Recension of boron nitride phase diagram based on high-pressure and high-temperature experiments

Cubic boron nitride and hexagonal boron nitride are the two predominant crystalline structures of boron nitride.They can interconvert under varying pressure and temperature conditions.However,this transformation requires overcoming significant potential barriers in dynamics,which poses great difficulty in determining the c-BN/h-BN phase boundary.This study used high-pressure in situ differential thermal measurements to ascertain the temperature of h-BN/c-BN conversion within the commonly used pressure range(3-6 GPa)for the industrial synthesis of c-BN to constrain the P-T phase boundary of h-BN/c-BN in the pressure-temperature range as much as possible.Based on the analysis of the experimental data,it is determined that the relationship between pressure and temperature conforms to the following equation:P=a+1/bT.Here,P denotes the pressure(GPa)and T is the temperature(K).The coefficients are a=-3.8±0.8 GPa and b=229.8±17.1 GPa/K.These findings call into question existing high-pressure and high-temperature phase diagrams of boron nitride,which seem to overstate the phase boundary temperature between c-BN and h-BN.The BN phase diagram obtained from this study can provide critical temperature and pressure condition guidance for the industrial synthesis of c-BN,thus optimizing synthesis efficiency and product performance.

The electrical properties of sulfur-implanted cubic boron nitride thin films

Cubic boron nitride （c-BN） thin films are deposited on p-type Si wafers using radio frequency （RF） sputtering and then doped by implanting S ions. Wile implantation energy of the ions is 19 keV, and the implantation dose is between 1015 ions/cm2 and 1016 ions/cm2. The doped c-BN thin films are then annealed at a temperature between 400℃ and 800℃. The results show that the surface resistivity of doped and annealed c-BN thin films is lowered by two to three orders, and the activation energy of c-BN thin films is 0.18 eV.

Structure evolution of cubic boron nitride under spark plasma sintering

Cubic boron nitride(CBN) micro powders and mixture of CBN micro powders with Al or Ti powders were fast heated at 1 300,1 400,1 450,1 500℃,and then kept for 5 min under spark plasma sintering (SPS).The obtained powders were analyzed with XRD.The results show that,simple CBN kept cubic structure after heated at 1 300℃;when the temperature rose to 1 400℃,some CBN was transformed into hexagonal structured boron nitride(hBN).As for CBN micro powders mixed with aluminum or titanium micro powders,the onset transforming temperature of CBN to hBN get raised.This results indicated that the structural transformation of boron nitride begun from the surface of CBN crystal particle,different coexist elements affect the surface situation of CBN particles.As the stabilities of CBN crystal particle surface improved,the onset structural transform temperature of CBN was also increased.

In situ infrared spectroscopic study of cubic boron nitride thin film delamination

This paper investigates the procedure of cubic boron nitride （cBN） thin film delamination by Fourier-transform infrared （IR） spectroscopy. It finds that the apparent IR absorption peak area near 1380cm^-1 and 1073 cm^-1 attributed to the B-N stretching vibration of sp2-bonded BN and the transverse optical phonon of cBN, respectively, increased up to 195% and 175% of the original peak area after film delamination induced compressive stress relaxation. The increase of IR absorption of sp2-bonded BN is found to be non-linear and hysteretic to film delamination, which suggests that the relaxation of the turbostratic BN （tBN） layer from the compressed condition is also hysteretic to film delamination. Moreover, cross-sectional transmission electron microscopic observations revealed that cBN film delamination is possible from near the aBN（amorphous BN）/tBN interface at least for films prepared by plasma-enhanced chemical vapour deposition.

Influence of oxygen on the growth of cubic boron nitride thin films by plasma-enhanced chemical vapour deposition

Cubic boron nitride thin films were deposited on silicon substrates by low-pressure inductively coupled plasmaenhanced chemical vapour deposition. It was found that the introduction of 02 into the deposition system suppresses both nucleation and growth of cubic boron nitride. At a B2H6 concentration of 2.5% during film deposition, the critical O2 concentration allowed for the nucleation of cubic boron nitride was found to be less than 1.4%, while that for the growth of cubic boron nitride was higher than 2.1%. Moreover, the infrared absorption peak observed at around 1230- 1280 cm^-1, frequently detected for cubic boron nitride films prepared using non-ultrahigh vacuum systems, appears to be due to the absorption of boron oxide, a contaminant formed as a result of the oxygen impurity. Therefore, the existence of trace oxygen contamination in boron nitride films can be evaluated qualitatively by this infrared absorption peak.

