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.     

Development of ultra-fine-grain binderless cBN tool for precision cutting of ferrous materials

A new cutting tool was developed from ultra-fine-grain (<100 nm), binderless cubic boron nitride (cBN) material fabricated by transforming hexagonal boron nitride to cBN by means of sintering under an ultra-high pressure of 10 GPa at 1800 °C. The cutting edges of the newly developed cBN tool can be made as sharp as those of single-crystal diamond tools. In this experiment, cBN and single-crystal diamond tools of the same shape were compared by precision cutting tests using stainless steel specimens and steel specimens coated with an electroless Ni-P layer. The surface roughness (R_z) of specimen surfaces cut with the cBN tool by means of planing was approximately 100 nm for both the Ni-P-coated steel and stainless steel specimens. Though similar R_z values were obtained for Ni-P layers cut by the cBN and diamond tools, an R_z value exceeding 2000 nm was obtained for stainless steel cut by the diamond tool. High-precision surfaces with R_z values of 50–100 nm were obtained for stainless steel specimens cut with the cBN tool under high-speed milling (942 m/min) conditions. These results indicate that the newly developed cBN tool is useful for the ultra-precision or precision cutting of ferrous materials.     

Fragmentation and stress response characteristics of cubic boron nitride under high pressure

Exploring the fragmentation behavior and stress response of cubic boron nitride (cBN) particles under high pressure offers insights into preparing polycrystalline cubic boron nitride (PcBN) with excellent properties. In this study, the distribution characteristics and micro-morphology of cBN particles with different sizes (2 μm, 15 μm and 40 μm) with and without aluminum (Al) binder are investigated using scanning electron microscopy (SEM) and laser particle size distribution instrument after cold compression at pressures up to 10.0 GPa. The results demonstrate that the fragmentation of the cBN particles without Al is more evident than that with Al. Moreover, the stress distribution among cBN grains is obtained via in-situ high-pressure synchrotron radiation X-ray diffraction experiments with diamond anvil cell (DAC). The results indicate that the stress difference in the cBN grains between the high-pressure and low-pressure zones is approximately 6.0 GPa under 4.2 GPa loading, while the stress difference reached to 40.0 GPa when compressed to 62.0 GPa. The main reason for the cBN particle breakage is the stress difference caused by mutual extrusion among particles under cold compression. These findings may provide a practical guide for preparing PcBN with excellent performance using high pressure sintering methods.     

Wear resistance and thermal stability enhancement of PDC sintered with Ti-coated diamond and cBN

Ti-coated diamond with different particle sizes and proper amounts of cubic boron nitride (cBN) was used to fabricate polycrystalline diamond composite (PDC) with improved wear resistance and thermal stability under high temperature and high pressure (5.5–6.5GPa, 1500–1650 °C). The ratio of Ti-coated diamond powder, cBN powder and normal diamond powder was W_30–50: W_4–8: W_0–1 = 70: 15: 15. Cobalt (Co) was used as a binder, and cemented tungsten carbide was used as a substrate to sinter a new high-performance PDC. Ti and TiC on the surface of Ti-coated diamond reacted with cBN under high temperature and high pressure to generate new ceramic phases such as TiB₂, TiN and TiN_0.3, which have high hardness and good wear resistance. Compared with the conventional PDC, the impact toughness and wear resistance of PDC with Ti-coated diamond and cBN addition were enhanced by 19% and 28%, respectively. The ceramic phase acts as a protective barrier, which enhances the initial graphitization and oxidizing temperature to 942–950 °C, which were 162–170 °C higher than the conventional PDC. The new ceramic barrier wrapped around the surface of the diamond and Co after the formation of the D-D (diamond-diamond) bonding will give priority to the oxidation reaction of Co and diamond with oxygen, which prohibits cobalt-catalytic graphitization of diamond, meeting the needs of PDC thermal stability and wear resistance in the field of drilling.     

A cBN-TiN composite coating for carbide inserts: Coating characterization and its applications for finish hard turning

Cubic boron nitride (cBN)-titanium nitride (TiN) composite coating combines the thermal stability and super abrasiveness of cubic boron nitride (cBN) and the good lubricity of TiN, offering the opportunity for designing cutting tools with application specific new geometries (flat, chip breaker, and round shape) and cost effectiveness. In particular, the cBN based coating on carbide inserts is complementary to widely used polycrystalline cubic boron nitride (PCBN) compact tools for finish hard turning applications. This paper reports the results of a study addressing the surface morphology, surface roughness, coating cross section, chemical composition, crystal structure, microhardness, adhesion, and the wear life of this cBN-based coating deposited on carbide inserts (SNMG432) for finish turning of hardened AISI 4340 steel bars. The surface quality of machined workpieces in terms of their surface roughness and white layer formation are also analyzed and the results are presented.     

