hBN Powder Research Articles

Functionalized boron nitride nanosheets and their polypropylene nanocomposites: influence on thermal, mechanical, rheological and wear behaviour

ABSTRACT The few-layer hexagonal boron nitride (hBN) nanosheets with hydroxyl (−OH) functional group at edges are synthesized using heat treatment of micron size hBN powder followed by sonication. These nanosheets are modified with a silane coupling agent, 3-Aminopropyl,triethoxysilane (APTES). The synthesized hBN nanosheets are mixed with the PP matrix using twin-screw extrusion followed by injection moulding. In case of APTES-modified hBN nanosheets incorporation in the PP matrix with PP-grafted maleic anhydride (PP-g-MA) shows the formation of an imide bond between the MA functional group of PP-g-MA and the amine group of APTES modified hBN nanosheets revealing compatibilization. The flow behaviour index values are lower for hBN nanosheets filled PP nanocomposites showing the improved processability from Rheological characterization. The few-layered – OH and APTES modified hBN nanosheet incorporation in the PP matrix improves the tensile and thermal properties. The incorporation of APTES modified hBN nanosheet in the PP matrix shows an increase in tensile modulus (18.1%) and tensile strength (8.1%) respectively. Wear studies show the incorporation of – OH and APTES modified hBN nanosheets in the PP matrix decreases the coefficient of friction and wear rate significantly. The wear rate at 4 min of wear testing for modified hBN nanosheet in the PP nanocomposites is ~ 96% less in comparison with neat PP. The wear mechanism is established from wear measurements and scanning electron microscopy (SEM) of worn-out wear surfaces of PP nanocomposites.

Tribological and Structural Effects of Titanium Carbide and Hexagonal Boron Nitride Reinforcement on Aluminum Matrix Hybrid Composites

This research involves the synthesis of a hybrid composite by adding titanium carbide (TiC) and hexagonal boron nitride (hBN) powders in certain weight ratios (2.5–5%) to pure aluminum (Al) powder. When previous studies were examined, it was seen that TiC and hBN powders were added separately to Al matrix powders; however, a hybrid composite was not produced as in this study. The obtained hybrid composites were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and X-ray diffraction (XRD) analysis. Microstructure, hardness and wear tests were carried out under 3 different loads (10 N, 20 N and 30 N) and dry conditions. Weight loss and coefficient of friction measurements were obtained for each hybrid composite during the wear tests. The TiC–hBN-reinforced specimen exhibited a significantly higher hardness value of 37.08% compared to the pure Al composite. It was also found that the synthesized Al–TiC–hBN hybrid composite exhibited a 59% reduction in the wear loss value for 10 N load, 30% for 20 N load and 60% for 30 N load compared to the pure Al sample. It is believed that the hybrid composites produced in this study have the ability to compete with Al matrix materials and exhibit the potential for longer durability and cost reduction in industries that use the production of aluminum parts.

Thermally Conductive Polymer Composites with Hexagonal Boron Nitride for Medical Device Thermal Management

Polymer composites with hexagonal boron nitride (hBN) have the potential to meet the heat dissipation and electrical insulation requirements of electronic and medical devices. In this study, hBN/polymer composites were fabricated with thermoplastic polyurethane (TPU) and epoxy as matrix materials. Three hBN powder types (BN1, BN2, BN3) with different platelet sizes and degrees of agglomeration were used. BN1 (with average size of 1 μm) and BN2 (with average size of 12 μm) mainly contained hBN platelets, while BN3 (with average size of 20 μm) contained both platelets and agglomerates of platelets. BN2 gave the highest thermal conductivity, while BN1 gave the lowest thermal conductivity. Thermal simulations were performed for a medical device with a limit for the maximum surface temperature. For the encapsulation of this device, several material combinations were simulated, using anisotropic thermal conductivity data. This included encapsulations with inner layers of commercial thermally and electrically conductive materials and an outer layer of the best thermally conductive (and electrically insulating) hBN/TPU composite fabricated by the authors.

