Grain Growth Inhibition Research Articles

Preparation of ultrafine WC-V8C7-Cr3C2-co cemented carbides by spark plasma sintering in-situ synthesis of composite grain growth inhibitors

The growing high-precision manufacturing industry is increasing the demand for cemented carbide which has fine grain size and excellent machinability. In this research, ultrafine cemented carbide was successfully prepared by the method of in-situ synthesis using spark plasma sintering as densification method, V, Cr, WC and carbon black as raw materials. The formation mechanism of in-situ preparation of grain growth inhibitors (GGIs) and its influence on the properties of alloys were investigated. An excellent mechanical property (HV 2254 kgf/mm2, KIC 9.20 MPa·m1/2) and uniform microstructure of the alloys (0.8 wt% V8C7–0.8 wt% Cr3C2) prepared under 1350 °C, 6 min, 25 MPa were demonstrated by the results. The WC grain growth was significantly inhibited (about 200 nm). The in-situ synthesized GGIs significantly inhibited grain coarsening by interfering with the dissolution-precipitation process of WC during liquid-phase sintering. The combination of SPS and in-situ synthesized GGIs offers a novel approach to exploration of the preparation of high-performance ultrafine or nanocrystalline cemented carbides.

Nanotechnology-enhanced castability of wrought aluminum alloys 2024 and 6063

In the realm of high-performance applications, wrought aluminum alloys are esteemed for their high mechanical properties and excellent strength-to-weight ratio. However, their limited castability poses challenges in economically producing intricate structures through casting processes. To address this issue, a small proportion of TiC nanoparticles is introduced into the melts of AA 2024 and AA 6063 for nano-treating. This nano-treatment imparts several beneficial effects, including the delayed release of latent heat, inhibition of grain growth, and improvement of wettability. These effects enhance the fluidity of the melt, eliminate hot cracking, and elevate the surface quality of the castings. The outcomes underscore the promising potential of emerging nano-treatment technology in rendering traditionally non-castable wrought aluminum alloys suitable for cost-effective casting processes, ultimately delivering high-performance products for a wide range of applications.

Effect of carbon content on the microstructure and mechanical properties of ultrafine WC-15Co cemented carbides using a Co-based solid solution binder phase

In this paper, a new method was proposed to improve the uniformity of the distribution of grain-growth inhibitors using a Co-based solid solution prepared with Co3O4, Cr2O3, and V2O5 as the raw materials through high-temperature hydrogen reduction. The effect of carbon content on the microstructure and mechanical properties of ultrafine WC-15Co cemented carbides using a Co-based solid solution binder phase were studied. The results demonstrated that the carbon content exerted a considerable influence on the composition of the binder phase, thereby affecting the morphology of the WC grains. With increasing the carbon content, Cr and V precipitated from the Co-based solid solution, adhering to the habit planes of WC or segregating at the WC-Co interface. This hindered the growth of WC grains, yielding an average particle size smaller than that of alloys containing 6.0wt.% carbon content. However, increased carbon content may enhance grain growth owing to the dissolution-precipitation process of WC grains during the liquid-phase sintering process. Thus, an alloy comprising 6.31wt.% carbon content and featuring trigonal prismatic-shaped WC grains with a mean particle size of 0.310 μm exhibited excellent comprehensive performance, characterized by a hardness, transverse rupture strength, and fracture toughness of 1579kg/mm2, 2581MPa, and 10.56MPa·m1/2, respectively.

Solution infiltrated lanthanum nickelate–GDC composite cathode via flash-light sintering for intermediate temperature solid oxide fuel cells

Solid oxide fuel cells (SOFCs) require high operating temperatures to minimize the oxygen reduction reaction resistance at cathode and increase the ionic conductivity of oxygen. However, at high operating temperatures, their stability during long-term operation degrades because of material deterioration and the mutual chemical reactions occurring at the interfaces. Herein, an electrode–electrolyte composite is fabricated by solution infiltration of lanthanum nickelate (LNO) electrode material into a GDC electrolyte layer to ensure more reaction sites compared with the conventional powder mixing of the electrode and electrolyte material. Further, the conventional thermal sintering process is replaced with the flash-light sintering process. Thus, the performance of the LNO–GDC cathode cell manufactured by flash-light sintering improves owing to suppression of grain growth of the infiltrated LNO particles. The microstructures of the infiltrated solution and composite layer of the electrolyte material are analyzed using field-emission scanning electron microscopy, and the crystallinity of the LNO nanoparticles is analyzed using high-resolution transmission electron microscopy. A maximum power density of 1.1 W/cm2 is achieved, an improvement of 58 % over the LSCF cell without infiltration at 750 ℃. This study is expected to contribute to the commercialization of SOFCs by replacing conventional thermal sintering.