Properties of nanostructured cubic boron nitride films prepared by the short-pulse laser plasma deposition techniques

Nanostructured cubic boron nitride (BN) films were synthesized on molybdenum substrates by using the short-pulse laser plasma deposition techniques. The surface morphologies, chemical compositions, bond structures, and mechanical properties of the obtained BN thin films have been investigated by scanning electron microscopy, Raman scattering, Fourier transform infrared spectroscopy (FTIR), energy dispersive spectra, and hardness measurements. High power density laser deposition yielded boron-rich BN nanorod arrays where tBN component dominates. Reducing power density down to 8 × 10⁷ W/cm² during laser plasma deposition produced flat cBN thin films. Typical TO and LO bands in the Raman and FTIR spectra of the cBN samples were identified. The cBN sample with hardness up to 40 GPa was obtained.     

Sintering of binderless cubic boron nitride and its modification by β-Si3N4 additive for hard machining applications

This study present the results of HP-HT sintering, microstructure, properties, and performance of binderless cBN tool material. Within the investigated sintering temperature range of 1900–2600 °C the optimum was found to be 2200–2300 °C. Lower temperature results in incomplete diffusion bonding between cBN grains, while higher temperature results in high degree of recrystallization of initial structure, grain growth, and even formation of hexagonal boron nitride in triple joints. Introduction of stress-inducing β-Si₃N₄ minor inclusions resulted in high overall mechanical and thermal properties: HK = 41 GPa; K_IC = 12.6 MPa·m^1/2; λ = 180 W/(m·K). Machining experiments in roughing of hardened tool steels show that binderless cBN material provides high performance in terms of resistance to tool cratering, chipping, and tool fracture.     

PCBN刀具切削性能和磨损机理研究综述

聚晶立方氮化硼(PCBN)刀具是继聚晶金刚石刀具之后的又一种超硬刀具,以其独特的“以车代磨”、“硬态加工”、“干式切削”等方式被誉为21世纪的绿色环保刀具。PCBN刀具在金属切削方面具有广泛的应用,主要用来加工各种淬硬钢、耐磨铸铁等铁基材料。本文介绍了PCBN刀具成分、几何形状、切削参数等对其切削性能的影响,在此基础上分析了不同材料加工时刀具的主要磨损机理,还简单对比了硬质合金和PCBN刀具切削性能上的差异。      

PCBN刀具断续干式切削ADI时切削力与寿命的研究

选用DBW85、DBC50、BN250、BN700四种牌号的PCBN复合片刀具断续干式车削等温淬火球墨铸铁(ADI),测定了在相同几何参数下的切削力和在不同速度下的刀具寿命。试验结果表明:(1)在所选用四种牌号PCBN刀具中,高CBN含量的BN700和DBW85断续加工ADI的性能,要优于低CBN含量的BN250和DBC50,其中DBW85性能最好。(2)高CBN含量的BN700和DBW85加工ADI时,切削速度可选择偏高一些,一般要大于130m/min,低CBN含量PCBN刀具加工ADI时,切削速度要选择偏低一些,在100m/min左右。(3)黏结剂中添加W元素可以有效抑制PCBN刀具切削ADI时的化学磨损,改善刀具韧性,有利于ADI的断续切削。     

纯相PCBN的研究进展

立方氮化硼以其优异的特性广泛应用于现代制造加工领域。随着制造要求的不断提高,对氮化硼的性能提出更高的要求,世界各国相继开发研究出纯相立方氮化硼的合成技术。本文对国内外纯相聚晶立方氮化硼的烧结、性能等进行了综述,并分析了各种纯相烧结方法。最后对纯相聚晶氮化硼的发展方向进行了展望。      

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.     

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.     

纯相PcBN的高温高压制备综述

PcBN是cBN的聚晶体,具有尺寸大、各向同性、无解理面等优点,因而应用广泛。商用PcBN大多采用添加黏结剂的方式进行烧结以降低烧结条件,通常是在压力为5.5～7.7 GPa、温度为1 600～2 300 K条件下合成的。但黏结剂也降低了产品的性能,其维氏硬度在22～45 GPa。鉴于材料本身就是最好的黏结剂,本文对使用4种不同初始材料制备纯相PcBN的烧结行为及材料性能进行介绍和评价。用cBN作为初始材料并配合相关工艺能制备出性能较好的纯相PcBN材料。     

Study of the proportioning design method and mechanical properties of a cBN–TiN composite

This study provides a proportioning design method for the polycrystalline cubic boron nitride (PcBN) composite based on dense packing theory with the use of the Horsfield dense filling theory and Dinger–Funk equation. Subsequently, three proportioning schemes of the cBN–TiN system were designed with different titanium nitride content. The samples were analysed through X-ray diffraction, scanning electron microscopy and transmission electron microscopy for density, hardness and actual cutting performance, respectively. The predicted optimal values were consistent with the experimental results, which proved the validity of the method. Three samples designed from the method had sufficient sintering reaction under high pressure and high temperature to form a uniform and compact sintering structure, which had excellent mechanical properties to meet the industrial application. A surface reaction zone was formed on the W grains and the substitution reaction between cBN and TiN occurs and directly combines with each other to form an obvious grain boundary. It also indicated that appropriate PcBN proportioning scheme, workpiece characteristics, and cutting parameters should be sufficiently considered and reasonably adjusted in order to achieve a higher tool life and excellent workpiece surface roughness in the actual cutting application.     

