Scanning electron microscopy (SEM) is an indispensable analytical tool for the microstructural characterization of hard materials, including WC-Co cemented carbides and cermets. However, interpreting SEM images accurately requires a fundamental understanding of electron-solid interactions and specific detector characteristics. This review provides a comprehensive guide for beginner to intermediate SEM users, focusing on the principles of secondary electrons (SE) and backscattered electrons (BSE), and the optimization of essential imaging parameters. Through practical observation examples of hard materials, we demonstrate how accelerating voltage, working distance (WD), and detector configurations (in-lens vs. out-lens) critically influence the resulting topographic and compositional contrast. Furthermore, we discuss the application of optimized SEM techniques for advanced fractography and energy-dispersive X-ray spectroscopy (EDS) analysis. By mastering these fundamental principles, researchers can effectively extract precise microstructural and fractographic information, thereby accelerating the development and failure analysis of advanced powder metallurgy products.

Single crystal growth of β-NaFe₂O₃, a mixed-valent layered iron oxide, is challenging because of the high volatility of sodium, the difficulty in controlling the valence state of Fe, and the narrow phase-stability range. In this study, β-NaFe₂O₃ single crystals were grown under ambient pressure by the floating-zone method. A slightly sodium-deficient single crystal was obtained in Ar using a growth rate of 10 mm h^-1. Magnetization measurements indicate transitions near 230 and 250 K and show that the magnetic easy axis is parallel to the c-axis. A change in magnetization around 125 K suggests the presence of a small amount of Fe₃O₄. These results provide a growth window for single-crystalline β-NaFe₂O₃ under ambient pressure.

Crystallographic orientation control of hydroxyapatite (HAp) ceramics is essential for optimizing their biological, mechanical, and optical properties. However, pure HAp possesses negative magnetic susceptibility anisotropy (Δχ_c-Δχ_a < 0), making its c-axis a hard magnetic axis that requires rotating magnetic fields for alignment. In this study, we demonstrate the complete inversion of magnetic anisotropy in HAp ceramics by substituting a trace amount of europium (0.6 at% Eu:HAp). Powder compacts were prepared via slip casting under 3 T static and rotating magnetic fields. X-ray diffraction revealed that while pure HAp required a rotating field for c-axis alignment, 0.6 at% Eu substitution converted the c-axis into the easy magnetic axis (Δχ > 0). Consequently, Eu:HAp achieved sharp c-axis alignment parallel to a 3 T static magnetic field, whereas a rotating field induced a-axis orientation along the sample normal. This anisotropy reversal is likely attributed to the Van Vleck paramagnetism of Eu³⁺ (J = 0) substituting at the Ca(2) site, where crystal-field-induced quantum mixing with the excited J = 1 state imparts strong positive anisotropy along the c-axis (Δχ_c,Eu >> Δχ_a,Eu). These findings offer a facile strategy for tailoring the magnetic orientation of HAp ceramics using static magnetic fields with minimal dopants.

To fabricate high-density transparent glass sintered bodies using the powder sintering method, it is critical to precisely control heating conditions in order to suppress crystallization while efficiently evacuating foaming gases. In this study, a two-step sintering process was applied to cold-isostatically pressed compacts to evaluate its effectiveness. In the primary sintering stage, low-temperature heat treatment was applied to suppress the driving force for crystallization while removing volatile impurities such as adsorbed water. In the secondary sintering stage at elevated temperatures, the heating process was precisely controlled to promote outgassing through interparticle open pores prior to full densification. Effective gas evacuation, particularly above the glass transition temperature (T_g), significantly suppressed bubble formation within the sintered body. These findings demonstrate that high-density transparent glass sintered bodies can be successfully fabricated within a narrow window of optimal heating parameters that simultaneously achieve impurity removal, gas evacuation, and crystallization suppression.

WC-Ni based cemented carbides are a superior alternative to WC-Co alloys for applications requiring non-magnetic properties and high corrosion resistance. Historically, their lower hardness and fracture toughness limited their industrial use. Recent advancements, such as multi-element additions (Cr, Mo, V) and the development of ultrafine-grained grades, have significantly narrowed this performance gap, achieving mechanical properties comparable to WC-Co alloys. Notably, while grain refinement is key to enhancing strength, grain size is strategically tailored to specific application requirements, ensuring that both ultrafine and conventional grades are utilized effectively. This paper provides a comprehensive review of the evolution of WC-Ni cemented carbides, focusing on phase equilibria, mechanical behaviors, magnetic properties, and electrochemical corrosion mechanisms. Specifically, it discusses the physical principles of stable paramagnetism through Curie temperature control and the inhibition of galvanic corrosion when coupled with stainless steel. Furthermore, the industrial effectiveness in sliding components is highlighted, alongside environmental advantages like lower toxicity and improved recyclability, positioning these alloys as essential sustainable materials for next-generation precision tooling and chemical engineering.