Investigation of the effect of strontium substitution in bismuth ferrites for enhanced structural and optical properties using experimental and DFT approaches

BiFeO3 doped with Sr, having the composition Bi1-xSrxFeO3 (0.00 ≤ x ≤ 0.20), was synthesized using the auto-combustion method. Various characterization techniques were employed to investigate the structural, morphological, and optical properties. X-ray diffraction (XRD) patterns confirmed that the materials exhibit a distorted rhombohedral structure with the space group R3c. The average crystallite size was determined to be in the range of 18–28 nm. A decrease in the lattice parameters was observed due to the contraction of the unit cell volume (373.83–371.49 Å) caused by Sr doping. Scanning electron microscopy (SEM) images revealed a reduction in grain size, suggesting the suppression of grain growth with Sr doping. Fourier-transform infrared (FTIR) studies identified two strong peaks at 552 cm−1 and 449 cm−1, confirming the perovskite structure of the materials. The optical band gap was found to decrease from 2.14 eV to 2.05 eV with increasing Sr concentration. Theoretical calculations of electronic and optical properties using density functional theory (DFT) were conducted. The calculated direct optical band gaps (2.0 eV, 2.22 eV, 2.1 eV, and 2.09 eV) for Bi1-xSrxFeO3 samples at doping levels x = 0.0, 0.10, 0.15, and 0.20, respectively, were in good agreement with the experimental results. These findings provide valuable insights into the tunability of electronic and optical properties in Sr-doped BiFeO3, making them promising candidates for various technological applications.

Investigation of the role of yttrium sesquioxide nanoparticles on the properties of zinc oxide ceramics

In this work, zinc oxide (ZnO) ceramics were synthesized containing 0-5wt% of cubic yttrium sesquioxide (Y 2 O 3) nanoparticles with solid state sintering technique at 1150°C. The secondary phase of Y 2 O 3 did not enter into the crystalline zinc oxide. The Y 2 O 3 acts as an inhibitor of grain growth. The absorption of the free charge carriers by the Y 2 O 3 phase influences the infrared transmissions. The minimization of the phase mismatch while transferring the electric signal caused lower losses when Y 2 O 3 was added to the zinc oxide matrices. The presence of the cubic sesquioxide at the grain boundary contributes to the interfacial polarization at lower frequencies when an alternating field is applied to the ceramics. These properties are anticipated to show a wider range of physical, optical and dielectric properties of ZnO: Y ceramics for optoelectronic applications.

Tuning of structural, magnetic, and optical properties of ZnO nanoparticles by Co and Cu doping

Undoped, Cu, and Co-doped ZnO nanoparticles were synthesized by a simple co-precipitation method. We studied the structural, chemical, magnetic, and optical properties of synthesized nanoparticles by using X-ray Diffraction, Fourier Transform Infrared, Scanning Electron Microscopy, Vibrating-Sample Magnetometer, and UV–VIS spectroscopy. The X-ray Diffraction analysis discovers the crystalline hexagonal wurtzite structure and confirms the incorporation of Cu2+ and Co2+ in the ZnO lattice. The SEM photographs show that the nanoparticles are agglomerated, and the grain size of pure ZnO is decreased upon doping, showing inhibition of grain growth through doping. From VSM the coercivity and saturation magnetization of Co-doped (0.0189 emu/g and 84.044Oe) is higher as compared to pure and Cu-doped ZnO. The energy gap of doped and un-doped nanoparticles determined from the absorption spectrum indicates that it increases by doping of Copper and cobalt.

