A theoretical and deep learning hybrid model for predicting surface roughness of diamond-turned polycrystalline materials

Polycrystalline materials are extensively employed in industry.Its surface roughness significantly affects the working performance.Material defects,particularly grain boundaries,have a great impact on the achieved surface roughness of polycrystalline materials.However,it is difficult to establish a purely theoretical model for surface roughness with consideration of the grain boundary effect using conventional analytical methods.In this work,a theoretical and deep learning hybrid model for predicting the surface roughness of diamond-turned polycrystalline materials is proposed.The kinematic–dynamic roughness component in relation to the tool profile duplication effect,work material plastic side flow,relative vibration between the diamond tool and workpiece,etc,is theoretically calculated.The material-defect roughness component is modeled with a cascade forward neural network.In the neural network,the ratio of maximum undeformed chip thickness to cutting edge radius RT S,work material properties(misorientation angle θ_(g) and grain size d_(g)),and spindle rotation speed n s are configured as input variables.The material-defect roughness component is set as the output variable.To validate the developed model,polycrystalline copper with a gradient distribution of grains prepared by friction stir processing is machined with various processing parameters and different diamond tools.Compared with the previously developed model,obvious improvement in the prediction accuracy is observed with this hybrid prediction model.Based on this model,the influences of different factors on the surface roughness of polycrystalline materials are discussed.The influencing mechanism of the misorientation angle and grain size is quantitatively analyzed.Two fracture modes,including transcrystalline and intercrystalline fractures at different RTS values,are observed.Meanwhile,optimal processing parameters are obtained with a simulated annealing algorithm.Cutting experiments are performed with the optimal parameters,and a flat surface finish with Sa 1.314 nm is finally achieved.The developed model and corresponding new findings in this work are beneficial for accurately predicting the surface roughness of polycrystalline materials and understanding the impacting mechanism of material defects in diamond turning.

New Vitrified Bond Diamond Grinding Wheel for Grinding the Cylinder of Polycrystalline Diamond Compacts

In this work, a kind of new vitrified bond based on Li2O-Al2O3-SiO2 glass ceramics was used to bond the diamond grains, which is made into grinding wheel and the cylindrical grinding process of polycrystalline diamond compacts （PDCs） by using the new vitrified bond diamond grinding wheel was discussed. Several factors which influence the properties of grinding wheel such as amount of vitrified bond and the kinds and amount of stuff in grinding wheel were also investigated. It was found that the new vitrified bond can firmly combine diamond grains, when there are only diamonds and vitrified bond in the structure of grinding wheel, the longevity of the grinding wheel is about 2.5-3 times as that of resin bond grinding wheel for processing PDCs. The grinding size precision of PDCs can be improved from 4-0.03 mm to 4-0.01 mm because of larger Young＇s modulus of vitrified bond than resin bond. The grinding time of a PDC product can be 1.75-2.0 min from 3.25-3.5 min, so this kind of grinding wheel can save much time for processing PDCs. Also, there is hardly noise when using this new vitrified bond diamond grinding wheel to process PDCs. The amount of vitrified bond in grinding wheel influences the longevity of grinding wheel. When the size of diamond grains is 90-107 μm, the optimal amount of vitrified bond in grinding wheel is 21% （wt pct）. When the amount of vitrified bond exceeds 21%, there are many pores in grinding block, which will decrease the longevity of grinding wheel. The existence of addition stuff such as Al2O3 or SiC can reduce the longevity of grinding wheel.

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 tensile residual stress,which is a fatal shortage to PDC,can also occur near the outer diameter area of PCD table,and the maximum value is 690 MPa.Distribution of tensile stress in the PCD table is given through experimental results,which is well consistent with the numerical results.This finding may be significant in designing new PDC cutters with lower residual stress and high cutting behavior.

