Spark Plasma Sintering Technique Research Articles

Preparation and Thermoelectric Properties of Novel Tellurium-Based Glassy Semiconductors

Vitrification of Tellurium-based(Te) chalcogenid semiconductors is explored as a new route to enhance their thermoelectric properties by maximizing the degree of structural disorder to produce the minimum thermal conductivity. Ga2Te3 -SnTe systems are focused in this paper and the optimized glass-forming composition is identified. Complete bulk (Ga2Te3) 34(SnTe)66 glass is successfully prepared by a spark plasma sintering technique and exhibited an ultralow low thermal conductivity and high Seebeck coefficient. Together with the tunable electrical conductivity, the newly obtained Ga2Te3-SnTe glasses broaden the research scope of Te-based semiconductor glasses and also provide a new option for the development of high-performance thermoelectric materials.

Graphene-Reinforced Titanium Enhances Soft Tissue Seal.

The integrity of soft tissue seal is essential for preventing peri-implant infection, mainly induced by established bacterial biofilms around dental implants. Nowadays, graphene is well-known for its potential in biocompatibility and antisepsis. Herein, a new titanium biomaterial containing graphene (Ti-0.125G) was synthesized using the spark plasma sintering (SPS) technique. After material characteristics detection, the subsequent responses of human gingival fibroblasts (HGFs) and multiple oral pathogens (including Streptococci mutans, Fusobacterium nucleatum, and Porphyromonas gingivalis) to the graphene-reinforced sample were assessed, respectively. Also, the dynamic change of the bacterial multispecies volume in biofilms was evaluated using absolute quantification PCR combined with Illumina high-throughput sequencing. Ti-0.125G, in addition to its particularly pronounced inhibitory effect on Porphyromonas gingivalis at 96 h, was broadly effective against multiple pathogens rather than just one strain. The reinforced material’s selective responses were also evaluated by a co-culture model involving HGFs and multiple strains. The results disclosed that the graphene-reinforced samples were highly effective in keeping a balance between the favorable fibroblast responses and the suppressive microbial growth, which could account for the optimal soft tissue seal in the oral cavity. Furthermore, the underlying mechanism regarding new material’s bactericidal property in the current study has been elucidated as the electron transfer, which disturbed the bacterial respiratory chain and resulted in a decrease of microbial viability. According to the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, the PICRUSt tool was conducted for the prediction of microbial metabolism functions. Consequently, it is inferred that Ti-0.125G has promising potentials for application in implant dentistry, especially in enhancing the integrity of soft tissue and improving its resistance against bacterial infections around oral implants.

Cu50Zr50 metallic glass flakes reinforced Al composites: Experimental and molecular dynamics nanoindentation response of matrix, interface, and reinforcement

In this study, we report experimental and molecular dynamics (MD) studies on the sintering and nanoindentation behavior of Cu50Zr50 metallic glass (MG) flakes reinforced Al composites. The mechanical response (yielding, elastic modulus, and hardness) of the individual components has been investigated in detail. Spark plasma sintering technique is used to synthesize Al powder (70 Vol. %) and Cu50Zr50 (30 Vol.%) MG flakes composite. The values of elastic modulus (Es) are found to be 71 GPa (Es, Al), 97 GPa (Es, MG), and 80.3 (Es, Al-MG interface). The values of hardness (H) are 8.5GPa in MG, 3.1 3.5 GPa in the Al-MG interface region, and 2.4 GPa in the Al region. MD simulations of sintering and nanoindentation are carried out comprising 583882 atoms. Embedded atom method (EAM) potential is used to model the atomic interactions between Al, Cu and Zr atoms. Simulation results are in good agreement with the experiments.

