cBN Powder Research Articles

Microstructure and phase composition of Ti-coated cBN powders intended for active coating technology (ACT) processes

Development of an active coating technology (ACT) was aimed at fabricating high strength sinters using metallized powders like in case of titanium coated cubic boron nitride (cBN). It helps to avoid inhomogeneity in distribution of the binder phase during their mixing, being the main defects in such compacts. The information concerning phase composition of the coating formed over cBN during their metallization would be of much help as it concerns setting a proper sintering temperature securing both durable fusion of boride particles and elimination of porosity. Presently, two commercial Ti coated cBN powders are available, i.e. CBN-B-TA, 6–12 µm, from Van Moppes, Switzerland and CeraMicron CM-CBN 80 Ti, 20–30 µm, from Ceratonia, Germany (coded as cBN-VM and cBN-CM, respectively). The present investigation was aimed at characterization of the coatings microstructure and phase composition, being necessary for optimising sintering procedure. The scanning and transmission electron microscopy observations backed with energy dispersive X-ray microanalysis (SEM/TEM/EDS) showed that the cBN-VM particles carried a coating of thickness varying from 50 nm to 150 nm consisting of TiB and TiN phases, while the cBN-CM ones were covered by a much thicker (∼500 nm) coating built of mostly of TiB and TiN2-type crystallites. As the columnar nitride phases formed bulk of the coatings, though at the coating/cBN substrate boundary a nano-crystalline layer of TiB phase was documented in both powders. The crystallites of boride phase were accompanied by a strings of porosity. The XRD measurements indicated also presence of small amounts of the α-Ti(N) phase, which was probably intermixed with the other phases without forming a separate sub-layer. The thinner coating, i.e. one that formed over cBN-VM powder, was contaminated with Cl and K being a residue from the molten salts synthesis (MSS) deposition, as well as some surface oxides. The gathered information makes a basis for elaboration of new generation of cBN sinters of improved properties.

Composition, microstructure and mechanical properties of PcBN composites with Al- Zr binder

The cBN, Zr, and Al powders were mixed to synthesize PcBN (polycrystalline cubic boron nitride) tool material under high-temperature, ultra-high-pressure conditions. X-ray diffraction and scanning electron microscopy were used to analyze the phase composition and microstructure of the tool material. The mechanical properties and microstructural trends of the tool material at various temperatures were investigated. Research indicates the formation of new phases in the PcBN material following high-temperature and ultra-high-pressure sintering. However, there is no significant difference in the types of formed new phases, all of which consist of BN, ZrB2, ZrN, and AlN. The sintering density of the tool material was higher at 1500 °C and 1600 °C, and the mechanical properties improved with increasing sintering temperature. The highest number of tool processing parts made of PcBN tool material synthesized at 1600 °C is 232.

Milling of TiBbm2 Particle Reinforced High-Modulus Steel

TiB2 particle reinforced high-stiffness steel is one of the composite materials that aim to improve Young’s modulus by compositing TiB2 particles into a stainless steel base phase. This material is designed to exhibit higher rigidity and strength than conventional iron-based materials by using TiB2 particles as the reinforcing phase, and is expected to reduce the weight of high-load components in engines. For this reason, tool life is very short when machining this material. Therefore, high Young’s modulus steel containing TiB2 particles is known to be one of the most difficult-to-cut materials. The purpose of this study was to investigate how to extend tool life in the milling of high-Young’s-modulus steel. Cutting speed dependence of tool life was investigated by end milling using a binderless CBN tool with excellent hardness and bending strength. In addition, the tool damage mechanism was also investigated. The results showed that tools composed of binderless CBN tool have a longer life than conventional CBN tool. In this type of binderless CBN tool, the tool wear rate tended to increase with increasing cutting speed. In addition, the longest tool life was obtained at a cutting speed of 1.25 m/s, though wear rate increased at a boundary cutting length of 1300 m. The wear rate was found to increase with increasing cutting speed. Temperature measurement results indicate that the primary cause of tool damage was mechanical wear, as the temperatures were much too low for a reaction between cBN and Fe. Friction tests revealed scratch marks on the tool originating from crushed cBN particles produced by the crushing of the cutting edge. This indicates that wear is accelerated by the high frictional energy of the cBN powder rubbing against the flank face.

