Microstructure Grain Research Articles

Surface blistering and deuterium retention in chemical vapor deposition tungsten exposed to deuterium plasma

Chemical vapor deposition tungsten (CVD-W) is a promising material for plasma-facing materials. This work evaluated CVD-W samples with a large grain size (CVD-L) and a small grain size (CVD-S) together with rolled W (ND-W) and recrystallized (Rec-W) samples for their performance under deuterium (D) plasma exposure with a flux of 1021 D m−2 s−1 and fluences up to 2 × 1025 D m−2 at a surface temperature of 500 K. Both CVD-L and CVD-S samples featured a columnar grain structure with a preferred orientation close to 〈001〉 || Z, with a more preferred orientation in CVD-L samples. Both CVD-L and CVD-S samples show good resistance to blistering and only few micron-diameter blisters were observed at fluences. In ND-W and Rec-W samples, the number and size of blisters increased with fluence. The D desorption spectra show two desorption peaks in both CVD-W samples at 520 K and 570–604 K. Whereas in ND-W and Rec-W samples, two peaks were at 520 K and 607–700 K. The total D retention in both CVD-L and CVD-S samples was less than 30 % of that in ND-W and Rec-W samples. The low D retention in CVD-W samples was attributed to the low desorption intensities with the peak at 570–604 K. It is suggested that the microstructure of the columnar grain and the 〈001〉 texture in CVD-W samples helps suppressing plasma-induced blistering, therefore reducing D retention. In terms of the stability of the surface integrity and hydrogen isotopes retention, CVD-W demonstrates a significant potential as a wall material for future fusion reactors.

Refining grain structure and improving elongation properties in AZ31 magnesium alloy sheets using hard plate accumulative roll bonding

Magnesium alloy sheet are an ideal choice for achieving material and structural light weighting. Traditional ARB technology can significantly reduce the size of magnesium alloy sheet, but it is faced with the challenge of strong plastic inversion. In addition, it is easy to produce edge cracking defects, and it is also difficult to control the quality of the sheet. In this study, we prepared AZ31 magnesium alloy sheet by HP-ARB process for the first time. The results show that compared to ARB, the HP-ARB sheet has remarkable improvements in and mechanical properties.After two passes, the average grain size of HP-ARB decreased from 6.19 μm to 4.58 μm, tensile strength reaches 291 MPa, and the elongation is 10.1%, which significantly increased to 55.4% compared with ARB. HP-ARB has the ability to transform part of shear stress into compressive stress, which improves the stress distribution on the sheet. On one hand, a large amount of energy stored in dislocations provides energy for DRX, which makes the process more complete, leading to microstructure refinement and grain orientation randomization. This leads to the deviation of texture orientation to TD direction, which leads to the decrease of pole density and weakening of the strong basal texture. On the other hand, dislocation density (ρD) of the sheet is relatively low. The average Schmidt factor of prismatic <a> slip and pyramidal <c+a> slip in the HP-ARB process is higher, which is beneficial to dislocation slip, thus promoting an increase of sheet elongation. This provides a new strategy for the forming and manufacture of high performance magnesium alloy sheet.

Extra-conventional strengthening mechanisms in non-recrystallized grains of an extruded Mg-Gd-Zr alloy

Mg-RE (RE = rare earth) based alloys generally exhibit outstanding mechanical properties. However, their high-strength seems to be unexplained using classic strengthening mechanisms in some cases. Herein, a Mg-13Gd-0.4Zr (wt%) alloy that was fabricated by a conventional differential thermal extrusion plus artificial aging treatment exhibits ultra-high yield strength over 510 MPa in both tension and compression. Characterizations using Cs-corrected scanning transmission electron microscopy (STEM) show two unusual microstructures in non-recrystallized grains as: a large density of basal stacking faults (SFs) and profuse distortion areas (DAs). Atomic-resolution STEM imaging indicates that basal SFs are consisted of two types of intrinsic SFs, namely I1 and I2, and DAs are self-assembled by 〈c〉 and 〈c + a〉 screw partials. Their strengthening mechanisms are analogous to grain boundary strengthening and dispersion strengthening, respectively, contributing satisfactory yield-strength increments of ∼46 MPa and ∼76 MPa, respectively. Moreover, DAs improved aging hardening by inducing novel clusters at DA-related boundaries, or increasing the number density of βH’ precipitate and promoting their distribution along a certain direction. This work supplements the strengthening mechanisms in traditional high-strength Mg-RE(-Zr) based alloys and provides novel insights in the development of ultra-high-strength Mg alloys.

