聚晶金刚石复合片(PDC)应力表征方法的探讨

聚晶金刚石复合片是采用HPHT方法生产的,所以不可避免地在界面处、以及聚晶金刚石层内部的缺陷处存在大量的残余应力。本文主要围绕聚晶金刚石复合片的应力表征问题进行了实验和理论分析。实验、研究表明,聚晶金刚石复合片在聚晶金刚石层内存在着宏观应力和微观应力,即第一类内应力、第二类内应力;聚晶金刚石表面应力的大小可以反映聚晶金刚石层的应力存在状况;XRD方法可以用于聚晶金刚石复合片应力的表征。     

聚晶金刚石复合片的残余应力测试与研究

聚晶金刚石复合片产品内部普遍存在残余应力,这是造成其非正常失效的主要因素。我们详细研究了金刚石复合片内部残余应力的组成,并采用X射线衍射仪建立了聚晶金刚石复合片残余应力的检测方法,研究了聚晶金刚石复合片的残余应力分布规律。利用XRD检测残余应力的方法,分别研究了聚晶金刚石层厚度、金刚石粒度尺寸、两相界面结合形状以及金属Co对复合片的残余应力的影响规律,为控制PDC内部应力提供参考。结果显示:金刚石层表面残余应力最大的压应力在中心位置,从中心到边缘,应力的大小逐渐降低;PCD层与硬质合金基体界面附近的应力值对PDC使用性能的影响最大。      

梯度聚晶金刚石复合材料的开发

应用粉末层铺法制备梯度聚晶金刚石复合片材料，并通过SEM、XRD、显微硬度等对该材料进行组织与性能分析。结果表明，在以钴作粘结剂的聚晶金刚石层中金刚石相实现了D-D结合，通过梯度过渡层与硬质合金基体结合既保证了聚晶金刚石的硬度，又改善了界面的结合状况，从而提高了聚晶金刚石复合片的性能和使用寿命。     

专利信息

有缺Co区的表面刻槽的聚晶金刚石硬质合金复合片 本发明公开了一种有缺Co区的表面刻槽的聚晶金刚石硬质合金复合片,包括硬质合金层和聚晶金刚石层;硬质合金层由碳化物（通常为碳化钨-WC）和结合剂（通常为Co）组成,聚晶金刚石层则由金刚石和催化粘结剂（通常为Co）组成;在金刚石层表面上刻划有刻槽 。     

PDC性能优化及其钎焊技术研究现状

聚晶金刚石复合片（PDC）因其优良的性质，广泛应用于机械加工、能源开采、地质勘探等方面。但是PDC温度敏感性较高，在高温下内部残余应力增大、金刚石层发生氧化、石墨化等现象，导致PDC金刚石骨架撕裂、金刚石颗粒剥落、甚至复合片失效。从PDC表面改性、粘结剂优化、PDC结构设计、晶粒细化以及PDC钎焊技术等五个方面综述了PDC国内外研究现状，讨论了PDC存在的共性问题，并对未来的研究方向进行了展望。     

金刚石复合片的界面形态及性能特点

聚晶金刚石复合片的失效主要发生在金刚石与基体之间的界面处,改变界面的化学组分和形状可以改善复合片的使用性能。本文介绍了几种优质复合片的界面形态及其性能特点。在金刚石层与基体之间添加镀碳的钨片,或在金刚石层外镀上几层金属,可以改善金刚石与基体的不匹配问题;在基体上加工出沟槽或锯齿,使复合片抗冲击性能显著提高;为了避免直线型沟槽的方向性以及降低在尖端出现的应力集中,将沟槽或锯齿做成环形并使其尖角改成光滑的圆角;降低锯齿尖端粘结剂的含量,可使基体与金刚石的膨胀系数和弹性模量更接近而提高热稳定性;把界面做成波浪形,并且使界面与复合片的轴线不垂直,以此来分散应力。     

