Pressureless Reactive Sintering Research Articles

Synthesis and characterization of a remarkable ternary boride: Mo2NiB2

In this communication, we report the synthesis of predominantly single phase Mo2NiB2 by pressureless reactive sintering. XRD analysis showed the samples were ≥95% pure. Both computational and experimental results showed the structure and space group to be orthorhombic and 71: Immm, respectively. Computational results showed Mo2NiB2 has superior mechanical properties as compared to ternary borides like MoAlB, WAlB and Cr2AlB2. As a representative example, the bulk modulus of Mo2NiB2 is 299.5 GPa, outperforming the range of 209.2–228.2 GPa observed in MAB phases. With experimental hardness of 12.0 ± 1.48 GPa and compressive strength of 2469.5 ± 84.6 MPa, Mo2NiB2 outperformed ternary borides like MoAlB, Fe2AlB2 and Mn2AlB2. Magnetic measurements by vibrating sample magnetometer showed Mo2NiB2 to be diamagnetic with minor ferromagnetism which was attributed to residual Ni in the samples.

In-situ fabrication and characterization of W-ZrC composites via pressureless reaction sintering

This research presents a study on the fabrication and characterization of tungsten‑zirconium carbide (W-ZrC), an ultra-high temperature ceramic, using an in-situ reaction sintering method. Tungsten carbide (WC) and zirconia (ZrO2) powders were used as precursors to synthesize composites with three different ratios. The thermodynamic phase stabilities of the precursor materials were analyzed, and the reaction products were determined based on the total pressure within the system. The fabricated composites were characterized by their microstructures, porosities, hardnesses, and thermal conductivities. The results show that the composites exhibited distinct crystal phases, including those of tungsten, tungsten carbide (W2C), zirconium carbide (ZrC), and tetragonal zirconia (t-ZrO2). The reaction pathways were determined based on the composition ratios and thermodynamic stability. The composites demonstrate good densification and interparticle bonding owing to the in-situ reaction sintering process, which simplifies the fabrication and lowers processing costs. The composites also exhibited desirable properties, such as high hardness and thermal conductivity (maximum 36.4 W·m−1·K−1), making them suitable for high-temperature applications. The findings of this study contribute to the understanding of the synthesis process and properties of W-ZrC composites and provide insights for their potential applications to industries such as aerospace, defense, and nuclear energy.

The formation mechanism of in-situ TaC/Ni0.9Ta0.1 composites prepared by pressureless reactive sintering

The in-situ Tantalum Carbide (TaC)/Ni0.9Ta0.1 composite was fabricated by pressureless reactive sintering method using Nickel (Ni), Tantalum (Ta) and graphite as raw materials. The formation mechanism was investigated through analyzing the phase and morphology evolution process during the reactive sintering process. Results showed that Ni, Ta and graphite completely reacted and dense TaC/Ni0.9Ta0.1 composite was obtained. With the increase of temperature, the solid-phase diffusion of atoms occurs at the interface of Ni, Ta and graphite, leading to the formation of Ni3C, Ni2Ta, Ni3Ta, Ni0.9Ta0.1 and TaC. Meanwhile, the reaction [Ta] (Ta atoms in Ni3Ta) + [C] (C atoms in Ni3Ta)TaC in Ni3Ta takes place, due to the high affinity between Ta and C atoms. The intermediate products Ni3C, Ni2Ta and Ni3Ta vanish, and the composite is consisted of Ni0.9Ta0.1 and TaC before the appearance of liquid phase. The formation of TaC included two ways, namely the diffusion of C into Ta particles and the reaction [Ta]+[C] = TaC in Ni3Ta. Ni0.9Ta0.1 was also generated through two ways, i.e., the diffusion of Ta into Ni and the transformation of Ni3Ta. The liquid phase sintering of composite occurs at about 1320 °C, and the optimum sintering temperature was about 1380 °C.