Boron nitride nanotubes synthesis from ammonia borane by an inductively coupled plasma

Boron nitride nanotubes (BNNTs) have been studied extensively due to their unique properties. Hydrogen-assisted induction thermal plasma with hBN powder has been reported in the past to produce high-yield small-diameter BNNTs. However, removal of unprocessed hBN and other BN-based impurities has been a challenge. This study presents a new approach for BNNT synthesis using ammonia borane (AB) as the raw material while maintaining the high yield and similar nanotube diameter and number of walls. Our findings demonstrate that the use of AB results in enhanced synthesis of BNNTs with reduced B and BN impurities formation. The presence of H in the proximity of B following AB decomposition facilitated more efficient formation of BH-based precursors that also lowered the partial pressure of B and restricted its condensation and coagulation into large B particles, ultimately leading to an increased density of B seeds required for BNNTs nucleation. Both the increased formation of BNNT precursors and B seeds contributed to more efficient BNNTs formation. XRD analysis revealed that AB-BNNTs contained no hBN, less tBN, and more BNNTs compared to hBN-BNNTs. Additionally, TGA and OES measurements confirmed formation of less B and production of more BH species, respectively. Our results suggest that AB as a feedstock for BNNT synthesis in induction thermal plasma offers a promising alternative to hBN powder.

BNNS formation through surface modification of hBN nanopowders with a silane coupling agent

The production of BNNSs through the surface modification of nano-sized hBN powders with vinyltrimethoxysilane (VTS) as a silane coupling agent was realized using the newly introduced process route. It aimed to investigate the effects of shear forces generated by ultrasonication and stirring, which were applied during hydroxylation before silanization, and also VTS concentration on surface chemistry, exfoliation, dispersibility, and stabilization of hBN nanopowder. SEM images exhibited that stirring used before ultrasonication throughout hydroxylation improved the dispersibility of BN platelets. Followed by hydroxylation through ultrasonication, the silanization with 0.5 mg/mL VTS resulted in weak absorbances between 1225–995 cm−1 on FTIR spectrum, dispersed and translucent BN platelets, reduction of Raman peak intensity at 1368 cm−1, and an increase of zeta potential (from −10.1 mV to −19.0 mV) as indications of BNNS formation and also improved dispersibility and stability of dispersions. A higher VTS concentration than 0.5 mg/mL concluded with aggregation and poor dispersibility, associated with depletion flocculation. In addition, the number of translucent BN platelets with a lateral size of ∼ 200 nm increased, Raman peak intensity further decreased, and zeta potential reached −28.8 mV after silanization with optimal VTS content (0.5 mg/mL) since both stirring and ultrasonication were applied along hydroxylation. These results indicate the production of thinner BNNSs with high crystallinity and higher dispersion stability.

Betacoronavirus ve S. aureus'un hekzagonal bor nitrür ile etkileşimi

Investigations on advance effects of boron-containing compounds have gained attention the last decade. This study was carried out to investigate the effect of hexagonal boron nitride nanoparticles (BNNPs) on Bovine Coronavirus (BCoV) and Staphylococcus aureus (S. aureus) by different methods. First, biological effects of different BNNPs concentrations lower than 0.5 mg/mL examined on HRT-18 (Human Rectal Tumor) for 5 days. Different concentrations of hBN mixed with BCoV in liquid, on membrane or directly on cells and examined for differences of titers or replications. And also Bacterial Filtration Efficiency (BFE) test of hBN powders coated on polypropylene fabric by spray method was applied against S. aureus. The compound was found slightly toxic on the HRT-18 cell line by live cell counting, while no remarkable morphological difference was observed. BNNPs treatment with 0.025 or 0.3mg/mL concentrations did not reduce the infective titer and create no inhibitory effect on in vitro replication. Stability of virus titer after treatment of BNNPs coated fabric also indicated no antiviral efficiency. But hBN applied fabric formed a barrier of ≥90.3%, while non hBN applied fabric formed ≥64.6% barrier. The present study demonstrate that, BNNPs alone is not a good candidate for disinfectant or drug for BCoVs, while it could be valuable to use as coated fabric in the areas needing easy sanitation especially for S. aureus.

Tribological Characteristics of Copper-Based Functionally Gradient Material for Wind Turbines Brake Pads