In this study, transparent and highly thermally conductive AlN ceramics were fabricated by employing CaF₂ as a sintering aid and applying crystallographic alignment under a strong magnetic field. AlN and CaF₂ powders were dispersed in ethanol, consolidated by slip casting under a magnetic field, and densified by spark plasma sintering (SPS). The influence of CaF₂ additive content on densification, grain boundary phase formation, crystallographic orientation, grain size, as well as on the optical transmittance and thermal conductivity, was systematically investigated. Further improvement in transmittance and thermal conductivity was achieved by post-sintering heat treatment to remove the grain boundary phase. These results demonstrate the significance of the sintering additive and the optimization of the processing parameters to enhance the functionality of AlN ceramics.

Fe₂O₃-Fe₃O₄/carbon composite particles were synthesized in a single step by mechanochemical treatment of α-Fe₂O₃ and polypropylene (PP) powders under an Ar atmosphere using a planetary ball mill. The effects of rotation speed and milling time on phase evolution, PP decomposition, carbon formation, optical absorption, and near-infrared (NIR)-induced heating were investigated. SEM observations revealed particle fragmentation, surface roughening, and secondary agglomeration after mechanochemical treatment. PXRD and Raman spectroscopy suggested that, in the presence of PP, α-Fe₂O₃ transformed through γ-Fe₂O₃ to Fe₃O₄ with increasing rotation speed and milling time, whereas no clear formation of Fe₃O₄ was observed without PP. For the sample milled at 800 rpm for 60 min (PP-800-60), the Fe₃O₄-equivalent content was semi-quantitatively estimated to be 34 wt% by the RIR method. Comparison of the milling conditions indicated that Fe₃O₄ formation depended not only on the total impact energy but also on the local mechanical stress generated at high rotation speed. Raman spectroscopy detected PP-derived carbon in PP-800-60, while GC-TCD analysis detected H₂ in the PP-containing samples and CO₂ only in PP-800-60, suggesting that PP-derived hydrogen species and carbon-mediated oxygen removal contributed to the reduction of α-Fe₂O₃. UV–Vis–NIR spectroscopy showed enhanced absorption from the visible to NIR region and a decrease in the apparent optical band gap from 2.13 to 1.96 eV. Under NIR irradiation at 750–1050 nm and 300 mW/cm² for 10 min, PP-800-60 reached 166.2°C, exceeding the physical Fe₂O₃/Fe₃O₄ mixture (149.5°C) and approaching pure Fe₃O₄ (168.9°C), despite its lower NIR absorptance. These results demonstrate that one-step mechanochemical processing is an effective route for simultaneously inducing iron oxide reduction, defect formation, and carbon incorporation, thereby producing Fe₂O₃-Fe₃O₄/carbon composite particles with an enhanced NIR-induced heating response.

The glassy volcanic sand produced mainly in the Kyushu region of Japan is called “Shirasu” and is composed of fine particles of silica-based compounds. Rapid heating to about 1000°C makes the Shiras particles to expand and foam. The particles form a balloon-like hollow structure called a “Shirasu balloon”. In this study, solidified bodies of shirasu particles were prepared by alkali activation and foamed at low temperatures. The effects of sample preparation conditions, such as the particle concentration, NaOH solution concentration, curing and drying on the foaming properties were investigated. The low-temperature foaming mechanism of the silica-based solidified products was clarified.

A porous mixed conductive phase consisting of (Ba,Sr)(Co,Fe)O_3-δ (BSCF) was fabricated on a stainless steel-zirconia dual-phase oxygen separation membrane by electrophoretic deposition. To suppress the reaction between stainless steel, zirconia, and BSCF, a gadolinium-doped ceria (GDC) buffer layer was inserted. The GDC buffer layer suppressed the formation of zirconate, a reaction product of BSCF and YSZ, and formed a uniform BSCF layer with a thickness of 10 micrometers. This layer showed good correlated adhesion.

In this study, Ti₃SiC₂, a nanolayered ternary carbide, which shows superior oxidation resistance than carbon and hexagonal-boron nitride (h-BN), was selected as the interphase for SiC_f/SiC composites, and Ti₃SiC₂ coating was formed on SiC fibers by the electrophoretic deposition (EPD) method. The SiC_f/SiC composites with the Ti₃SiC₂ interphase with the different thickness were prepared, and the effect of the Ti₃SiC₂ interphase on their mechanical properties was discussed. Whereas the SiC_f/SiC composites using uncoated SiC fibers showed brittle fracture behavior without fiber pullout and interfacial debonding, the SiC_f/SiC composites with Ti₃SiC₂ interphase exhibited pseudo-ductile fracture behavior with the large amount of fiber pullout and interfacial debonding. Bending strength and fracture energy of the SiC_f/SiC composites with Ti₃SiC₂ interphase were much higher than those of the SiC_f/SiC composites without Ti₃SiC₂ interphase. From the results of mechanical properties of the SiC_f/SiC composites with Ti₃SiC₂ interphase varying the thickness, it was suggested that the Ti₃SiC₂ interphase thickness affected their bending strength and fracture energy. It was demonstrated that Ti₃SiC₂ interphase was successfully formed on SiC fibers by EPD method, the SiC_f/SiC composites with excellent mechanical properties were achieved by controlling the Ti₃SiC₂ interphase thickness, and Ti₃SiC₂ was effective as the interphase for SiC_f/SiC composites.