含硼聚晶金刚石复合片(B-PDC)的研究

利用国产六面顶压机,在高温高压的条件下,采用黏结剂Co熔渗催化方法合成含硼聚晶金刚石复合片。对加入不同体积分数的含硼金刚石合成的样品进行性能测试,最后对样品的性能测试结果进行讨论分析,并对聚晶金刚石层微观结构做了扫描电镜观察和XRD物相分析。结果表明:样品的抗冲击韧性和耐热性比普通金刚石复合片有显著提高,当添加含硼金刚石微粉体积分数为2a%～3a%时综合性能最好。     

基于声发射技术的PDC复合片性能的分析

PDC钻头在钻进过程中出现崩齿、掉片以及聚晶金刚石(PDC)层脱落是影响钻头工作的关键因素。使用声发射仪采集了PDC复合片在加载过程中的声发射信号,并且采用小波分析方法对PDC的声发射信号进行了时频分解。结果表明,通过时频分解可以得到PDC复合片的AE特征信号;PDC复合片中弹性变形的信号频率集中出现在低频信号中,且AE信号的幅度与载荷大小呈正相关;高频信号中的突发型信号可以反映PDC层在载荷作用下的损伤情况。     

聚晶金刚石复合片

聚晶金刚石复合片采用金刚石微粉与硬质合金衬底在超高压高温条件下烧结而成。聚晶金刚石复合片既具有金刚石的高硬度、高耐磨性与导热性,又具有硬质合金的强度与抗冲击韧性,是制造切削刀具、钻井钻头及其他耐磨工具的理想材料,也是功能材料的新突破。     

影响聚晶金刚石复合片性能的因素及改进方法

聚晶金刚石复合片作为PDC钻头的切削元件，其质量的好坏直接影响着整个钻头的钻进速率及使用寿命。影响复合片质量和性能的主要因素是金刚石与粘接剂的配比、粘接剂的种类、金刚石的粒度、金刚石／硬质合金界面结构以及烧结工艺等。本文探讨了不同种类粘接剂的优、缺点；介绍了如何通过改变金刚石颗粒的粒度分布提高复合片的耐磨性和抗冲击性能；在金刚石，硬质合金界面处添加碳化物形成元素薄片以及采用金属镀层(如W等)实现界面的冶金结合，从而提高界面的结合强度；采用锯齿形界面并伴随成分梯度过渡、以及采用正弦曲线形界面结构可明显改善复合片的性能。这些方法可为工业上生产优质复合片提供参考。     

Thermal residual stress of polycrystalline diamond compacts

Thermal residual stresses in polycrystalline diamond compact(PDC)cutter arising from the difference in thermal expansion between the polycrystalline diamond(PCD)and the supporting tungsten carbide substrate after sintering at high pressure and high temperature were investigated using finite element simulation,laboratory tests and theoretical analysis.The obtained results show that although compressive residual stresses exist both in the interface of PCD table and in the most region of PCD table surface, the...     

聚晶金刚石复合片界面微观结构对性能的影响

以硬质合金基体及优选的主晶为25μm的金刚石颗粒为原料,在2种工艺下用国产铰链式六面顶压机高温高压制备聚晶金刚石复合片(PDC),研究PDC界面处微观结构对其性能的影响。结果表明：工艺1制备的PDC界面处存在类树枝状枝晶金属池,其是硬质合金中的金属元素向聚晶金刚石层方向迁移形成的,主要元素为C、W、Co;而工艺2制备的PDC中不存在此类现象。工艺1制备的PDC的耐热温度为870℃,抗冲击等级为32,磨口面积为5.860 mm²;工艺2制备的PDC的耐热温度为920℃,抗冲击等级为45,磨口面积为5.166 mm²。工艺2制备的PDC相对于工艺1制备的PDC,其耐热温度、抗冲击性能和耐磨性能分别提高50℃、40.6%和11.8%。     