Effect of Ce addition on the nucleation and growth of austenite in ultra-high-strength steel

The effect of varying rare earth element cerium (Ce) contents (0∼0.0792 wt%) on the austenite grain size of ultra-high-strength engineering steel has been studied under different austenitization conditions (holding time of 5∼360 min at temperatures ranging from 900 °C to 1200 °C). Results show that the addition of Ce can refine grains, and the refining effect becomes more pronounced as the Ce content increases. The inhibition of austenite grain growth by fine Ce-containing inclusions during the holding process has been observed through laser scanning confocal microscopy (LSCM) and field-emission scanning electron microscope (FE-SEM) equipped with an energy dispersive spectrometer (EDS), and the pinning effect of Ce-containing inclusions on the austenite grain boundaries is the primary factor for the refinement of austenite grains. Besides, theoretical calculations have shown that the lattice misfits between the (100) plane of CeP and the (111) plane of the γ-phase is 7.83%, indicating that CeP could serve as a heterogeneous nucleation core for the γ-phase and was moderately effective. Furthermore, the uniformization effect of Ce on the grains is more prominent than the refining effect at the holding temperatures of 1000 °C and 1200 °C.

More microscopic interfacial segregation slowers macroscopic grain growth: A case in WC-Co cemented carbides

In industrial practice, combining grain growth inhibitors (GGIs) with low carbon content effectively restrains WC grain growth in WC-Co cemented carbides. However, the intricate relationship between carbon content, WC grain microstructure, and GGI impact remains unresolved. This study investigates two WC-Co sample sets, maintaining constant VC inhibitor levels but varying carbon content near upper (HC) and lower (LC) limits. SEM analysis revealed distinct morphologies: HC displayed truncated prism shapes, exposing long basal and prismatic terraces, while LC exhibited a saw-tooth morphology with finer grains. EBSD stereology quantified anisotropic WC grain growth, revealing suppressed growth perpendicular to both basal (HC: 0.51 μm vs. LC: 0.38 μm) and prismatic planes (HC: 0.44 μm vs. LC: 0.37 μm) with decreased carbon content. Atomic-resolution EDS showed higher V solute excess in LC at WC(basal)-Co, WC(prismatic)-Co interfaces, and step corners (HC: 4.6, 0.9, and 4.4 atoms/nm2; LC: 5.5, 0.9, and 7.8 atoms/nm2). Our findings elucidate a clear physical understanding that a low carbon content enhances V atom solubility within liquid cobalt, increasing the thickness of complexions to quad-layer on WC (basal)-Co interfaces and forming V-rich nanoprecipitates at step corners. Those inhibitory effects further limited step flow, resulting in pronounced step bunching and a saw-tooth fine-grained morphology in LC sample. This study highlights that complexions housing more inhibitory solute elements exert a stronger drag effect on grain growth front migration. This approach has the potential for studying grain growth in anisotropic materials, highlighting the importance of constructing experimental complexion diagrams in engineering fine-structured ceramics and metals.

Influence of Pulsed Interference Laser Heating on Crystallisation of Amorphous Fe77Cu1Si13B9 Ribbons.

Amorphous Fe77Cu1Si13B9 ribbons were treated with pulsed laser interference heating (PLIH). The research results will significantly contribute to a better understanding of the impact of PLIH on crystallisation and magnetic properties in precisely defined micro-areas of Fe77Cu1Si13B9 (FeCuSiB) ribbons, which has not yet been described in the literature. It was confirmed here that the use of the laser heating process allowed for the achievement of two-dimensional crystallised micro-areas, periodically distributed (at a distance of 17 µm) on the surface of the amorphous ribbons. The correlation between structural changes (SEM, TEM, HRTEM) and the distribution of magnetic field lines of heated amorphous Fe77Cu1Si13B9 ribbons is presented. Particular attention is paid to structural changes in micro-areas where, by controlling the laser interference heating process, the partial crystallisation of amorphous alloys and the formation of clusters or single nanocrystallites (α-Fe(Si)) embedded in an amorphous matrix occur. The addition of copper to the FeSiB alloy promoted the inhibition of grain growth. Electron holography of micro-areas confirmed shifts in the magnetic field lines in the areas of nanocrystallites, the presence of which in the structure caused the magnetisation of the surrounding amorphous matrix.