Microstructure and mechanical properties of (Zr,Ti)B2–SiC composites obtained by pressureless sintering of ZrB2–SiC–TiO2 powder mixtures

Multiphase ceramics have been highlighted due to the combination of different properties. This work proposes to obtain the multiphase composite of (Zr,Ti)B2–SiC based on the mixture of ZrB2, SiC, and TiO2 sintered without pressure. The effect of TiO2 addition on solid solution formation with ZrB2, densification, microstructure, and mechanical properties was investigated. For this, 2.0 wt% TiO2 was added to ZrB2–SiC composites with 10–30 vol% SiC and processed by reactive pressureless sintering at 2050 °C with a 2 h holding time. Sinterability, crystalline phases, microstructure, Vickers hardness, and indentation fracture toughness of these composites were analyzed and compared to the non-doped ZrB2–SiC samples. The XRD analysis and EDS elemental map images indicated the incorporation of Ti atoms into the ZrB2 crystalline structure with solid solution generation of (Zr,Ti)B2. The addition of TiO2 resulted in matrix grain size refinement and a predominant intergranular fracture mode. The relative densities were not significantly modified with the TiO2 addition, though a higher weight loss was detected after the sample sintering process. The composites doped with TiO2 showed an increase in fracture toughness but exhibited a slightly lower Vickers hardness compared to composites without TiO2 addition.

Microstructure evolution, enhanced hardness and toughness in the solid-solution ceramic composite by reaction pressureless sintering of ZrB2 and TiC powders

Fully dense ZrB2–TiC composites were produced by reactive pressureless sintering using ZrB2 and TiC as the starting reactants. The effect of TiC content on microstructure and mechanical properties of ZrB2–TiC composites was investigated. The densification and grain refinement were achieved due to the reaction and solid solution coupling effect. Besides, elongated (Ti, Zr)B2 plate-like grains with a high aspect ratio were obtained for the first time by the reaction of ZrB2 and TiC. The ZrB2-70 mol%TiC composite exhibited good comprehensive mechanical properties of high hardness of 29.0 GPa, flexural strength of 555 MPa, and fracture toughness of 5.4 MPa m1/2 due to grain-refinement and solid solution strengthening, and plate-like grains toughening effects.

Effect of Ni on the formation mechanism of TiC/Ni composites fabricated by reactive sintering

The TiC/Ni composites with 0 wt%, 55 wt% and 70 wt% Ni contents were fabricated by pressureless reactive sintering to study the effect of Ni on the formation mechanism of composites. The results show that the solid reaction between Ti and graphite is controlled by the diffusion of C through TiC layer, and the morphology of TiC layer is similar to the graphite sheet in sample without Ni. By contrast, graphite would dissolve into Ni in samples with Ni, and Ni particles would form continuous skeleton around Ti particles by solid phase sintering. Meanwhile, Ni diffuses into Ti particles to form NiTi compound. Therefore, graphite and C in Ni skeleton reacts with Ti to form TiC layer on whole surface of NiTi particles, resulted in the similar morphology of TiC layers to original Ti particles. Moreover, Ni plays one key role in the liquid phase sintering of TiC/Ni composites by forming NiTiC eutectic phase. The relative density of TiC/Ni composites are higher than 96%, while the samples without Ni shows no obvious shrinkage. The increase of Ni also contributes to the decrease of sintering temperature by enhancing the solution-precipitation process.

The formation mechanism of TiC/Ni composites fabricated by pressureless reactive sintering

TiC/Ni composites were innovatively fabricated by pressureless reactive sintering method using Ni, Ti and graphite as raw materials. According to the sintering shrinkage curve, phase and microstructure evolution process of composites during reactive sintering, the formation mechanism of dense TiC/Ni composites could be divided in two stages. In the first stage, TiC layer is formed on Ti particles by the solid reaction between Ti and graphite, while Ni atom diffuses into Ti particles to generated NiTi, Ti2Ni and Ni3Ti. Besides, the solid-state sintering of Ni particles also occurs. At 1250 °C, the Ti is completely consumed, resulting in the TiC layer on Ni and continuous Ni skeleton in composites. In the second stage, the eutectic liquid phase of Ni-Ti-C is formed, and then shrinkage process begins through the dissolution-reprecipitation of TiC in Ni matrix. The relative density of TiC/Ni composites reaches 98.14% at 1360 °C.

