放电等离子烧结钼的组织和性能

研究了放电等离子烧结（SPS）钼的致密化,组织和硬度,与其它烧结方法相比,SPS是一种时间短,温度低的先进快速烧结法。利用SPS在比CIP－S和热压烧结（HP）低180－500℃下进行烧结,保温3min,得到钼的相对密度是95．2％－97．9％,硬度比其它方法烧结的高出HV20－HV75。SPS烧结钼的密度呈现随烧结温度的升高而增加的趋势。但是其硬度有所下降,SPS在较低温度下烧结的钼的硬度较高,原因是其晶粒较细,SPS烧结钼的断口呈沿晶断裂,属于脆性断裂。     

立方氮化硼刀具的合理使用

立方氮化硼刀具是一种先进的切削刀具。过去主要用于精加工,近十几年来通过改进生产工艺,控制原料纯度和晶粒尺寸,采用复合材料和热压工艺等,韧性提高,使用可靠性大大改善,已可作为常规刀具在生产中应用,对提高工效、保证产品质量起着重要作用。文中介绍了立方氮化硼刀具的种类、性能与合理使用方法。     

等离子放电烧结制备10ScSZ细晶块体及其烧结温度探究

采用燃烧法制备10ScSZ粉体,通过等离子放电烧结(SPS)制备10ScSZ细晶致密陶瓷块体。根据SPS上下电极间距随烧结温度的变化绘制烧结曲线,在1200℃附近电极间距最小,判断陶瓷致密化温度在1200℃左右。为验证该方法的可靠性,选取1050,1100,1150,1200,1250℃作为烧结温度分别制备样品。结果表明,在1150℃烧结的10ScSZ样品具有最高的致密度,达到99.4%,且具有平均晶粒尺寸为194 nm的细晶结构,与推测结果基本相符。该实验结果证实了在SPS烧结中通过烧结曲线判断合适的烧结温度是一种高效可行的方法。     

立方氮化硼单晶的热分析图谱特征及热稳定性

本文探讨了国产黑色、琥珀色立方氮化硼的热分析图谱特征;立方氮化硼的氧化过程分三个阶段进行;立方氮化硼的热稳定性大于１２００℃。     

放电等离子烧结温度对超细晶W-40Cu复合材料的影响

采用高能球磨法制备了W-40Cu超细晶复合粉体,继而进行了放电等离子烧结(SPS),获得了致密的超细晶W-40Cu块体复合材料,着重研究了烧结温度对复合材料组织和性能的影响.结果表明,随着烧结温度升高,材料的致密度、硬度和电导率也随之升高;在950℃烧结5 min的W-40Cu复合材料,W颗粒尺寸约300～500 nm,相对致密度达98％,显微硬度HV为287,电导率为17.9 MS/m.     

反应烧结制备新型Al基结合剂立方氮化硼复合材料

以Al/Ti/C/CBN粉体为原料,通过原位反应烧结技术,制备Al基金属陶瓷复合结合剂立方氮化硼材料。使用X射线衍射仪(XRD)、扫描电镜(SEM)结合能谱仪(EDS)分析试样。研究结果表明:在1 000℃保温1 h,反应烧结得到Al/TiC或Al/Al3Ti金属陶瓷复合结合剂立方氮化硼材料。Al质量分数较低时,产物的主相为Al和TiC;而当Al质量分数较高时,产物的主相则为Al和Al3Ti。同时,氮化硼与Ti和Al反应合成了AlN和TiB。试样的物相分析和断口形貌都表明基体与氮化硼有良好的结合。     

Preparation of polycrystalline cubic boron nitride compact by high-pressure infiltration using cemented carbide

Polycrystalline cubic boron nitride (PcBN) compacts, using the infiltrating method in situ by cemented carbide (WC–Co) substrate, were sintered under high temperature and high pressure (HPHT, 5.2 GPa, 1450 °C for 6 min). The microstructure morphology, phase composition and hardness of PcBN compacts were investigated by using scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The experimental results show that the WC and Co from WC–Co substrate spread into cubic boron nitride (cBN) layer through melting permeability under HPHT. The binder phases of WC, MoCoB and Co₃W₃C realized the interface compound of PcBN compact, and the PcBN layer formed a dense concrete microstructure. Additionally the Vickers hardness of 29.3 GPa and cutting test were performed when sintered by using cBN grain size of 10–14 μm.     