The Adhesion Improvement of Cubic Boron Nitride Film on High Speed Steel Substrate Implanted by Boron Element

Cubic boron nitride(c-BN) films were deposited on W6Mo5Cr4V2 high speed steel(HSS) substrate implanted with boron ion by RF-magnetron sputtering. The films were analyzed by the bending beam method, scratch test, XPS and AFM. The experimental results show that the implantation of boron atom can reduce the internal stress and improve the adhesion strength of the films. The critical load of scratch test rises to 27.45 N, compared to 1.75 N of c-BN film on the unimplanted HSS. The AFM shows that the surface of the c-BN film on the implanted HSS is low in roughness and small in grain size. Then the composition of the boron implanted layer was analyzed by the XPS. And the influence of the boron implanted layer on the internal stress and adhesion strength of c-BN films were investigated.

碳纳米管对混合粒径PcBN复合材料性能的影响

为提高高温高压制备的聚晶立方氮化硼(PcBN)复合材料的性能,以颗粒尺寸分别为0~0.5μm和0.5~1.0μm的混合粒径立方氮化硼(cBN)为原材料,Al-Ti-Al_(2)O_(3)为结合剂,加入不同质量分数的碳纳米管,在高温高压条件下烧结制备PcBN复合材料,研究碳纳米管质量分数对PcBN复合材料结构和性能的影响。结果表明:添加碳纳米管后,PcBN和碳纳米管间没有发生化学反应,碳纳米管以增强体的形式存在于复合材料内部;复合材料较致密,碳纳米管的添加使PcBN的相对密度先增大后减小。当碳纳米管添加质量分数为1.5%时,PcBN的相对密度有最大值97.9%,同时PcBN有最大的显微硬度和断裂韧性,分别为3892 HV和6.82 MPa·m^(1/2);当碳纳米管的添加质量分数为1.0%时,PcBN有最大的抗弯强度和磨耗比,分别为584 MPa和6873。碳纳米管拔出和桥连作用提高了PcBN复合材料的力学性能。

单颗CBN磨粒超声振动辅助磨削AISI 304材料去除机理

为了解释超声作用下磨粒切削材料的去除机理,对单粒磨削过程进行了分析,建立了未变形切削厚度和磨粒与试件的固定速度比(vs/vw)的数学模型.在AISI 304试件上进行了固定速度比的普通磨削(conventional grinding,CG)、切向超声振动辅助磨削(tangential ultrasonic vibration assisted grinding,TUVAG)以及径向超声振动辅助磨削(radial ultrasonic vibration assisted grinding,RUVAG)的单颗粒试验.结果表明,在固定速度比条件下,试件在CG与TUVAG作用下都是以塑性变形的形式去除,但超声辅助显著提高了材料去除率.试件在RUVAG作用下材料的去除方式与未变形切削最大厚度agmax的值息息相关.agmax小于0.8μm时,试件表现为脆性断裂的形式去除;之后随着agmax逐渐增大,试件转变为塑性变形的形式去除.

Low pressure synthesis of boron nitride with (C_2H_5)_2O·BF_3 and Li_3N precursor

Cubic boron nitride（c-BN） was synthesized through benzene thermal method at a lower temperature of （300℃） by selecting liquid（（C2H5）2O·）BF3 and Li3N as reactants. Hexagonal boron nitride（h-BN） and orthorhombic boron nitride（o-BN） were also obtained. The samples were characterized by X-ray powder diffractometry and Fourier transformation infrared spectroscopy. The results show that all the BF3, BCl3 and BBr3 in the same family compounds can react with Li3N to synthesize BN since the strongest bond of B—F can be broken. Compared with BBr3, liquid （C2H5）2O·BF3 is cheaper, less toxic and more convenient to operate. Li3N not only provides nitrogen source but also has catalytic effect on accelerating the formation of c-BN at low temperature and pressure.

铝合金电泳-电沉积Ni-cBN-PTFE复合镀层及其性能

[目的]通过表面强化处理提高铝合金的耐蚀性、硬度、耐磨性等性能有利于拓宽其应用范围。[方法]先通过磁场辅助电泳沉积在铝合金表面得到由cBN(立方氮化硼,平均粒径50 nm)和PTFE(聚四氟乙烯,平均粒径200 nm)纳米颗粒组成的电泳层,再通过电镀将纳米颗粒包裹在Ni镀层中,得到Ni-cBN-PTFE复合镀层。研究了MgCl_(2)·6H_(2)O质量浓度、纳米颗粒添加量、电压、温度和时间对电泳沉积量的影响。分析了Ni-cBN-PTFE复合镀层的结合力、微观形貌、元素组成、显微硬度、水接触角、耐磨性和耐蚀性。[结果]为制备纳米颗粒均匀分布且厚度适宜的电泳层,较优的电泳工艺条件为:MgCl_(2)·6H_(2)O 0.6 g/L,电压60 V,cBN 3.5 g/L,PTFE 3.5 g/L,磁感应强度2.5 mT,温度25℃,时间4 min。在较优条件下所得Ni-cBN-PTFE复合镀层的厚度约为18μm,表面元素分布均匀,cBN颗粒与PTFE颗粒的含量较高,显微硬度为426 HV,结合力、疏水性、耐磨性及耐蚀性良好。[结论]采用电泳−电沉积技术可在铝合金表面制得cBN和PTFE含量较高的Ni-cBN-PTFE复合镀层,显著提高铝合金的综合性能。

