theoretical guideline for the designing of PDC.d) The shortcomings of the present measuring method of the wear-resistant of PDC were analyzed. The weighing of PDC was considered as an important factor influencing the veracity of testing results. The length of the abrasion facet of PDC is suggested to be measured by microscope, and then the abrasion volume can be calculated rather than weighted. A formula for calculating the volume based on the length of the abrasion facet was derived:This improvement is proved in the practice to have increased the accuracy of the testing result and simplified the testing process.e) The PDC with transition layer inside was developed by combining the non-planer interface technology with transition layer technology; its wear-resistant, thermo stability and toughness are shown to be superior to ordinary ones in performance test. On-site drilling result shows that the total footage of this kind of PDC can drill is 600-1600ft deeper than that of the common ones.This kind of PDC has now put into production.