Abstract Copper matrix incorporated with solid lubricant and hard ceramic reinforcement is a proven potential material for wind turbine brake pad applications. Though brake pads as bulk composites possess high wear resistance, hard ceramic reinforcements at the contact area weaken the joint strength with the brake caliper. This may lead to cataclysmic failure of the mechanical braking. This study aims to develop a functionally gradient materials (FGM) for brake pads that shows variations in composition and properties along its cross section. The brake pad comprises Cu, Fe, hBN, SiC, and Al2O3 powder to obtain a gradient composition profile. Metallographic studies showed the homogeneous distribution of minor matrix (Fe), solid lubricant (hBN), and reinforcement (SiC, Al2O3). Phase analysis was carried out using XRD, and Vickers microhardness tests were performed. A maximum hardness of 133.3 HV was obtained at the top layer of the FGM. Pin-on-disc wear apparatus was used to evaluate the wear-rate and the coefficient of friction (COF) of the sintered specimen at varied loads. Specimens exhibited a low wear-rate of 2.36 × 10−7 g/N m with 0.48 as the COF value at a maximum loading condition (70 N). Surface characterization (morphology, chemical composition, and phase composition) of worn specimens was performed using FESEM, EDS, and XRD analytical techniques. The results inferred that the predominant wear mechanism was oxidative and abrasive wear mechanism at high loads.

Effect of ball milling on hexagonal boron nitride (hBN) and development of Al-hBN nanocomposites by powder metallurgy route

Abstract This study reports on the exfoliation of bulk hexagonal boron nitride (hBN) by high-energy ball milling and the development of Al-hBN (alumninum-hexagonal boron nitride) nanocomposites by the powder metallurgy (PM) route via the incorporation of the exfoliated hBN in the Al matrix as a nanoreinforcement. The effect of ball milling on the morphology, crystallite size, lattice strain, and thermal stability of hBN powder have also been reported in this paper. Commercially available bulk hBN was ball milled for up to 30 hours in a high-energy planetary ball mill in order to exfoliate the hBN. Although no new phases were formed during milling, which was confirmed by the XRD (x-ray powder diffraction) spectra, ball milling resulted in the attachment of functional groups like hydroxyl (OH) and amino (NH2) groups on the surface of the hBN, which was confirmed by FTIR (Fourier Transform Infrared Spectroscopy) analysis. HRTEM (high resolution transmission electron microscopy) analysis confirmed the synthesis of hBN having few atomic layers of hBN stacked together after 20 hours of milling. After 20 hours of milling, the hBN particle size was reduced from ~1 μm to ~400 nm, while the crystallite size of the 20-hour-milled hBN powder was found to be ~18 nm. Milling resulted in a flake-like structure in the hBN. Although milling involved both exfoliation as well as reagglomeration of the hBN particles, a significant decrease in the diameter of the hBN particles and their thickness was observed after a long period of milling. The average thickness of the 20-hour-milled hBN flakes was found to be ~32.61 nm. HRTEM analysis showed that the hexagonal structure of the milled hBN powder was maintained. Al-based nanocomposites reinforced with 1%, 2%, 3%, and 5% by weight hBN were fabricated by PM route. The Al-hBN powder mixtures were cold-compacted and sintered at 550°C for 2 hours in argon (Ar) atmosphere. The maximum relative density of ~94.11% was observed in the case of Al-3 wt.% hBN nanocomposite. Al-3 wt.% hBN nanocomposite also showed a significant improvement in hardness and wear resistance compared to the pure Al sample that was developed in a similar fashion. The maximum compressive strength of ~999 MPa was observed in the case of Al-3 wt.% hBN nanocomposite and was approximately twice that of the pure Al sample developed in a similar fashion.

Hexagonal Boron Nitride as Anode for Sodium-Ion Battery – A Reality Check!

Sodium-ion batteries (SIBs) have gained enormous attention as an alternative electrochemical energy storage system. A significant challenge for its practical viability is finding an anode material that can provide high specific capacity along with good cycling stability. Recently, numerous theoretical works have proposed hexagonal boron nitride (hBN) as a promising anode material for SIBs. Nevertheless, there has been no reported experimental verification for the said theoretical claims. To fill the knowledge gap, here, the electrochemical performance of hBN has been investigated under the capacity of a potential anode for SIBs. The effect of particle morphology on the electrochemical performance of hBN has also been investigated using bulk hBN powder and nanoplatelets hBN as active materials. Unexpectedly, hBN showcased minimal charging capacity with effectively no reversible intercalation/de-intercalation of Na-ions. The obtained results provide experimental insight into the ineffectiveness of hBN in serving as SIB anode material, unlike the previous theoretical claims. We believe it is essential to report these discrepancies in the computational and experimental findings for the benefit of experimentalists working enthusiastically to explore and develop new anode materials related to boron nitride systems.

