亚微米级聚晶金刚石的高温高压合成

聚晶金刚石作为超硬材料具有很广泛的应用,常用于油气钻探、切削刀具、耐磨零件等领域。目前,工业上合成聚晶金刚石的内部晶粒尺寸一般都在微米量级以上,而合成微米级以下的聚晶金刚石则要面临很多困难。本工作使用熔渗法在高温高压的条件下合成了亚微米级聚晶金刚石,并对合成的样品进行了X射线衍射、扫描电子显微镜、电子背散射衍射、能谱、硬度等分析测试,结果表明:在5.5GPa、1 500℃、保温15min的情况下成功合成了维氏硬度高达57.0GPa的亚微米级聚晶金刚石;分层组装的方法可以使Co均匀地分散在聚晶金刚石样品中,呈现出圆孔状,从而保证样品具备均匀、优异的性能。同时,通过对烧结工艺的探索发现,温度和保温时间在亚微米级聚晶金刚石的合成过程中起着非常重要的作用。     

微米晶单斜氧化锆高压相变制备亚微米四方多晶氧化锆

高压相变已逐渐发展成为一种制备纳米/亚微米多晶陶瓷块体材料的有效方法。高压可以抑制原子的长程扩散进而抑制晶粒长大,高压下截获的新相不受初始材料晶粒尺寸的制约,通过热力学调控可以得到晶粒尺寸更小的多晶块体材料。陶瓷材料在特定热力学条件下通常会发生相变,新相的形成要经历形核、生长的过程。采用晶粒尺寸为2μm的单斜ZrO2与晶粒尺寸为50 nm的Y2O3以97:3的摩尔比混合,在5.5 GPa、800～1700℃温压区间内对初始材料进行烧结,采用X射线衍射、扫描电镜、透射电镜对所得样品进行表征。研究结果表明:高压下截获了单斜相和亚微米四方相复合的多晶ZrO2块体材料,1200、1400、1600和1700℃温度下获得的四方相的平均晶粒尺寸为(145±62) nm、(246±165) nm、(183±62) nm和(245±107) nm。利用高压相变以微米晶制备细晶粒多晶块体材料,可以避免常规方法中以纳米粉末为初始材料制备细晶粒多晶块体材料存在的团聚、吸附及晶粒长大的问题,进而发展一种以微米晶为初始材料通过高压相变制备高性能细晶粒多晶块体材料的方法。     

放电等离子烧结制备纳米Ni块体材料

 采用自悬浮定向流法制备纳米Ni粉体,利用放电等离子烧结技术制备出了直径10 mm、厚2 mm,致密度为96.8 %,显微硬度为4.17 GPa的纳米块体材料。用X射线衍射仪、扫描电子显微镜和显微硬度计分析了烧结块体样品的相组成、晶粒尺寸、微观形貌和显微硬度。研究表明：随烧结温度的升高,块体样品的致密度和晶粒尺寸增大,当烧结温度为650 ℃时,致密度最高,晶粒尺寸为44.8 nm;显微硬度随烧结温度的增高先增大后减小,当烧结温度为550 ℃时,显微硬度最大为4.33 GPa;较高烧结温度下,断口微观形貌的纳米级韧窝出现,显示了韧性断裂的特征。     

B_6O/TiB_2复合材料的高温高压反应烧结

以B和TiO2为初始原料,依据压力可抑制原子长程扩散的动力学效应,通过高温高压(4~5GPa,1 200~1 500℃)一步反应烧结法制备B6O/TiB2复合材料。当B和TiO2物质的量之比为14.0∶0.8时,在5GPa、1 200℃、保温30min条件下得到的烧结样品性能较好,非晶硼(纯度93%~94%)过量混合粉末样品的硬度最高约为29GPa,高纯晶体硼(纯度99.99%)过量混合粉末样品的硬度最高约为32GPa,相对密度可高达99%。实验结果表明:高压抑制晶粒过度长大,同时又有利于B6O的合成,使其合成温度比常压下有所降低;在高压反应烧结过程中,合成的第二相TiB2晶粒和样品中的非晶相有效地消耗了残余应力,起到了增韧作用。     