Experimental research on the residual stress of polycrystalline diamond compacts for oil drilling

Practical experiences gained in the past several years show that the thermal residual stress(TRS) is a main cause leading polycrystalline diamond compacts(PDC) to premature failure.It is the very important to measure the TRS accurately for optimizing the interface and improving the service performance of PDC.In this paper,the TRS in 1913 flat-interface PDC was measured using improved stress-release method(ISRM). The TRS on the surface of polycrystalline diamond(PCD) table was obtained,which can be used to calculate the radial thermal residual stress(RTRS) at the interface of PCD table via a refutation process.The obtained results show that there are compressive residual stress at the PCD table interface and in the most region of PCD table surface.The exception occurs near the outer diameter of the PCD table,where the PDC begins to bend and put the PCD table surface into a tension state,an undesirable state for a brittle material.The ISRM has covered the shortage existing in traditional stress-release method,in which only finite points on the surface of PCD table can be tested for one specimen and one time.Simple as the experimental procedures are,the test results are also very accurate and reliable.This method provides the theoretical and experimental basis for testing TRS of PDC accurately.

Residual stress and radial stress gradient in polycrystalline diamond compacts

The differential thermal expansion of the polycrystalline diamond layer and the tungsten carbide substrate results in large residual stresses as PDC cutters cooling after sintering.The residual stresses on the top surface of the diamond layer of PDC were measured at five points along the radial direction of PDC using X-ray Diffraction Residual Stress Instrument,thus the stresses and their radial distribution were obtained.The results show that the stresses on the diamond surface are compressive,the biggest stress appears at the central point(about 1200 MPa),and that from the center to the edge of PDC,the magnitude of the stress decreases. A finite element analysis(FEA) was made to check the validity of the testing results.The FEA modeling results were found to correlate well with the measured values.Factors leading to the deviation between XRD experimental measurements and the calculations of residual stress by FEA were also analyzed.

Failure analysis of polycrystalline diamond compact cutters for breaking rock by bending waves theory

The breakage mechanism of the polycrystalline diamond compact(PDC) cutters was analyzed by the energy theory of bending waves. The cutting tests of granite block were conducted on a multifunctional testing device by using the cutter at three kinds of negative fore angles of 30°, 45° and 60°. The results show that, when the edge of the PDC layer is broken, the layer of tungsten cobalt is broken a little under the angle of 30°, while the layer of tungsten cobalt is broken continuously under the angle of 60°, their maximum depths are about 2 and 7 mm respectively in the two cases. The eccentric distance mainly depends on the negative fore angle of the cutter. When the cutter thrusts into the rock under an attack angle of 60°, the energy of bending waves reaches the maximum since the eccentric distance is the maximum. So the damage of cutter is the most serious. This test result is consistent with the conclusion of theoretical analysis well. The eccentric distance from the axial line of cutter to the point of action between the rock and cutter has great effect on the breakage of the cutter. Thus during the process of cutting, the eccentric distance should be reduced to improve the service life of PDC cutters.

PCD刀具激光加工技术及其装备研究进展

聚晶金刚石(PCD)刀具在硬脆材料的高精高效加工方面具有显著优势,但常规的PCD刀具制造技术存在加工效率低、局限性大等问题,激光加工是一种实现PCD刀具高效高质加工的有效技术。本文总结了PCD材料激光加工去除机理,归纳了激光加工中波长、脉宽等工艺参数对PCD材料加工质量的影响规律,重点概述了激光加工技术在PCD刀具切削刃、表面纹理、烧蚀成型等方面的应用现状,介绍了国内激光加工装备的研发进展与现状。

A large-grain-size thick-film polycrystalline diamond detector for x-ray detection

A diamond film with a size of 6×6×0.5 mm^3 is fabricated by electron-assisted chemical vapor deposition. Raman spectrum analysis, x-ray diffraction and scanning electron microscope images confirm the high purity and large grain size, which is larger than 300 μm. Its resistivity is higher than 10^12 W· cm. Interlaced-finger electrodes are imprinted onto the diamond film to develop an x-ray detector. Ohmic contact is confirmed by checking the linearity of its current–voltage curve. The dark current is lower than 0.1 n A under an electric field of 30 k V cm^-1. The time response is 220 ps. The sensitivity is about 125 m A W^-1 under a biasing voltage of 100 V.A good linear radiation dose rate is also confirmed. This diamond detector is used to measure x-ray on a Z-pinch, which has a double-layer 'nested tungsten wire array'. The pronounced peaks in the measured waveform clearly characterize the x-ray bursts, which proves the performance of this diamond detector.

