Reaction Sintering Research Articles

Influence of Powder Size on Pore Characteristics and Intermetallic Phase Kinetics in Porous Ti-Al Alloys

This study investigates the impact of varying powder size on porosity, pore parameters, and intermetallic phase reaction during the reactive sintering of porous TiAl alloys. Ti52Al48 alloys were prepared using coarse (200 mesh) and fine (325 mesh) Ti powders through elemental powder metallurgy and were subsequently sintered at different temperatures, 600 and 1200 °C. Our findings reveal a consistent pore morphology and intermetallic phase microstructure across both alloys. However, samples containing fine Ti powder exhibited a higher number density of small pores compared to those incorporating coarse Ti powders. Additionally, alloys prepared with fine Ti powders demonstrated a higher porosity than those prepared with coarse powders. Consequently, fine Ti powder promoted enhanced diffusion between Ti and Al during sintering, as reflected by the lower onset temperature and enthalpy of intermetallic reaction during sintering.

Porous (Y0.25Ho0.25Yb0.25Lu0.25)2Si2O7: A novel high‐entropy ceramic with high porosity and excellent thermal stability

AbstractWith the rapid development of hypersonic vehicles, the thermal protection systems face great challenges due to the severe aerodynamic heat. As a result, conventional fiber insulation tiles would experience severe shrinkage at high temperatures (>1500°C), endangering the safety of the aircraft. To solve the problem, a high‐entropy effect was introduced to increase the high‐temperature resistance of thermal insulation materials, and highly porous (Y0.25Ho0.25Yb0.25Lu0.25)2Si2O7 was prepared by in situ reaction sintering process in this work. The fabricated porous samples present excellent overall properties, including superhigh porosity (95.09%–93.10%), lightweight (0.29–0.41 g/cm3), and very low thermal conductivity (0.066–0.085 W/(m·K)). More importantly, porous (Y0.25Ho0.25Yb0.25Lu0.25)2Si2O7 has outstanding high‐temperature dimensional stability. Although the porosity of the sample is higher than 90%, its linear shrinkage at 1550°C for 2 h is less than 1%. The results demonstrate that porous high‐entropy (Y0.25Ho0.25Yb0.25Lu0.25)2Si2O7 is a promising thermal insulation material in extreme high‐temperature environments.

Correlative characterization of plasma etching resistance of various aluminum garnets

AbstractPlasma etching is a crucial step in semiconductor manufacturing. High cleanliness and wafer‐to‐wafer reproducibility in the etching chamber are essential in order to successfully achieve nanometer‐sized integrated functions on the wafer. The trend toward the application of more aggressive plasma compositions leads to higher demands on the plasma resistance of the materials used in the etching chamber. Due to its excellent etch resistance, yttrium aluminum garnet Y3Al5O12 (YAG) is starting to replace established materials like SiO2 or Al2O3 in this kind of application. In this study, reactive spark plasma sintering (SPS) was used to manufacture highly dense YAG ceramics from the respective oxides. In addition, yttrium was replaced with heavier lanthanoids (Er, Lu), intending to investigate the role of the A‐site cation in the garnet type structure on the plasma erosion behavior. The produced materials were exposed to fluorine‐based etching plasmas mimicking the conditions in the semiconductor manufacturing apparatus and the erosion behavior was characterized by atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM), and profilometry. The induced chemical gradient in the samples is limited to a few nanometers below the surface, which makes its characterization challenging. For advanced analysis, we developed a correlative characterization method combining SIMS and scanning TEM (STEM)–energy‐dispersive spectroscopy (EDS) enabling us to examine the structural and chemical changes in the reaction layer locally resolved. In the case of lanthanoid aluminates, an altered reaction layer and reduced fluorine penetration compared to YAG were found. However, a correlation between the characteristics of the induced chemical gradient and the determined physical erosion rates was not evident.