Preparation, Characterization, and Drug Delivery of Hexagonal Boron Nitride-Borate Bioactive Glass Biomimetic Scaffolds for Bone Tissue Engineering

In this study, biomimetic borate-based bioactive glass scaffolds containing hexagonal boron nitride hBN nanoparticles (0.1, 0.2, 0.5, 1, and 2% by weight) were manufactured with the polymer foam replication technique to be used in hard tissue engineering and drug delivery applications. To create three-dimensional cylindrical-shaped scaffolds, polyurethane foams were used as templates and covered using a suspension of glass and hBN powder mixture. Then, a heat treatment was applied at 570 °C in an air atmosphere to remove the polymer foam from the structure and to sinter the glass structures. The structural, morphological, and mechanical properties of the fabricated composites were examined in detail. The in vitro bioactivity of the prepared composites was tested in simulated body fluid, and the release behavior of gentamicin sulfate and 5-fluorouracil from glass scaffolds were analyzed separately as a function of time. The cytotoxicity was investigated using osteoblastic MC3T3-E1 cells. The findings indicated that the hBN nanoparticles, up to a certain concentration in the glass matrix, improved the mechanical strength of the glass scaffolds, which mimic the cancellous bone. Additionally, the inclusion of hBN nanoparticles enhanced the in vitro hydroxyapatite-forming ability of bioactive glass composites. The presence of hBN nanoparticles accelerated the drug release rates of the system. It was concluded that bioactive glass/hBN composite scaffolds mimicking native bone tissue could be used for bone tissue repair and regeneration applications.

High-Temperature Wear Performance of hBN-Added Ni-W Composites Produced from Combustion-Synthesized Powders

This work reports on the spark plasma sintering (SPS) of self-propagating high-temperature-synthesis (SHS)-derived Ni-W and Ni-W-2wt%hBN (4:1 molar ratio of metals) powders. The synthesis was carried out from a mixture of NiO and WO3 using Mg + C combined reducers through a thermo-kinetic coupling approach. Experiments performed in the thermodynamically optimal area demonstrated the high sensitivity of combustion parameters and product phase composition to the amount of reducers and hBN powder. The powder precursors with and without the addition of hBN were consolidated using SPS at a temperature and pressure of 1300 °C and 50 MPa, respectively, followed by a thorough phase and microstructural characterization of the obtained specimens. SHS-derived powders comprised the nano-sized agglomerates and were characterized by a high sinterability. The specimens of >95% density were subjected to ball-on-plate dry sliding wear tests at a sliding speed of 0.1 ms−1 and a distance of 1000 m utilizing an alumina ball of 10 mm in diameter under a 15 N normal load. The tests were performed at a temperature of 800 °C. A significant improvement in wear behavior was demonstrated for SHS-processed composites in comparison with their counterparts produced via conventional high-energy ball milling technique owing to the phenomena of ‘micro-polishing’, cyclic ‘self-healing’ and fatigue. However, the decisive effect of hBN addition in imparting lubrication during an HT wear test was not confirmed.

Towards practical applications of quantum emitters in boron nitride

We demonstrate quantum emission capabilities from boron nitride structures which are relevant for practical applications and can be seamlessly integrated into a variety of heterostructures and devices. First, the optical properties of polycrystalline BN films grown by metalorganic vapour-phase epitaxy are inspected. We observe that these specimens display an antibunching in the second-order correlation functions, if the broadband background luminescence is properly controlled. Furthermore, the feasibility to use flexible and transparent substrates to support hBN crystals that host quantum emitters is explored. We characterise hBN powders deposited onto polydimethylsiloxane films, which display quantum emission characteristics in ambient environmental conditions.

Formation of superhydrophobic surface with enhanced hardness and wear resistance by electrical discharge coating process

Electrical discharge coating (EDC) process is applied for preparation of hard and wear-resistant coating by using green compact tool of Cu+MoS2+WS2+hBN powder. XRD analysis suggests that the coating morphologies comprises of hard and soft phases. Further, EDS line scan along cross-section reveals that concentration of coating elements increases from workpiece to coating surface direction. FESEM results indicate that applied coatings exhibit a hierarchical rough structure. Due to the hierarchical coating structure, the water contact angle (WCA) is raised to a super-hydrophobic state (152.2°). The developed coatings also exhibit higher microhardness and low specific wear rates than substrate. It is aimed that the enhancement in mechanical durability of superhydrophobic surfaces will be beneficial for the extensive application of a superhydrophobic coating.

