Boron Nitride Compacts Research Articles

High pressure sintering of cubic boron nitride using Co–V–Al alloy as bonding media

Fine-grained polycrystalline cubic boron nitride compacts were prepared using the mixture of cubic BN and Co–V–Al powders at 5.6GPa and 1700°C for 0.5h. The weight percent of Co, V and Al to cubic BN powder was 10wt.% or 20wt.%. Results of electron dispersive spectrum were suggested that binder composition was changed from metallic binder of Co and V was dominant to VN and AlN mixture was dominant with increase of atomic percent of Al to BN in the sample. Microstructures of the sintered samples were observed by scanning electron microscope and back scattered electron image. The region of atomic weight ratio of Al to V that was about 1–5 showed homogeneously sintered microstructure of less than 3μm of cubic BN grain size. The Vickers hardness trend that showed higher values in the region of atomic weight ratio of Al to V was about 1–5. The highest Vickers hardness resulted in the present study was about 40.7GPa for the 20wt.% metallic binder that contained a 1.39 atomic weight ratio of Al to V and 0.5–2μm size of starting cubic BN powder was used.

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, 5.2GPa, 1450°C for 6min). 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 29.3GPa and cutting test were performed when sintered by using cBN grain size of 10–14μm.

A novel cBN composite coating design and machine testing: A case study in turning

A composite coating series based on nano- and micro-sized cubic born nitride particulates and choice of application-specific binders were developed for turning engineering materials. The coating series were produced via two sequential processes: electrostatic spray coating of cubic boron nitride particles with size less than 2μm for a conformal porous coating preform of designed thickness; and chemical vapor infiltration of ceramic binder phase(s) at a temperature of around 1000°C for a dense and well adherent composite coating. In this paper, the coating design for different applications is discussed. As a study case, cubic boron nitride–titanium nitride composite coating was characterized by use of different techniques for coating cross-section, elemental composition, crystal phases, and adhesion strength. Characterization results indicated a composite coating with uniform coating thickness and evenly distributed cubic boron nitride particles in a titanium nitride matrix. Additionally, the coating was tested for its machining performance in continuous turning of AISI 4340 hardened steels and AISI 4140 pre-hardened steels at representative application conditions, and compared to corresponding industrial benchmarks. Testing results showed that the composite coating outperforms its industrial counterparts, polycrystalline cubic boron nitride compacts, titanium aluminum nitride coating by physical vapor deposition, multi-layer coating by chemical vapor deposition, and aluminum oxide bulk tools, in their respective applications.

The Bonding Structure of the Various High Purity or Binderless Polycrystalline Cubic Boron Nitride Compacts Sintered at 5 to 7GPa and 1600 to 2000 °C

The cBN-cBN direct bonding structure of some cBN compacts made by the method of the direct conversion of the pyrolytic-BN (pBN) or wurtzite-BN (wBN) to cubic-BN at the pressure of 7GPa and temperature 2000 °C and the cBN compact made by the method of sintering the cBN powder along with polyvinylidene chloride (PVDC) at the condition of 5.5GPa and 1600 °C has been studied. The XRD, SEM, TEM analysis and the wear resistance on the ductile cast iron machining has been investigated. While the XRD analysis of the above cBN samples showed that all samples consist only of cBN, and the SEM observation showed that they all have the cBN-cBN direct bonding structure, A STEM analysis showed the existence of the impurities at the cBN crystal boundary. The starting materials and the sintering method affect the degree of these impurities.

High pressure sintering of cubic boron nitride compacts with Al and AlN

Cubic boron nitride (cBN) compacts, using 15 wt.% Al and 20 wt.% AlN respectively as additives, were sintered in the temperature range of 1300–1700 °C for 20 min under high pressure of 5.0 GPa. The hardness, microstructure, phase composition and cutting performance of the high pressure sintered samples were investigated. A liquid phase sintering and reaction process was observed in the cBN–Al system, which leads to the formation of AlN and AlB 2 as confirmed by X-ray diffraction (XRD) in the sintered compacts. Scanning electron microscopy (SEM) analysis shows that the samples have a homogeneous microstructure. The hardness decreases with increase of sintering temperature and reaches the highest Vickers hardness of 32.1 GPa at 1350 °C. While in the cBN–AlN system, AlN grains agglomerate heavily at temperature below ~ 1500 °C. As the sintering temperature increasing, Al 2O 3 appeared and the AlN agglomeration disappeared gradually. A highest cBN–AlN composite hardness of 29 GPa was achieved when sintered at 1600 °C. Turning tests showed that cBN compacts with 15 wt.% Al as the additive has a longer tool life as compared to that with 20 wt.% AlN. Our results indicated that cBN–Al system is more favourable to obtain well-sintered cBN compacts comparing with the cBN–AlN system.

Synthesis, microstructure and hardness of bulk ultrahard BN nanocomposites

Ultrahard boron nitride compacts containing nanosized domains of the cubic (c-BN), wurtzitic (w-BN), and hexagonal (h-BN) phase were synthesized at high-pressure/high-temperature (HP/HT) conditions. Hot-pressed and pyrolytic BN, both containing h-BN as a main component, were used as starting materials. The HP/HT products were investigated by x-ray diffraction via Rietveld and line-profile analysis, as well as high-resolution transmission electron microscopy. c-BN was the dominant phase in all products, complemented by up to 25 wt% w-BN and some remaining “compressed h-BN.” In particular samples, partial crystallographic coherence of adjacent crystallites to x-rays was observed, which has been previously found in superhard transition metal nitride-based nanocomposite coatings. In the BN nanocomposites, the partial coherence of nanocrystallites to x-rays was improved by their strong local preferred orientation, which is made possible by the well-known orientation relationships among h-BN, w-BN, and c-BN phases. The correlation between the weight fraction and the average size of the c-BN crystallites helped to describe the formation of c-BN/(w-BN) nanocomposites from submicron-sized h-BN domains in the starting materials. The Knoop and Vickers hardness of specimens with crystallite sizes ranging from 6 to ∼50 nm was found to be significantly higher than that of c-BN single crystals, despite the presence of residual h-BN.