Structural and magnetic properties of La-doped strontium-hexaferrites ceramics obtained by spark-plasma sintering

Polycrystalline samples of Sr1−xLaxFe12O19 (x = 0.1, 0.3, and 0.6) hexaferrite were prepared by spark-plasma sintering (SPS) and its structural and magnetic properties have been investigated. The SPS process were performed under vacuum, at 900 °C, and in only 5 min. X-ray powder diffraction patterns showed that before SPS sintering samples are composed by several phases where the SrFe12O19 (SrM) is not higher than 12%. From Rietveld refinement method, we have found that after SPS process the content of SrM phase increased, in mean, up to 68%. However, it was found the presence of secondary phase such as α-Fe2O3 and LaFeO3 (%) whose phase content also vary with increasing the La-content. A finite element simulation model were used to study the temperature evolution within the sample during the SPS treatment. Magnetization measurements at room temperature yielded values of saturation magnetization between ~43 to ~27 emu/g and coercivities, HcB, in the range 3.11 to 2.88 kOe with increasing x. The influence and possible interaction between detected magnetic phases was studied by means of first-order reversal curves (FORCs) measurements. Results indicated that magnetic behavior of the La-doped strontium hexaferrites obtained by SPS technique are analogous a system composed of a broad distribution particles that are exchange-coupled with a certain number of other of neighboring particles. From FORC maps the coercivity profiles of the studied samples were extracted. The asymmetric behavior of these profiles were related to a broad distribution of the particle size and/or the influence of the secondary magnetic phases.

Radio-photoluminescence properties of silver-doped cesium chloride transparent ceramics

We discovered and reported that 0.01, 0.1 and 1% Ag-doped CsCl transparent ceramics by spark plasma sintering technique showed radiophotoluminescence (RPL). All the samples showed high transmittance (50–70%) in the visible range. Under 340 nm ± 40 nm excitation, the PL emission was observed around 450 nm before X-ray irradiation while PL emission peaks appeared around 450 and 610 nm after X-ray irradiation. Judged from excitation and emission spectra and lifetimes, the origins of emission bands around 450 and 610 nm would be Ag0/Ag2+ and Ag2+ centers, respectively. The RPL signal was confirmed to be stable over 3 min under an excitation of 340 nm ± 40 nm. Among the synthesized samples, the lowest detectable sensitivity for the 1% Ag-doped CsCl samples was 3 mGy for the emission range of 400–550 nm.

Sodium ion conduction in sodium lanthanum zirconate ceramics prepared by spark plasma sintering

Dense ceramics of Na3xLa2/3−xZrO3−δ with orthorhombic (Pnma) perovskite structure have been prepared by spark plasma sintering (SPS) to investigate their Na+ ion conducting behaviors combining with crystal chemistry. Despite of suppressed Na volatilization owing to the SPS technique, the Na component tends to be partially lost during sintering, and consequently, the chemical composition of perovskite is limited to a small range, 3x = 0.32–0.35, which is favored under an equilibration with secondary phases of La2Zr2O7 pyrochlore and ZrO2. A sample with Na0.32La0.48ZrO2.9 exhibits an enhanced bulk conductivity (7.2 × 10−5 S cm−1 at 350 °C) and a much lower activation energy (0.26 eV) as compared with those observed in isostructural titanate-derivative of Na3xLa2/3−xTiO3, indicating that the expanded perovskite lattice by the Zr-substitution for Ti offers migration pathways wide enough for Na+ ion.

Preparation and properties of graphene nanoplatelets reinforced aluminum composites

Abstract 5.0 vol.% graphene nanoplatelets (GNPs) and aluminum powders were mixed to prepare GNPs/Al composites via high-energy ball milling (HEBM). The mixed powders were subjected to spark plasma sintering (SPS) and subsequent hot extrusion. The microstructure and mechanical properties of extruded composites were investigated by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and tensile tests. In the extruded composites, 5.0 vol.% GNPs were dispersed homogeneously and no serious GNP−Al interfacial reaction occurred. As a result, the yield strength and ultimate tensile strength of the extruded GNPs/Al composites reached 462 and 479 MPa, which were 62% and 60% higher than those of the extruded Al matrix, respectively. The enhanced mechanical properties were attributed to the effective load transfer capacity of dispersed GNPs. This demonstrated that it may be promising to introduce dispersed high-content GNPs via HEBM, SPS and hot extrusion techniques and GNP−Al interfacial reaction can be controlled.

Effect of electric load characteristics on the arc erosion behavior of Ag-8wt.%Ni electrical contact material prepared by spark plasma sintering

To clarify the effect of electric load characteristics on the arc erosion behavior of Ag-Ni electrical contact material, the Ag-8 wt.%Ni material was prepared by powder metallurgy and spark plasma sintering techniques. The arc-erosion tests were performed at inductive and resistive load, respectively. Based on the analysis of the arc parameters, mass change, and eroded morphology, the arc erosion mechanisms were discussed as well. The results show that the bounce height significantly influence the arc parameters. Furthermore, the gradual deterioration of eroded surface can also cause the change in bounce height with operation times, which further results in the variation in arc parameters. Additionally, the resistive load causes far below mass loss than the inductive load, meanwhile, the lower arc power presents at the resistive load. This can be attributed to the current/voltage shock triggered by the inductor and the high current level maintained also by the inductor due to the frequent connection and interruption of current.

