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。      

Micro-Raman and X-ray diffraction stress analysis of residual stresses in fatigue loaded leached polycrystalline diamond discs

Polycrystalline diamond (PCD) cylindrical tool-bits used in oil well drilling are susceptible to fracture due to the hostile environment of randomly occurring high impact loads. These tool-bits generally comprise of a PCD layer sintered onto a Co-cemented tungsten carbide substrate. The cobalt metallic phase primarily aids the formation of the diamond to diamond bonds, however during application the same cobalt expands much quicker than the diamond, breaking the very same bonds it helped to form in the first place, leading to premature failure of the tool bits. As the PCD is virtually a two-phase material comprised of cobalt and diamond, substantial volumes of the metallic phase can be removed through a leaching process without compromising the cohesiveness of the diamond matrix, with reported improved wear resistance and thermal stability. X-ray diffraction and Raman spectroscopy techniques were used to investigate residual stresses in leached polycrystalline diamond disc samples. A systematic investigation and evaluation of the average in-plane residual stress fields using the Raman technique showed a progressive shift of the residual stress state from a compressive stress state to an average tensile stress state as a function of increasing number of loading cycles. In contrast the X-ray diffraction method recorded compressive stresses for all the measurements even at the highest number of loading cycles. The apparent disagreement between the two sets of results were satisfactorily explained by considering the probing beam size and sampling depth for the two different but complementary techniques.     

A Study of the Origin of Weak Ferromagnetism in Zn1−x Co x O

To study the origin of ferromagnetism in Zn_1?x Co _x O thin films, its thermal diffusivity, in addition to its magnetization measurements, were analyzed. Thin films of Zn_1?x Co _x O (x = 0.03) were deposited on Si (100) substrates through ultrasonic spray pyrolysis. Magnetization M(B) measurements at low temperature showed a hysteresis loop that indicated the existence of ferromagnetic ordering in Zn_0.97Co_0.03O. However, the magnetic moment per Co ion was much lower than expected. A comparison of M(T) measured at zero-field-cooled and field-cooled conditions showed a superparamagnetic-like behavior, with a blocking temperature of about 130 K. Temperature dependence on the thermal diffusivity of Zn_0.97Co_0.03O showed a pronounced lambda-shaped minimum at 130 K, which indicated the existence of a second-order phase transition at this temperature. The weak ferromagnetism in the Zn_0.97Co_0.03O with the Curie temperature of 130 K was ascribed to the uncompensated magnetic moment at the surface of CoO nanoclusters.     

Enhanced tribological behaviors of sintered polycrystalline diamond by annealing treatment under humid condition

The tribological behaviors of the 700 °C annealed sintered polycrystalline diamond (PCD) at various relative humidity (RH) levels were systematically investigated. The comparison of tribological behaviors between the 700 °C annealed PCD and the pristine PCD was made to further understand the tribological mechanisms. The results reveal that the friction inducing carbonaceous transfer film and oxidation and hydrolysis induced tribochemistry reaction dominant the tribological behaviors of the annealed PCD at various RH levels. The low coefficient of friction (COF) obtained in dry environments is attributed to carbonaceous transfer film on the worn Si₃N₄ surface, which was formed by the layers shearing action of massive tiny diamond grains exfoliated from the annealed PCD surface. The graphitization, oxidation and stress relaxation of the PCD induced by the 700 °C annealing treatment make the tiny diamond grains more easily to exfoliate and be grinded on the Si₃N₄ interface. It facilitates the formation of friction reducing carbonaceous transfer film, and finally results in the 30% lower COFs than those of pristine PCD at low RH levels (5%–50% RH). Meanwhile, an enhanced wear resistance of PCD can be achieved after 700 °C annealing treatment. The tribochemistry reaction induced by the oxidation and hydrolysis of Si₃N₄ governs the tribological behaviors of the annealed PCD at high RH levels (60%–99.9% RH). It reveals higher COFs accompanied with serious wear of Si₃N₄ ball and nearly no wear loss of annealed PCD. The produced SiO₂ and silicic acid embeds into massive spalling pits on the annealed PCD surface, resulting in slighter wear of the PCD and Si₃N₄ than that of the pristine PCD/Si₃N₄. These results propose that the tribological behaviors of PCD under humid environment can be significantly improved by the 700 °C annealing treatment.     