Densification of zirconia-based ceramics by non-conventional sintering processes and chemical pathways

The present work reports an overview of the main results we have obtained from non-conventional sintering approaches towards the densification of 3mol.% yttria stabilized zirconia (3YSZ), the lessons learned from these results, and open questions that still need to be addressed. A wide range of techniques have been developed in the field of ceramic sintering, both in high temperature regime with extreme heating rates (>10 000 °C/min), as well as in very low temperatures (<400 °C) regime involving chemical reactivity to activate sintering mechanisms. In this context, we have recently explored several of these methods in order to understand and control the different sintering parameters and their impact on microstructure, crystallinity, grain boundaries and defect chemistry. Due to its complex chemistry, 3YSZ is a playground for the exploration of sintering capabilities and their influence on ceramic properties. Our recent studies in this field are presented in the present work, highlighting the effect of high heating rates through Flash Spark Plasma Sintering ( Flash-SPS) and Ultra High temperature Sintering (UHS) on sintering, but also the combination of low temperature Cold Sintering Process (CSP) and the associated precursors chemistry, with Spark Plasma Sintering (SPS). It also shows the possible densification by reactive hydrothermal sintering, using hydroxide precursors, and the effect of High Pressure SPS (HP-SPS) on 3YSZ nanopowders. All of these results touch upon current trends in the field of sintering, and highlight the possibilities in terms of chemical reactivity of precursors and physical parameter control. In particular, they show the importance of defect chemistry, related to the sintering atmospheres and their impact on both microstructures and properties.

Performance improvement of polyethersulfone membranes with Ti3AlCN MAX phase in the treatment of organic and inorganic pollutants

In this work, the hydrophobic polyethersulfone (PES) membrane was modified by incorporating Ti3AlCN MAX phase. Synthesis of Ti3AlCN MAX phase was performed using the reactive sintering method. The scanning electron microscopy (SEM) images showed a 3D compressed layered morphology for the synthesized MAX phase. The Ti3AlCN MAX phase was added to the casting solution, and the mixed-matrix membranes were fabricated by the non-solvent induced phase inversion method. The performance and antifouling features of bare and modified membranes were explored by pure water flux, flux recovery ratio (FRR), and fouling resistance parameters. Through the modification of membranes by introducing the Ti3AlCN MAX phase, the enhancement of these features was observed, in which the membrane containing 1 wt% of MAX phase showed 17.7 L/m2.h.bar of permeability and 98.6% for FRR. Also, the separation efficiency of all membranes was evaluated by rejecting organic and inorganic pollutants. The Ti3AlCN MAX membranes could reject 96%, 95%, and 88% of reactive blue 50, Rose Bengal, and azithromycin antibiotics, respectively, as well as 98%, 80%, 86%, and 36% of Pb2+, As5+, Na2SO4, and NaCl, respectively. Finally, the outcomes indicated the Ti3AlCN MAX phase was an excellent and efficient novel additive for modifying the PES membrane.

Исследование железоматричных композитов с карбидным упрочнением, полученных спеканием механоактивированных смесей титанидов железа с углеродом