Effect of scanning speed on fatigue behavior of 316L stainless steel fabricated by laser powder bed fusion

The effect of the scanning speed on the fatigue behavior of Laser Powder Bed Fusion (LPBF)-fabricated 316L steel is investigated in this paper. To this end, fatigue limits of specimen manufactured by different scanning speeds are determined by the self-heating approach. EBSD experiments and relative density measurements are carried out to characterize the microstructure and porosity. To analyse the influence of scanning speed on the microstructure (grain morphology, texture, dislocation density and stored energy) and fatigue property, a dislocation-density, crystal plasticity and stored energy-based fatigue model is developed. The inverse optimization method is combined with EBSD experiments and uniaxial tension experiments to identify the model parameters. The experimental results show a critical scanning speed, below which the fatigue limit stays almost unchanged and decreases drastically while the scanning speed is increased beyond. Furthermore, the simulation results show that the predicted fatigue limits correspond well to the experimental fatigue ones. From experimental and numerical results, it is deduced that the critical stored energy density and maximum temperature variation are functions of the porosity and can be used to differentiate the types of fatigue: microstructure-dominated or defect-dominated. This article provides new insights which can be further used in the optimization of fatigue behavior of LPBF 316L steel with respect to the scanning speed.

Experimental investigation on the effect of process variables for the quality characteristics of AA 2024 processed in cold extrusion

Extrusion process has many applications in manufacturing industries due to its ability to produce products of high quality. Extrusion process can be classified into hot extrusion and cold extrusion. The cold forward extrusion is carried out at ambient temperature and has the additional benefit of improved mechanical characteristics. The metarial is compressed under intense pressure through a die orifice with a specific shape during the extrusion process. This process is effected by a few process variables, including die angle, punch speed, and lubrication are in greater extent towards the extrusion force requirement, microstructure and the product quality. Hence, the present experimental work focuses on extrusion of circular billet to produce cylindrical rod. Studying the behaviour of the material and the importance of the input process parameters during the cold extrusion process is the primary goal of this work. The experiments are carried out with AA 2024 alloy because of its wide applications in navy and aircraft structures. The varying die angles (10°, 20° &amp; 30°) as well as punch speed (1.6 mm/min, 3.2 mm/min and 4.8 mm/min) and lubricants (molybdium sulphide (MoS2), zinc stearate and grease) chosen as input parameters. The out put responses of this extrusion process are extrusion force, displacement, time and surface roughness. Extrusion forces are calculated based on flow stress curves at the locations of greatest elastic deformation. The results shows that increasing the punch speed and die angle increases the extrusion force. The microstructure evolutions and grain refinement at different die angles are examined using electron back scatter diffraction analysis. At 30° die angle, the microstructure showed grain refinement. It is also noted that the damage is significant at 30° die angle with a punch speed above 4.8 mm/min.

Influence of Microstructure on the Material Properties of LLZO Ceramics Derived by Impedance Spectroscopy and Brick Layer Model Analysis.