Sinterização de pastilhas de nitreto cúbico de boro utilizando como ligantes compostos de titânio

O Nitreto Cúbico de Boro (cBN) é uma forma alotrópica sintética do nitreto de boro que é obtida sob condições de altas pressões e altas temperaturas (HPHT), geralmente a partir do nitreto hexagonal de boro (hBN). Compactos sinterizados de cBN são produzidos sinterizando cBN e ligantes na faixa de 6,0-8,0GPa e cerca de l600-2000°C em tempos que variam até 30 minutos. No presente trabalho, compósitos de cBN com ligantes a base de titânio em l0%p foram sinterizados em parâmetros de 7,7GPa e 2000K. Análises por MEV apresentaram uma estrutura parcialmente sinterizada. A dureza e resistência ao desgaste foram estudadas demonstrando resultados promissores. As propriedades mecânicas dos compósitos foram avaliadas em situações reais de trabalho, por meio de usinagem do aço AISI 4140 endurecido a 54-HRC.

A influência de tratamento térmico complementar sobre a resistência ao desgaste de pastilha de nitreto cúbico de boro

Os compósitos a base de nitreto cúbico de boro (cBN) atualmente se destacam na usinagem de metais e ligas de dureza elevada, podendo substituir a retífica. A efetividade de utilização dos compósitos de cNB depende, em geral, do estudo da tenacidade do inserto. A obtenção de pastilhas de cBN, realiza-se sob altas pressões até 8 GPa e temperaturas de até 2000ºC. Em condições não hidrostáticas, as tensões internas têm valores significantes, diminuindo a vida útil da ferramenta. Para aumentar a tenacidade e a eficiência de uso foi proposto o tratamento térmico complementar em condições de vácuo sob temperaturas de até 1000ºC e tempo de 1hora. As pastilhas de cBN foram sinterizadas à pressão de 7,7 GPa e temperatura de 1600ºC. A composição da pastilha utilizada foi de 65%p de cBN e 35%p de ligante. Para determinação de nível de desgaste durante usinagem foi utilizado aço 4140 com dureza de 56-58HRc. Comparando a efetividade de usinagem das pastilhas de cBN obtidas com o compósito Elbor®, pôde ser notado que o tratamento térmico complementar aumentou a capacidade de usinagem da pastilha de cBN em 40%.

Experimental study of plastic deformation during sintering of cubic boron nitride compacts

Abstract In this work polycrystalline cubic boron nitride compacts (PcBN), prepared with and without binder, were sintered at 8 GPa and 1850°C using different processing times. X-ray diffraction and Raman spectroscopy were used to investigate the kinetics of plastic deformation during sintering. For compacts sintered in short processing times, both Raman and X-ray diffraction linewidths increased, indicating a high plastic deformation of the grains. For longer processing times (30–120 s) the linewidth decreased, tending to the value of the pristine cBN grains. This dependence on the processing time was interpreted as a result of the competition between the plastic deformation of the grains, dominant for short processing times, and the defect annealing process, which becomes significant for longer processing times. When aluminum binder was used for sintering, it was observed that the processing time required to recover the original linewidth is longer, and the maximum broadening of the lines occurs at a longer processing time compared to the case without binder. These results indicated that the binder phase significantly affects both plastic deformation and defect annealing processes.

Cutting properties of polycrystalline boron nitride compacts sintered in shock waves: V.I. Kovtun et al, Poroshkovaya Metallurgiya, No 1, 1992, 81–87 (in Russian)

Cutting properties of polycrystalline boron nitride compacts sintered in shock waves: V.I. Kovtun et al, Poroshkovaya Metallurgiya, No 1, 1992, 81–87 (in Russian)

Characterization of wurtzitic boron nitride compacts

Characterization of sintered polycrystalline wurtzitic boron nitride compacts was carried out regarding the different crystalline phases that are formed at high temperature and high pressure, composition, particle size distribution of BN and binder and hardness. Wurtzitic boron nitride, cubic boron nitride, TiC/TiN solid solution, TiB and TiB2 were the crystalline phases that have been observed in sintered wurtzitic boron nitride compacts. The particle size distribution of BN and the binder was found to be comparable (1 to 5μm), with about 80% of the particles lying between 2 and 3μm. Weight percentages of different elements present in these compacts were determined. The average Knoop hardness values under 500 g load were measured, and the variation of hardness as a function of position on the specimen surface was studied.

Characterization of cubic boron nitride compacts

Abstract c-BN compacts find extensive applications in machining and shaping of hard ferrous materials. These compacts are synthesized at high temperature and high pressure in the presence of suitable binders. A comparative study of c-BN compacts synthesized at the National Physical Laboratory, New Delhi and those obtained from three other sources have been made regarding crystalline phases, composition, particle-size distribution of c-BN and binders, and the hardness in these compacts.