Study on wear mechanisms and grain effects of PCD tool in machining laminated flooring

Polycrystalline diamond (PCD) tools have gained increasing application in woodworking industry for the phenomenal tool life and cutting finish compared with carbide tools. In the paper, machining experiments with PCD tools were conducted to mill laminated flooring with Al₂O₃ overlay. Four kinds of PCD products with different original diamond grain sizes were used to fabricate the cutters. Wear volume was measured by optical microscopy and wear morphology was examined by SEM and optical microscopy.The experimental results show that the wear mechanisms of PCD tools, in the machining process, involve inter-granular wear and partial cleavage fracture. The microcracks in PCD tools are a key reason for the wear of tools. By comparing the flank wear, the experiments reveal that PCD tools with middle original diamond grain size have long tool life. The influences of original diamond grain size on cutting edge and wear properties have also been discussed in detail.     

The influence of tungsten carbide contamination from the milling process on PCD materials oxidation

The most popular polycrystalline diamond (PCD) is a compact with cobalt bonding phase. The thermal resistance of this material is rather low, up to 700 °C. The best way to obtain a higher thermal resistance for diamond compacts (PCD materials) is to limit cobalt content or to sinter the diamond either without a bonding phase or with a ceramic bonding phase. The second group of commercial PCDs, used mainly in rock drilling, are materials with the Si bonding phase. Because of their residual porosity, these materials are not used for metalworking applications, where low roughness value is required. The main focus of the studies presented was the influence of methods of mixture preparation on the microstructures and selected properties of diamond compacts. The traditional method of preparing diamond powders with a bonding phase is to use WC-Co millers. This method causes tungsten carbide contamination of the material, which in these materials decreases their resistance to oxidation during machining. The second aim of these researches was lowering the level of residual porosity. The presence of nanoparticles between diamond microsize particles limits the residual porosity of diamond compacts and improves the roughness properties of cutting tools, but the addition of nanopowders requires intensive milling for good distribution of the ingredients, which increases the WC-Co contamination. In these studies, mixtures containing 90 wt.% diamond with 10 wt.% nanometric TiB₂ powders were prepared with the use of the milling method and the ultrasonic method. The resulting mixtures were formed into discs (15 mm in diameter) by pressing in a steel matrix under the pressure of 100 MPa. The samples were heated using an assembly equipped with an internal graphite heater. The compacts were sintered at the pressure of 8.0 ± 0.2 GPa and the temperature of about 2000 °C in a Bridgman-type ultra high pressure apparatus. The density of the materials was measured. Hardness measurements were carried out with a Vickers apparatus at 9.8 N load. Young's modulus was measured using the ultrasonic method. Phase composition of the diamond compacts was identified by X-ray diffraction analysis. The method of the mixtures preparation has a strong influence on the microstructure and the properties of diamond compacts. The preparation of mixtures in a PULVERISETTE 6 Planetary mill with WC grinding balls results in tungsten contamination, and thus in the presence of WC, WB and W₂C_0,84 in the compacts. The ultrasonic method of mixing allows to receive diamond materials with nanometric bonding phases without tungsten contamination.     