Densification, solid solution formation, and microstructural investigation of reactive pressureless sintered HfB2-TiB2-SiC-MoSi2 quadruplet composite

Dense HfB2-TiB2-SiC-MoSi2 quadruplet composite was produced by a reactive pressureless sintering method at 2050 °C for 5 h. The relative density was improved and reached 98% by in situ formation of SiC and MoSi2 phases. Microstructural studies proved that SiC and MoSi2 second phases were mostly formed during the sintering process. Moreover, the Sintering mechanism of the composite was investigated by HSC software. TiB2 co-matrix was improved the sinterability of the composite by the formation of (Hf,Ti,Mo)–B and (Hf,Ti,Mo)–C solid solutions.Mechanical properties such as Vickers hardness (23.2 GPa), fracture toughness (5.4 MPa m1/2), and elastic modulus (430 GPa) were effectively enhanced by tailoring the composite.

Oxidation behaviour of SiC ceramic coating for C/C composites prepared by pressure-less reactive sintering in wet oxygen: Experiment and first-principle simulation

SiC ceramic coating, for prevention of C/C composites against oxidation, was prepared by pressure-less reactive sintering to investigate the oxidation behaviour in an oxidising environment containing water vapour at 1773 K. The experimental results demonstrated that the oxidation behaviour of porous SiC ceramics could be divided into two stages, following the parabolic model, which was attributed to the variation in the contact area involved in the oxidation reactions. During the entire oxidation process, water vapour could accelerate the oxidation of the SiC ceramics, according to the weight change. By first-principle calculations, the accelerated oxidation rate of the SiC ceramics was attributed to weakened Si–O and Al–O bonds in the formed glassy scale, which were caused by hydroxide radicals from the water. Atomic thermal motions at high temperature could lead to the breakage of the network structure, promoting the diffusion and solution of oxidising gases. When the as-prepared SiC ceramics were applied as anti-oxidative coatings for the C/C composites, the SiC ceramic coating and C/C matrix could be sealed and protected faster per unit time, because water vapour was beneficial to the formation of a glassy layer. The weight loss of the C/C matrix could be attributed to unsealed microcracks inside the SiC coating in the initial stage.

Effect of in situ VSi2 and SiC phases on the sintering behavior and the mechanical properties of HfB2-based composites

In situ HfB2–SiC–VSi2 composite was fabricated by reactive pressureless sintering at the temperature of 2150 °C for 4 h under a vacuum atmosphere. In situ SiC and VSi2 reinforcements were formed using VC and Si powders as starting materials according to the following reaction: VC + 3Si = SiC + VSi2. Microstructural studies and thermodynamic calculations revealed that in situ VSi2 and SiC phases were mostly formed and homogeneously distributed in HfB2 skeleton. The results showed that the density of in situ HfB2–SiC–VSi2 composite was 98%. Besides, the mechanical properties of the composite were effectively enhanced by the formation of in situ second phases. The Vickers hardness and the fracture toughness of the composite reached 20.1 GPa and 5.8 MPa m−1/2, respectively.

Preparing B4C-SiC-TiB2 composites via reactive pressureless sintering with B4C and TiSi2 as raw materials

B4C-SiC-TiB2 composites with high densification were fabricated by in-situ reactive pressureless sintering with B4C and TiSi2 as the raw materials. The phase composition, relative density, microstructure, mechanical properties and fracture mode of the fabricated composites were investigated. Besides, the reaction mechanism and toughening mechanism were studied. The results indicate that TiSi2 can react with B4C and C to form TiB2 and SiC below 1400 ℃. A multi-component eutectic liquid phase is formed in the sintering process due to the presence of impurities, which enhances the densification. The relative density, hardness and fracture toughness of the composites sintered at 2200 ℃ with 30 wt% TiSi2 are 97.2%, 27.9 GPa and 3.8 MPa m1/2, respectively. The fracture mode of different-size TiB2 phase in the composites is the coexistence of intergranular and transgranular fracture according to the crack propagation path and the observation of fracture surface. The toughening effect is owing to the high-toughness second phase (SiC), the coexistence of intergranular and transgranular fracture of TiB2 and the stepped fracture in TiB2 phase.