Manganese substitution effect on physical properties of sol-gel derived DyFeO3 orthoferrite

A simple composite DyFe(1-x)MnxO3 (x = 0, 0.1, 0.3, 0.5) powders were successfully prepared by the sol–gel method. The effect of Mn modification on the structure, thermal and phase transition behaviour of DyFeO3 orthoferrite was investigated. Mn modification didn't show any structural change and all the samples confirmed the pure orthorhombic phase with Pbnm space group. However, a contradicting trend in the variation of lattice parameters were observed due to the presence of mixed oxidation state of Dy, Fe and Mn in the sample leading to oxygen vacancies. The presence of mixed oxidation state was confirmed through X-ray photoemission spectra (XPS). Scanning electron microscopy (SEM) and Williamson Hall (WH) plot confirmed a decrease in particle sizes with increasing Mn concentration leading to an increase in the specific surface area which suggested an inhibition of grain growth with Mn modification. The defects-initiated change in physical behaviour in terms of structural, thermal, microstructural and dielectric are analyzed and discussed in detail.

Analysis of the Luminescent Emission during Flash Sintering of 8YSZ and 20SDC Ceramics

Light-emission data were collected before, during, and after the occurrence of the flash event in pressureless electric-field-assisted (flash) sintering experiments on ZrO2: 8 mol% Y2O3 (8YSZ) and CeO2: 20 mol% Sm2O3 (20SDC) ceramic green pellets to analyze the luminescent emission from the samples. The experiments were performed at 800 °C with an applied electric field of 100 V·cm−1 at 1 kHz, limiting the electric current to 1 A. Luminescence data were obtained in the 200–1200 nm (ultraviolet–visible–near-infrared) range. The deconvolution of the optical spectra allowed for the identification of emission bands in the visible range due exclusively to the samples. The wavelength maxima of the emission bands in 8YSZ were found to be different from those in 20SDC. It is suggested that these bands might originate from the interaction of the electric current, resulting from the application of the electric field, with the depleted species located at the space-charge region at the grain boundaries of these ceramics. The main results represent a contribution to help to clarify the mechanisms responsible for the fast densification with inhibition of grain growth in electroceramics.

Influence of Grain-Growth Inhibitors on Modified (Ba,Sr)(Sn,Ti)O3 for Electrocaloric Application.

The paper reports on effect of grain-growth inhibitors MgO, Y2O3 and MnCO3 as well as Ca modification on the microstructure, dielectric, ferroelectric and electrocaloric (EC) properties of Ba0.82Sr0.18Sn0.065Ti0.935O3 (BSSnT). Furthermore, the effects of the sintering time and temperature on the microstructure and the electrical properties of the most promising material system Ba0.62Ca0.20Sr0.18Sn0.065Ti0.935O3 (BCSSnT-20) are investigated. Additions of MgO (xMgO = 1%), Y2O3 (xY2O3 = 0.25%) and MnCO3 (xMnCO3 = 1%) significantly decreased the mean grain size of BSSnT to 0.4 µm, 0.8 µm and 0.4 µm, respectively. Ba0.62Ca0.20Sr0.18Sn0.065Ti0.935O3 (BCSSnT-20) gained a homogeneous fine-grained microstructure with an average grain size of 1.5 µm, leading to a maximum electrocaloric temperature change |ΔTEC| of 0.49 K at 40 °C with a broad peak of |ΔTEC| > 0.33 K in the temperature range from 10 °C to 75 °C under an electric field change of 5 V µm-1. By increasing the sintering temperature of BCSSnT-20 from 1350 °C to 1425 °C, the grain size increased from 1.5 µm to 7.3 µm and the maximum electrocaloric temperature change |ΔTEC| increased from 0.15 K at 35 °C to 0.37 K at 20 °C under an electric field change of 2 V µm-1. Our results show that under all investigated material systems, BCSSnT-20 is the most promising candidate for future application in multilayer ceramic (MLC) components for EC cooling devices.

High temperature performance of RE2Zr2O7 high-entropy ceramics designed by thermophysical performance-oriented principle