Variants of garnet-type Li7La3Zr2O12 are being intensively studied as separator materials in solid-state battery research. The material-specific transport properties, such as bulk and grain boundary conductivity, are of prime interest and are mostly investigated by impedance spectroscopy. Data evaluation is usually based on the one-dimensional (1D) brick layer model, which assumes a homogeneous microstructure of identical grains. Real samples show microstructural inhomogeneities in grain size and porosity due to the complex behavior of grain growth in garnets that is very sensitive to the sintering protocol. However, the true microstructure is often omitted in impedance data analysis, hindering the interlaboratory reproducibility and comparability of results reported in the literature. Here, we use a combinatorial approach of structural analysis and three-dimensional (3D) transport modeling to explore the effects of microstructure on the derived material-specific properties of garnet-type ceramics. For this purpose, Al-doped Li7La3Zr2O12 pellets with different microstructures are fabricated and electrochemically characterized. A machine learning-assisted image segmentation approach is used for statistical analysis and quantification of the microstructural changes during sintering. A detailed analysis of transport through statistically modeled twin microstructures demonstrates that the transport parameters derived from a 1D brick layer model approach show uncertainties up to 150%, only due to variations in grain size. These uncertainties can be even larger in the presence of porosity. This study helps to better understand the role of the microstructure of polycrystalline electroceramics and its influence on experimental results.

Effect of gradient microstructure on the bendability of AZ31 alloy sheet

Extensive researches have elucidated the pronounced benefits of gradient microstructures for the mechanical properties of metallic materials. However, the ramifications of gradient microstructures on formability, particularly regarding their effects on bendability, remain inadequately understood. In this work, the effects of gradient microstructure on the bendability of AZ31 Mg alloy sheet are systematically investigated by comparing the microstructure evolution and strain distribution in the sheets with uniform microstructure (grain size = 12.8 µm and 91.3 µm) and gradient microstructure (grain size = 11.5–75.4 µm). The results show that the bendability of the sheet with gradient microstructure is significantly improved when the fine grains (FGs) are placed at the outer side (TBE-FG sample) and the bendability is increased by 93.1% compared to the sample with fine and uniform microstructure (CE-FG sample). With coarse grains (CGs) placed at the inner side, the strain at the compressive region of the TBE-FG sample is higher than its counterparts, while the tensile strain at the extended region is lowest among the four samples. Quasi-in-situ bending experiments reveal that the CGs at the inner side of the TBE-FG sample undergo more twinning. Moreover, the increment of residual dislocation density at the outer side of the TBE-FG sample is lower than those of other samples, which extends the bending potential. This work provides a novel perspective to improve the bendability of the Mg alloy sheet.

Study on the process optimization and wear resistance of electron beam cladding AlCoCrFeNi coating on 253MA austenitic stainless steel surface

This study employs a continuous scanning electron beam to deposit AlCoCrFeNi composite cladding on the surface of 253MA austenitic stainless steel to enhance its surface properties. The characteristics were examined through a scanning electron microscope (SEM), backscattered electron diffraction (EBSD), and white light interferometric three-dimensional surface profile instrument. This study investigated the effect of electron beam process parameters on the surface organization and mechanical properties of 253MA steel. The sample surface was divided into four zones: overlay, bonding, thermal influence, and substrate, according to the results. Coarse columnar and island-shaped crystals composed the overlay zone, while equiaxed austenite grains primarily constituted the substrate. With the increase of the beam current, the microstructure's grain size decreased, the substructures increased, and the BCC phase transformed into the FCC phase. The grain size slightly decreased, substructures changed marginally, and the BCC phase increased as the scanning speed increased. Additionally, the microhardness and mechanical properties of the overlay layer increased significantly, and wear volume and wear rate decreased progressively with the increase in beam current and scanning speed. At a beam current of 18 mA and a scanning speed of 200 mm/min, the surface hardness of 253MA steel reached the maximum value of 520 HV. When the beam current was 24 mA, and the scanning speed was 200 mm/min, the wear volume and wear rate of the overlay sample were minimal, accounting for 37.4% of the original sample's, and its wear resistance was 2.67 times more than that of the substrate.