Reactive-sintering B4C matrix composite for armor applications

The B4C matrix composite intended for armor applications still presents restrictions, such as low sintering density, production of large parts and inherited brittleness. Herein, research on this topic is discussed in detail. First, the material outlook of armor applications is organized from the development of composite armor and ceramic materials for armor to the B4C matrix composite and reactive-sintering method. In the second section, the technologies are reviewed for reactive pressureless sintering, reactive hot-pressing sintering, reactive discharge plasma sintering and self-propagating high-temperature sintering. Thereafter, our previous works on the TiB2/SiC/B4C composite and laminated Ti/B4C composite are employed to illustrate their microstructural evolution, phase transformation and fracture model. These studies provide a potential method for producing tough and high-strength ceramic composites for armor application. In the final section, the mechanism, evaluation method and influencing factors of anti-penetration for ceramic armor and B4C matrix composite are reviewed.

SHS of Ti3SiC2-Based Materials in the Ti–Si–C System: Impact of Silicon Excess

For SHS of Ti3SiC2-based materials in the Ti–Si–C system, we explored the impact of silicon excess on the composition of resultant MAX-phase material by XRD and SEM methods. After hot pressing, SHS-produced MAX-phase material was found to contain over 88 wt % of Ti3SiC2. The SHS-produced powders are sinterable and deserve further studies on their hot pressing and pressure-less reactive sintering.

Mechanism of the Intermediary Phase Formation in Ti-20 wt. % Al Mixture during Pressureless Reactive Sintering.

This work aims to describe the mechanism of intermediary phases formation in TiAl20 (wt. %) alloy composition during reactive sintering. The reaction between titanium and aluminum powders was studied by in situ diffraction and the results were confirmed by annealing at various temperatures. It was found that the Ti2Al5 phase formed preferentially and its formation was detected at 400 °C. So far, this phase has never been found in this alloy composition during reactive sintering processes. Subsequently, the Ti2Al5 phase reacted with the titanium, and the formation of the major phase, Ti3Al, was accompanied by the minor phase, TiAl. Equations of the proposed reactions are presented in this paper and their thermodynamic and kinetic feasibility are supported by Gibbs energies of reaction and reaction enthalpies.

Pressureless reaction sintering and hot isostatic pressing of transparent MgAlON ceramic with high strength

A fine-grained (~ 10 µm) MgAlON ceramic combining the advantage of high strength and high transparency was reported by pressureless reaction sintering and hot isostatic pressing (HIP) at relative lower processing temperature (~ 150–200 °C lower than reported previously) for the first time. It was sintered from MgO, AlN and Al2O3 mixed powders at 1650 °C for 15 h, followed by HIP at 1670 °C for 5 h under 180 MPa Ar. Sintering and densification were carefully investigated by the microstructure and phase evolution at 1600–1800 °C. It turned out that, the densification was mainly attributed to the solute drag effect of residual Al2O3 before full solid-solution at 1650 °C, thus resulting in limited grain growth. The in line transmittance and flexural strength reached 86.1% (3.7 µm), 386 ± 5 MPa (> 40% higher than previous results), respectively. The origin of the high strength was the combination of Hall-Petch effect (finer grains) and twin lamella strengthening mechanism. The MgAlON transparent ceramic exhibited the prospect of high-performance infra red (IR) dome to rival AlON and sapphire.

The effects of carbon/carbon composites blasting treatment and modifying SiC coatings with SiC/ZrB2 on their oxidation and cyclic ablation performances

To enhance the oxidation and ablation performances of SiC coating, C/C composites with a porous surface layer were designed via blasting treatment and then followed by ZrB2 additive in the process of pressure-less reactive sintering. Cyclic ablation test using oxyacetylene torch from 1750 °C to room temperature showed that the coating possessed good ablation performance accompanying with the formation of Zr-O-Si glassy protective layer. The good sintering performance combined with the increased coating/substrate interfaces contributed to reduce the cyclic thermal stress and enhance the stability of the Zr-O-Si layer to the denudation of oxyacetylene torch, thus promoting the ablation performance.

