Surface Self-Diffusion Induced Sintering of Nanoparticles.

Despite the critical role of sintering phenomena in constraining the long-term durability of nanosized particles, a clear understanding of nanoparticle sintering has remained elusive due to the challenges in atomically tracking the neck initiation and discerning different mechanisms. Through the integration of in situ transmission electron microscopy and atomistic modeling, this study uncovers the atomic dynamics governing the neck initiation of Pt-Fe nanoparticles via a surface self-diffusion process, allowing for coalescence without significant particle movement. Real-time imaging reveals that thermally activated surface morphology changes in individual nanoparticles induce significant surface self-diffusion. The kinetic entrapment of self-diffusing atoms in the gaps between closely spaced nanoparticles leads to the nucleation and growth of atomic layers for neck formation. This surface self-diffusion-driven sintering process is activated at a relatively lower temperature compared to the classic Ostwald ripening and particle migration and coalescence processes. The fundamental insights have practical implications for manipulating the morphology, size distribution, and stability of nanostructures by leveraging surface self-diffusion processes.

Densification and Properties of Bimodal 316L Stainless Steel Produced by Binder Jetting Printing with Addition of B4C.

Boron-based aids are commonly introduced to tackle the unsatisfactory densification of SS316L parts fabricated by binder jetting (BJ) technology. However, there is scarce study on the effect of sintering aids on the mechanical performance. This work investigates the effect of B4C aids and sintering temperature on the mechanical performance and microscopic morphology of BJ printing SS316L parts. SS316L powders with a bimodal size distribution were adopted to enhance density and reduce the shape distortion. Besides, B4C was added as a sintering aid to promote densification during sintering. The results show that the bimodal powder is in favour of the density increase and the sintering process. The sintering temperature is largely reduced with the addition of B4C. Further, the mechanical performance is mainly affected by the final density and B4C content. In view of a comprehensive evaluation of shape retention and properties, B4C content of 1 wt.% and sintering temperature of 1250°C are expected to be the optimal parameters.

Spark Plasma Sintering of Complex Metal and Ceramic Structures Produced by Material Extrusion.

Alternative approaches to laser fusion for the additive manufacturing (AM) of metals are often hampered by the need for long sintering cycles. Typical sintering cycles require heating at temperatures above 80% of the melting point for several hours. The process is time- and energy-consuming, particularly when high-melting materials are involved. Applying pressure can drastically reduce the time and temperature required for densification. Recently, a particular kind of pressure-assisted sintering process known as spark plasma sintering (SPS) or field-assisted sintering (FAST) received considerable attention in academia and industry due to its ability to enhance densification. However, conventional SPS/FAST techniques cannot be directly applied to the densification of objects presenting a complex geometry. This work shows how a modified SPS/FAST setup, operating in a pseudoisostatic mode, can be used for debinding and sinter objects produced by material extrusion. This approach can be applied to metals and metal-based and ceramic-based composites when their geometry does not include closed cavities. Depending on the characteristics of the pressure-transfer medium, some level of anisotropy in the volume reduction associated with the densification can be observed. Still, it can easily be corrected by appropriately compensating sintering deformation during printing. Using this approach, the time required for the debinding and sintering can be reduced considerably. It represents an alternative approach to the AM of a wide range of inorganic materials characterized by a relatively low-cost, high material flexibility, and low environmental impact.

Experimental Investigation on Friction Behavior of Selective Laser Sintering Processed Parts.

Selective laser sintering (SLS) is a powder bed fusion additive manufacturing process that uses polymer powders to produce functional parts directly from digital 3D models. SLS supports small- to medium-batch fabrication of customized products for various end-use applications. These parts can be used as tooling to support conventional manufacturing and inspection where mechanical and tribological behaviors are important. This article evaluates the friction behavior of parts fabricated by SLS polyamide (PA12) and glass bead-filled polyamide (PA-GF) materials. Pin-on-Disk tribometer was used to characterize the behavior in dry sliding conditions with part build orientation, load, and speed as factors. Taguchi's approach and analysis of variance are used to quantify the influence of these factors on the friction coefficient. Both materials show reduction in friction coefficient with the increase in load; on the other hand, an increase in speed affects adversely. However, the influence of part orientation is comparatively lesser than the other two factors considered in this study. The debris, pin, and disk wear surfaces were examined to learn wear mechanisms. It is observed that surface porosity resulting from the fabrication process plays a significant role in friction behavior. The glass beads in PA-GF material function as reinforcement against load and influences the friction behavior. Low friction and wear characteristics make both materials as a prospective contender for tooling application.