Introduction. The addition of dispersed solid particles of refractory compounds (carbides, borides, silicides) to the structure of alloy is a widely used effective way to increase the wear resistance of steels and alloys. Composites with a matrix of iron-based alloys (steel and cast iron) strengthened by titanium carbide particles are of great practical interest. The main structural characteristics, which define hardness and wear resistance of the composites, are volume fraction, dispersion and morphology of the particles of the strengthening carbide phase. The structure of composites depends on the method of its preparation. The methods of powder metallurgy combined with preliminary mechanical activation of powder mixtures have become widespread. It is previously established that in mechanically activated powder mixtures of FTi35S5 ferrotitanium, consisting of 82 % of (Fe,Al)2Ti phase, and P-803 carbon black, a reaction occurs with the formation of a composite consisting of a steel binder and titanium carbide. The synthesis reaction of carbides occurs in a solid-phase mode at combustion’s temperatures of 900–950 °C. Therefore, there is no coarsening of the structure due to the growth of carbide particles, which is typical for reactions in the presence of a liquid phase. FTi35S5 alloy contains a plenty of impurities (silicon, aluminum and etc). The purpose of the work is to investigate the phase composition and structure of the products of the interaction of Fe2Ti and FeTi iron titanides with carbon under the conditions of reaction sintering of mechanically activated powder mixtures and to determine the possibility of synthesizing iron-matrix composites strengthened with submicron titanium carbide particles. Research methods. The structure and phase composition of sintered compacts from mechanically activated powders were studied by optical metallography, X-ray diffraction (XRD) and scanning electron microscopy (SEM) using determination of the elemental composition by energy-dispersive X-ray spectroscopy (EDX). Experimental technique. The reaction mixtures were prepared using intermetallic powders obtained by vacuum sintering of compacts from iron and titanium powder mixtures of 2Fe+Ti and Fe+Ti compositions. Carbon black was added to the intermetallic powders to convert all the titanium containing in the intermetallic compounds into carbide. The titanides – carbon black mixtures were processed by an Activator 2S planetary ball mill for 10 min milling time at a rotation speed of 755 rpm (40g). The mechanically activated mixtures were cold compacted into cylindrical samples with a diameter of 20 mm, which were sintered in vacuum at а temperature of 1,200 °C and an isothermal holding time of 60 minutes. Results and discussion. According to the results of X-ray diffraction analysis, almost all titanium contained in iron titanides reacts with carbon to form carbide and reduced iron. The sintering products of compacts of both compositions contain target phases: titanium carbide with a slight shift from the equiatomic ratio and α-iron, which has the lattice parameters close to the reference data, and also a few of other phases. The titanium carbide particles in the iron binder were identified on the back-scattered electron (BSE) images due to the tonal contrast: the heavy iron appears darker against the carbide, which is composed of lighter elements. According to EDX analysis, the relative content of titanium and carbon in the carbide particles indeed corresponds to the composition of non-stoichiometric titanium carbide. Conclusion. The composites including titanium carbide and α-iron binder were obtained by sintering of iron titanides and carbon (carbon black) mechanically activated powder mixtures. The granules of composite powders obtained by crushing of sintered compacts are of interest as feedstocks for wear-resistant coatings and additive technologies, as well as for manufacturing of dense materials by other compaction methods: spark plasma sintering (SPS) or hot pressing (HP).

Microstructure, dielectric properties and phase transition of Y2O3-doped barium tin titanate ceramics

BaCO3, SnO2 and TiO2 et al were used as crude materials, and Y2O3 was used as dopant, BaSnxTi1-xO3 (BTS) ceramics were prepared by solid-state reaction sintering technology. The results show that the doping of Y element does not change the lattice structure of barium tin titanate obviously, and there is no new phase, however, owing to the Y3+ ion doping, the diffraction peak position is changed as the Y3+ doping amount increasing. Interestingly, Curie temperature of the sample increased from 35 o C (blank sample) to 50 o C (0.05 mol%), and then the Curie temperature moved to low temperature as the doping amount increased continuously, which is related to the doping mechanism of Y3+ ion. After doping Y2O3, the dielectric loss of the samples decreases, especially when the doping amount reaches 0.10 mol%, the specimen shows excellent temperature stability of dielectric loss, making it superior candidates for applications.

Reactive cold sintering of dense barium sulfate ceramics for high-reliability chip packaging in integrated circuits

Reactive cold sintering (RCS) is an innovative ceramic consolidation technique that combines a low-temperature reaction with the cold sintering process. In this work, equimolar (CH3COO)2Ba and (NH4)2SO4 were homogeneously mixed to obtain a reactive activator abbreviated as RA and then added to barium sulfate (BaSO4) powder obtaining BaSO4–xwt%RA (x = 5, 7.5, 10, 12.5, and 15). Dense (>96 % theoretical) BaSO4 ceramics were successfully fabricated via RCS of BaSO4–xwt%RA at 200℃ with a constantly applied pressure of 250 MPa. The Woolfrey-Bannister method provided quantitative insights into the activation energy, indicating that RA effectively reduced the energy required for densification. The Vickers hardness (1.76 GPa) and coefficient of thermal expansion (CTE, 18.8 ppm/°C) of the RCSed BaSO4 ceramics were comparable to the high-temperature (850 °C) sintered counterparts. Moreover, finite element analyses confirmed the high CTE value of the RCSed BaSO4 ceramics holds great promise for high-reliability chip packaging applications.