An investigation of process parameter influences on dissimilar friction stir welding of cast aluminum alloy joints

ABSTRACTCast alloys find suitable employability in industrial applications favoring automotive and aerospace sectors owing to their high specific strength, low porosity, excellent fluidity, and machinability. The present study focuses on friction stir welding of cast aluminum alloys (AA356 and AA2014) with a varied range of process parameters, namely, tool pin shape (cylinder, cone, square, and threaded cylinder), tool speed (1800–2100 rpm), and tool feed (5–20 mm min−1). The novelty of the present work spotlights/features the implementation of L16 orthogonal design with the analysis of variance, grey relational analysis, fuzzy logic system, and artificial neural network approaches to contemplate the weld quality of cast joints. The microstructural analysis and grain size estimation is comprehended in the study. Regression models have been developed based on the analysis of variance. The prime factors favoring the ultimate tensile strength and microhardness were 2100 rpm, 10 mm min−1, and threaded cylinder shape. The findings from the analysis of variance and grey relational analysis are in concurrence with each other. The results of fuzzy logic showcased a substantial improvement in terms of grey relational grade. The results from the artificial neural network deliver rational evidence for the analysis of variance conducted on the selected tool pin shapes.

Microstructure, texture and mechanical properties of Al–Zn–Mg–Zr cylindrical part with thin-wall and high-rib formed by integral-accuracy-extrusion

The complex section cylindrical part with thin-wall and high-rib was obtained through integral-accuracy-extrusion, and the microstructure evolution, recrystallization behavior, texture configuration and strengthening and toughening mechanism were investigated. Samples of different positions all exhibit the microstructure of predominant elongated grains along extrusion direction (ED) surrounded by fine equiaxed grains, but the width of elongated grains in the rib is higher than that in the thin-wall. Except for particle-stimulated nucleation (PSN) mechanism due to the MgZn2, the dominant recrystallization mechanism of all samples should be discontinuous dynamic recrystallization (DDRX), and the parent grains with the orientation of (001)//ED are more susceptible to recrystallization than other orientations. Additionally, more prone to continuous dynamic recrystallization (CDRX) results in a higher recrystallization fraction and a lesser average grain size in the thin-wall. Samples in the rib are dominated by strong copper-type texture, showing the feature of deformation texture; as for sample in the thin-wall, a high strength of Cube texture is displayed. The ultimate tensile strength (UTS) of the sample in the rib is 20 MPa higher than that in the thin-wall, which is mainly attributed to texture strengthening caused by hard orientation grains with smaller Schmid factor (SF), but the elongation of sample in the thin-wall is 30% higher than the rib (15.1% vs 11.6%), showing a superior plasticity, which is related to higher SF, higher recrystallization fraction and more homogeneous microstructure. This research will theoretically guide the manufacture of high-performance complex section Al–Zn–Mg–Zr cylindrical part with thin-wall and high-rib.

Structural and optical properties of micro-diamonds with SiV− color centers

Isolated, micro-metre sized diamonds are grown by micro-wave plasma chemical vapour deposition technique on Si(001) substrates. Each diamond is uniquely identified by markers milled in the Si substrate by Ga+ focused ion beam. The morphology and micro-grain structure analysis, indicates that the diamonds are icosahedral or bi-crystals. Icosahedral diamonds have higher (up to = 2.3 GPa), and wider distribution ( = 4.47 GPa) of hydrostatic stress built up at the micro-crystal grain boundaries, compared to the other crystals. The number and spectral shape of SiV− colour centres incorporated in the micro-diamonds (MDs) is analysed, and estimated by means of temperature dependent photoluminescence measurements, and Monte Carlo simulations. The Monte Carlo simulations indicates that the number of SiV− colour centres is a few thousand per MD.