This study utilizes modulation of ionic disorder and electronegativity differences for targeted component design of high-entropy ceramic compositions. A series of novel multicomponent ceramics with the general formula (LaGdYSm)x2Ybx1Zr2O7 (x1+4x2 = 2, x1 = 0.6,0.4,0.2,0) were prepared by solid-state reaction. The evolution patterns of their microstructures were analyzed using XRD and TEM, and the anti-sintering ability and thermophysical properties were evaluated. The results confirm that the multicomponent ceramics gradually transform from the coexistence of pyrochlore/fluorite dual-phase structure to pyrochlore structure with the tuning of the size disorder degree. After 50h of exposure to air at 1500 °C, the ceramics retained excellent phase stability. Segregation of La and Yb elements with large differences in radius size occurs, forming a mixture of the La-rich pyrochlore and the Yb-rich fluorite phases. The specimen with the maximum size disorder exhibits the lowest grain growth rate and the greatest thermal insulation properties. Large lattice distortions and sluggish diffusion effects are responsible for the mutual inhibition of grain growth in the two-phase coexistence zone. The thermal insulation properties of the ceramics show well correlated with the degree of the size disorder, further validating the effectiveness of the component design. Meanwhile, the thermal expansion coefficients of prepared ceramic can reach 11.49 × ∼11.58 × 10−6 K−1 at 1000–1100 °C. The customization principles used in this work fill a gap in the compositional design methodology for multicomponent lanthanum zirconate-based high-entropy ceramics. It is essential for developing rare-earth zirconates with tunable thermophysical properties in the area of thermal barrier coatings.

Ultrafine‐grained WC‐based ceramics prepared via two‐step oscillatory pressure sintering

AbstractGrain growth in ceramic‐based composites during sintering has always been an unavoidable problem. Based on the theory of fine‐grained reinforcement, the concept of rapid densification was coupled with the inhibition of grain growth to fabricate ultrafine‐grained WC‐based ceramics. Herein, by combining two‐step sintering with oscillatory pressure sintering (OPS), a new sintering process—two‐step oscillatory pressure sintering (TSOPS), was used for the preparation of ultrafine‐grained WC‐based ceramics. The comparison of the OPS with the TSOPS validated the feasibility of the strategy in achieving homogeneous and fine‐grained microstructures. The optimum mechanical properties of Vickers hardness, fracture toughness, and flexural strength reached up to 29.56 GPa, 7.97 MPa m1/2 and 1591 MPa, respectively. A developed TSOPS process was proposed and proved to dominate the grain size distribution homogenizing, which contributed to the simultaneous enhancement of mechanical properties of the ceramics.

Grain-growth Inhibitor with Three-section-sintering for Highly Dispersed Single-crystal NCM90 Cubes.

Single crystallization of LiNix Coy Mn1-x-y O2 (NCM) is currently an effective strategy to improve the cycling life of NCM cathode, owing to the reduced surface area and enhanced mechanical strength, but the application of single crystal NCM(SC-NCM) is being hindered by severe particle agglomeration and poor C-rate performance. Here, a strategy of three-section-sintering(TSS) with the presence of grain-growth inhibitor was proposed, in which, the TSS includes three sections of phase-formation, grain-growth and phase-preservation. While, the addition of MoO3 inhibits the grain growth and restrains the particle agglomeration. With the help of TSS and 1 mol % of MoO3 , highly dispersed surface Mo-doped SC-NCM(MSC-NCM) cubes are obtained with the average diameter of 1.3 μm. Benefiting from the surface Mo-doping and the reduced surface energy, the Li+ -migration preferred (1 0 4) crystalline facet is exposed as the dominant plane in MSC-NCM cubes, because of which, C-rate performance is significantly improved compared with the regular SC-NCM. Furthermore, this preparation strategy is compatible well with the current industrial production line, providing an easy way for the large-scale production of SC-NCM.

Two- and Three-Dimensional Modeling and Simulations of Grain Growth Behavior in Dual-Phase Steel Using Monte Carlo and Machine Learning.

Dual-phase (DP) steel has been widely used in automotive steel plates with a balance of excellent strength and ductility. Grain refinement in DP steel is important to improve the properties further; however, the factors affecting grain growth need to be well understood. The remaining problem is that acquiring data through experiments is still time-consuming and difficult to evaluate quantitatively. With the development of materials informatics in recent years, material development time and costs are expected to be significantly reduced through experimentation, simulation, and machine learning. In this study, grain growth behavior in DP steel was studied using two-dimensional (2D) and three-dimensional (3D) Monte Carlo modeling and simulation to estimate the effect of some key parameters. Grain growth can be suppressed when the grain boundary energy is greater than the phase boundary energy. When the volume fractions of the matrix and the second phase were equal, the suppression of grain growth became obvious. The long-distance diffuse frequency can promote grain growth significantly. The simulation results allow us to better understand the factors affecting grain growth behavior in DP steel. Machine learning was performed to conduct a sensitivity analysis of the affecting parameters and estimate the magnitude of each parameter's effects on grain growth in the model. Combining MC simulation and machine learning will provide one promising research strategy to gain deeper insights into grain growth behaviors in metallic materials and accelerate the research process.