高温高压烧结高硬度高致密度块体金属钨及钨基合金W-TiC

采用高温高压烧结方法,烧结纯钨和TiC颗粒弥散增强W-TiC合金材料,对钨及W-TiC合金的烧结致密化行为和力学性能进行了研究。结果表明:在压力为5.0GPa、温度为1 500℃的条件下烧结15min可获得良好的烧结样品,块体钨的致密度达到99.3%,硬度达到6.43GPa;在相同的高温高压烧结条件下,添加质量分数为1.5%的TiC,获得的W-TiC合金致密度达到99.0%,硬度达到7.58GPa。极端高压环境不但能抑制钨及钨合金在烧结过程中的晶粒长大,还能降低烧结温度,提高烧结效率,增加烧结体的致密性。在此基础上进一步探索了钨及钨基合金W-TiC的高压烧结动力学、微观结构、机械性能与烧结压力和烧结温度的关系。     

二硼化钛的高温高压制备及其物性

以化学计量配比的Ti,B元素为原料,在高温高压条件下成功制备出颗粒均匀、致密性大于99％的二硼化钛(TiB2)体材料.物性测试结果表明:TiB2的维氏硬度高达39.6 GPa(接近超硬材料的40 GPa);并呈现出金属导电特性,电阻率在10-8 Ω.m的数量级(接近TiB2单晶样品值).TiB2的高硬度与金属特性,可能与该方法制备的TiB2体材料中均匀的细小晶粒尺寸有关.该方法为制备功能陶瓷材料提供了新的思路.     

AlNBN复相纳米陶瓷的高温高压合成与表征

利用直流电弧等离子体方法制备了氮化铝纳米粉,用行星式球磨机制备纳米级的氮化硼粉,将这两种纳米粉均匀混合,经过5 GPa、1500 ℃的高温高压处理,最终制备出AlN/BN纳米复相陶瓷,对合成的产物进行了X射线衍射（XRD）、透射电子显微镜(TEM)和扫描电子显微镜(SEM)的分析,得到样品的结构和形貌特征,结果表明合成产物为AlN/BN纳米复相陶瓷.      

核壳纳米粉体制备Y_2O_3-MgO复相陶瓷（英文）

由于优异的光学和机械性能,Y_2O_3-MgO复相纳米陶瓷被认为是红外透明陶瓷的重要候选材料。尽管如此,在近红外和中红外波段严重的光散射和不必要的吸收方面仍然存在巨大的挑战,这阻碍了该材料在极端恶劣环境中的应用。在目前的工作中,先通过尿素沉淀法制备了Y_2O_3-MgO核壳结构纳米粉体,然后在放电等离子体烧结下制备了Y_2O_3-MgO复相纳米陶瓷。通过热重和差示扫描量热法(TG/DSC)、X射线衍射和扫描电子显微镜分析了核壳结构纳米粉及复相纳米陶瓷。Y_2O_3-MgO核壳结构纳米粉体的尺寸约为250 nm,并且制备的陶瓷的平均晶粒尺寸约为360 nm。透过率在6μm处为57%,维氏硬度为820 HV。粉末合成方法为复相纳米陶瓷提供了一种新颖的解决方案,可以轻松调节粒径和不同组分的比例。     

压致硼酸盐晶态物质的非晶化现象研究

 本文用X射线衍射、Eu²⁺的发射谱与激发谱、拉曼谱以及扫描电镜（SEM）颗粒形貌，研究了常压下合成的具有正交结构的SrB₂O₄:Eu²⁺晶体在3.0~7.0 GPa压力下的晶态非晶化现象。分析结果表明，压力导致晶粒细化和晶态非晶化。晶粒尺寸由常压下的微米量级细化为几十个纳米量级，随压力的变化为：2 μm（0.1 MPa），49.4 nm（3.0 GPa），29.7 nm（5.0 GPa），25.1 nm（7.0 GPa）。晶态与非晶态体积比随压力增加而减小，分别为：70/30（3.0 GPa），63/37（5.0 GPa），57/43（7.0 GPa）。在压力下Eu²⁺是处在晶态与非晶态两种不同的低对称的环境中。纳米级晶粒是以亚晶粒形式存在于微米级大晶粒中的，压致非晶态可能组成了纳米亚晶粒的界面区。     

氧化锌纳米晶高压下的晶粒演化和性能

用GS-1B型六面顶压机研究了ZnO纳米晶高压下的晶粒演化和性能，用X射线衍射仪和场发射扫描电子显微镜对高压样品的晶粒尺寸、微观形貌进行了表征.结果表明，高压下ZnO纳米晶存在压致晶粒碎化效应.硬度和伏安特性实验表明，高压调制后样品的显微硬度约是常压烧结样品硬度的2.3倍，非线性伏安特性明显优于常压烧结样品. 关键词： 氧化锌纳米晶 高压 压致碎化 非线性伏安特性     

Fracture toughness evaluation of WC–10 wt% Co hardmetal sintered under high pressure and high temperature