Microstructure evolution and grain fragmentation induced by the co-activation of slip and [formula omitted] nanotwin during cryo-forging of a Ti-6Al-4V alloy

The nanostructured titanium alloy usually exhibits superior mechanical properties than the coarse-grained titanium alloy. In the present work, the α-grain fragmentation induced by slip/nanotwin co-activation during cryo-forging was studied in a bimodal Ti-6Al-4V alloy, in which the nanosized (022‾1‾) deformation twin was revealed. The results show that the lamellar α-grains fragmented to small globular grains after 25% compression at 0.1 mm/s and 0.5 mm/s. The high strain rate and large deformation increased the dislocation density and flow stress, therefore strengthened the deformation texture and promoted the grain fragmentation. The (0001) <112‾0> basal slip system was regarded as the dominant slip mode during cryo-forging, which activated more intensely in lamellar α-grains than that in equiaxed α-grains, and was promoted as the deformation ratio and stain rate increased. In addition, the activation of basal slip system was inhomogeneous in lamellar α-grains. The partial lattice rotation caused high angle grain boundary (HAGB) formation and grain fragmentation. On the other hand, the (022‾1‾) nanosized deformation twins appeared within fragmented α-grains after 25% cryo-forging at 0.5 mm/s, in which the (011‾1) planes between matrix and twin existed a ∼27° misorientation. The (022‾1‾) deformation twins contributed to grain fragmentation by twin boundary grooving and twin-twin intersection. This work demonstrated an available route to achieve refined or gradient grained structure in Ti-6Al-4V alloy by slip/twinning co-activation.

Theoretical model of magnetoacoustic emission considering the microstructure of ferromagnetic material

Magnetoacoustic emission (MAE) holds great promise for evaluating the mechanical properties of ferromagnetic materials. To refine the problems of the current theoretical and numerical models of MAE, a theoretical MAE model that considers the microscopic dependence of the hysteresis properties is proposed in this paper. The microstructure (dislocation density and grain size) and the correlation of MAE jumps are considered and incorporated into the model. Then, the influences of magnetization parameters and microstructure parameters on the envelope of the MAE signal are analyzed by the proposed theoretical model. The proposed theoretical model is then fully evaluated by simulations and experiments. The MAE experiments are conducted on ferromagnetic specimens with different hardnesses, and the MAE signals with different hardnesses are simulated by inverting the basic parameters of the MAE model with the genetic algorithm. Further, the crucial hysteresis parameters of the specimens are calculated using the results of microscopic measurements and the calculated parameters agree well with inversion results from experimental signals. The results demonstrate that the proposed theoretical model is valid for the MAE signal simulation. The trends of different hardnesses can be predicted by the MAE simulation signals. Moreover, the model can be used for theoretical analysis of the microscopic dependence of the MAE signal.

Crystal structure, Raman spectra, and microwave dielectric properties of a novel temperature-stable LiY9Si6O26 ceramic with hexagonal structure

This study presents a comprehensive investigation into the dielectric properties of LiY9Si6O26 ceramics, which were prepared for the first time using the solid-state method. XRD patterns and Rietveld refinement analysis conclusively demonstrate that LiY9Si6O26 adopts a hexagonal crystal structure with space group P63/m (176). Furthermore, Raman spectroscopy reveals a significant correlation between the quality factor and the FWHM of the A1g(O) mode at 879 cm−1. Transmission electron microscopy (TEM) was employed to verify the ordered layered structure inherent in the hexagonal LiY9Si6O26 ceramics. The microstructure of the ceramic grains was analysed using scanning electron microscopy (SEM), which revealed a remarkably high relative density of 96.4% for the LiY9Si6O26 ceramic. The Si–O bond valences (VSi–O) were found to be closely associated with the τf in LiY9Si6O26 ceramics. Remarkably, the microwave dielectric properties of LiY9Si6O26 ceramics sintered at 1425 °C were ascertained to be εr = 10.54, Q × f = 25,579 GHz (f = 10.3 GHz), and τf = 2.64 ppm/°C. These outstanding properties position LiY9Si6O26 ceramics as promising candidates for high-performance dielectric materials.