Effect of HfC addition on the microstructure and properties of W–4.9Ni–2.1Fe heavy alloys

In this study, W–4.9Ni–2.1Fe-xHfC mixed alloy powders were prepared by secondary high-energy ball milling and secondary hydrogen annealing, and then sintered and consolidated by spark plasma sintering (SPS) techniques. The microstructure, mechanical properties, wear resistance and corrosion behavior of alloy were obtained by Vickers hardness tester, X-ray diffraction, scanning electron microscopy, reciprocating frictional wear testing machine, CHI 660 E electrochemical workstation and electronic universal testing machine. The results showed that a certain amount of Hafnium carbide (HfC) could effectively inhibit the growth of W particles during sintering process, make the bonding phase disperse more evenly, and effectively improve the hardness, relative density, compression strength, friction and wear properties as well as corrosion resistance of alloy. When the content of HfC was excessive, the inhibition effect of particle growth would be weakened and the bonding phase tended to agglomerate, affecting the strength and hardness, and reducing the abrasion performance and corrosion resistance of alloy. By comparison, the alloy with 0.4 wt% HfC showed the best comprehension performance.

Enhanced Hardness in Transition-Metal Monocarbides via Optimal Occupancy of Bonding Orbitals.

An efficient strategy that can guide the synthesis of materials with superior mechanical properties is important for advanced material/device design. Here, we report a feasible way to enhance hardness in transition-metal monocarbides (TMCs) by optimally filling the bonding orbitals of valence electrons. We demonstrate that the intrinsic hardness of the NaCl- and WC-type TMCs maximizes at valence electron concentrations of about 9 and 10.25 electrons per cell, respectively; any deviation from such optimal values will reduce the hardness. Using the spark plasma sintering technique, a number of W1-xRexC (x = 0-0.5) have been successfully synthesized, and powder X-ray diffractions show that they adopt the hexagonal WC-type structure. Subsequent nanoindentation and Vickers hardness measurements corroborate that the newly developed W1-xRexC samples (x = 0.1-0.3) are much harder than their parent phase (i.e., WC), marking them as the hardest TMCs for practical applications. Furthermore, the hardness enhancement can be well rationalized by the balanced occupancy of bonding and antibonding states. Our findings not only elucidate the unique hardening mechanism in a large class of TMCs but also offer a guide for the design of other hard and superhard compounds such as borides and nitrides.

Preparation of anorthite ceramics using SPS

A mixture of kaolin (92 wt.% of kaolinite) and laboratory-grade CaCO3 was used for anorthite preparation using the spark plasma sintering (SPS) technique. The powder was heated up to the maximum temperature (850 °C–1100 °C with a step of 50 °C, heating rate 50 °C/min) using the SPS device. The as-prepared samples were compared with a reference sample produced by dry pressing and conventional firing. Rietveld refinement performed on the X-ray diffraction data revealed that before anorthite formation, gehlenite and Ca-feldspar appeared, which gradually transformed into anorthite with increasing temperature. The sample prepared by SPS at 1100 °C contained 90 wt.% of anorthite, while the anorthite content in the reference sample reached only 47 wt.%. The porosity of the samples prepared by SPS reached significantly lower values compared to that of the reference sample. Therefore, SPS can be considered as a promising technique in the preparation of anorthite ceramics at lower temperatures.

Preparation and 1500 °C oxidation behavior of crack-free bentonite doped MoSi2 protective coating on molybdenum

Spark Plasma Sintering technique was applied to fabricate MoSi2 and MoSi2-bentonite coatings on molybdenum. The phase composition, morphologies and anti-oxidation properties of the coatings at 1500 °C were investigated. Penetrated cracks generated in MoSi2 coating after SPS while the composite coating was crack-free because of the reduction of CTE mismatch. Cracks existed in the silica layer of MoSi2 coating after oxidation while the silica layer of bentonite-containing coating showed dense and crack-free morphologies. Compared with MoSi2, the composite coating possessed thinner Mo5Si3 diffusion layer and silica layer, exhibiting less loss of substrate and coating with improved oxidation resistance.