Evaluation of the Influence of Technological Parameters of Selected 3D Printing Technologies on Tribological Properties.

The article presents the results of tribological research of sample models manufactured using three separate 3D printing technologies: selective laser sintering-SLS, photo-curing of liquid polymer resins-PolyJet Matrix (PJM) and fused deposition modeling-FDM. The impact of process parameters (printing direction, layer thickness, and energy density for SLS) on tribological properties was assessed through linear wear and coefficient of friction. The research was carried out to assess the possibility of using 3D printing for the quick manufacturing of casting models, which has a significant impact on shortening the time of implementation for mass production of the casting process. The research results proved the possibility of controlling the technological process in a manner allowing to produce models with controlled properties, including tribological parameters. In addition, the results for three additive technologies and different materials were compared by using the same friction parameters.

Preparation and Electrothermal Transport Behavior of Sn8[(Ga2Te3)34(SnTe)66]92 Bulk Glass.

High-conductivity tellurium-based glasses were anticipated to be the attractive candidates in chalcogenide glass systems on account of their distinctive characteristics and extensive application prospects. In this paper, the high-density (>96%) Sn8[(Ga2Te3)34(SnTe)66]92 bulk glass with the density of 5.5917 g/cm3 was successfully prepared by spark plasma sintering (SPS) technology at 460 K, using a 5 min dwell time and 450 MPa pressure. The room-temperature thermal conductivity of Sn8 bulk materials significantly decreased from 1.476 W m-1∙K-1 in the crystalline sample to 0.179 W m-1∙K-1 in the glass, and the Seebeck coefficient obviously increased from 35 µV∙K-1 in to 286 µV∙K-1, indicating that the glass transition of tellurium-based semiconductors could optimize the thermal conductivity and Seebeck coefficient of the materials. Compared to the conventional tellurium-based glassy systems, the fabricated Sn8 bulk glass presented a high room-temperature conductivity (σ = 6.2 S∙m-1) and a large glass transition temperature (Tg = 488 K), which was expected to be a promising thermoelectric material.

Cu-Al-Ni Nanocrystalline Compacts Obtained by Spark Plasma Sintering of Mechanically Alloyed Powders.

The aim of this work is to obtain Cu-13.5Al-4Ni alloy for use as shape memory alloy by Spark Plasma Sintering (SPS) of mechanically alloyed powder. The study investigates the structural and microstructural changes in terms of crystal parameters, crystallite sizes, and phases evolution during mechanical alloying and spark plasma sintering of Cu-13.5Al-4Ni powders. We obtained alloyed powders with a structure composed of α(Cu), AlNi intermetallic compound and small amounts of elemental Al through the mechanical alloying technique. After spark plasma sintering at 900 °C, the microstructure consists of an AlNi compound distributed at the edge of α(Cu) grains. The crystallite sizes of both, α(Cu) and AlNi are in nanoscale order after 16 h of milling (9 and 6.5 nm respectively). After sintering at 900 °C (in Ar atmosphere, without holding time), the crystallite sizes increase to 46 nm for α(Cu) and to 40 nm for AlNi compound. Also, the Cu-13.5Al-4Ni compacts achieve a final density after sintering at 900 °C of around 80% from the theoretical density.

Electrochemical Performance of LiTa2PO8-Based Succinonitrile Composite Solid Electrolyte without Sintering Process.

Solid-state batteries (SSBs) have been widely studied as next-generation lithium-ion batteries (LiBs) for many electronic devices due to their high energy density, stability, nonflammability, and chemical stability compared to LiBs which consist of liquid electrolytes. However, solid electrolytes exhibit poor electrochemical characteristics due to their interfacial properties, and the sintering process, which necessitates high temperatures, is an obstacle to the commercialization of SSBs. Hence, the aim of this study was to improve the interfacial properties of the lithium tantalum phosphate (LTPO) solid electrolyte by adding succinonitrile (SN) on the interface of the LTPO particle to enhance ionic conductivity without the sintering process. Electrochemical impedance spectroscopy (EIS), the Li symmetric cell test, and the galvanostatic cycle test were performed to verify the performance of the SN-containing LTPO composite electrolyte. The LTPO composite solid electrolyte exhibited a high ionic conductivity of 1.93 × 10-4 S/cm at room temperature (RT) compared to the conventional LTPO. Also, it showed good cycle stability, and low interfacial resistance with Li metal, ensuring electrochemical stability. On the basis of our experimental results, the performance of solid electrolytes could be improved by adding SN and lithium salt. In addition, the SN can be used to fabricate the solid electrolytes without the sintering process at high temperatures.

