Synthesis Of High-Quality Polycrystalline Diamond Compact (PDC) With Low Residual Stress Under HPHT

The development of tools is the motive force of human civilization, and the naissance of diamond tools has an epoch-making significance. Growth-type polycrystalline diamond compacts (PDC), consisting of a polycrystalline diamond (PCD)-Co layer with high strength D-D bond structure on a WC-Co substrate, are sintered at HPHT. The material properties of PDC include high hardness and strength, combined with moderate toughness of WC-Co alloy, which are widely used in a variety of drilling and machining applications. Since the early 1970s, the PDC material has been carried on extensive and in-depth research by domestic and foreign scholars, because of its excellent performance and great range of application markets.Because the sintering ways and compound mechanism of PDC materials are different, their product performance will also show obvious difference. It can be seen from the application situation the wear-resisting performance has satisfied the requirement of basic indices from composite cutter product in various system, and then self-sharpness and resistance impact have been both elevated to the important position. At present, one of the important factors to appraise the PDC tool is the residual stress, which is primarily due to the large mismatch in coefficients of thermal expansion between diamond and the solvent metals which arises from the pressure relief and the cooling of PDC. The practical applications indicate that oversize residual stress will result in shorter in life performance of PDC. Lin et al. showed that high residual compressive stresses (up to 1.40 GPa) may exist in the PCD layer. Catledge et al.also reported the PCD layer has an average compressive stress ranging from 0.87 to 1.30 GPa. In addition, sintering process parameters such as temperature, the diamond size and content of binder additive were all found to affect residual stress levels, but few researches have been carried about these aspects of the regularity and mechanism. Based on the many methods used, Raman spectroscopy is widely used in a variety of applications as testing the residual stress due to the advantage of nondestructive samples, no specimen preparation and focuses of small size (1 m). Despite considerable success of that the Raman method in stress characterization in CVD films, little attempt has been made to study stress in diamond composites.Therefore, how to fully use the advantages of domestic cubic-anvil high-pressure apparatus and its technology, further optimize the reaction cavities of PDC synthesis process, study on interface and compound mechanism more in-depth and develop excellent performance of PDC materials with low stress will become an important direction in the field of superhard materials researches.In this paper, the preparation and properties of high-quality growth-type PDC with low residual stress, which synthesized under high temperature and high pressure (HPHT, 5.0-5.6GPa, 1350-1500 ) in a china-type cubic-anvil high-pressure apparatus were carried out.First, the alloy iron nickel-based infiltration technique was used to prepare PDC.And the design of the PDC assembly technique was optimized under high temperature and pressure. The metal solvent ratio is easier to control and the maneuverability is stronger, which also has greatly improved on performance of the preparation of PDC than that of the traditional powder-mixed method technology. Combined with the PDC about 8 15mm of specifications, optical microscope (OM) scanningelectron microscopy (SEM) X-ray diffraction (XRD) and micro-Raman spectroscopy were used to investigate the effects of the growth behavior of PCD layer and interface microstructure of PDC. The preparation characteristics of PDC using different metal solvent under high-pressure were contrastively researched.Secondly, the effect factors and laws from the different synthetic parameters (pressure, temperature, diamond grain size, etc.) and thickness of PCD layer on wear-resisting performance impact of PDC samples were discussed. And the high-quality of PDC cutting tools was made.Again, the biaxial and hydrostatic stress model of micro-Raman spectroscopy and X-ray diffraction (XRD) were used to measure the distribution characteristics and form of residual stress in the diamond layers. The influence law from different synthesis parameters on the residual stress between PCD layers was represented. Considering the influence factors of the stability of PDC striking body, the basic preparation principles of the high-quality PDC with low stress were given. The metal alloy infiltrating method, compared to that of elemental binder, effectively reduced the thermal expansion difference and supplied an adequate proportion between the diamond and binder, which played a positive role to prepare PDC of low stress levels. In the preparation of PDC samples, residual stresses in the form of compressive stress are uniformly distributed on axial and radial. The diamond layer of PDC sample with low stress has high density structure. X-ray diffraction (XRD) performed on a PCD layer confirmed the presence of cubic diamond, alloy, WC, CoxWxC, no graphite phase was detected.Finally, the infiltration force model of PDC sintered by the infiltration method was put forward. XRD SEM EDS and Raman were used to study diamond growth (D-D bond) mechanism, and combined with high pressure physics chemistry reactions during sintering PDC, the interface growth forms and compound mechanism of PDC were also researched, which can provide reference basis for the PDC sintering theory.In conclusion, the high-pressure infiltration technique was used to synthesize high quality and wear-resisting PDC with low stress which not only has theory instruction function to improve the properties of PDC materials but also has promote significance to improve the sintering process of other types of body materials.