室温脱钴对PCD微观结构及力学性能的影响

为提高PCD使用过程中的热稳定性,选用硫酸-过氧化氢混合溶液在室温下对PCD进行脱钴处理,研究其脱钴机理及脱钴对PCD微观结构及力学性能的影响。通过SEM观察到PCD在室温脱钴48 h后表面出现较大深度的腐蚀坑,钴相基本被去除,上下表面脱钴深度分别为176 μm和162 μm;通过EDS可确定脱钴层剩余钴的质量分数为0.93%,而未脱钴层钴的质量分数为7.64%,表明87.83%的钴在实验中被硫酸-过氧化氢混合溶液溶解而去除。对PCD样品进行残余应力测量,脱钴之前的残余压应力为483.91 MPa,脱钴之后的残余压应力为330.35 MPa,后者相对前者减少31.73%,说明脱钴可以有效降低PCD内部残余压应力。      

Synthesis and characterization of Ba(CoxNb1-x)O3 nanoparticles by hydrothermal processing

The nanosized Ba(Co_xNb_1–x)O₃(BCN) particles were prepared under high temperature and pressure conditions by precipitation from metal nitrates with aqueous potassium hydroxide. Ba(Co_xNb_1–x)O₃ powders were obtained in the temperature range of 170–210 °C for 6 h. The results show that the average size of the synthesized particles increases with increasing reaction temperature. The average size of the synthesized particles is about 10 nm. The crystalline phase of the synthesized particles is found to be Ba(Co_xNb_1–x)O_3. Ceramics derived from the nano BCN powders could achieve high sintering density at a relatively low sintering temperature.     

Research Progress on the Crack Formation Mechanism and Cracking-Free Design of gamma' Phase Strengthened Nickel-Based Superalloys Fabricated by Selective Laser MeltingEI北大核心CSCD

传统牌号高强镍基高温合金具有较宽的凝固温度区间、较高比例的低熔点共晶相,在增材制造快速非平衡凝固过程中易产生裂纹等缺陷;同时,热处理过程中残余应力释放和γ’相快速析出导致应变时效裂纹的形成,严重限制了其在激光增材制造领域的应用与推广。基于此,本文综述了近年来国内外研究组及作者团队在选区激光熔化高强镍基高温合金裂纹形成机理与抗裂纹设计(成形工艺参数优化、热处理制度调控以及合金成分设计)领域相关的研究进展,并对激光增材制造γ’相强化镍基高温合金裂纹调控的研究进行了展望。     

Improvement in adhesion of diamond film on Cu substrate with an inlay structured interlayer

Diamond films were fabricated by using a two-step process on copper substrates in this study. The first step involved electroplating a chromium (Cr)–diamond composite interlayer on copper substrate and in the second step continuous diamond film was deposited on top using the hot-filament chemical vapor deposition (HFCVD) method. The interfacial characteristics was investigated by indentation tests and the thin film surface morphology, phase structure and residual stress analyzed by scanning electron microscopy (SEM), X ray diffraction (XRD) and Raman spectroscopy. The results show that the diamond particles are deeply imbedded in the chromium layer and the amorphous Cr in the composite interlayer was carburized to Cr₃C₂ during the CVD process. Low residual stress was detected in the diamond film and good adhesive strength between film and substrate was obtained due to the diamond particles anchored deep in the Cr₃C₂ matrix. Concentric cracks but no delaminated areas and radial cracks were observed on the periphery of the indentation at indentation load of 441 N.     

Interfacial microstructure and properties of diamond/Cu-<Emphasis Type="Italic">x</Emphasis>Cr composites for electronic packaging applications

Diamond/Cu-xCr composites were fabricated by pressure infiltration process.The thermal conductivities of diamond/Cu-xCr(x = 0.1,0.5,0.8) composites were above 650 W/mK,higher than that of diamond/Cu composites.The tensile strengths ranged from 186 to 225 MPa,and the bonding strengths ranged from 400 to 525 MPa.Influences of Cr element on the thermo-physical properties and interface structures were analyzed.The intermediate layer was confirmed as Cr3C2 and the amount of Cr3C2 increased with the increase of Cr concentration in Cu-xCr alloys.When the Cr concentration was up to 0.5 wt.%,the content of the Cr3C2 layer was constant.As the thickness of the Cr3C2 layer became larger,the composites showed a lower thermal conductivity but higher mechanical properties.The coefficients of thermal expansion(CTE) of diamond/Cu-xCr(x = 0.1,0.5,0.8) composites were in good agreement with the predictions of the Kerner’ model.     