This work focused on fracture toughness studies of WC–10?wt% Co hardmetal fabricated through the high pressure/high-temperature technique. A powder mixture of WC–10?wt% Co was sintered at 1500–1900°C under a pressure of 7.7?GPa for 2 and 3?min. Vickers hardness test at two different loads of 15 and 30?kgf was done and fracture toughness of the sintered bodies was measured using the indentation method to obtain the effect of sintering parameters. Structural analyses were also performed via X-ray diffraction to investigate structure-related properties. Full density was achieved for high sintering temperature along with abnormal grain growth that reduced hardness. High hardness was observed ranging from 1200 to 1670?HV and fracture toughness increased with increasing sintering temperature up to the highest value of 17.85?MPa/m^1/2.     

Pressure‐induced incompressibility and point singularity of mechanical properties of TaC in NiAs‐type structure

The structural and elastic properties of TaC in NiAs‐type structure under high pressure have been investigated using first principles calculations based on density functional theory. Results indicate that the incompressibility along the c‐axis of TaC exceeds that of diamond under higher pressure. Particularly, an interesting point singularity exists in its mechanical properties as the pressure increases from 20 GPa to 40 GPa. The minimal shear modulus, Young's modulus, Debye temperature, and maximum Poisson ratio of TaC are simultaneously obtained at 28 GPa. The calculations of hardness indicate that the NiAs‐type TaC crystal possesses excellent mechanical properties. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

正交试验法优化金刚石复合片合成工艺

 通过正交试验法,以磨耗比、电阻、完整性、硬度为指标,设计了金刚石复合片的合成工艺。正交试验可以减少合成工艺试验次数,优化合成工艺。试验结果表明,较合理的烧结工艺为：合成压力5.5 GPa,升温速度为200 ℃/min,保温时间16 min,冷却时间14 min,烧结温度1 350 ℃。从压力、温度和时间等因素的影响方面讨论了金刚石复合片的性能。认为：适当地提高温度有利于提高磨耗比及硬度;延长加热时间有利于性能均匀性的提高;延长冷却时间可减少残余热应力。     

Novel structures and mechanical properties of Zr2N:Ab initio description under high pressures

With the formation of structural vacancies,zirconium nitrides(key materials for cutting coatings,super wearresistance,and thermal barrier coatings) display a variety of compositions and phases featuring both cation and nitrogen enrichment.This study presents a systematic exploration of the stable crystal structures of zirconium heminitride combining the evolutionary algorithm method and ab initio density functional theory calculations at pressures of 0 GPa,30 GPa,60 GPa,90 GPa,120 GPa,150 GPa,and 200 GPa.In addition to the previously proposed phases P42/mnm-,Pnnn-,and Cmcm-Zr2 N,five new high-pressure Zr₂N phases of PA/nmm,IA/mcm,P2₁/m,P3 m1,and C2/m are discovered.An enthalpy study of these candidate configurations reveals various structural phase transformations of Zr2 N under pressure.By calculating the elastic constants and phonon dispersion,the mechanical and dynamical stabilities of all predicted structures are examined at ambient and high pressures.To understand the structure-property relationships,the mechanical properties of all Zr₂N compounds are investigated,including the elastic moduli,Vickers hardness,and directional dependence of Young’s modulus.The Cmncm-Zr2 N phase is found to belong to the brittle materials and has the highest Vickers hardness(12.9 GPa) among all candidate phases,while the I4/mcm-Zr2 N phase is the most ductile and has the lowest Vickers hardness(2.1 GPa).Furthermore,the electronic mechanism underlying the diverse mechanical behaviors of Zr2 N structures is discussed by analyzing the partial density of states.     

Synthesis and characterization of in situ nanocrystalline intermetallic phase reinforced AlTiSi amorphous matrix composite

Composites with partially amorphous matrix were synthesized by mechanical alloying of an Al₅₀Ti₄₀Si₁₀ elemental powder blend in a high energy planetary ball-mill, followed by high pressure (8 GPa) low temperature (350–450°C) sintering. Microstructural studies and compositional micro-analysis were carried out using scanning and transmission electron microscopy, and energy dispersive spectroscopy, respectively. Phase evolution as a function of milling time and isothermal temperature and their thermal stability was determined by X-ray diffraction at room or elevated temperature and differential scanning calorimetry, respectively. The microstructure of composites sintered between room temperature and 450°C showed nano-size (≈50 nm) crystalline precipitates of Al₃Ti dispersed in an amorphous matrix. The composites sintered at 400°C with 8 GPa pressure exhibited the highest density (3.58 Mg/m³), nanoindentation hardness (8.8 GPa), Young's modulus (158 GPa) and compressive strength (1940 MPa). A lower hardness and modulus on sintering at 450°C is attributed to additional amorphous to nanocrystalline phase transformation and partial coarsening of Al₃Ti.     