Studies on the effect of applied load, sliding speed and temperature on the wear behavior of M50 steel reinforced with Al2O3 and / or graphene nanoparticles

The effects of applied load, sliding speed & temperature on the wear behavior of pure M50 alloy steel (M sample) and M50 reinforced with 10 wt.% Al2O3 (MA sample) & M50 hybrid reinforced with Al2O3 and graphene (MAG sample) were studied. The powders were mechanically mixed and sintered by spark plasma sintering (SPS) technique under Argon atmosphere at 1000 °C for 5 min under 35 MPa pressure. The sample surfaces were mechanically prepared to study the wear & friction behaviors via applying mechanical polishing using 0.05 μm diamond pastes and 1200 grit emery papers to enhance the surface roughness. The phase structure and microstructure were estimated using XRD, Electron Probe Micro-Analysis (EPMA, JAX-8230) and Energy Dispersive Spectroscopy (EDS, GENESIS 7000). The hardness and density of all samples were investigated according to HVS-1000 Vickers' hardness test and Archimedes’ principles, respectively. Friction and wear tests were carried on a high-temperature pin-on-disk tribometer (HT-1000). The investigated samples were cut into disk-shaped specimens with 8 mm thickness and 25 mm diameter. Then, the prepared specimens were sliding against silicon nitride (Si3N4) balls. The samples were exposed to four different loads (2, 5, 8, and 11 N). Also, four different sliding speeds (0.18, 0.36, 0.54, and 0.72 m/s) was performed at room temperature (RT). Another group of samples were tested at constant applied load of 11 N and constant sliding speed of 0.72 m/s for four different temperatures (RT, 150, 300, and 450 °C). MAG exhibited enhanced tribological properties compared with M and MA thanks to the synergic action between Al2O3 and graphene as well as the creation of iron oxides, aluminum dioxide, chromium oxide, molybdate, and silicon oxide on the formed tribo-film.

The nonlinear optical properties of silver nanoparticles decorated glass obtained from sintering mesoporous powders

ABSTRACTSilver nanoparticles (Ag NPs) have excellent third‐order nonlinear optical properties but it is still difficult to obtain silica glass containing Ag NPs with homogenous dispersion and small particle size. Herein, silica glass with homogenously distributed Ag NPs in its matrix was derived from sintering a famous type of mesoporous silica (FDU‐12) encapsulated with Ag NPs (Ag NPs/FDU‐12) through Spark Plasma Sintering (SPS) technique. Benefited from the low‐temperature sintering property of the Ag NPs/FDU‐12 powders (~930°C within 5 min), the Ag NPs can be directly trapped in the derived silica glass with small particle size (<3.0 nm) and without mass loss. The as‐prepared Ag NPs/glass showed a typical reverse saturable absorption curve, which is measured via the Z‐scan method by using a 532 nm nanosecond laser. The nonlinear coefficient and imaginary third‐order susceptibility were calculated as 11.46 cm/GW and 2.22 × 10−12 esu, respectively, indicating the excellent third‐order nonlinear optical properties of the Ag NPs/glass. This study demonstrates a great potential for preparing silica glasses functionalized with well dispersed ultrafine functional particles, which is appealing in photonic field.

Fabrication of graphite reinforced TiCxNy by spark plasma sintering technique: A comparative assessment of microstructural integrity and nanoindentation properties