Bi-layer cBN-based composites reinforced with oxide and non-oxide microfibers of refractory compounds

Research into new composites utilizing cubic boron nitride (PcBN) shows promise for enhancing cutting tool performance. The unique properties of these materials stem from the addition of microfibers made of refractory compounds to their structure. This study looks at developing two-layer composites based on cBN group BL, reinforced with SiCw and Al2O3w microfibers. The goal is to improve tool stability when cutting hardened steels with impact loads. PcBN composite samples were made by sintering a mixture of cBN powder with bundles and microfibers under 7.7 GPa pressure. Bond material selection was based on analyzing the relationship between Poisson's ratio (η) and plasticity parameter (G/B). The density, Young's modulus, Poisson's ratio, and hardness of the composites were determined, and the microstructure of samples with TiCN bond was studied. Tool-life tests were conducted on two-layer cutting inserts made of PcBN reinforced with SiCw and Al2O3w microfibers during the machining of hardened KhVG steel (HRC 55) under impact loads at cutting speeds of 100 and 200 m/min.

СТРУКТУРНИЙ СТАН КОМПОЗИТІВ, СПЕЧЕНИХ ІЗ ПОРОШКІВ сBN З ПОКРИТТЯМ ЗІ СПОЛУК Ті

The paper presents the results of experimental studies of the structural state of composites obtained at high temperatures and pressures from cBN powders with coatings deposited by CVD from Ti compounds using a gas transport reaction. The features and quantitative parameters of the structure of the composites depending on the presence of Ti in the coating were determined. It has been experimentally established that the matrices of the obtained composites are formed by submicron grains of TiN and TiB2, the quantitative differences of which correspond to the concentration of Ti in the coating - from 3 to 8 %. The structure of the obtained composites is characterized by a uniform distribution of the ceramic matrix between the cBN grains, which is achieved due to the high-quality encapsulation of individual grains of the superhard phase in the coating. The ceramic layers have the largest dimensions (up to 10-12 μm) in the area of triple joints, the width of the zone between two adjacent cBN particles is < 1 μm. When moving from a coated powder to a composite, the shape of the diffraction peaks changes, which is associated with the stresses of the first and/or second kind inherent in the studied samples. Sintering of the powder leads to a decrease in the size of the blocks from 56 nm to 27 nm, an increase in the lattice strain from 0.11 to 0.24 %, in TiN - to an increase in the lattice parameter in the composite by 10% (from 0.4244 nm to 0.4253 nm), a decrease in the size of crystallites within individual grains from 100 nm to 20 nm, and an increase in the lattice strain by 0.47 %. At the same time, TiN nitride is supersaturated with nitrogen, which is a significant increase in its lattice parameter, and the coating formed in this case is exclusively oriented in the (022) direction.

Synthesis and characterization of environment-friendly spherical cubic boron nitride magnetic abrasives by plasma molten metal powders bonding with hard materials

In this investigation, globular cubic boron nitride magnetic abrasive powders (cBN-MAPs) were synthesized with additive-free via plasma molten metal powders bonding with hard materials (PM2BH) for finishing hard and brittle materials. Experiments were carried out with cBN powder flow rates of 60–300 g/min, which significantly affected the performance and microstructure of the composites. It illustrates that: the composites are composed of cBN and α-Fe; the cBN is not transformed into hBN, which can be reused; a linear increase in the amount of cBN grains bound to the apparent layer of the ferrous substrate with increasing powder flow rate, the proportion of MAPs in the 180–230 μm size distribution and the magnetic permeability decrease; when the powder flow rate is maximum, the powder embedded in ferrous substrate completely covers the surface of the matrix, forming spherical MAPs, after 50 min of machining, surface finish of AlN ceramics improved from 342 nm to 93.5 nm, with cBN-MAPs showing normal wear within 80 min. A novel, highly efficient strategy for additive-free cBN/Fe composites is presented in this paper.

Sintering high-mechanical-properties microcrystalline PcBN by isothermal compression

Mechanical-performance of polycrystalline cubic boron nitride (PcBN) sintered using micron-sized powder particles might exceed that of samples produced from submicron crystals. However, no effective method has been found yet. In this study, commercial cubic boron nitride (cBN) powder (∼5 μm) was used to sinter high-performance PcBN without a binder. Two processes, isothermal compression (IC) and isothermal isobaric sintering (IIS), were used and compared. PcBN sintered with the former method possesses much more excellent mechanical performance, with the average Vickers hardness and indentation crack resistance of 73 GPa and 8.4 MPa·m1/2. The new temperature and pressure path adopted in the IC process can largely improve the hardness of PcBN sintered even with micro-sized powder. The quantitative analysis results of the defect structure in samples can be used as a reference for controlling the defect structure density to improve the material performance.