Size Effects of Copper(I) Oxide Nanospheres on Their Morphology on Copper Thin Films under Near-Infrared Femtosecond Laser Irradiation.

The femtosecond laser direct writing of metals has gained significant attention for micro/nanostructuring. Copper (I) oxide nanospheres (NSs), a promising material for multi-photon metallization, can be reduced to copper (Cu) and sintered through near-infrared femtosecond laser pulse irradiation. In this study, we investigated the size effect of copper (I) oxide nanospheres on their morphology when coated on Cu thin films and irradiated by near-infrared femtosecond laser pulses. Three Cu2O NS inks were prepared, consisting of small (φ100 nm), large (φ200 nm), and a mixture of φ100 nm and φ200 nm NSs. A unique phenomenon was observed at low laser pulse energy: both sizes of NSs bonded as single layers when the mixed NSs were used. At higher pulse energies, the small NSs melted readily compared to the large NSs. In comparisons between the large and mixed NSs, some large NSs remained intact, suggesting that the morphology of the NSs can be controlled by varying the concentration of different-sized NSs. Considering the simulation results indicating that the electromagnetic fields between large and small NSs are nearly identical, this differential morphology is likely attributed to the differences in the heat capacity of the NSs.

Investigation on the Coalescence of Filaments in Fused Filament Fabrication Process for Amorphous Polyether Ketone Ketone for Varying Nozzle Diameters and Chamber Temperatures.

The use of Fused Filament Fabrication (FFF) of high-performance polymers is becoming increasingly prevalent, leading to the exploration of new applications. The use of such materials in critical cases for aerospace applications necessitates the verification of industry standards, particularly with regard to the requirements for part porosity. The authors investigate the effect of nozzle diameter and cooling temperature printing parameters on the porosity of the part by using existing modelling methods based on the sintering of cylinders and spheres and comparing the results to microscope snapshots of sections of parts. The models are able to be used as limits for predicting the longitudinal neck growth of the part. The authors show through experiments that the value of the cooling temperature of the deposited filament has a minimal effect on the outcome, while nozzle diameter has a strong impact on the resulting porosity. The modelling results show that there is a significant impact of both the nozzle diameter and cooling temperature on the porosity of the part. This implies that further refinement of the models is needed for the resulting parts to be applied in critical structures.

Effects of porcelain layer thickness and luting resin cement on the opalescence properties of porcelain veneers.

BACKGROUND: When discolored teeth are repaired with porcelain veneers, the thickness of the restorations should be increased appropriately using opaque porcelain and bonded by applying opaque luting resin cement to cover discolored substrates. However, its impact on the opalescent performance has not been reported yet. PURPOSE: To analyze the effects of opacity, body porcelain layer thickness, and luting resin cement on the opalescence properties of porcelain veneer restorations for discolored teeth. METHODS: Ninety IPS d. SIGN A3 porcelain veneer specimens were prepared via powder-paste coating and sintering. Specimens were divided into three groups according to ceramic type and cement used or not: body porcelain group as control, body/opaque porcelain group and body/opaque porcelain-resin cement composite group. Each group was subdivided into three subgroups based on the thickness, 0.50, 0.75, and 1.00 mm (n = 10). Variolink N Bleach XL luting resin cement with thickness of 0.1 mm was applied to the bottoms of body/opaque porcelain specimens to produce body/opaque porcelain-resin cement composites. The opalescence (OP) values were calculated and the micromorphological characteristics were analyzed by scanning electron microscope (SEM). Statistical analysis was performed by using ANOVA test (P < 0.05). RESULTS: The opalescence values determined for the body porcelain groups with thicknesses of 0.50, 0.75, and 1.00 mm and body/opaque porcelain specimens with thicknesses of 0.45/0.05, 0.70/0.05, and 0.95/0.05 mm were 3.35 ± 0.15, 3.83 ± 0.10, 6.73 ± 0.25, 7.95 ± 0.34, 15.16 ± 0.60, and 16.49 ± 0.89, respectively. The specimens in the body and body/opaque porcelain groups exhibited significant increases in their opalescence values with increasing thickness (P = 0.00). The opalescence values of the specimens increased significantly with the addition of a 0.05 mm opaque porcelain layer (P = 0.00). The opalescence values of the composites containing body/opaque porcelain layers with thicknesses of 0.45/0.05, 0.70/0.05, and 0.95/0.05 mm and luting resin cement were 9.46 ± 0.17, 16.47 ± 0.15, and 18.38 ± 0.47, respectively. The opalescence values of the composite specimens increased significantly with an increase in the thickness of the porcelain layer(P = 0.00). CONCLUSIONS: The opaque porcelain layer and opaque resin cement can significantly improve the opalescence properties of porcelain laminate veneers for discolored teeth, but the opalescence performance is still poor than natural teeth. The body porcelain only contributes to opalescence within a certain thickness range.