Developing novel high-lead equivalence transparent ceramic windows for effective γ-ray shielding

In response to the limitations of current transparent window materials in γ-ray shielding scenarios, herein, high-lead equivalent (0.865 mmpb) Yb2Hf2O7 transparent ceramics (YbHO-TCs) were prepared via a solid-state reaction and vacuum sintering. The fabricated YbHO-TC shows high transparency, where the in-line transmittance up to 78.9 % at 1200 nm, which is extremely close to their theoretical limit (79 %). Additionally, the linear absorption coefficient of YbHO-TC for γ-rays is 0.482, approximately twice that of the state-of-the-art lead glass materials widely employed in radiation-shielding windows. Remarkably, YbHO-TC displayed no discoloration, and its in-line transmittance exhibited little change even when exposed to a radiation dose as high as 800 kGy. The innovative developed YbHO-TC integrates high transparency and high-lead equivalent properties, not only rending them highly promising for deployment as γ-rays shielding windows but also inspiring the controllable design of high-performance optical windows tailored for use in radiation shielding applications.

Ti/WO3, a nanothermite for special purposes: An experimental study

A new nanothermite system, composed of titanium and tungsten trioxide is reported. Initial investigations show that it has low-average sensitivity to mechanical stimuli (friction, impact), but that its sensitivity to laser irradiation can be controlled in a moderately wide range. The combustion of this nanothermite system takes place at a very high apparent temperature (> 3695 K) and it follows the key predictions of the established reactive sintering mechanism, as supported by SEM-EDS and XRD analyses.

Effects of diamond as a main carbon source on the fabrication and mechanical properties of reaction-bonded SiC

RBSC with a low residual Si less than 5 vol% was fabricated using SiC–C preform with diamond as a main carbon source by a conventional reaction sintering process at the temperature range between 1500 °C and 1800 °C. The diamond content in the SiC–C preform varied from 10 wt% to 17 wt%. The diamond as the main carbon source used in SiC–C preform effectively minimized the residual Si in RBSC by increasing the reaction of diamond due to the enhanced Si melt infiltration even in SiC–C preform with high carbon content. The Si melt infiltration should be performed above 1600 °C for the complete reaction of diamond particles with size of 0.5 μm because of the relatively low dissolution rate of diamond in Si melt. The flexural strength of RBSC with residual Si content less than 7 vol% exceeded 400 MPa. The flexural strength of RBSC was increased with decreasing residual Si content, but sharply decreased by the residual carbon accompanying pores in RBSC. RBSC with low residual Si content displayed moderate flexural strengths around 200 MPa even above Si melt temperature because of the formation of continuous SiC structure in RBSC by the enhanced grain growth of SiC. Vickers hardness of RBSC was steadily increased from 17.7 GPa to 24.6 GPa with decreasing residual Si.

Multifunctional Nanocomposites in B4C-Tic-Tib2-Sic-BN-Al2O3-Sialon-C Carbon Fiber System for Armor Fillets, Turbine Discs and Wings, High-Temperature Wear Resistant Nodes

Goal - to receive on first stage β - SIALON containing nanocomposites by reactive sintering method at 14000C, with nitrogen pro-cess from origin composition in TiC-BN-SiC-B4C-Si-Al-Al2O3 (nanopowder) system. By using this method of synthesis, it became possible to receive nanocomposites with different percentages of β - SIALON. Our task was to study the phase composition of re-ceived consolidated materials in the TiC-TiB2-BN-SiC-B4C-β-SiAlON-Al2O3 (nanopowder-400nm.) system. Method. The obtained mass was grounded in an attritor and the consolidated composite was obtained by hot pressing at 16200C during 40 minutes, with glass perlite (Armenia) dope 2 mass%, delaying at final temperature for 8 min, under 30 MPa pressure and vacuum – 10-3 Pa. Perlite from Aragatc contained 96 mas. % glass. To study the phase composition of the composites, we conducted an X-ray structural analysis on the DRON-3 device. And to study the microstructure, we conducted research on an optical microscope -AC100 and a raster electron microscope “Nanolab 7” of the company "OPTON”. The values of the electrical parameters of the studied composites were calculated on the basis of the ob-tained "lgp- t" dependence. We have studied mechanical properties. Result. In TiC-TiB2-BN-SiC-B4C- β-SiAlON-Al2O3 – C Carbon Fiber system we obtained nanocomposites with high mechanical proper-ties. The advantage of this method is that compounds, which are newly formed thanks to interaction going on at thermal treat-ment: Si3N4, Si, AlN are active, which contributes to β-SiALON formation at relatively low temperature, at 1300-13500C. It is evi-dent that inculcation of ALN in crystal skeleton of ß-Si3N4 is easier since at this temperature interval crystal skeleton of Si3N4 is still in the process of formation. ß-SiAlON was formed at 14500C. Part of boron carbide was transformed into boron nitride in ni-trogen environment and in titanium diboride, which in the case of both composites is in small quantities. Conclusion. The phase composition of the obtained composite provides high physical-technical and performance properties of these nanocomposites. Compression strength-2198 MPa, Bending strength-271 MPa, Thermal expansion coefficient a20-700-3.8 10-6 0C.