SiC nanowire-induced fabrication of fine-grained and highly-density SiC coating by pressure-less reactive sintering

Fine-grained and high-density SiC coating was fabricated on carbon materials by incorporating SiC nanowires during the pressure-less reactive sintering for the first time. The grain size, relative density, and fracture toughness of the as-fabricated coating are 1.5 ± 0.6 μm, 95%, and 5.03 ± 0.73 MPa m1/2, respectively, resulting in a good oxidation protective ability, which can efficiently protect carbon materials from oxidation at 900 °C for more than 70 h or at 1500 °C for more than 90 h. The formation of such microstructure may be associated to the increasing nucleation rate resulting from the microstructure evolution and phase transformation of SiC nanowires during the sintering process.

ZrB2\u2013SiC based composites for thermal protection by reaction sintering of ZrO2+B4C+Si

Synthesis and sintering of ZrB2–SiC based composites have been carried out in a single-step pressureless reaction sintering (PLRS) of ZrO2, B4C, and Si. Y2O3 and Al2O3 were used as sintering additives. The effect of ratios of ZrO2/B4C, ZrO2/Si, and sintering additives (Y2O3 and Al2O3), was studied by sintering at different temperatures between 1500 and 1680 °C in argon atmosphere. ZrB2, SiC, and YAG phases were identified in the sintered compacts. Density as high as 4.2 g/cm3, micro hardness of 12.7 GPa, and flexural strength of 117.6 MPa were obtained for PLRS composites. Filler material was also prepared by PLRS for tungsten inert gas (TIG) welding of the ZrB2–SiC based composites. The shear strength of the weld was 63.5 MPa. The PLRS ZrB2–SiC composites exhibited: (i) resistance to oxidation and thermal shock upon exposure to plasma flame at 2700 °C for 600 s, (ii) thermal protection for Cf–SiC composites upon exposure to oxy-propane flame at 2300 °C for 600 s.

Preparation and mechanical properties of TiCx–(NiCu)3Al–CuNi2Ti–Ni hybrid composites by reactive pressureless sintering pre-alloyed Cu/Ti3AlC2 and Ni as precursor

Ni based hybrid composites were fabricated from Ni/Cu/Ti3AlC2 powder mixtures. After pressureless sintering, almost fully dense TiCx-(NiCu)3Al-CuNi2Ti-Ni hybrid composites were obtained and the in situ formed ultrafine TiCx grains were homogeneously distributed in the metal matrix. The as prepared hybrid composites exhibited superior mechanical properties due to precipitation of submicron sized TiCx and (NiCu)3Al particles homogeneously dispersed in the matrix. The hardness, yield stress and ultimate compressive strength of the hybrid composites fabricated from 3.5Ti3AlC2/15.1Cu/81.4Ni reactant mixture attained mean values 2.66±0.10GPa, 837±36MPa and 1123±15MPa, respectively. The enhancement of the mechanical properties was attributed to a size dependent particle strengthening mechanism as well as formation of large amount of dimples.

On the Low Temperature Densification of Reactively Hot Pressed Non-Stoichiometric ZrC and (Zr,Ti)C

Reactive hot pressing (RHP) as a low temperature processing route is explored in the present work. For this purpose, metal-carbide mixtures, 1:1 molar ratio of zirconium (Zr): zirconium carbide (ZrC) and titanium (Ti): ZrC, are chosen, along with a temperature of 900°C and 50 MPa pressure. Further, pressureless reaction sintering (RS) is done at 1300-1600°C temperature. It has been found that after 1400°C RS, both the compositions reach almost full density. Ti, ZrC composition shows higher hardness (13 vs 11 GPa) than the Zr, ZrC composition. This process would allow dense products to be made by RHP more economically at lower temperature.