Mechanical properties and microstructure revolution of vibration assisted wire arc additive manufacturing 2319 aluminum alloy

In this study, a hybrid wire arc additive manufacturing (HWAAM) process that combines low-frequency vibration with cold metal transfer (CMT) arc is proposed to address the problems of porosity, coarse grains, and low mechanical performance encountered in WAAM aluminum alloys. The effects of different vibration frequencies on the microstructure and mechanical properties were investigated. The results indicated that as the vibration frequency increases, the grain size refinement reaches a maximum of 19.1% compared with the non-vibrated specimen. Vibration can enhance the fluidity and the cooling rate of the weld pool. The fatigue fracture of dendrite arms is the main mechanism of microstructure grain refinement caused by vibration. The dynamic bending stress induced by vibration on the dendrite arms and the root remelting phenomenon are the dominant factors for the dendrite fragmentation. Increasing the vibration frequency did not result in an obvious improvement in the tensile strength of the specimens, but did significantly increase the elongation. With the increase in vibration frequency, the maximum transverse and longitudinal elongation reached 22.2% and 23.5% respectively, a raise of 15.6% and 38.2% compared with non-vibrated specimen. Vibration reduced the size and distribution density of pores on the fracture surface, and increased the dimpled microstructure, improving the mechanical performance of the aluminum alloy.

(Digital Presentation) Electrochemical Properties of Ta-Doped Li7La3Zr2O12 Ceramic Electrolyte Sintered with Ga2O3 Additive

A garnet-type oxide with the formula of Li7La3Zr2O12 (LLZO) has attracted much attention because of its high Li ion conductivity at room temperature, excellent thermal performance, and high stability against Li metal.1,2) However, poor interfacial connection causes non-uniform Li plating and intergranular penetration of Li dendrite in polycrystalline LLZO when the cell is cycled particularly at high current densities, resulting in internal short-circuit failure.3,4) It has been pointed out that the tolerance for Li dendrite growth into LLZO is influenced by many factors such as the interfacial resistance between LLZO and Li anode, cell stacking pressure and microstructure (density and grain size) of LLZO. In this study, we fabricated Ta-doped LLZO (Li6.55La3Zr1.55Ta0.45O12) solid electrolytes with Ga2O3 additive and investigated the effects on the microstructure and electrochemical properties.Ta-doped LLZO with Ga2O3 additive were synthesized via a conventional solid-state reaction process. 1-7 mol % Ga2O3 powder was mixed with calcined Ta-doped LLZO powder. The mixture was pelletized and then sintered at different temperatures with an Al-free crucible. In XRD analysis, each sintered sample has a cubic garnet phase and diffraction peaks from other phases were not detected. In SEM observation, microstructure of sintered sample was strongly influenced by sintering temperature and Ga2O3 addition, due to the sintering with liquid Li-Ga-O phase during high temperature sintering.5, 6) The high total (bulk + grain-boundary) ionic conductivity above 1 mS cm-1 at room temperature was obtained in samples composed of large grains with the size of several 10 to 100 µm. However, the tolerance for Li dendrite growth characterized in a symmetric cell is improved remarkably in the samples with uniform microstructure composed of fine grains with the size of below 5 µm. Since the interfacial resistance between Li and solid electrolyte was adjusted to the same level, the difference in tolerance for Li dendrite growth is mainly attributed to the difference in microstructure depending on both the sintering condition and the amounts of Ga2O3 addition.

Li7La3Zr0.5Nb0.5Ta0.5Hf0.5O12 High-Entropy Li-Garnet with Fine Microstructure and Promising Properties