Experimental results on the high-pressure phase diagram of boron nitride

We present the boron nitride (BN) phase diagram at 3–6 GPa and 1100 °C–2200 °C using a modified belt-type high-pressure apparatus. The cubic BN (cBN)–hexagonal BN (hBN) phase boundary was determined using the hBN–Mg3BN3 catalyst system as a starting material at 4–5.5 GPa. Additional experiments were conducted at 3–4 and 4–6 GPa using cBN powder or hBN–Ca3B2N4 catalyst as a starting material. In the hBN–catalyst system, the rate of cBN nucleation was reduced by the growth of metastable hBN crystals under the cBN-stable pressure–temperature conditions. The stable BN phases were identified from the samples reacted with a longer run duration. The phase boundary line between hBN and cBN was determined as the equation P (GPa) = T (°C)/400 + 0.3, which agreed with the boundary lines calculated by Gruber and Grüneis and by Nikaido et al.

Origin of superhard pure PcBN: A relation to the fragment and its plastic mechanism under the high pressure

Cubic boron nitride (cBN) as a superhard material has significant potential to provide solutions for the thermostability problems of the high-speed cutting tools to adapt the harsh mechanical working environments. Granularity-induced improvements in hardness and the thermal resistance of pure polycrystalline cBN (PcBN) is highly conductive to fragment and plastic behaviors of the pristine cBN particles in the first step of high-pressure induced synthesis process. Rapid detection of them with respect to different sizes of pristine cBN powders is realized by the analysis of the internal stress through the methods of X-ray diffraction (XRD) profile and Raman spectrum. It is deduced that the plastic deformation with significant fragment of the relatively coarse-grained PcBN was dominated by the effect of strain strengthening and then recrystallization, resulting in the optimized performance with a combination of the enhanced mechanical properties (Vickers hardness of Hv3958 and compressive strength of 2.38 GPa) and the high thermal resistance (1202 °C). The proposed fundamental plastic deformation theory of the strengthening polycrystalline cBN is of great guiding significance for the field of high-precision cutting tools.

Synthesis and characterization of cubic boron nitride (Al)-Al2O3 composites under high pressure and high temperature conditions

Cubic boron nitride (cBN) (Al)-Al2O3 composites were synthesized by Chinese multi-anvil high pressure apparatus (CHPA) sintering at 5.0 GPa and 1200–1500 °C using Al-coated cBN (cBN (Al)) and Al2O3 powders. The effects of Al coating, phase composition, densification, Vickers hardness and thermogravimetry of the composites were investigated. Al coating on cBN powder activated the surface of cBN in the composites and reacted with cBN to produce AlN under high pressure and high temperature (HPHT) environment, which helped to promote the bonding strength of cBN and Al2O3. The hardness of cBN (Al) + 15 vol% Al2O3 is 29.7 GPa when sintered at 5.0 GPa and 1350 °C. Compared to cBN-Al2O3 composites, the hardness of cBN (Al)-Al2O3 composites increased by 37.5%. AlN, the reaction product of cBN with Al under HPHT environments, acts as a bridge phase and joins the two phases of cBN and Al2O3 in the form of chemical bonds. This is the intrinsic mechanism of hardness improvement of cBN (Al)-Al2O3 composites.

Determination of impurities in cubic boron nitride (cBN) by inductively coupled plasma mass spectrometry (ICPMS)

The phase stability of cBN is critically dependent on the content and amount of impurities present. While studies have shown qualitatively that the addition of certain impurities can either increase or decrease the cBN-hBN phase transition temperature, studies have yet to show this effect quantitatively. This is because analytical methods to characterize minor and trace impurities in cBN are currently lacking. To this end, we present flux fusion methods capable of fully digesting cBN samples for ICPMS analyses. The materials used in this study are commercially available cBN powders in three different sizes. Two types of fluxes (LiOH and NaOH·H2O) are utilized so that both Li and Na impurities can be determined. To ensure the accuracy of Si measurements, a column chromatography method has been developed to purify Si from flux materials in order to increase the amount of dissolved sample sent to the ICP. Detection limits have been determined using procedural blanks and are found to be below 20 μg/g for all 58 elements analyzed except for Si, for which the detection limit is 312 μg/g. Nonetheless, all cBN powders studied are found to have high Si impurity levels that are above detection limit. This study provides a much-needed analytical protocol to enable comprehensive screening of impurities in cBN.

Improving wear resistance of cBN-based cutting tools using TiN coating on cBN powder surface

TiN-coated cBN was successfully synthesized using the liquid phase deposition method with TiF4 as the Ti source. The crystal phase of the TiOx coating layer was transformed into Ti4O7 and TiN via sintering under a reduction atmosphere in a vacuum furnace. It was then completely converted to the TiN phase at a sintering temperature of 1200 °C. The coating layers exhibited a uniform thickness of approximately 20–40 nm, regardless of the sintering temperature. PcBN cutting tools prepared using the cBN@TiN powders showed excellent wear resistance under heavy cutting conditions; delivering an average machining distance of 10,766 m and a flank wear width of 0.3 mm in 108 min. This wear resistance is approximately four times that of a cutting tool manufactured using cBN powder.