Effect of sintering temperature on the structure and properties of polycrystalline cubic boron nitride prepared by SPS

The polycrystalline cubic boron nitride (PcBN) with Si₃N₄–AlN–Al₂O₃–Y₂O₃ ceramic system as binding agents was prepared by spark plasma sintering (SPS). The starting materials Si₃N₄, AlN, Al₂O₃, Y₂O₃, and cBN in the ratio of 22:14:10:4:50 were heated to a sintering temperature between 1250 °C and 1450 °C at a heating rate of 300 °C/min, with a holding time of 5 min in nitrogen atmosphere. The microstructure, phase constitution, microhardness and fracture toughness of the prepared PcBN were then studied. It was shown that the Si₃N₄–AlN–Al₂O₃–Y₂O₃–cBN polycrystalline materials were densified in a very short sintering time resulting in materials with relative densities of more than 95%. When the sintering temperature increased, the microhardness and fracture toughness of prepared PcBN were also increased. The microhardness of PcBN prepared at 1250–1450 °C was between 28.0 ± 0.5 GPa and 48.0 ± 0.9 GPa, and its fracture toughness K_IC was from 7.5 ± 0.2 MPa m^1/2 to 11.5 ± 0.3 MPa m^1/2. Microstructure study showed that the ceramic-binding agents bonded with cubic boron nitride particles firmly. Our work demonstrated that spark plasma sintering technology could become a novel method for the preparation of PcBN cutting materials.     

六方氮化硼直接转化合成多晶立方氮化硼的研究

以六方氮化硼为初始材料,采用直接转化法在9～15 GPa、1500～2100℃的条件下合成多晶立方氮化硼.采用X射线衍射仪、扫描电子显微镜、维氏硬度计,对多晶立方氮化硼块材的微观结构和力学性能进行表征.结果表明:在合适的温度、压力条件下,六方氮化硼可转化为纯相多晶立方氮化硼,其晶粒尺寸最小约为70 nm,最大可达10μ...     

聚晶立方氮化硼的制备方法及应用进展

对近年来国内外聚晶立方氮化硼(polycrystalline cubic boron nitride,PCBN)及其复合片的制备方法和工业应用进行了综述,主要介绍了烧结型、生长型和生长–烧结型聚晶立方氮化硼的制备方法;系统论述了采用直接转化法、钎焊法和一次烧结法制备聚晶立方氮化硼复合片的进展;并对聚晶立方氮化硼在汽车制造、轴承和超精密工具等行业中的应用进行了概述。最后,对聚晶立方氮化硼及其复合片未来发展方向进行了展望。     

聚晶立方氮化硼（PCBN）的制备及应用研究进展

本文通过CBN与其他刀具材料的对比,指出PCBN的高硬度、高耐磨性和高热稳定性的特点.文献表明有结合剂的PCBN正朝着高断裂韧性、高耐磨性方向发展,同时尺寸越来越大,结合剂体系以金属陶瓷为主,其中陶瓷组分包括TiN、AlN、Si3N4、TiC等,金属有Co、Ti、Al等.无结合剂的纯PCBN和表面镀覆PCBN也正在积极研究中,高纯PCBN具有与纯CBN接近的力学性质.根据加工材料的成分和微观结构决定PCBN刀具的应用,努力使切割工具和工具材料标准化.     

六方氮化硼的制备方法及在合成立方氮化硼中的应用

对中国生产六方氮化硼(hBN)的厂家的制备方法进行了研究,采用感应耦合等离子发射光谱(ICP)、X射线衍射、激光粒度分析及比表面积测定等方法对不同方法制备的hBN粉末进行了检测分析对比。结果发现,其杂质含量、颗粒形貌、结晶度等性能无明显的差异,均属纯度一般的粗制hBN。合成立方氮化硼(CBN)的试验及生产使用表明,虽然不同方法制备的hBN合成CBN的效果和适用性有差别,但均能满足我国CBN单晶合成的需要,为国产合成CBN提供了基础原材料保证。     

Self-bonding mechanism of pure polycrystalline cubic boron nitride under high pressure and temperature