高温高压下碳纳米管的相转变及金刚石的合成

 利用透射电子显微镜（TEM）和扫描电子显微镜（SEM）研究了碳纳米管在高压高温下的相转变。研究发现在高压高温条件下碳纳米管是不稳定的,在5.5 GPa压力下,770 ℃到950 ℃间退火时碳纳米管趋向形成碳纳米葱。在5 GPa、1 000 ℃条件下合成了金刚石。     

Hardness and elastic moduli of high pressure synthesized MoB2 and WB2 compacts

High pressure and high temperature synthesized MoB₂ and WB₂ compacts were investigated using X-ray diffraction, energy dispersive spectroscope, scanning electron microscope, Vickers indentation test and ultrasonic measurements. Experiments showed that both MoB₂ and WB₂ compacts are phase pure and with a grain size of 100–200 nm. Vickers indentation test under a large loading force of 49 N showed that the Vickers hardness of MoB₂ and WB₂ are about 21 and 22 GPa, respectively. The bulk modulus and shear modulus are about 296 GPa, and 190 GPa for MoB₂ and 349 and 200 GPa for WB₂ through ultrasonic measurements. Our results indicate that MoB₂ and WB₂ are both hard materials with a hardness similar to that of tungsten carbide, which is widely used in industry.     

Ceramic synthesis of 0.08BiGaO_3–0.90BaTiO_3–0.02LiNbO_3 under high pressure and high temperature

In this paper, the preparation of 0.08BiGaO_3–0.90BaTiO_3–0.02LiNbO_3 is investigated at pressure 3.8 GPa and temperature 1100–1200?C. Experimental results indicate that not only is the sintered rate more effective, but also the sintered temperature is lower under high pressure and high temperature than those of under normal pressure. It is thought that the adscititious pressure plays the key role in this process, which is discussed in detail. The composition and the structure of the as-prepared samples are recorded by XRD patterns. The result shows that the phases of Ba TiO_3, BaBiO_(2.77), and Ba_2Bi_4Ti_5O_(18) with piezoelectric ceramic performance generate in the sintered samples. Furthermore, the surface morphology characteristics of the typical samples are also investigated using a scanning electron microscope. It indicates that the grain size and surface structure of the samples are closely related to the sintering temperature and sintering time. It is hoped that this study can provide a new train of thought for the preparation of lead-free piezoelectric ceramics with excellent performance.     

High pressure infiltration sintering behavior of WC-Co alloys

In this paper, two average tungsten carbide particle sizes of 2, 0.5?μm are placed respectively, in contact with a WC-16Co substrate, pressed at the pressure of 4.5–5.5?GPa, and heated to temperatures ranging from 1350°C to 1500°C in a large-volume cubic press. During the process Co was forced out of the WC-16Co substrate into the compressed powder. The resulting infiltrated samples were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), Vickers hardness and cutting performance tests. The results of XRD confirmed that the sintered bulks have WC and Co phases. The scanning electron microscopy (SEM) analysis reveals that the WC grains in well-sintered alloys are round in shape and cobalt with lower content is uniformly dispersed in the WC grain boundaries. The sintered sub-micron WC-Co alloy with a cobalt content of 3.8?wt% exhibits a prominent combination of high hardness value of 23.1?GPa and a large fracture toughness value of 8.6?MPa?m^½. The high-speed cutting tests indicating its cutting performance is significantly superior to the commercial YG6X (WC-6?wt%Co with WC grain size of 0.5?μm).     

高温高压下钠长石的阻抗谱实验研究

 在压力为1.0、2.0 GPa和温度为673～973 K条件下,采用交流阻抗谱法在YJ-3000t紧装式六面顶高压设备上原位测量了钠长石的电导率。实验结果表明：在实验的温度和压力范围内,钠长石的电导率在10^-3.0～10^-5.5 S/m变化;钠长石复阻抗的模和相角对频率有很强的依赖性;随着温度T升高,钠长石的电阻率迅速减小,电导率σ增大,并且lg σ与T^-1之间符合Arrhenius关系;在实验压力范围内,随着压力升高,钠长石的电导率降低。采用离子导电机制,对高温高压下钠长石的导电行为进行了合理解释。