Effect of Si3N4 Additive on Microstructure and Mechanical Properties of Ti(C,N)-Based Cermet Cutting Tools.

Development of high-performance cutting tool materials is one of the critical parameters enhancing the surface finishing of high-speed machined products. Ti(C,N)-based cermets reinforced with and without different contents of silicon nitride were designed and evaluated to satisfy the requirements. In fact, the effect of silicon nitride addition to Ti(C,N)-based cermet remains unclear. The purpose of this study is to investigate the influence of Si3N4 additive on microstructure, mechanical properties, and thermal stability of Ti(C,N)-based cermet cutting tools. In the present work, α-Si3N4 "grade SN-E10" was utilized with various fractions up to 6 wt.% in the designed cermets. A two-step reactive sintering process under vacuum was carried out for the green compact of Ti(C,N)-based cermet samples. The samples with 4 wt.% Si3N4 have an apparent solid density of about 6.75 g/cm3 (relative density of about 98 %); however, the cermet samples with 2 wt.% Si3N4 exhibit a superior fracture toughness of 10.82 MPa.m1/2 and a traverse rupture strength of 1425.8 MPa. With an increase in the contents of Si3N4, the Vickers hardness and fracture toughness of Ti(C,N)-based cermets have an inverse behavior trend. The influence of Si3N4 addition on thermal stability is clarified to better understand the relationship between thermal stability and mechanical properties of Ti(C,N)-based cermets.

Microstructure and mechanical properties of high-entropy diboride-based ceramic assisted by Ti3AlC2 additive

Ti3AlC2 was used as the additive to fabricate a novel (Zr0·2Ta0·2Nb0.2Hf0.2Mo0.2)B2-based (HEBTAC) ceramic using spark plasma sintering at 1900 °C. The as-prepared HEBTAC ceramic sample consists of (Ti, Zr, Hf, Ta, Nb, Mo)B2, multiscale (Zr, Hf, Ta, Nb, Mo)C, and Al2O3 phases, which are produced by the decomposition of Ti3AlC2 and subsequent exchange reaction & solid solution reactions during the sintering process. The relative density, hardness, fracture toughness, and flexural strength of the HEBTAC ceramic sample are 99.43 %, 27.92 ± 1.87 GPa, 5.84 ± 0.14 MPa m1/2, and 629 ± 8.7 MPa, respectively, which are even better than the same class of high-entropy diboride ceramics previously published. Solid-solution strengthening, dislocation strengthening and nano-HEC strengthening existed in the ceramic sample contribute to its excellent mechanical properties. The in situ formed Al2O3 and (Zr, Hf, Ta, Nb, Mo)C effectively enhances the toughness of the HEBTAC ceramic sample through the synergistic effect of intrinsic and extrinsic toughening. This study presents a new approach for reactive sintering densification of high-entropy diborides with both high strength and high toughness.