碳纳米葱(OLC)与微米金刚石(MD)烧结制备纳米聚晶金刚石复合材料(nPCD)的表征分析

在4~6GPa/1000~1400℃/5~30min条件下,用微米金刚石(MD)和碳纳米葱(OLC)混合物作为原材料制备了纳米聚晶金刚石(nPCD)复合材料。采用XRD、FESEM、HRTEM、Archimedes原理和Vickers硬度计表征了nPCD复合材料的组成、形貌、微观结构、密度和硬度。研究了MD和烧结参数对nPCD复合材料的组成、微观结构、性能。结果表明,MD在nPCD复合材料中分布均匀。MD作为晶核促进OLC向金刚石的转换。烧结压力的增加提高了nPCD复合材料的密度和硬度。当烧结压力从4GPa提高到6GPa时,nPCD复合材料的密度从2.72g/cm^(3)增加到3.02g/cm^(3),硬度从41.85GPa增加到56GPa。提高烧结温度和延长保持时间使nPCD复合材料的密度和硬度先升高后降低。在nPCD复合材料中nPCD区域具有孪晶结构。孪晶结构的存在提高了nPCD复合材料的硬度。

Energy beam-based direct and assisted polishing techniques for diamond:A review

Diamond is a highly valuable material with diverse industrial applications,particularly in the fields of semiconductor,optics,and high-power electronics.However,its high hardness and chemical stability make it difficult to realize high-efficiency and ultra-low damage machining of diamond.To address these challenges,several polishing methods have been developed for both single crystal diamond(SCD)and polycrystalline diamond(PCD),including mechanical,chemical,laser,and ion beam processing methods.In this review,the characteristics and application scope of various polishing technologies for SCD and PCD are highlighted.Specifically,various energy beam-based direct and assisted polishing technologies,such as laser polishing,ion beam polishing,plasma-assisted polishing,and laser-assisted polishing,are summarized.The current research progress,material removal mechanism,and infuencing factors of each polishing technology are analyzed.Although some of these methods can achieve high material removal rates or reduce surface roughness,no single method can meet all the requirements.Finally,the future development prospects and application directions of different polishing technologies are presented.

Ultrahigh pressure sintering of polycrystalline diamond cubes

Polycrystalline grits(polygrits) have been used widely in industry as abrasives.Due to their higher impact strength and the friable nature,polygrits are more endurable and more efficient than monocrystal grits (monogrits) in material removal applications.For example,polygrits of alumina may last longer and cut faster than monogrits.Similarly,polygrits of cubic boron nitride is a superior superabrasive than monogrits of the same. Although diamond superabrasives have been indispensable for constructional sawing applications and industrial grinding applications,there has no polygrits of diamond that are commercially available.In this research,we used a novel technology to sinter micron diamond fines to form polygrits of diamond.The characterization demonstrated that polygrits of diamond can be tough to withstand impact.But due to the presence of micro grains,the grit can sharpen itself without dulling by shedding the worn grains.This paper revealed many examples of using diamond polygrits.