Growth of ultrathin Al2O3 islands on hBN particles by atomic layer deposition in a custom fluidized bed reactor using Al(CH3)3 and H2O

Hexagonal boron nitride (hBN) powder is widely used in industry because of its unique physical and chemical properties. Atomic layer deposition (ALD) allows the growth of such ultrathin coatings. This technique is performed in a fluidized bed reactor (FBR) using trimethylaluminum (TMA) and H2O as precursors under atmospheric pressure. In this study, the homemade heat-resistant stainless steel fluidized bed was designed and constructed as a vertical, circular cross-section column for conducting the thermal ALD process.Al2O3 growth mechanism is challenging and depends on surface properties. After the ALD process, island growth mode was observed. The deposition of ultrathin alumina islands was successfully obtained on hBN. Growth per cycle (GPC) values were calculated between 0.03–0.1 nm/cycle based on TEM imaging. The thickness growth rate (TGR) of a (mean) value was increased from 1.07 nm at 10 cycles to 1.49 nm at 50 cycles, and b (mean) value was increased from 5.67 nm at 10 cycles to 10.9 nm at 50 cycles. With increasing number of cycles, the growth of the island can reach the highest values both vertically and horizontally according to the schematic depicting a hemisphere-shaped island form model. We found a non-linear growth according to substrate-inhibited growth.

Wear Behaviors of TiN/WS2 + hBN/NiCrBSi Self-Lubricating Composite Coatings on TC4 Alloy by Laser Cladding

TiN and WS2 + hBN reinforced Ni-based alloy self-lubricating composite coatings were fabricated on TC4 alloy by laser cladding using TiN, NiCrBSi, WS2, and hBN powder mixtures. Energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffractometry (XRD), and optical microscopy (OM) were adopted to investigate the microstructure. The wear behaviors of the self-lubricating composite coatings were evaluated under large contact load in room temperature, dry-sliding wear-test conditions. Results indicated that the phases of the coatings mainly include γ-Ni, TiN, TiNi, TiW, WS2, and TiS mixtures. The average microhardness of the composite coating is 2.3–2.7 times that of the TC4 matrix. Laser cladding TiN/WS2 + hBN/NiCrBSi self-lubricating composite coatings revealed a higher wear resistance and lower friction coefficient than those of the TC4 alloy substrate. The friction coefficient (COF) of the coatings was oscillating around approximately 0.3458 due to the addition of self-lubricant WS2 + hBN and hard reinforcement TiN. The wear behaviors testing showed that the wear resistance of the as-received TC4 was significantly improved by a laser cladding TiN/WS2 + hBN/NiCrBSi self-lubricating composite coating.

Improving Formation Conditions and Properties of hBN Nanosheets Through BaF2-assisted Polymer Derived Ceramics (PDCs) Technique.

Hexagonal boron nitrite (hBN) is an attractive material for many applications such as in electronics as a complement to graphene, in anti-oxidation coatings, light emitters, etc. However, the synthesis of high-quality hBN at cost-effective conditions is still a great challenge. Thus, this work reports on the synthesis of large-area and crystalline hBN nanosheets via the modified polymer derived ceramics (PDCs) process. The addition of both the BaF2 and Li3N, as melting-point reduction and crystallization agents, respectively, led to the production of hBN powders with excellent physicochemical properties at relatively low temperatures and atmospheric pressure conditions. For instance, XRD, Raman, and XPS data revealed improved crystallinity and quality at a decreased formation temperature of 1200 °C upon the addition of 5 wt% of BaF2. Moreover, morphological determination illustrated the formation of multi-layered nanocrystalline and well-defined shaped hBN powders with crystal sizes of 2.74–8.41 ± 0.71 µm in diameter. Despite the compromised thermal stability, as shown by the ease of oxidation at high temperatures, this work paves way for the production of large-scale and high-quality hBN crystals at a relatively low temperature and atmospheric pressure conditions.

Novel Functionalized BN Nanosheets/Epoxy Composites with Advanced Thermal Conductivity and Mechanical Properties.