Al添加量对PcBN复合片显微结构和性能的影响

将cBN微粉添加体积分数为5%、10%、15%、20%的Al粉进行高温高压烧结制备出PcBN复合片。利用X射线衍射仪、扫描电子显微镜分析PcBN复合片的物相组成和显微结构,并研究其磨耗比和抗冲击性能。结果表明,PcBN层主要由cBN晶粒和AlN组成。随着Al粉添加量的增加,AlN的体积分数逐步增加,PcBN复合片的性能也发生相应变化。Al粉添加量为体积分数10%时,PcBN复合片的磨耗比为21 842,冲击次数超过100次,综合性能最好。     

PCBN刀具硬态车削的磨损机制研究

PCBN刀具用于高速切削、硬态切削、干切削以及加工自动化和难加工材料等先进切削工艺时显示出了卓越的性能,为了推动PCBN刀具在我国的推广使用,充分发挥PCBN刀具的潜能,有必要对PCBN刀具切削过程中的行为规律进行研究。目前国内外已经有很多这方面的研究报道,本文旨在对前人已进行的工作进行一个系统的总结,以期能得到PCBN硬态车削时的主要的磨损机制。     

多晶立方氮化硼在高压熔渗法烧结过程中的晶界键合机理研究

为了探究多晶立方氮化硼（PCBN）在高压熔渗法烧结过程中的晶界键合机理,分别采用高压熔渗法和混合法,在烧结压力5.0~5.5 GPa,温度1300~1600℃,加热时间10~15 min条件下,对立方氮化硼（CBN）的烧结行为进行对比研究,并对烧结后的样品进行X射线衍射（XRD）物相分析,扫描电镜（SEM）分析和硬度测试。实验结果显示:在压力为5.5 GPa,温度为1500℃条件下,利用熔渗法烧结的PCBN样品中出现了大量的CBN-CBN晶粒间键合;在同等压力温度条件下,利用熔渗法烧结样品的维氏硬度可达到CBN单晶硬度（45~50 GPa）的80%以上,明显高于利用混合法烧结的样品。通过上述PCBN高温高压烧结行为的对比研究,系统分析高压熔渗法烧结过程中的CBN晶界键合机理。高压熔渗法有利于高温高压下CBN晶粒的塑性形变和晶粒间孔隙闭合,在CBN晶粒相互挤压处形成局部高应力区,从而在Si熔媒渗入CBN层后促进CBN-CBN晶粒间的键合。      

Impact of tool wear on joint strength in friction stir spot welding of DP 980 steel

Abstract

Friction stir spot welding has been shown to be a viable method of joining ultra high strength steel, both in terms of joint strength and process cycle time. However, the cost of tooling must be reasonable in order for this method to be adopted as an industrial process. Recently a new tool alloy has been developed, using a blend of polycrystalline cubic boron nitride (PCBN) and tungsten rhenium (W–Re) in order to improve the toughness of the tool. Wear testing results are presented for two of these alloys: one with a composition of 60% PCBN and 40% W–Re, and one with 70% PCBN and 30% W–Re. The sheet material used for all wear testing was 1·4 mm DP 980. Lap shear testing was used to show the relationship between tool wear and joint strength. The Q70 tool provided the best combination of wear resistance and joint strength.     

Effect of workpiece sulphur content on the degradation of a PCBN tool material

Tool degradation may be significantly different depending on small variations in chemical compositions of the workpiece material. The present study is an in-depth microstructure investigation of worn low content polycrystalline cubic boron nitride tool materials after dry hard turning of steels with low and high sulphur contents. The results illustrate the important role of sulphur content on the degradation of the crater zone. Sulphides tend to adhere on the wear surface and form layers that protect the tool from workpiece ingress. In the absence of sulphides in the workpiece material, no protective layer can form and iron compounds make their way into the tool microstructure already at lower cutting speeds (150 m/min) and preferably attack cBN grains compared to Ti(C,N) grains.     

Growth behavior of cubic boron nitride (cBN) phase in B-C-N film deposited on Si substrate with non-uniform ion flux

B-C-N film with a ～450 nm thickness was prepared on a (100) oriented silicon wafer (4 cm × 4 cm) by unbalanced magnetron sputtering of a B₄C target with a unipolar pulsed DC substrate bias. At a substrate bias of ?250 V, a cubic boron nitride (cBN) phase appeared in the B-C-N film when the nitrogen content was over 6.7 vol% in Ar-N₂ reactive gases. For the B-C-N film deposited on unipolar pulsed DC biased Si substrate with Ar-16.7%N₂ reactive gas, the content and formation behavior of the cBN phase along with the film thickness were critically dependent on the substrate position due to the difference in ion flux. In contrast to the circular central region of a substrate 2.5 cm in diameter, where cBN was nucleated and grown on hexagonal boron nitride (hBN) in a layered manner, the cBN phase was co-grown with the hBN phase and was surrounded by hBN at the circumference region of the circle. Only hBN was observed at the outer region of the circle. The microstructure of B-C-N film in which cBN is surrounded by hBN is believed to be effective in reducing residual stress developed by the nucleation of a cBN phase.