【作者】 徐国平；

【导师】 尹志民； 陈启武；

【作者基本信息】 中南大学 ， 材料物理与化学， 2010， 博士

【摘要】 本文以提高钻探用聚晶金刚石复合体(PDC)的性能为目的,从PDC合成块尺寸的计算、合成块组装方式的改进出发,采用SEM、EDX、XRD、Raman光谱、DTA-TG和有限元分析等研究方法,对PDC的高压烧结过程、残余应力检测、性能表征与优化等方面进行了研究。基于有限元方法,探讨了合成块反应腔温度场的分布及其影响因素；在分析不同烧结时间PDC金刚石层表面XRD图谱的基础上,证实了PDC的烧结经历了金刚石的石墨化,发现了烧结过程中WC衍射峰强度的变化规律；分别采用应力释放法、XRD法和Raman光谱法测定了PDC金刚石层表面的残余应力,通过与有限元模拟结果对比,确认了这三种方法测定PDC残余应力的可行性；对PDC耐磨性、耐热性和抗冲击性能的表征方法进行了探讨并提出了改进措施；在优化PDC制备工艺的基础上设计并合成出了内置过渡层的PDC。对照国内外有关PDC的研究情况,本研究取得如下创新性成果：1、针对六面顶压机,提出了合成PDC所用叶腊石块的临界边长(Lk)、实用边长(L0)与顶锤端面正方形边长(a)的关系式：LO/Lk=0.985exp(-a/9.05)+1.135使得根据硬质合金顶锤参数准确计算所用叶腊石合成块边长成为可能,对高压物理的研究和超硬材料的工艺设计具有重要的实用价值。2、对传统的PDC合成块组装设计进行了改进,对改进后合成块反应腔温度场的有限元模拟表明：PDC烧结反应区域轴向温差在30°C左右,径向温差约15°C,完全可以满足高品质PDC烧结的要求；分析了合成块预热温度和初始顶锤温度对反应腔温度场的影响,发现预热温度的增加可缩短反应腔体达到平衡温度的时间,但对进入“平衡态”后合成块的温度场分布以及腔体内的最高温度几乎没有影响。初始顶锤温度的提高对反应腔温度场和反应腔温度达到平衡的时间影响不大,但会使合成腔内最高温度明显增加。3、分别用XRD法和有限元分析方法对金刚石层表面残余应力进行了测定和计算,测试值与计算值基本相同；通过X射线应力检测仪测试,得到了PDC中心和边缘表面残余应力与金刚石层厚度(h)的关系式：σφ中心=758h-2294.5,σφ边缘=253.8h-366,这一关系式可为PDC的结构设计提供理论指导。4、鉴于采用现行的PDC磨耗比测试标准易产生称量误差以及较大规格PDC受天平称量范围限制的问题,笔者提出了以PDC的体积磨损代替重量磨耗的评估方法,并推导出了PDC磨损体积v与磨损面弦长L1的关系式：实践证明这一改进可提高测试结果的准确性,且大大简化了测试过程。5、将非平面连接技术及梯度过渡技术相结合研制出了内置过渡层的PDC。经过检测,其耐磨性、耐热性和抗冲击性均优于普通PDC。油田钻探的现场应用结果显示这种PDC钻头的总进尺比普通钻头深200-500米,研究成果现已应用于生产。更多还原

【Abstract】 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.更多还原