Cubic boron nitride (cBN) powders with different grain size were used as a starting material, and the pure polycrystalline cubic boron nitride (PcBN) samples were sintered under the same conditions at 7GPa, 1700 °C, 270 s. Abrasion resistance and compressive strength of sintered pure PcBN samples were tested, and the microstructure was observed and analyzed by SEM, HRTEM, XRD and Raman spectrum. The results show that the particle size of cBN has not only a great influence on microstructure and property of the sintered pure PcBN un-der the same conditions but also influence on the bonding mechanism of the cBN particles. The inner stress of the pure PcBN sintered with the cBN particle size of 10 μm during the high pressure sintering process is about 199–222% higher than that of the sample with the cBN size of 1 μm. The wear ratio and the compressive strength of PcBN samples sintered with 10 μm cBN was increased by 47.7% and 39.7% than that of the sintered sample with 1 μm cBN respectively. The coarser-grained PcBN contains serious deformation and crushing, which can be attributed to the twin boundary and the stacking faults in the samples. As a consequence, the abrasion ratio and compressive strength of the pure PcBN are dramatically increased. It is assumed that self-bonding mechanism generated from plasticity deformation, which is a main bonding mechanism for the high pressure sintering of pure cubic boron nitride.     

Some properties and cutting performance of polycrystalline cubic boron nitride with no additives

Hexagonal BN disks made by chemical vapor deposition were treated under ultra high pressure of 6.8 GPa and at temperatures from 1800 to 2500 °C for 1.8 ks. When treated at temperatures above 2100 °C, only a c-BN phase was detected. The sample treated at 2100 °C had a homogeneous microstructure having fine grain size less than 1 μm, whereas that treated at 2300 °C had a heterogeneous one with some large grains. The sample treated at 2500 °C showed remarkable grain growth. Some physical properties and cutting performance of these compacts were investigated. Then hardness clearly decreased at 2500 °C and the thermal conductivity was higher when synthesized at 2500 °C than at 2100 °C. The fine grained compact of 2100 °C exhibited better wear resistance than the coarse grained one of 2500 °C in cutting of Co base super alloy and cemented carbide.     

Electron cyclotron resonance plasma deposition of cubic boron nitride using N-trimethylborazine

N-Trimethylborazine has been used as precursor in a downstream electron cyclotron resonance (ECR) plasma process to deposit cubic boron nitride (c-BN). N-Trimethylborazine ((CH₃-N-B-H)₃) is a non-corrosive and non-explosive liquid with a low toxicity.

As plasma gas an argon-nitrogen mixture was used and N-trimethylborazine vapour was fed into the downstream region of the ECR plasma source. BN deposits on silicon (111) were characterized by IR spectroscopy, electron probe microanalysis and X-ray diffraction. The formation of nanocrystalline c-BN depends strongly on the process parameters and requires a substrate temperature of above 800°C. Furthermore, the application of a negative substrate bias—in our experiments achieved with a low frequency (100–450 kHz) generator—is essential to increase the c-BN fraction of the deposit. As shown by IR spectroscopy, a stepwise transition from hexagonal BN into wurtzite-type BN and finally into c-BN takes place by changing the deposition conditions. From these observations some conclusions concerning the growth mechanism of c-BN can be derived.

Owing to the merits of N-trimethylborazine, its processing—compared with that of diborane or boron trihalides—is uncomplicated and promising for future applications of c-BN.     

Multi-stage spark plasma sintering to study the densification mechanisms of boron carbide

The densification kinetics of boron carbide (B₄C) during multi-stage spark plasma sintering was studied. The densification mechanisms were analyzed according to the stress exponent n and the apparent activation energy Q_d using a creep deformation model. The results showed that the densification mechanisms were controlled by viscous flow and grain boundary diffusion at the low effective stress with initial temperature range of 1600–2000 °C, while the dominant mechanism is the dislocation climb at the effective stress regime with final temperature of 2100 °C and the multi-stage sintering can reduce the apparent activation energy. Meanwhile, the scheme of multi-stage sintering can obtain nearly theoretical dense B₄C and avoid grain growth. Therefore, the basic mechanical properties suggesting a good combination of high hardness (37.63GPa) and bending strength (539.86 MPa) was obtained by the multi-stage sintering.