Structure and Wettability Engineering of Polycrystalline Diamond Films Treated by Thermally Oxidation,Second Growth and Surface Termination

High-quality polycrystalline diamond films with dominated(100)-oriented grains are realized by combining the thermally oxidation and the homogeneous second growth processes.Moreover,we investigate the wettability property of the polycrystalline diamonds in various stages.Different surface structures(with various grain sizes,voids,and orientations,etc.)and terminations(hydrogen or oxygen)have significant effects on the wettability of polycrystalline diamond films.The wettability is further closely related to the polarity of solutions.By measuring the contact angle and calculating the dispersion and polarity components,we estimate the surface energy of polycrystalline diamond films,and explore the factors affecting the surface energy.The modulations in growth quality and wettability property of polycrystalline diamond films provide valuable data for development of diamond-based multiple devices in practical applications.

PCD/PcBN超硬刀片的刃磨

近几十年,超硬刀片被广泛应用于汽车制造、3C电子等要求刀具寿命长、生产节拍高的领域。这也对超硬刀片的批量化生产提出了更高的要求。本文对超硬刀具及材料特性、制作工艺与特点进行了探究,介绍了超硬刀片刃磨的三种加工方式,尤其对机械磨削方式进行了深入探讨,在中小批量人工刃磨的工艺基础上,创造和研发了自动化无人值守生产所需的刃磨工艺及算法,并融入其自动化机床产品当中。

Multiple enlarged growth of single crystal diamond by MPCVD with PCD-rimless top surface

We report the simultaneous enlarged growth of seven single crystal diamond(SCD) plates free from polycrystalline diamond(PCD) rim by using a microwave plasma chemical vapor deposition(MPCVD) system. Optical microscope and atomic force microscope(AFM) show the typical step-bunching SCD morphology at the center, edge, and corner of the samples. The most aggressively expanding sample shows a top surface area three times of that of the substrate. The effective surface expanding is attributed to the utilization of the diamond substrates with(001) side surfaces, the spacial isolation of them to allow the sample surface expanding, and the adoption of the reported pocket holder. Nearly constant temperature of the diamond surfaces is maintained during growth by only decreasing the sample height, and thus all the other growth parameters can be kept unchanged to achieve high quality SCDs. The SCDs have little stress as shown by the Raman spectra. The full width at half maximum(FWHM) data of both the Raman characteristic peak and(004) x-ray rocking curve of the samples are at the same level as those of the standard CVD SCD from Element Six Ltd. The nonuniformity of the sample thickness or growth rate is observed, and photoluminescence spectra show that the nitrogen impurity increases with increasing growth rate. It is found that the reduction of the methane ratio in the sources gas flow from 5% to 3% leads to decrease of the vertical growth rate and increase of the lateral growth rate. This is beneficial to expand the top surface and improve the thickness uniformity of the samples. At last, the convenience of the growth method transferring to massive production has also been demonstrated by the successful simultaneous enlarged growth of 14 SCD samples.

基于超快激光的PCD超硬材料加工研究

选取聚晶金刚石(PCD)为研究对象,利用1064 nm皮秒激光采用不同激光功率、重复频率、加工速度、填充线宽、加工次数等参数进行加工,并对各区域的加工深度和烧蚀现象进行观测。结果表明,不同激光参数对PCD的烧蚀程度不同,其加工深度与激光功率和加工次数呈正相关,与加工速度和填充线宽呈负相关。此外,加工PCD后出现了石墨化现象,证明皮秒激光对PCD超硬材料的烧蚀机制为石墨化机制。

降低井底岩石抗钻能力的钻速提高方法研究及钻头设计

为解决深部地层岩石硬度大、研磨性强、地应力高及可钻性差导致的钻头破岩效率低、钻井速度慢的问题,在分析现有提速技术的基础上,提出了释放地层应力、降低井底岩石抗钻能力的钻井提速新思路,基于该思路设计了井底应力诱导卸荷钻头、聚能攻击卸荷井底应力钻头、差压式钻头、中心差压式钻头、诱导卸荷与磨料射流联合作用钻头、阶梯式钻头和自激轴冲与诱导卸荷耦合破岩钻头等7种新式钻头。通过室内试验、现场试验,验证了其中2种钻头的提速效果:中心差压式钻头在室内试验中提速30.01%,现场试验最高提速318.11%;诱导卸荷与磨料射流联合作用钻头在室内试验中钻进石灰岩和红砂岩时分别提速59.0%和336.0%。该方法的提出及钻头的研制,为解决深部难钻地层的提速问题提供了新途径。