Densification enhancement and property improvement must be achieved in tandem, and controlling the dispersion state of sintering aids is crucial for this purpose. In this study, we propose a new addition method in which a sintering-aid component is uniformly coated onto the target particle surfaces at the nanoscale to suppress segregation within the sintered body. LiTa₂PO₈ (LTPO) was synthesized by a solid-state reaction, and an MgO coating precursor solution was prepared via a metal alkoxide process. LTPO–MgO core–shell particles ([MgO]/[LTPO] = 0.05 and 0.1) were obtained by wet coating process. These powders were sintered by spark plasma sintering (SPS), and after a decarbonization treatment, the microstructure, relative density, and electrochemical properties were evaluated by SEM/elemental mapping, and electrochemical impedance spectroscopy (EIS). The coating-based addition suppressed local Mg segregation and produced a denser microstructure with fewer pores than that obtained by conventional powder mixing, resulting in a marked increase in densification. A maximum relative density of 99.2% was achieved, while the electrochemical performance was optimized at [MgO]/[LTPO] = 0.05, where the grain-boundary resistance was most significantly reduced and the total lithium-ion conductivity reached 4.6 × 10^-5 S cm^-1. These results demonstrate that combining nano-coating for sintering-aid dispersion control with SPS is an effective approach to simultaneously realize densification and improved grain-boundary ionic transport.

ZrO₂, TiO₂, and TiO₂-ZrO₂ composite oxide gels prepared by the sol-gel method underwent mechanical milling treatment, and their crystallization behaviors and structures were analyzed in comparison to heat treatment. Oxide gels in the TiO₂-ZrO₂ system exhibited the formation of high-temperature, high-pressure phase ZrO₂ and Ti_1+xZrO_2(2+x) crystals through milling treatment, which were not formed by heat treatment. These results suggest that mechanical milling of sol-gel-derived gels is a method of high potentiality to obtain novel or high-performance functional oxides at ambient conditions.

Aerosol (Gas) Deposition (AD or AGD) has evolved as a film deposition technique capable of forming dense films at room temperature without heating and melting ceramic powders. This paper reviews the current understanding of the film formation mechanism in AGD (including AD), focusing particularly on alumina film formation. It outlines the effects of raw powder characteristics, deposition conditions, and advancements in deposition equipment on film structure and electrical properties.

The room-temperature film deposition mechanism has been explained by particle fragmentation and plastic deformation. However, phenomena such as plasma emission, the formation of atomic-scale bonding interfaces, and the generation of zirconia’s high-temperature phase suggest the involvement of electrostatic induction plasma and sputtering processes arising from particle charging and discharge. Building on these findings, a target-based AGD (T-AGD) method was developed, where particles collide with a target to generate reactive species, successfully forming highly insulating alumina films. Furthermore, combining this with a masking technique suppressed large particle contamination, demonstrating the feasibility of forming large-area, highly reliable insulating films. As a room-temperature film deposition technique integrating powder engineering and thin-film technology, the AGD method holds promise for further mechanism elucidation and application development.

The ultra-high-temperature sintering (UHS) method, developed by Wang et al. in 2020, utilizes carbon felt as a resistive heating element to achieve temperatures up to 3000°C within seconds. Since its introduction, UHS has been widely adopted as a superior sintering technique capable of achieving rapid densification. However, new applications leveraging its unique utility as a general heat treatment method are increasingly being reported. This paper reviews three topics conducted by our research group. WC-Co cemented carbides were fully densified in just 65 seconds at 1400°C. This rapid process successfully suppressed cobalt volatilization via insulation between carbon felts and green compacts. Microcracks on yttria-stabilized zirconia were completely healed within 20 seconds, facilitated by accelerated neck formation driven by rapid heating. A conductive TiO layer was formed on (001) surface of SrTiO₃ single crystals via UHS. The strong reducing atmosphere generated by the carbon felt induced selective strontium volatilization, creating a metallic TiO surface phase. These findings demonstrate that the UHS method is a powerful tool not only for rapid densification but also for advanced materials processing.