On the potential of Transparent Rare-Earth-Free ZnAl2O4 Ceramics targeted at the UV-C to UV-B emission

Materials capable of emitting in the ultraviolet UV-C to UV-B spectral range have received considerable attention due to their potential applications in biophotonics, plant lighting, optical cleaning, sterilization, and disinfection. However, progress in the development of phosphors that emit in this short-wavelength range has been relatively sluggish. Most UV-C phosphors developed to date are based on hosts doped with the rare-earth cation Pr3+ due to its bright UV luminescence originating from the 4f15d1 → 4f2 interconfigurational transitions. In this study, we explore how the UV emission can be tailored to different wavelength ranges by developing rare-earth-free materials. Specifically, we demonstrate that UV-C to UV-B emission can be achieved in transparent ZnAl2O4 – based ceramics. For the first time, such transparent ceramics have been successfully produced with the help of reactive spark plasma sintering with SiO2 or LiF additives, which modified the process of grain growth resulting in an increase in the average grain size from 250 nm to 4 µm. Moreover, these additives also improved the optical transmission properties, with in-line transmission measurements at a wavelength of 550 nm reaching values of 50 % and nearly 65 % in the infrared region. Depending on the addition of SiO2 and LiF, the excitation by photons with energy exceeding 6.2 eV has generated the deep UV emission peaks in the range from 230 to 300 nm. Based on the analysis of the results of luminescence spectroscopy and EPR studies, the observed UV-C emission is suggested to originate from the excitons localised near oxygen vacancies. The number of vacancies is the highest in undoped ZnAl2O4 ceramics, whereas adding SiO2 and LiF suppresses their number and modifies their local environment due to changes in charge compensation, which in turn allows tuning the spectral position of the UV-C band. The quantum yield of the UV-C emission reached 5 % for undoped ZnAl2O4 ceramics. The sintered ZnAl2O4 transparent ceramic shows a versatile solution for next-generation rare-earth-free deep-UV devices.

High electrical conductivity and enhanced thermoelectric properties in La-Nb co-doped (Sr1/3Ba1/3Ca1/3)TiO3-based oxides

Here, we report a series of (Sr1/3Ba1/3Ca1/3)TiO3-based oxides with different La-Nb doping levels synthesized by solid-state reaction and graphite-burial sintering method. The results indicate that La-Nb co-doping significantly enhances the electrical conductivity by increasing carrier concentration, leading to a remarkable improvement in power factor (∼1665 μW/(m·K2) at 773 K). Additionally, the lattice thermal conductivity is reduced due to the enhanced phonon scattering caused by point defects and pores. As a result, a peak ZT value of 0.36 at 773 K is achieved for the 5% La-10% Nb co-doped sample, 200% higher compared to the un-doped sample. This work highlights the promising potential of the (Sr1/3Ba1/3Ca1/3)TiO3-based oxides as environmentally-friendly thermoelectric materials.

Microstructure and phase evolution of Fe-20Ni-20W foams during high-temperature redox cycling

Freeze-cast Fe-20Ni-20 W (at%) foams suitable for high-temperature redox cycling show excellent microstructural stability and regenerative porosity formation, but they exhibit slower reduction kinetics as compared to previously studied Fe-25 W foams. The Fe-20Ni-20 W lamellar foams, after initial hydrogen reduction, consist of a two-phase mixture of µ-Fe7W6 and γ-Fe(Ni,W), with significant microporosity due to the sintering inhibition of W. During oxidation by steam at 800 °C, these phases are oxidized to a three-phase mixture of (Fe,Ni)WO4, Fe3O4, and γ-Ni(Fe); upon subsequent reduction by H2, the foams return to their initial composition. The chemical vapor transport reduction of FeWO4 results in the formation of submicron pores during each reduction half-cycle which accelerate subsequent reaction and limit sintering in the reduced state. The reduction of mixed oxide is relatively sluggish, which is likely due to the increased stability of the (Fe,Ni)WO4 phase brought on by the substitution of Ni in Fe sites in FeWO4.

High strength and ductility high-entropy intermetallic matrix composites reinforced with in-situ hierarchical TiB2 particles