This study investigated the fabrication of three different binderless TiCxNy (where the values of x and y are 0.5, 0.7, 0.9 and 0.5, 0.3, 0.1 respectively) reinforced with 0.5 wt%, 1.0 wt%, and 1.5 wt% graphites. The reinforcement particles were dispersed in TiCN matrix using the high energy ball milling technique, and the admixed powders were sintered using the novel spark plasma sintering method. The phase analysis and the structural morphologies of the starting powders and sintered specimens were analyzed using field emission scanning electron microscope (FE-SEM), Transmission electron microscope (TEM), and X-ray diffractometer (XRD), respectively. The milling process outcomes showed that the composite powders contain some isolated graphite powders distributed around the matrix as titanium carbonitride. The stoichiometry of the processed powders gave some consistency in the carbon-rich phase. The significant improvement in the properties of as-sintered composites, including microstructure, elastic modulus, fracture toughness, and hardness, was due to the presence of graphite in the ceramic composite. The graphite were also observed to improve the relative densities of specimens as the optimum relative density was achieved at 99.56% when 1.5 wt% of graphite was dispersed in TiC0.9N0.1. The nanohardness and elastic modulus values of the most improved composites are as follow; From the nanohardness test, the composites with 0.5 wt% graphite + TiC0.5N0.5, 1.5 wt% graphite + TiC0.7N0.3 and 1.0 wt% graphite + TiC0.9N0.1 had their nanohardness values recorded as 34.5 GPa, 33.3, and 35.1 GPa, respectively, while the highest elastic modulus of 350 GPa was recorded in TiC0.5N0.5 and TiC0.7N0.3 with respective reinforcement addition of 0.5 and 1.5 wt% graphite respectively. There is a clear increase in grain growth and graphite segregation when 1.5 wt% of graphite was dispersed in TiC0.9N0.1. However, the uniform distribution of grains was observed when the same (1.5 wt% graphite) proportion of nanoparticle was dispersed in TiC0.5N0.5 and TiC0.7N0.3 composites.

DFT and experimental study on the thermal conductivity of U3O8 and U3O8-X; (X=Al and Mo)

In this article, a theoretical and experimental investigation on the phonon thermal conductivity (κL) of α-U3O8 in the temperature range of 300 to 1000 K is reported. The theoretical calculations of the κL were performed via the density functional theory (DFT) unified with the Boltzmann transport equation (BTE). An extensive investigation of the mode-wise scattering rate, group velocity (vg), and the Grüneisen parameters (γ) were also conducted. The theoretically predicted thermal conductivities of U3O8 were compared with the measured values obtained through the transient method. Spark plasma sintering technique (SPS) was applied for sample preperation . In addition to the thermal properties of U3O8, an investigation on the effects of the addition of aluminum (Al) and molybdenum (Mo) is also reported. Our theoretical prediction corroborated the larger directional dependence of κL in U3O8, for example, at 300 K, they are 0.97, 0.67, and 3.05 W.m−1.K−1 along (100), (010), and (001) directions, respectively. The average κL values of U3O8 decreases as a function of temperature from 1.57pleasedelete to 0.49 W.m−1.K−1 when the temperature increases from 300 to 1000 K. The reason for the low thermal conductivity in U3O8 has been explained by evaluating the mode-dependent scattering rates and γ. Also, the prediction of vg corroborated the larger directional dependence of κL. Finally, the effect of Al (with 15, 20, and 30vol% of U3O8 in Al matrix) and Mo (with 8.2 and 12.5vol% of Mo in U3O8) on the thermal conductivity of U3O8 has been reported. At 300 K, thermal conductivities of U3O8-Al samples with 15, 20, and 30vol% of U3O8 dispersions are 50.91, 33.79, and 16.53 W.m−1.K−1,respectively. Moreover, the samples with 8.2 and 12.5 vol% of Mo reported 59% and 104% respective thermal conductivity enhancements at ~300 K. Ultimately, this work determined the possibility of sintering U3O8 based nuclear fuels using SPS and demonstrated the thermal conductivity enhancement of U3O8 with Al and Mo additives.

Effects of graphene on morphology, fracture toughness, and electrical conductivity of titanium dioxide

This study reports the role of graphene in improving the mechanical and electrical properties of TiO2/graphene nanoplatelets (GNPs) composite. Graphene oxide (GO), as a precursor was used with varying concentrations of 0, 0.5, 1, and 2 wt%. The GO was being reduced simultaneously with the TiO2 matrix, providing uniform distribution of rGO nanoplatelets among the matrix particles. Spark plasma sintering technique (SPS) was used for sintering initial powder of the TiO2/rGO composite. Alongside the sintering of the powder, SPS induces rGO transformation to graphene nanoplatelets at high temperatures and provides the densification of TiO2/GNPs as a final composition. Morphology and microstructure of prepared samples were characterized by XRD and SEM. Density and microstructural studies were used to determine the sintering quality and compared to the theoretical density of TiO2 and TiO2/GNPs composites. Vickers microhardness method was used to calculate hardness and fracture toughness depending on the crack propagation alongside the indentations. The two-probe method was applied to study the electrical conductivity by resistance measurement. The results indicated that there was a significant change in the structural and physical properties of TiO2/GNPs composites. The rGO takes an important role as a grain growth inhibitor, acting as the barrier for crack propagation and leading to increased fracture toughness. Thus, GNPs can be considered as a good reinforcement for titanium dioxide ceramic in order to improve the material's brittleness and electrical conductivity without adversely affecting its microhardness.