聚晶金刚石复合片(PDC)残余应力的检测方法

本文介绍了三种近期国外检测PDC残余应力的方法：应变片测试法、中子衍射法和带高能同步加速器X射线衍射法。三种方法均能有效检测出PDC的残余应力且各有其特点。应变片测试法比较直观、简单,不过这种方法是破坏性的,而且在材料去除过程中容易引入误差;中子衍射具有较深穿透力,然而较弱的散射使其取样体积不能小于1mm^3;高能同步加速器产生的散射X射线能穿透直径19mm的PDC样品,空间分辨率高,测量体积可精确至0．014mm^3,能详细地呈现出金刚石层、D／WC界面以及WC基体外径部分的二维应变分布情况,但测试易受Co峰的干扰。     

Control of exaggerated tungsten carbide grain growth at the diamond-substrate interface of polycrystalline diamond cutters (PDC)

Exaggerated tungsten carbide grain growth is common at the interface between the diamond table and the cobalt-cemented tungsten carbide (WC-Co) substrate in polycrystalline diamond cutters (PDC). The exaggerated WC grains at the interface can grow as large as 50 μm with an aspect ratio of 50:1. These large grains can also grow as clusters. The presence of large WC grains/clusters creates weakness at the diamond-substrate interface and impairs the strength of the PDC tool. In the present investigation, we tried to understand the root cause of exaggerated WC grain growth at the interface. Our findings show that WC grain growth at the interface decreases with a decrease in the carbon/tungsten (C/W) ratio. By adding 5 wt.% pure tungsten powder to the diamond, the C/W ratio decreased and we found no WC grain growth. By adding fully stoichiometric WC, which has 6.13 wt.% carbon, grain growth was reduced but still observed. Sintering on a substrate having η-phase (carbon deficient phase) also decreased the C/W ratio, and we did not observe WC grain growth.     

Wear resistance and thermal stability enhancement of PDC sintered with Ti-coated diamond and cBN

Ti-coated diamond with different particle sizes and proper amounts of cubic boron nitride (cBN) was used to fabricate polycrystalline diamond composite (PDC) with improved wear resistance and thermal stability under high temperature and high pressure (5.5–6.5GPa, 1500–1650 °C). The ratio of Ti-coated diamond powder, cBN powder and normal diamond powder was W_30–50: W_4–8: W_0–1 = 70: 15: 15. Cobalt (Co) was used as a binder, and cemented tungsten carbide was used as a substrate to sinter a new high-performance PDC. Ti and TiC on the surface of Ti-coated diamond reacted with cBN under high temperature and high pressure to generate new ceramic phases such as TiB₂, TiN and TiN_0.3, which have high hardness and good wear resistance. Compared with the conventional PDC, the impact toughness and wear resistance of PDC with Ti-coated diamond and cBN addition were enhanced by 19% and 28%, respectively. The ceramic phase acts as a protective barrier, which enhances the initial graphitization and oxidizing temperature to 942–950 °C, which were 162–170 °C higher than the conventional PDC. The new ceramic barrier wrapped around the surface of the diamond and Co after the formation of the D-D (diamond-diamond) bonding will give priority to the oxidation reaction of Co and diamond with oxygen, which prohibits cobalt-catalytic graphitization of diamond, meeting the needs of PDC thermal stability and wear resistance in the field of drilling.     

硬质合金基体上金刚石膜的XRD研究

采用直流等离子体射流CVD法在硬质合金 (WC + 8wt.%Co)基体上生长金刚石膜 ,主要借助XRD分析方法对CVD金刚石膜的微观结构和残余应力进行了研究 ,探讨了CVD金刚石膜中残余应力的形成及其对金刚石膜粘附性能的影响。研究结果表明 :CVD金刚石膜中通常存在GPa数量级的残余压应力 ,膜中存在适中的残余压应力 ,有利于CVD金刚石膜获得最佳的粘附性能