Cd2+-enhanced the structure, electrical and magnetic properties of low-temperature sintered NiCuZn ferrites

Ferrite materials are urgently demanded in high-frequency miniaturized power electronics for their high electromagnetic properties and high electrical resistivity. However, traditional NiZn ferrites are faced with low resistivity and high loss at low-temperature sintering, which severely restrict their applications. In this study, CdO was substituted into Ni0.22Cu0.2Zn0.58Fe2O4 ferrites at a presintered stage to refine the grain size and to achieve superior performance at low-temperature sintering. Interestingly, the electrical, magnetic and gyromagnetic properties of the NiCuZn ferrites exhibited a strong dependence on the concentration of Cd2+ ions. The Cd2+ ions entered into the lattice and substituted for Fe3+ at the octahedral site. SEM image results showed that CdO-substituted NiCuZn ferrites for the first sintering stage possess inhibition of abnormal grain growth, which can effectively solve the problem of shrinkage and grain compaction of ferrite materials in LTCC technology. Furthermore, to promote the grain growth at low sintering temperature, the optimized Bi2O3 additives were added at final sintering stage. The resistivity of the optimized Cd2+ ions is significantly enhanced from 2.41 × 108 Ω cm to 8.51 × 108 Ω cm. Finally, the NiCuZnCd (x = 0.15)-1.2 wt% Bi2O3 ferrites with the highest densification possess ρ = 8.51 × 108 Ω cm, ε′ = 18, tan δε = 6.0 × 10−3, μ′ = 81, fr = 117 MHz, tan δμ = 4.8 × 10−2 and ΔH = 281 Oe. This work provides a new doping method for the design of the high frequency LTCC device.

Effect of lanthanide and transition metal on the structure, magnetic, and electric properties of nickel ferrites

A series of nanocrystalline Ni1−xMnxCexFe2−xO4 (x = 0.0, 0.02, 0.04, 0.06, 0.08, and 0.1) were prepared using the citrate auto-combustion method. X-ray diffraction (XRD) indicates that the spinel materials formed in a cubic single phase up to the sample x = 0.02. The average crystallite size is reduced from 61 to 31 nm due to the suppression of grain growth upon cerium occupation at the octahedral site. The cubic spinel structure was confirmed by Fourier-transform infrared (FT-IR) analysis. Scanning electron microscope (SEM) showed agglomerated and rod-shaped structures at various concentrations. AC conductivity and dielectric properties were measured over a frequency range of 20 Hz to 8 MHz. The AC conductivity increases with an enhancement in frequency. The prepared materials have great potential for utilization in microwave devices. The magnetic parameters were estimated from the measured hysteresis loops at room temperature and 100 K using a vibrating sample magnetometer (VSM), which indicated that the samples were suitable for magnetic memory device applications.

An experimental and computational framework to investigate the thermal cycling approach for strengthening low SFE FeMnNi medium entropy alloy

Thermal cycling treatment was adopted for the microstructural engineering of a ternary equiatomic FeMnNi medium entropy alloy (MEA) for achieving different strength-ductility combinations using instrumented indentation and electron backscatter diffraction. A computational model based on cellular automata that accounts for the thermodynamic and kinetic aspects of microstructural evolution was used for predicting recrystallization and grain growth during conventional isothermal single-step and cyclic annealing. The current investigation suggests that an equivalent isotemporal thermal cycling treatment produces a recrystallized microstructure of lower average grain size with a more uniform grain size distribution and a lower variance as a result of inhibition of grain growth. Superior strength-ductility combinations are obtained for all the thermal cycling samples compared to single-step annealed samples. The thermally cycled recrystallized sample demonstrated a yield strength of 561±10 MPa with ductility of 46.7±3.5% against the isothermally recrystallized sample with a yield strength of 406±11 MPa and elongation up to 35.1±5.2%. Thus, the present study demonstrates that thermal cycling treatment provides superior control over the microstructure and optimum combination of strength and ductility in FeMnNi MEA.