Characterization of Nickel-Cubic Boron Nitride Coating via Electroless Nickel Deposition on High Speed Steel and Carbide Substrates

Ceramic-metal surface coating is very well known for its high thermal, wear and corrosion resistance. The paper discussed on comparison of characterization of Nickel-cubic boron nitride (Ni-CBN) composite coating on two types of substrate. The substrates used are High Speed Steel (HSS) and Carbide due to good hardness, low cost and easily available. The composite Ni-CBN has been used in machining industries recently. It is desirable to get high ceramic of CBN to metal Ni ratio for corrosion, thermal and wear resistance. A sample of HSS and carbide substrate of CBN was used as the base for composite deposition. The surface coating of Ni-CBN was deposited via electroless nickel where the process of involved chemical reactions as the ceramic CBN powders was embedded within the coating. The characterization of the composite deposition was done by JSM-7800F Field Emission Scanning Electron Microscope (FESEM) coupled with Energy Dispersive X-Ray (EDX). The FESEM image proves that nano CBN powders were embedded in HSS substrate and distributed consistently on the coating surface.

Synthesis of TiN-Coated cBN Powder by Sol-Gel Method Using Titanium (IV) Isopropoxide

Synthesis of TiN-Coated cBN Powder by Sol-Gel Method Using Titanium (IV) Isopropoxide

Thermal Stability of TiN Coated Cubic Boron Nitride Powder.

Wear-resistant, super hard ceramic composites based on cubic boron nitride (cBN) are of great interest to industry. However, cBN is metastable under sintering conditions at normal pressure and converts into the soft hexagonal BN (hBN). Therefore, efforts are being made to avoid this process. Besides short sintering times, the use of coated cBN-particles is a way to minimize this process. Therefore, the thermal stability of TiN coated cBN powders in high purity argon and nitrogen atmospheres up to temperatures of 1600 °C was investigated by thermogravimetry, X-ray phase analysis, scanning electron microscopy and Raman spectroscopy. The TiN coating was prepared by the atomic layer deposition (ALD)-method. The investigations showed that the TiN layer reacts in Ar at T ≥ 1200 °C with the cBN and forms a porous TiB2 layer. No reaction takes place in nitrogen up to temperatures of 1600 °C. Nevertheless, the 20 and 50 nm thin coatings also undergo a recrystallization process during heat treatment up to temperatures of 1600 °C.

Investigation on Cutting Feasibility on Ni-CBN on HSS Substrates for Aerospace Material

The study involves coating the high-speed steel (HSS) tool with cubic Boron via electroless nickel co-deposition. The surface coating of Ni-CBN was deposited via electroless nickel where the process of involved chemical reactions as the ceramic CBN powders was embedded within the layer. By introducing the electroless nickel process, the coating cost and procedure could be simplified. The electroless deposition has been extensively practised in industry, and the most prevalent coating offers excellent corrosion, wear and abrasion resistance, ductility, lubricity, electrical properties, and hardness. Thus, the introduction of the new electroless nickel (Ni-CBN) tools can be a contribution to the industry. This paper discussed on comparing the performance of Nickel-cubic boron nitride (Ni-CBN) HSS tool substrates and with uncoated HSS tool for its surface tolerance in milling of Aluminium Alloy 7075. The process variables selected during experimentation based on Taguchi L9 are cutting speed, feed rate, and depth of cut with three different levels for each parameter. Result shows, the lowest flank wear for coated measured is 51.34 μm while the highest is 380.26 μm. The highest surface roughness for uncoated is 1.154 μm and lowest 0.42μm. Meanwhile, for coated substrates, the highest Ra is 0.787μm and lowest 0.251μm. At the end of the analysis, the Ni-CBN HSS cutting tools are generally able to slightly reduce the tool wear with the longest tool lifetime 195 minutes compared uncoated 143 minutes. Therefore, it is concluded that the Ni-CBN HSS tool end mill are generally able to reduce the tool wear.