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。

屏蔽杯材质对高cBN含量PcBN复合片的影响

通过改变高cBN含量PcBN复合片屏蔽杯的材质(锆杯、钼杯和铌杯),在合成温度为1400℃~1500℃、压力5~5.5 GPa和烧结时间20~25 min条件下烧结成型。经后加工平面磨及外圆磨后,对比不同屏蔽杯材质对合成得到复合片的缺陷及抗冲击韧性所带来的变化。试验结果表明,针对高cBN含量PcBN复合片的合成,应选择熔点更高的钼和铌作为屏蔽材料,既避免高温对复合片边缘过烧,拓宽合成区域,提高合成稳定性和抗冲击韧性,又降低制刀过程中聚晶层开裂现象,显著提高产品成品率和客户满意度。

不同粘结剂组分PcBN复合片微观组织和相分析

为阐明不同粘结剂组分对PcBN复合片微观组织和相态的影响及其作用机理,通过将立方氮化硼(cBN)与不同组分的TiC、Al、Co等进行共混并球磨细化,在高温(1450℃)、高压(5 GPa、5.5 GPa、6 GPa)下烧结制备了聚晶立方氮化硼(PcBN)复合片。采用扫描电镜(SEM)、能谱分析(EDS)、X射线衍射(XRD)等对不同质量分数的cBN-TiC-Al-Co烧结体的微观组织、各组分元素的分布及物相构成进行了分析表征。研究结果表明:cBN与Al在高温高压下反应生成了AlN、AlB2、AlB12等新物相,与Ti、Co在高温高压下反应成了TiN、TiB2、CoN、Co2B等新物相。

High-Pressure Nitrides and Microdiamonds from Tibetan Ophiolite

The samples of microdiamond as an inclusion of Os Ir alloy, coesite, stishovite, high pressure form of Tio2, high pressure nitrides associated with SiC along with boron carbide, have been reported in the past from the placer deposits of Luobasa ophiolite of Yarlung Zangbo region of Tibet. For the formation of these ultra high findings, pressure in the range of 4 to 9 Gpa and temperature in the range of 700° C - 1300° C is required. Thus these minerals can either be incorporated into the chromitite in the deep upper mantle or they have an impact origin. In absence of impact crater, Prof. Fang and others have favored the mantle origin but for the formation of nitrides in the deep mantle, the source of N is not clear. However, the event of comet impact provides better explanation for the formation process. It also simplifies the explanation of coexistence of most of these minerals in a single crystal with the shallow origin and the perfect preservation of the coesite as consequence of rapid cooling after the shock metamorphism.

Tribological and anti-corrosion performance of epoxy resin composite coatings reinforced with differently sized cubic boron nitride(CBN)particles

A series of high solid content(30 wt%)epoxy resin(EP)composite coatings reinforced with differently sized cubic boron nitride(CBN)particles were fabricated successfully on 304 L stainless steel.Polydopamine(PDA)was used to improve the dispersibility of CBN particles in EP.The structural and morphological features of the CBN particles and the composite coatings were characterized by Raman spectroscopy,scanning electron microscopy(SEM),and transmission electron microscopy(TEM).Moreover,a UMT-3 tribometer and surface profiler were used to investigate the tribological behaviors of the as-prepared composite coatings.Electrochemical impedance spectroscopy(EIS)and Tafel analysis were used to investigate the coatings'anti-corrosion performance.The results demonstrated that the CBN fillers could effectively enhance the tribological and anti-corrosion properties of the EP composite coatings.In addition,when the additive proportion of the microsized(5μm)and nanosized(550 nm)CBN particles was 1:1,the tribological property of the EP composite coatings was optimal for dry sliding,which was attributed to the load carrying capability of the microsized CBN particles and the toughening effect of the nanosized CBN particles.However,when the additive proportion of the microsized and nanosized CBN particles was 2:1,the tribology and corrosion resistance performance were optimal in seawater conditions.We ascribed this to the load-carrying capacity of the microparticles,which played a more important role under the seawater lubrication condition,and the more compact structure,which improved the electrolyte barrier ability for the composite coatings.