The design guided by entropy enables the attainment of superior mechanical properties and further extends the concept of high-entropy alloys to intermetallic systems, thus forming high-entropy intermetallic compounds and even high-entropy intermetallic matrix composites. In this study, a novel high-entropy intermetallic matrix composites incorporating in-situ hierarchical TiB2 particles was successfully synthesized through the spark plasma sintering. This method enables precise control over the microstructure, ensuring uniform distribution of the in-situ formed TiB2 particles within the high-entropy intermetallic matrix. The in-situ formation of TiB2 particles is achieved through a reactive sintering mechanism, which not only contributes to the composite's enhanced mechanical properties but also ensures excellent bonding between the precipitates and intermetallic matrix. The composites were composed of the ordered L12 intermetallic matrix and the hierarchical hexagonal-close-packed TiB2 particles. Due to the L12 intermetallic matrix and the heterogeneous distribution of TiB2 reinforcement, the intermetallic matrix composites demonstrate a high ultimate tensile strength of ∼1400 MPa. The TiB2 play a pivotal role in impeding the propagation of cracks and the collaborate with distinctive disordered interfaces at grain boundaries, ensuring enough ductility. The disordered interfaces, exhibiting an average width in the range of 5 nm–10 nm, possess the capability to delay fracture and promote the strain-hardening rate during plastic deformation. The intermetallic matrix composites overcome the limitations typically associated with conventional intermetallics and offer an excellent strength and ductility balance. These findings are expected to formulate additional strategies for designing in-situ reinforcement-strengthened high-entropy intermetallic matrix composites with exceptional mechanical properties.

The Microstructure, Mechanical, and Friction-Wear Properties of Boron Carbide-Based Composites with TiB2 and SiC Formed In Situ by Reactive Spark Plasma Sintering.

The paper presents the influence of the temperature of the sintering process on the microstructure and selected properties of boron carbide/TiB2/SiC composites obtained in situ by spark plasma sintering (SPS). The homogeneous mixture of boron carbide and 5% vol. Ti5Si3 micropowders were used as the initial material. Spark plasma sintering was conducted at 1700 °C, 1800 °C, and 1900 °C for 10 min after the initial pressing at 35 MPa. The heating and cooling rate was 200 °C/min. The obtained boron carbide composites were subjected to density measurement, an analysis of the chemical and phase composition, microstructure examination, and dry friction-wear tests in ball-on-disc geometry using WC as a counterpart material. The phase compositions of the produced composites differed from the composition of the initial powder mixture. Instead of titanium silicide, two new phases appeared: TiB2 and SiC. The complete disappearance of Ti5Si3 was accompanied by a decrease in the boron carbide content of the stoichiometry formula B13C2 and an increase in the content of TiB2, while the SiC content was almost constant. The relative density of the obtained boron carbide composites, as well as their hardness and resistance to wear, increased with the sintering temperature and TiB2 content. Unfortunately, the reactions occurring during sintering did not allow us to obtain composites with high density and hardness. The relative density was 76-85.2% of the theoretical one, while the Vickers hardness was in the range of 4-12 GPa. The mechanism wear of boron carbide composites tested in friction contact with WC was abrasive. The volumetric wear rate (Wv) of composites decreased with increasing sintering temperature and TiB2 content. The average value of coefficient of friction (CoF) was in the range of 0.54-0.61, i.e., it did not differ significantly from the value for B4C sinters.

The role of Mg content in regulating microstructures and mechanical properties of Al–Mg–ZnO composites fabricated via in-situ reaction sintering

Al–Mg-oxides composite system exhibits great potential for achieving aluminum matrix composites (AMCs) with exceptional mechanical properties. However, the effects of Mg element on in-situ reaction mechanism and precipitation behavior remains largely unknown. In this work, Al–Mg–ZnO composite was successfully fabricated by using segmented ball milling, reaction sintering and heat treatment, resulting in an ultimate tensile strength of ∼760 MPa and fracture elongation of ∼3.5 %. The Mg content-dependent reaction pathway and precipitation evolution were systematically investigated through thermodynamic analysis and microstructural characterization. The results revealed that the relatively high Mg content promotes the in-situ generation of the hybrid reinforcements composed of MgAl2O4 and MgO. Additionally, the semi-coherent reinforcement-matrix interface facilitates interfacial precipitation by reducing the energy barrier for nucleation. Consequently, solute-rich/vacancy-rich Guinier-Preston (GP) zones are activated to form η′ and T′ precipitates. These high-density nano-sized secondary phases contribute to the considerable strengthening effect of the composite. The present work provides valuable theoretical insight into the effect of Mg content on the microstructure evolution of Al–Mg–ZnO composite system, which offers promising avenues for achieving AMCs with superior mechanical properties.