Utilization of moderate pressure and elevated temperatures in the optimization of Ti2AlC‐cBN composites using SPS technique

AbstractThe formation reaction mechanism of Ti2AlC cubic boron nitride (cBN) composite materials was investigated using different particle sizes at different volume percentages of cBN (20 and 40 vol%), at a constant moderate pressure while varying time and temperature. The results show that, under the investigated conditions, Ti2AlC decomposed at 1300°C with a simultaneous hexagonalization of the cBN, resulting in the creation of secondary phases including TiB2, TiC, TiN and AlN. It was observed that the optimum time and temperature for fabricating Ti2AlC‐cBN composites, where both phases were abundantly present, was 1250°C for 5 minutes for all composites. Under these conditions, there was no hBN in the resulting composites. Increasing the average particle size of cBN powder enhanced the stability of the Ti2AlC and cBN in the samples. Also, the increase in volume fraction of cBN was observed to further promote the stability of Ti2AlC and cBN in the samples. This was due to the decrease in surface area of cBN, which hampered hexagonalization of cBN. Whatever excess hBN present reacted completely with the MAX phase in the final composites. The secondary phases formed in the samples were TiAl2, Ti3Al, TiCb, TiB2, TiCxNy (in samples containing 100 µm cBN) and TiN (in samples containing 20 vol.% cBN). The reaction area between Ti2AlC and cBN was strongly bonded to the cBN and Ti2AlC phases. A controlled method of simultaneous hexagonalization of cBN and reaction of the resultant hBN with Ti2AlC has proved superior in forming composites of Ti2AlC with cBN.

Study on the properties and fracture mode of pure polycrystalline cubic boron nitride with different particle sizes

In this paper, pure polycrystalline cubic boron nitride (cBN) without additives was synthesized by a direct sintering method at 7.3 GPa and 2100 °C using industrial cBN powders with different particle sizes. High-pressure experiments without heating verified that the actual pressure of the cBN particles in the cavity was lower than that of the fine-grained samples during the sintering of coarse-grained samples. The best hardness (4900 HV2) and density (3.342 g/cm2) of sintered bodies were obtained when using fine-grained (2–4 μm) particles. The fracture modes of fine-grained and coarse-grained sintered bodies were investigated using scanning electron microscopy, and the microstructures of intra-grain and grain boundaries were systematically studied using high-resolution transmission electron microscopy. It was concluded that the main fracture mode of the fine-grained sample was transgranular fracture, while that of the coarse-grained sample was intergranular fracture. Moreover, a large number of dislocations and high-density twins were generated in the cBN grains under high temperature and high pressure, which improved the hardness of samples and caused transgranular fracture in fine-grained (2–4 μm) samples. This study of the fracture mode of industrial pure polycrystalline cBN is important to enable its use as a high-precision machining tool material.

Transformation of boron nitride from cubic to hexagonal under 1-atm helium

The transformation of boron nitride from the cubic to hexagonal phase has been investigated between 1560 and 1660 °C. High-purity cBN powders of three different particle sizes (<0.5 μm, 2–4 μm and 35–45 μm) were heat treated at ambient pressure in a dry flowing helium atmosphere over this temperature range for up to 8 h. Microscopy reveals surface growth of hBN on the cBN particles, although the morphology and texture of the hBN phase is different between the largest particles (35–45 μm) and the smaller particle sizes (<0.5 μm and 2–4 μm). X-ray diffraction was used to measure the weight fraction of each phase in the powder samples. Transformation rates as measured by weight fraction of the hexagonal phase over time correspond to a zero-order transformation of cBN to hBN, which becomes inhibited as the particle size decreases. Variations in surface growth morphology between the particle sizes suggest growth inhibition due to a reduction in nucleation site availability. Activation energies as determined from Arrhenius plots are 357 ± 29 kJ∙mol−1, 738 ± 168 kJ∙mol−1 and 1490 ± 65 kJ∙mol−1 for the <0.5 μm, 2–4 μm and 35–45 μm, respectively. Increasing surface area of the powders by decreasing the particle size corresponds with both decreased activation energy and collision frequency factor.

Granularity-induced plastic deformation mechanism of pure polycrystalline cubic boron nitride

Combined X-ray diffraction(XRD) profile analysis and HRTEM observation, a method for exploration of plastic deformation in pure polycrystalline cubic boron nitride (PcBN) samples with sizes of primary cBN powders was developed. XRD profile results showed that the coarse-grained PcBN exhibited a larger micro-strain ε, a greater deformation stacking faults probability fD, which was an order of magnitude larger than that of fine-grained PcBN, but a smaller twin stacking faults probability fT. It was deduced that the plastic deformation of the coarse-grained PcBN was dominated by stacking faults and mechanical twins mode, which would result in strain strengthening and then recrystallization. While the manner of growth twins was the mainly modes of fine-grained PcBN by phase transform, especially utilized the curled SP2 structure as a basis for a cubic structure nucleation. Fundamental plastic deformation principles of the ultrafine polycrystalline cBN was crucial for the field of high-precision cutting tools.