We demonstrated the processing of Li7La3Zr0.5Nb0.5Ta0.5Hf0.5O12 high-entropy Li-garnet with promising properties for lithium batteries. We first synthesized the LLZNTH Li-garnet powders which have a single cubic garnet phase without any secondary phases as well as uniform elements distributions. We further studied the formation, sintering, and mechanical properties of Li7La3Zr0.5Nb0.5Ta0.5Hf0.5O12 (LLZNTH) high-entropy Li-garnet with the comparison with Li6.75La3Zr1.75Ta0.25O12 (LLZT). The study indicates that the LLZNTH sample has a finer particle size after both calcination and ball mill than LLZT. Both samples can be densified to a relative density up to ~93-94% at a temperature of 1100°C, however, they show significant different sintering and grain growth behaviors. The LLZNTH sample takes 16 hours to reach the maximum relative density while the LLZT sample only needs 12 hours. LLZNTH sample has a significant lower grain growth parameter due to sluggish effects of high-entropy compounds so that it maintains fine microstructures (grain size ~10µm) than the LLZT sample (grain size over 100 µm). Due to the fine microstructures, the LLZNTH sample shows both higher flexural strength (84.8±6.9MPa compared with 47.9±10.1MPa) and hardness (8.5±0.8GPa compared with 7.7±0.4GPa) than the LLZT sample. Ionic conductivity characterizations indicate that the LLZNTH sample shows a moderate conductivity of 4.67×10-4 S cm-1 at room temperature and a low activation energy of 0.25eV. Figure 1

Effects of Sintering Processes on Microstructure Evolution, Crystallite, and Grain Growth of MoO2 Powder

MoO2 micro-powders with a mean pore size of 3.4 nm and specific surface area of 2.5 g/cm3 were compacted by dry pressing, then pressureless sintered at a temperature of 1000–1150 °C for 2 h or for a sintering time of 0.5–12 h at 1050 °C in an N2 atmosphere. Then, their microstructure evolution for morphology, crystallite, and grain growth were investigated. By sintering at a certain temperature and times, the irregular shape of the MoO2 powders transformed into an equiaxed structure, owing to the surface energy, which contributed to faster grain growth at the initial stage of sintering. The crystallite and grain sizes exponentially increased with the sintering time, and the growth exponent, n, was approximately 2.8 and 4, respectively. This indicates that the crystallite growth is governed by dislocation-mediated lattice diffusion, and the grain growth is determined by surface diffusion-controlled pore mobility. The increase in sintering temperature increased both crystallite and grain size, which obeyed the Arrhenius equation, and the activation energies were determined to be 95.65 and 76.95 kJmol−1 for crystallite and grain growths, respectively.

Effect of TaC and graphene nanoplatelets on the microstructure and mechanical properties of ZrB2

In this experiment, in order to investigate the effect of TaC addition on the microstructure, densification and mechanical properties of ZrB2 composites reinforced with graphene nanoplatelets (GNP), three composites were fabricated via spark plasma sintering (SPS) at 1900 °C. Relative density was determined by Archimedes method. The XRD and EDS analyses were used to explore the phase composition and elemental distribution. Also, Field emission scanning electron microscopy (FE-SEM) was employed to characterize the microstructure (grain size and porosity). Flexural strength, fracture toughness and hardness were determined by three-point bending test, single-edge notched beam (SENB) and macro and micro Vickers methods, respectively. The results showed that the presence of the GNP, alone and combined with TaC, increases the relative density sharply to 99.6 %. In addition, full densification occurred by the addition of 10 and 20 vol% TaC compared to the monolithic ZrB2 ceramic with 83 % relative density. Maximum flexural strength and fracture toughness of 580 MPa and 4.5 MPa.m0.5 were obtained, respectively, for ZrB2- GNP and ZrB2- GNP doped with 10 vol% TaC.

Ultra-rapid debinding and sintering of additively manufactured ceramics by ultrafast high-temperature sintering

In recent years, additive manufacturing (AM) of ceramics has significantly advanced in terms of the range of equipment available, printing resolution and productivity. Most techniques involve the use of ceramic powders embedded in an organic binder which is typically removed through a slow thermal debinding process.Herein, we prove for the first time that ultra-rapid debinding and sintering are possible for complex 3YSZ components produced using material extrusion technology. The printed components were first chemically debinded in acetone thus removing about one-half of the binder, and then thermally debinded and densified by ultrafast high-temperature sintering (UHS) in a single-step process (30–120 s). Fully dense components were obtained with tailored microstructure and nanometric grain size. The sintered artefacts were crack-free even at the microscopic level.This approach paves the way for rapid processing (debinding and sintering) of additively manufactured ceramics with reduced energy consumption and carbon footprint.