Synthesis and characterization of ceramic refractories based on industrial wastes.

The possibility of reusing ceramic roller waste to produce cordierite and mullite refractories was investigated. Five batches were designed using wastes representing ceramic roller waste, magnesite, and silica sand, shaped and fired at 1300 °C/2 h, and one batch was selected at 1200 °C. The chemical composition and precipitated phases of the used raw materials and the fired batches were analyzed using XRF and XRD techniques, respectively. Densification parameters, morphology, microstructure and electrical properties were also studied to evaluate the effect of the formed phases on the properties of fired materials. Bulk density increases with an increase in mullite and a decrease in cordierite, and it also increases with increasing temperature, whereas porosity and water absorption show a opposite behavior to density (it decreases with an increase in mullite and temperature). The main phases developed after firing at 1300 °C/2 h were cordierite, mullite, corundum, baddeleyite, and spinel. Bending strength increases with increasing mullite percentage and density, and decreasing grain size and porosity. The microstructure develops and becomes finer with increasing mullite percentage and density. The grain size of the crystals was very fine at 1200 °C/2 h and increased at 1300 °C/2 h. Broadband dielectric spectroscopy was employed to study the electrical and dielectric behavior of the investigated samples. The increase in mullite concentration shows a remarkable increase in ε', especially at lower frequencies, as it is three times higher than that of M10. At f > 103 Hz ε', frequency independence is accompanied by an increase in mullite concentrations due to the lag of dynamics fluctuations after the alteration of the electric field. The generation of new free ions leads to the enhancement of conductivity as the mullite concentration increases.

Laser Sintering by Spot and Linear Optics for Inkjet-Printed Thin-Film Conductive Silver Patterns with the Focus on Ink-Sets and Process Parameters.

The implementation of the laser sintering for inkjet-printed nanoparticles and metal organic decomposition (MOD) inks on a flexible polymeric film has been analyzed in detail. A novel approach by implementing, next to a commonly 3.2 mm diameter spot laser optic, a line laser optic with a laser beam area of 2 mm × 80 mm, demonstrates the high potential of selective laser sintering to proceed towards a fast and efficient sintering methodology in printed electronics. In this work, a multiplicity of laser parameters, primary the laser speed and the laser power, have been altered systematically to identify an optimal process window for each ink and to convert the dried and non-conductive patterns into conductive and functional silver structures. For each ink, as well as for the two laser optics, a suitable laser parameter set has been found, where a conductivity without any damage to the substrate or silver layer could be achieved. In doing so, the margin of the laser speed for both optics is ranging in between 50 mm/s and 100 mm/s, which is compatible with common inkjet printing speeds and facilitates an in-line laser sintering approach. Considering the laser power, the typical parameter range for the spot laser lays in between 10 W and 50 W, whereas for the line optics the full laser power of 200 W had to be applied. One of the nanoparticle silver inks exhibits, especially for the line laser optic, a conductivity of up to 2.22 × 107 S‧m-1, corresponding to 36% of bulk silver within a few seconds of sintering duration. Both laser sintering approaches together present a remarkable facility to use the laser either as a digital tool for sintering of defined areas by means of a spot beam or to efficiently sinter larger areas by means of a line beam. With this, the utilization of a laser sintering methodology was successfully validated as a promising approach for converting a variety of inkjet-printed silver patterns on a flexible polymeric substrate into functionalized conductive silver layers for applications in the field of printed electronics.

Low Sintering Temperature Effect on Crystal Structure and Dielectric Properties of Lead-Free Piezoelectric Bi0.5Na0.5TiO3-NaFeTiO4.