In situ synthesis of polycrystalline cubic boron nitride in cBN-Al-Ti system with different Gd_(2)O_(3) additions

Polycrystalline cubic boron nitride was sintered under high temperature(1400℃)and high pressure(5.5 GPa)using an in situ synthesis method.The composition,microstructure,relative density and mechanical properties of the polycrystalline cubic boron nitride(PcBN)with different contents of Gd_(2)O_(3) were studied by means of X-ray diffraction(XRD),scanning electron microscopy(SEM)and energy-dispersive spectroscopy(EDS).The results show that the phases of TiB_(2),TiN,AIN,AlTi_(2)N and GdB_(6) are formed through in situ synthesis of cBN-Al-Ti-Gd_(2)O_(3) system.With the Gd_(2)O_(3) content increasing,the relative density increases and mechanical properties of PcBN begin to increase and then decrease.Proper amount of Gd_(2)O_(3) can advance the formation of TiB_(2) and improve the aspect ratio of TiB_(2).When Gd_(2)O_(3) content is 1.0 wt%,the PcBN exhibits optimal comprehensive mechanical properties,with a microhardness of 33.35 GPa and a flexural strength of 972.37 MPa.

BONDING INTERFACE AND WEAR BEHAVIOR OF CBN GRAINS BRAZED USING NANO-TiC POWDER MODIFIED FILLER

A new kind of composite fillers,composed of Ag-Cu-Ti alloy and nano-TiC powders,is utilized to braze cubic boron nitride （CBN） grains and tool substrate. The bonding system,including the interfacial microstructure and reactive products between CBN grains and filler layer,is observed by optical microscope and scanning electron microscope （SEM）. Resistant-to-wear experiments of the brazed grains are performed. Results show that the nano-TiC powders evenly distribute in the filler layer so that the resultants grow compactly and uniformly on the surface of CBN grain. This indicates that the chemical bond is established between CBN grains and nano-TiC modified filler. Accordingly,the bonding strength of the grains is ensured. The CBN grains are worn smoothly without grain pull-out.

自润滑金属结合剂CBN砂轮干式磨削特性分析

针对钛合金难磨削加工性,提出了自润滑金属结合剂砂轮,综合液相烧结与钎焊工艺制备了自润滑金属结合剂立方氮化硼(Cubic Boron Nitride,CBN)砂轮,分析了砂轮强度和微观组织,完成了自润滑CBN砂轮与碳化硅砂轮干式磨削钛合金的性能试验。通过砂轮磨损、工件表面形貌、金相显微组织和显微硬度等特性研究表明:自润滑CBN砂轮干式磨削钛合金切削性能明显优于绿色碳化硅砂轮,在vs=15m/s,vw=2m/min,ap=0.025mm磨削条件下,自润滑金属结合剂砂轮具有较好的磨削性能。

用hBN合成cBN

分别用硼砂和氯化铵、硼砂和尿素为原料，在９５０ ℃下合成出 ２种结晶度相近、平均颗粒度分别为５．６×１０－６和 １．４２×１０－６ｍ的ｈＢＮ．在高温高压条件下，使用锂系催化剂，由前１种ｈＢＮ合成的ｃＢＮ为黄色透明体，由后一种ｈＢＮ合成的ｃＢＮ大部分为黑色半透明体，并且在ｃＢＮ晶体表面上观察到生长台阶．以硼氢化钾和氯化铵为原料合成出的ｈＢＮ为无定形态，平均颗粒度为１２．４３×１０－６ｍ，使用锂系催化剂，该ｈＢＮ未能合成出ｃＢＮ．探讨了ｃＢＮ的形成机制．

活性元素Ti在CBN与钎料结合界面的特征

通过扫描电镜、能谱仪、X射线衍射仪研究了Ag-Cu-Ti钎料中的活性元素Ti在钎料与立方氮化硼(CBN)磨粒高温钎焊结合界面的扩散现象,并运用动力学分析对界面反应层的生长过程及反应激活能进行了探讨。结果表明:钎焊过程中,钎料中的活性元素Ti明显向磨粒侧扩散偏聚并发生化学反应,实现了磨粒与基体材料的牢固结合;钎焊CBN磨粒表面生成的TiB2和TiN化合物形貌接近平衡状态下生长的理想形貌;界面反应层在钎焊温度1153K～1193K,保温时间5min～20min之间依据抛物线生长法则所得扩散激活能值表明其生长过程主要受新生TiN影响。