The effective dissipation of heat is critical to the performance and longevity of high-power electronics, so it is important to prepare highly thermally conductive polymer-based packaging materials for efficient thermal management. Due to the excellent thermal conductivity of boron nitride nanosheets (BNNSs), the hexagonal boron nitride (hBN) powder was dissolved in a mixed solution of isopropanol and deionized water for ultrasonic exfoliation to obtain hydroxylated BN nanosheets. Then, the prepared BNNS was functionalized with (3-aminopropyl)triethoxysilane (APTES) to enhance its dispersibility and interfacial compatibility in the epoxy resin, which play an important role in the improvement of the thermal conductivity of the composites. Finally, APTES-BNNS was uniformly dispersed in the epoxy resin by solvent mixing, and the oriented APTES-BNNS/epoxy composites were prepared through spin-coating and hot-pressing methods. It was found that APTES-BNNS/epoxy composites prepared herein exhibited significant anisotropic thermal conductivity. The results show that the thermal conductivity of APTES-BNNS/epoxy composites reached 5.86 W/mK at a filler content of 40 wt % and these composites have favorable thermal stability and mechanical properties. The APTES-BNNS/epoxy composite prepared in this paper has excellent thermal management capability and can be applied to the packaging of high-power electronic devices.

Low temperature self-densification of high strength bulk hexagonal boron nitride

Hexagonal boron nitride (hBN) ceramics are expected to have wide applications at high temperatures as both a structural and functional material. However, because of its flake structure and general inertness, it is currently impossible to sinter hBN powder to a dense bulk (with a relative density of above 96%) even at 2000 °C. Here, we report dense bulk hBN with 97.6% theoretical density achieved at a lower preparation temperature (1700 °C) via a self-densifying mechanism without sintering additives. During the sintering process, cubic boron nitride particles incorporated into the hBN flake powders transform into BN onions with a significant volume increase, thus filling in voids among the hBN flakes and highly densifying the hBN bulks. The resulting dense hBN ceramics possess 2–3 times the strength of traditional hBN ceramics. This phase-transition-induced volume expansion strategy could lead to dense sintered compacts with high performance in other ceramic systems.

Evaluation of nanomechanical and tribological properties of laser surface alloyed boride-nitride-carbide ceramic matrix composite coatings

Interesting mechanical and tribological properties, favorable for both ambient and high temperature applications, can be gathered by composites consisting of multiple reinforcing phases. The present study focuses on the characterization of ceramic matrix composite coatings with in-situ reinforcements, developed through combination of laser triggered chemical reaction and subsequent laser treatment. A preplaced precursor mixture of TiO2, SiO2, hBN and graphite powders in stoichiometric proportions is used for the chemical reaction activated by a high power laser beam to produce coatings containing TiB2, TiN, SiC and hBN. Minor modifications in the constituents of the preplaced precursor mixture helped in developing coatings different in terms of the amount of hBN and SiC present in it. This compositional variation brought significant changes in mechanical and tribological properties of the coatings. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) are used to confirm the presence of all the reaction products in the CMC coatings developed. Evaluation of nanomechanical properties and studies on the tribological properties of these coatings are performed thoroughly. Reduced modulus (Er) and nanohardness (H) of the composite coatings deposited on AISI 1025 steel have been measured from load–displacement curves. The stress-strain curves of composite coatings help in characterizing its damage tolerance and determining design stresses to find suitability to any application. Presence of hBN in composite coating causes reduction in coefficient of friction. Coatings formed with SiC in precursor helps in improving the specific wear rate. Top surface morphology and tribological properties of these coatings, after they are exposed to high temperature, are also explored.

High hardness cubic boron nitride with nanograin microstructure produced by high‐energy milling

AbstractHigh‐energy shaker milling of hexagonal boron nitride (hBN) powders was used to produce powders rich in sp3 bonding. The powders contained up to 68% sp3 bonding and were found to nucleate nanosize cBN grains during consolidation at 5.5 GPa and 1400°C. The effect of hBN starting particle size, milling time, and powder‐to‐milling ball ratio were studied. The amount of sp3 bonding for milled hBN powders was determined, using 11B solid‐state NMR. The milled material was also analyzed by XRD, Raman spectroscopy, and HRTEM. The results indicate that the material has a nanosized microstructure comprised of a disordered hBN matrix and cBN nuclei in the form of sp3‐rich domains. Eight different milled powders were produced and consolidated at pressures of either 5.5 or 6.5 GPa and temperatures of either 1400°C or 1450°C into 12 mm diameter and 5 mm thick pellets. Consolidated pellets formed from milled hBN with 68% sp3 bonding had Vickers hardness of 42 ± 1 GPa and fracture toughness 3.8 ± 0.1 MPa.m1/2. Vickers hardness of 49 ± 1 GPa and fracture toughness of 4.6 ± 0.1 MPa.m1/2 was achieved with a precursor that contained milled hBN and 50 vol. % of 0.5 μm diameter cBN crystals.