SiC基GaN上多晶金刚石散热膜生长及其影响

通过微波等离子体化学气相沉积(MPCVD)法,在SiC基GaN高电子迁移率晶体管(HEMT)异质结构材料上生长多晶金刚石散热膜,采用光学显微镜(OM)、拉曼光谱、非接触霍尔测试系统、X射线衍射(XRD)和扫描电子显微镜(SEM)对生长样品进行表征,研究了生长温度、多晶金刚石散热膜厚度对GaN HEMT异质结构材料性能的影响。测试结果表明,当多晶金刚石生长温度为625℃,散热膜厚度为20μm时,GaN材料载流子迁移率降低9.8%,载流子浓度上升5.3%,(002)衍射峰半高宽增加40%。生长温度越高,金刚石散热膜的生长速率越快。当金刚石散热膜厚度相差不大时,生长温度越高,GaN所受拉应力越大,材料电特性衰退越明显。多晶金刚石高温生长过程中,金刚石引入的应力未对GaN结构产生破坏作用,GaN材料中没有出现孔洞等缺陷。

凸棱非平面聚晶金刚石齿的破岩机理及在含砾地层中的应用

为提高聚晶金刚石复合片(PDC)钻头在含砾、软硬交错等不均质地层中的抗冲击性能,开展了凸棱非平面PDC齿的研究。通过仿真和室内实验对比分析了凸棱非平面齿与常规平面齿的破岩机理。与平面齿相比,凸棱非平面齿与岩石的接触应力分布更均匀,切削破岩过程中的载荷波动幅度明显更小,切削稳定性更高。凸棱齿特殊的非平面结构改变了切削齿与岩石的互作用方式,在不均质地层得到成功应用。

美国能源部地热钻井技术研发最新部署及干热岩开发示范创新实践

与其他主要的可再生能源相比,地热能是唯一能够提供基本负载电力的能源。干热岩是指不含原生水或含少量水的高温深部岩体,可通过水力刺激改造形成增强型地热系统储层,从而提取数量可观的地热能。干热岩型地热资源的开发面临两方面主要技术挑战,一是花岗岩和玄武岩等极坚硬岩石对机械钻速的限制,二是钻井所处地层温度超过随钻测量和旋转导向等工具电子设备的运行温度上限。近年来,美国能源部资助的FORGE计划犹他州项目为测试新的钻头技术和优化钻井作业流程提供了机会,以逐步提升机械钻速并降低钻井成本。本文综述了美国能源部地热技术办公室近年发展规划中对地热钻井技术研发的部署,重点分析了犹他州项目在钻井实践过程中对基于物理限制因素重新设计的工作流程的应用,总结了美国能源部围绕地热钻井技术开展的多次规划编制以及部署实施的相关项目涉及的主要领域,以及犹他州项目在探索和实践钻井作业流程优化方面取得的认识。

PCD刀具高速铣削TA15钛合金切削力的研究

通过利用回归正交设计和单因素试验设计方案,进行了PCD刀具高速铣削钛合金TA15的切削力试验。对高速加工过程中的动态铣削力进行了频谱分析,分析了高频振动对切削力波形的影响。然后利用单因素试验分析了工件坐标系中三向分力以及刀具坐标系中切向分力随切削用量的变化规律。通过回归正交设计,建立了PCD刀具高速铣削钛合金时切削用量与动态切削力之间的数学模型,并进行了方差分析,验证了模型的可靠度。分析结果为PCD刀具高速铣削钛合金的工艺参数优化及建立高速铣削数据库奠定了基础。