Thermoelectric power and electrical resistivity of Ag-doped Na1.5Co2O4

Polycrystalline samples of Na_1.5Co_2−xAg_xO₄ (x = 0, 0.1 and 0.2) were synthesized from powder precursors prepared by a polymerized complex (PC) method. The thermoelectric power (S) and electrical resistivity (ρ) of Na_1.5Co_2−xAg_xO₄ (x = 0, 0.1, 0.2) were measured simultaneously in a helium atmosphere, in the temperature range from room temperature to 973 K. The thermoelectric power and power factor of Na_1.5Co_1.8Ag_0.2O₄ are higher than that of Na_1.5Co₂O₄ over a wide range of temperatures.     

Co-Sn单相合金深过冷凝固时Co3Sn2 相生长形貌的演变机制

开展了(Co₆₀Sn₄₀)_100-xNb_x (x=0,0.4,0.6,0.8,at%)单相合金的深过冷凝固实验,研究了Co₃Sn₂相生长形貌的演变机制。结果表明,在小过冷度下,Co₃Sn₂相在x=0,0.4以海藻状的模式进行生长,随着添加的Nb含量增加至0.6at%,其生长形貌转变为树枝晶,并在x=0.8进一步转变为分形海藻晶,这主要是由于界面能各向异性和动力学各向异性的变化。随着过冷度的增加,(Co₆₀Sn₄₀)_99.4Nb_0.6合金中Co₃Sn₂相生长形貌在过冷度大于28 K时从树枝晶转变为分形海藻,当过冷度高于143 K时转变为密集海藻。少量的Nb添加在小过冷度和中间过冷度时能提高Co₃Sn₂相的生长速度,但是在大过冷度下会显著降低生长速度。Co₃Sn₂相生长速度随过冷度变化规律的转变对应其生长形貌从分形海藻向密集海藻的转变。     

大面积聚晶金刚石复合片电火花加工温度场及应力场的数值模拟

在研究电火花加工机理的基础上,基于有限元原理,建立了电火花连续脉冲放电磨削聚晶金刚石复合片时的物理模型,对磨削过程工件表面的温度场、应力场分布及工件材料的变形规律进行了模拟分析.研究了脉冲宽度及峰值电流对温度场、应力场分布及复合片变形量的影响规律.结果表明,有限元法是分析大面积聚晶金刚石复合片电火花磨削过程中温度场、应力场及变形的一种有效方法,其计算结果可用来指导制定合理的加工工艺参数以提高加工质量和加工效率.     

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...     

Deposition of cobalt oxide thin films by plasma-enhanced chemical vapour deposition (PECVD) for catalytic applications

Plasma-enhanced chemical vapour deposition (PECVD) was used to prepare thin films of cobalt oxide. Cobalt oxide-based (CoO and Co₃O₄) catalysts were chosen due to their efficiency in mineralisation of organic pollutants achieved by catalytic ozonation. In this work, two types of PECVD processes were used for the production of cobalt oxide thin films. In the first one, a solution of nitrate salt of cobalt was sprayed into a RF low pressure plasma discharge (40 MHz, 600 Pa, 200 W) to obtain Co_xO_y layers. In the second MOPECVD (metal organic plasma-enhanced chemical vapour deposition) process, cobalt oxide thin films were deposited using a capacitive coupled external electrodes RF plasma reactor (13.56 MHz, 100 Pa, 200 W) with cobalt carbonyl Co₂(CO)₈ dissolved in hexene as precursor sprayed in a gas carrier (argon and oxygen).In the case of coatings produced from a solution of cobalt nitrate salt, a layer of 1 μm of Co₃O₄ in crystalline form was obtained after annealing. Considering the thin films obtained from cobalt carbonyl precursor, analyses confirmed the presence of cobalt oxide in a polymeric layer on the surface of the substrate. XRD investigation showed the presence of a crystalline phase of Co₃O₄ (crystallite size of about 40 nm).     