Bi0.5Na0.5TiO3 (BNT) emerges as a promising ferroelectric and piezoelectric lead-free candidate to substitute the contaminant Pb[TixZr1-x]O3 (PZT). However, to obtain optimal ferroelectric and piezoelectric properties, BNT must be sintered at high temperatures. In this work, the reduction of sintering temperature by using iron added to BNT is demonstrated, without significant detriment to the dielectric properties. BNT-xFe with iron from x = 0 to 0.1 mol (∆x = 0.025) were synthesized using high-energy ball milling followed by sintering at 900 °C. XRD analysis confirmed the presence of rhombohedral BNT together with a new phase of NaFeTiO4 (NFT), which was also corroborated using optical and electronic microscopy. The relative permittivity, in the range of 400 to 500 across all the frequencies, demonstrated the stabilization effect of the iron in BNT. Additionally, the presence of iron elevates the transition from ferroelectric to paraelectric structure, increasing it from 330 °C in the iron-free sample to 370 °C in the sample with the maximum iron concentration (0.1 mol). The dielectric losses maintain constant values lower than 0.1. In this case, low dielectric loss values are ideal for ferroelectric and piezoelectric materials, as they ensure minimal energy dissipation. Likewise, the electrical conductivity maintains a semiconductor behavior across a range of 50 Hz to 1 × 106 Hz, indicating the potential of these materials for applications at different frequencies. Additionally, the piezoelectric constant (d33) values decrease slightly when low concentrations of iron are added, maintaining values between 30 and 48 pC/N for BNT-0.025Fe and BNT-0.05Fe, respectively.

Exploring the Potential of Cold Sintering for Proton-Conducting Ceramics: A Review.

Proton-conducting ceramic materials have emerged as effective candidates for improving the performance of solid oxide cells (SOCs) and electrolyzers (SOEs) at intermediate temperatures. BaCeO3 and BaZrO3 perovskites doped with rare-earth elements such as Y2O3 (BCZY) are well known for their high proton conductivity, low operating temperature, and chemical stability, which lead to SOCs' improved performance. However, the high sintering temperature and extended processing time needed to obtain dense BCZY-type electrolytes (typically > 1350 °C) to be used as SOC electrolytes can cause severe barium evaporation, altering the stoichiometry of the system and consequently reducing the performance of the final device. The cold sintering process (CSP) is a novel sintering technique that allows a drastic reduction in the sintering temperature needed to obtain dense ceramics. Using the CSP, materials can be sintered in a short time using an appropriate amount of a liquid phase at temperatures < 300 °C under a few hundred MPa of uniaxial pressure. For these reasons, cold sintering is considered one of the most promising ways to obtain ceramic proton conductors in mild conditions. This review aims to collect novel insights into the application of the CSP with a focus on BCZY-type materials, highlighting the opportunities and challenges and giving a vision of future trends and perspectives.

Superior Piezoelectric Performance in Textured CaBi2Nb2O9 Ferroelectric Ceramics through Rare-Earth Gadolinium Doping and Spark Plasma Sintering.

High-performance piezoelectric ceramics with excellent thermal stability are crucial for high-temperature piezoelectric sensor applications. However, conventional fabrication processes offer limited enhancements in piezoelectric performance. In this study, we achieved a significant breakthrough in the piezoelectric performance of highly textured CaBi2Nb2O9 (CBN) ceramics by incorporating rare-earth gadolinium doping and utilizing spark plasma sintering. The resulting Ca0.97Gd0.03Bi2Nb2O9 (CBN-3Gd) ceramics exhibited superior piezoelectric properties, with a high piezoelectric constant d33 of 26 pC/N and a high Curie temperature TC of 946 °C. We employed piezoresponse force microscopy (PFM) to observe the morphology and dimensions of the ferroelectric domains, revealing a rod-shaped 3D domain configuration. This configuration facilitated polarization rotation in the textured ceramics, as analyzed using X-ray photoelectron spectroscopy (XPS) and polarization-electric field (P-E) hysteresis loops. Furthermore, the textured CBN-3Gd ceramics demonstrated exceptional thermal stability and reliability. The piezoelectric constant d33 decreased by only 11.8% over a temperature range of room temperature to 500 °C, and the DC electrical resistivity remained at 6.7 × 105 Ω cm at 600 °C. This work not only highlights the great potential of textured CBN-based ceramics for high-temperature piezoelectric sensors but also provides a viable strategy for enhancing the performance of piezoelectric materials with large aspect ratio micromorphology.

Role of 3Y-TZP grain boundaries in glazing and layering.