Effect of the Heating Rate on the Spark-Plasma-Sintering (SPS) of Transparent Y2O3 Ceramics: Microstructural Evolution, Mechanical and Optical Properties

High strength transparent Y2O3 ceramics were fabricated from commercial powders using spark plasma sintering (SPS) technique by optimizing the heating rate. The heating rate significantly influenced the microstructures and the optical/mechanical properties of the Y2O3 ceramics. Grain growth was limited accordingly with increasing the heating rate. The ball milling process of the commercial Y2O3 powders is likely to further enhance the sinterability during the SPS processing. The dense Y2O3 ceramics, which were sintered by SPS with 100 °C/min, showed good transmittance range from visible to near infrared (IR). For a high heating rate of 100 °C/min, the in-line transmittance at a visible wavelength of 700 nm was 66%, whereas for a slow heating rate of 10 °C/min, it reduced to 46%. The hardness Hv tends to increase with increasing the heating rate and rigorously followed the Hall–Petch relationship; that is, it is enhanced with a reduction of the grain size. The toughness KIC, on the other hand, is less sensitive to both the heating rate and the grain size, and takes a similar value. This research highlighted that the high heating rate SPS processing can fabricate fully dense fine-grained Y2O3 ceramics with the excellent optical and mechanical properties.

Electric field assisted solid‐state interfacial joining of TaC‐HfC ceramics without filler

AbstractThe application of ultra‐high‐temperature ceramics (UHTCs) demands effective ways of joining in overcoming the problems associated with the fabrication of complex‐shaped components. In this study, we choose to investigate a new method of rapidly joining pre‐sintered TaC and HfC ceramics without any filler material using the spark plasma sintering (SPS) technique. A well‐bonded TaC–HfC interface was observed with no apparent cracking and porosity at the joint. The joining mechanisms were predominantly driven by solid‐state diffusion and localized plastic deformation. The nanomechanical properties of the TaC‐HfC joint are better than the HfC while comparable to that of the TaC. High‐load indentation (up to 200 N) results suggest that the TaC–HfC interface is stronger than the parent UHTCs with no crack propagating at the interface. Upon comparison with the parent UHTCs, the damaged area and the average crack length at the interface, reduced up to ~94% and ~56%, respectively. This study shows that the SPS technique can also apply to joining other UHTCs without any filler, resulting in the new field of developing complex components for the thermal protection system (TPS).

The toughening of pyrochlore La2Zr2O7 by a ferroelastic NdAlO3 second phase for potential thermal barrier coating applications

AbstractThe poor fracture toughness of La2Zr2O7 severely limits its application as a high temperature thermal barrier coating topcoat material. To toughen it, a ferroelastic second phase, NdAlO3, with a Curie temperature of 1367°C has been introduced to form x NdAlO3/(1‐x) La2Zr2O7 composite ceramics by a spark plasma sintering technique, where x = 10, 20, 30, 40, and 50 mol%. The fracture toughness of sintered composite ceramic compacts is measured at both room temperature and 1200°C, respectively, by a single‐edge‐notch beam test method. The results show that, at room temperature, the residual compressive stress in the La2Zr2O7 matrix plays an important role in the toughening of composite ceramics. By eliminating this factor, the remaining toughening effects agree with the measured fracture toughness at 1200°C, suggesting that the other toughening is probably ferroelastic domain switching toughening and that it is still valid at high temperature. Furthermore, the toughening effect arising from ferroelastic domain switching is governed by the overall domain switching zone, which is determined by both individual domain switching zone width and the “concentration” of ferroelastic phases. A relatively high coercive stress of NdAlO3 and relatively low residual tensile stress in NdAlO3 second phases contribute to negligible influence of residual tensile stress on domain switching zone width, leading to the continuous increase of fracture toughness of composite ceramics with more NdAlO3 added at room temperature.