Effects of SO2/SO2 on the efficiency with which MgO inhibits vanadic corrosion in residual fuel fired gas turbines

The use of MgO as a fuel additive to combat vanadic corrosion is widely accepted practice for boilers and turbines operating on residual or low grade fuels. MgO has the ability to form high melting stable vanadates but the presence of SO₂/SO₂ can react with the magnesium and reduce its effectiveness. This paper aims to quantify the effectiveness of MgO as an inhibitor in the presence of increasing amounts of SO_x. A method of determining permissible levels of SO_x to satisfy predetermined corrosion rates or additive efficiencies is described. Examples of the loss of additive efficiency with volume of SO_x at temperatures of 750 and 850°C are given for both nickel and cobalt base alloys.     

Effect of Praseodymium on Magnetic Properties and Phase Composition of a Material of the Nd - Pr - Dy - Fe - Co - B System

Sintered magnetically hard materials with compositions (Nd_{0.5 − x} Pr _x Dy_0.5)₁₈(Fe_0.7Co_0.3)_remB_5.5 (x = 0.12 − 0.5) and (Nd_{0.6 − x} Pr _x Dy_0.4)₁₅(Fe_0.8Co_0.2)_remB₆ (x = 0.03 − 0.4) are studied. The role of praseodymium (at invariable content of dysprosium and cobalt) in the change of magnetic properties of the material (residual induction, coercive force, temperature stability) is determined. The phase composition of the material is identified. The role of praseodymium in the magnetic properties of the material is interpreted. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 12 – 16, June, 2005.     

Magnetic properties of the Mn1.9 − x Co x Ge compounds with a hexagonal crystal structure

Concentrational dependences of the lattice parameters, spontaneous magnetic moment, and magnetic ordering temperature of nonstoichiometric Mn_{1.9 ? x} Co _x Ge (0.8 < x < 1.65) compounds with a hexagonal crystal structure of the Ni₂In type have been studied. As the Co content (x) increases from 1.1 to 1.2, the Curie temperature and magnetic moment were found to increase abruptly. The magnetization curves measured for oriented single crystals indicate the presence of a concentrational spin-reorientation transition in this system. The experimental data obtained are discussed taking into account the results of energy-band electronic-structure calculations.     

Electrochemical properties of LiNi0.8Co0.2?xAlxO2 (0≤x≤0.1) cathode particles prepared by spray pyrolysis from the spray solutions with and without organic additives

Fine-sized LiNi_0.8Co_0.2−xAl_xO₂ (0≤x≤0.1) cathode particles were prepared by spray pyrolysis from the spray solutions with and without organic additives. Citric acid, ethylene glycol, and Drying Control Chemical Additive (DCCA) were used as organic additives and improved the morphologies and electrochemical properties of the cathode particles. The LiNi_0.8Co_0.2−xAl_xO₂ (0≤x≤0.1) cathode particles obtained from the spray solutions with organic additives were of micro size and had slightly aggregated morphologies. The initial discharge capacities of the LiNi_0.8Co_0.2−xAl_xO₂ (0≤x≤0.1) cathode particles obtained from the spray solutions without organic additive changed from 169 mAhg⁻¹ to 190 mAhg⁻¹ when the x changed from 0 to 0.1. However, the initial discharge capacities of the cathode particles obtained from the spray solutions with organic additives changed from 196 mAhg⁻¹ to 218 mAhg⁻¹. The initial discharge capacity of the LiNi_0.8Co_0.15Al_0.05O₂ cathode particles obtained from the spray solution with organic additives was maintained after the 20th cycle at a current density of 0.1 C.