OBJECTIVES: Monolithic 3 mol% Yttria-stabilized tetragonal zirconia polycrystal or 3Y-TZP exhibits transformation toughening phenomena which is suitable for dental restorations with minimizing the risk of fracture and to decrease reduction of natural tooth. However, the staining/glazing or layering is required to achieve of a match with the optical properties of natural dentition. The hypothesis under examination is that the physical, chemical, and structural aspects of the 3Y-TZP grain boundaries after the staining/glazing or layering. METHODS: The three sintering temperatures of 1400 °C, 1500 °C, and 1600 °C were considered followed by vacuum annealed at 750 °C for 1 min; and air post-annealed at 750 °C for 1 min RESULTS: The initial sintering step in the fabrication of zirconia restorations plays a critical role in the outcomes of the subsequent stages of glazing and layering. SIGNIFICANCE: The current study revealed for first time the advantage of vacuum annealing by the presence of ferroelastic domain switching toughening mechanism.

Developing High-Performance Ceramics from Multicomponent Grain Boundary Entropy Design.

Grain boundary (GB) glassy phase often results in poor ceramic performances. Here, a Multicomponent Grain Boundary Entropy (MGBE) descriptor extracted from high-throughput first-principle calculations is proposed to capture the nature of high-entropy GB phases in ceramics. In a Si3N4 ceramic model system, MGBE is found to have a direct correlation with GB phase crystallinity, element segregation, and formation of pores. The predicted highest MGBE sintering additive combination (MgO-Y2O3-Er2O3-Yb2O3) leads to high-performance ceramics of homogenous microstructure and pure GB (YErYb)2Si3O3N4 phase without observable glassy film. Conversely, low MGBE additives result in a substantial amount of GB glassy phase, element segregation, and pore clusters. The MGBE descriptor can make a rapid screening of multicomponent sintering additives, offering a novel approach for rational designing of ceramics with targeted microstructure and performances.

Effect of microwave sintering on density, microstructural and magnetic properties of pure strontium hexaferrite at low temperatures and heating rate.

In recent decades, the rising demand for permanent magnetic materials has driven manufacturers to explore substitutes for rare earth elements in response to their fluctuating prices and negative environmental impact. M-type hexaferrites considered as good alternatives and studies have focused on enhancing their magnetic and structural properties through various approaches. In this study, new approach using low heating rate microwave sintering has been applied to investigate the changes on density, microstructure, and magnetic properties of strontium hexaferrite from core to surface. Sintering temperatures of 950 °C, 1000 °C, 1050 °C, and 1100 °C with 10 °C/minute heating rate were applied accordingly. The bulk density, FESEM, XRD and VSM tests were conducted to study materials' properties. The outcomes of the study showed exponential relationship between density and sintering temperature reaching optimum value of 91.4 % at 1050 °C and then declined slightly at observed to analysis confirmed the magnetoplumbite structure P63/mmc in all samples and high crystallized structure at 1050 °C, with the occurrence of α-Fe2O3 at 1100 °C. Grain growth and crystallization observed to increase at higher sintering temperature with agglomeration while denser and melted boundaries at lower temperatures. Magnetic properties especially remanence magnetization Mr and saturation magnetization Ms fluctuated with sintering temperature achieving optimum values of 28.188 emu/g and 55.622 emu/g at 1000 °C respectively. Coercivity Hc and magnetic energy density BH max recorded optimum values at 1050 °C. The findings emphasize the critical role of microwave sintering in tailoring the properties of strontium hexaferrite for magnetic applications.

Transforming Nanocrystals into Superhard Boron Carbide Nanostructures.

Boron carbide (B4+δC) possesses a large potential as a structural material owing to its lightness, refractory character, and outstanding mechanical properties. However, its large-scale industrialization is set back by its tendency to amorphize when subjected to an external stress. In the present work, we design a path toward nanostructured boron carbide with greatly enhanced hardness and resistance to amorphization. The reaction pathway consists of triggering an isomorphic transformation of covalent nanocrystals of Na1-xB5-xC1+x (x = 0.18) produced in molten salts. The resulting 10 nm B4.1C nanocrystals exhibit a 4-fold decrease of size compared to previous works. Solid-state 11B and 13C NMR coupled to density functional theory (DFT) reveal that the boron carbide nanocrystals are made of a complex mixture of atomic configurations, which are located at the covalent structural chains between B11C icosahedral building units. These nanocrystals are combined with a spark plasma-sintering-derived method operated at high pressure. This yields full densification while maintaining the particle size. The nanoscaled grains and high density of grain boundaries provide the resulting nanostructured bodies with significantly enhanced hardness and resistance to amorphization, thus delivering a superhard material.