Preface to the Special Issue on Advanced Microstructural Characterization of Materials

Microstructural characterization is a vital part in materials science, as it plays a key role in understanding the structure-property relationship in materials. Various advanced microstructural characterization techniques have emerged, for example, scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, high resolution (scanning) transmission electron microscopy, electron backscatter diffraction, energy dispersive x-ray spectroscopy, electron energy loss spectroscopy, precession electron diffraction, energy-filtered transmission electron microscopy, and atom probe tomography. The applications of these techniques have greatly advanced the understanding of material microstructures on different scales from micrometer to atomic scale. Advanced microstructural characterization can be applied to a variety of materials such as metals, alloys, ceramics, polymers and composites

Deformation mechanisms in bulk nanostructured metals and strategies to improve their ductility

Bulk nanostructured (NS) metals, with structural units falling in the nanometer range, are of interest in part as a result of drastically improved strength over that corresponding to conventional coarse-grained (CG) materials. Examples of ultrahigh-strength bulk NS metals will be provided in this lecture and strengthening mechanisms will be briefly discussed. In the case of conventional CG metals, plastic deformation is based on the motion of lattice dislocations, which are usually unit dislocations nucleated inside grain interiors or at GBs. In the case of bulk NS metals, with significantly reduced grain size and therefore very limited space in grain interiors, and drastically increased grain boundary (GB) volume fraction, the deformation mechanisms are different from those -corresponding to CG metals. In this presentation, deformation mechanisms in bulk NS metals will be reviewed and discussed, including full/partial dislocation emission from GBs, deformation twinning, GB sliding, grain rotation induced grain coalescence, stress-coupled GB migration, and de-twinning. Deformation mechanisms during dynamic and cyclic deformation of bulk NS metals, e.g., grain rotation induced grain coalescence and de-twinning, will be discussed in detail. Stress/deformation induced grain growth, with underlying deformation mechanisms of grain rotation-coalescence and stress-coupled GB migration, will be discussed in detail, and a theoretical framework that incorporates the influence of second-phase particles and solute/impurity segregation at GBs on grain growth during hot deformation will be formulated and discussed. Owing to the different deformation mechanisms in bulk NS metals, and particularly to the limited dislocation accumulation and therefore little strain hardening during deformation, bulk NS metals tend to have limited ductility. Strategies to improve ductility will be discussed in detail, e.g., bimodal/multimodal grain size distribution, nanoscale twins, low dislocation density, second-phase nanoscale precipitation within grains, and phase transformations during deformation

A Naturalist Version of Confucian Morality for Human Rights

This article analyzes the source of Confucian universal morality and human dignity from the perspective of the classic saying, “what follows the dao is good, and what dao forms is nature” (jishan chengxing) found in the Great Commentaries of the Book of Changes. From a Classical Confucian perspective, human nature is generated by the natural dao of tian, so human dignity and morality also emerge from the natural dao of tian. This article discusses the relationship between the Confucian dao of tian and the moral notion of human rights which ensues from the historical tradition of Chinese exegesis on this subject. Specifically, the authors reconstruct a naturalist version of Confucian morality which inherently motivates the beneficial outcomes generally associated with the modern Western conception of human rights. The authors argue that such a framework, which would draw upon Confucian “natural goodness within human nature” differs significantly from the more commonly accepted Mencian version of human morality dependent upon the premise that “human nature is good”. This intra-mural differentiation within Chinese philosophy can be helpful in structuring dialogue with various Western theories of human rights

Additive Manufacturing Of (MgCoNiCuZn)O High-entropy Oxide Using A 3D Extrusion Technique And Oxide Precursors

This report presents an additive manufacturing approach, for the first time, to producing high-entropy oxides (HEOs) using a 3D extrusion-based technique with oxide precursors. The precursors were prepared by a wet chemical method from sulfates. Additives were utilized to optimize the rheological properties of the printing inks with these precursors, and the properties of the printed HEOs were improved by increasing the solid content of the inks. When ink with a solid content of 78 wt% was used for printing, the resulting HEO exhibited a relative density of 92% and a high dielectric constant after undergoing pressure less sintering at 800 °C. Compared to traditional methods of manufacturing HEOs, the 3D extrusion technique is a very promising method for producing HEOs with complex geometries

Additive Manufacturing Of SiC-Sialon Refractory With Excellent Properties By Direct Ink Writing

Additive manufacturing of SiC-Sialon refractory with complex geometries was achieved using direct ink writing processes, followed by pressure less sintering under nitrogen. The effects of particle size of SiC powders, solid content of slurries and additives on the rheology, thixotropy and viscoelasticity of ceramic slurries were investigated. The optimal slurry with a high solid content was composed of 81 wt% SiC (3.5 µm+0.65 µm), Al2O3 and SiO2 powders, 0.2 wt% dispersant, and 2.8 wt% binder. Furthermore, the accuracy of the structure of specimens was improved via adjustment of the printing parameters, including nozzle size, extrusion pressure, and layer height. The density and flexural strength of the printed SiC-Sialon refractory sintered at 1600 °C were 2.43 g/cm3 and 85 MPa, respectively. In addition, the printed SiC-Sialon crucible demonstrated excellent corrosion resistance to iron slag. Compared to the printed crucible bottom, the crucible side wall was minimally affected by molten slag

Additive Manufacturing of Continuous Carbon Fiber-Reinforced Sic Ceramic Composite with Multiple Fiber Bundles by an Extrusion-Based Technique

Due to the high cost, complex preparation process and difficulty in structural design, the traditional methods for carbon fiber reinforced SiC ceramic composite preparation have great limitations. This paper presents a technique for the additive manufacturing multiple continuous carbon fiber bundle-reinforced SiC ceramic composite with core-shell structure using an extrusion-based technique. A conventional nozzle system was modified to print simultaneously a water based SiC paste with continuous carbon fibers. Different levels of binder contents were investigated to optimize the stickiness, viscosity, thixotropy and viscoelasticity of the paste. After sintering, SiC whiskers were generated on the surface of fiber, which is conjectured to be due to the reaction between SiO and carbon fiber at high temperature. The continuous carbon fiber reinforced SiC ceramic composite exhibited non-brittle fracture. The flexural strength of the additively manufactured Cf/SiC composites improved from 162 MPa with no fiber bundles to a maximum of 219 MPa with three fiber bundles

Improving Strength and Microstructure of SiC Reticulated Porous Ceramic through In-Situ Generation of SiC Whiskers within Hollow Voids

SiC Reticulated Porous Ceramic with Excellent Strength and High-Density Ceramic Struts Was Successfully Prepared using the Polymer Replica Method, Followed by Pressureless Sintering under a Buried Charcoal Atmosphere. First, a Polyurethane (PU) Template Was Coated with a Si Slurry and Then a SiC-Containing Slurry, and Subsequently Heated under the Buried Charcoal Atmosphere. to Ensure Excellent Coating Ability of the Slurries, the Viscosity, Thixotropy, and Yield Stresses of the Si Slurry Were Optimized by Adjusting the Content of the Thickening Agent. during Heating, Si in the Coating Layer Reacted with the Residual C and CO Gas from the PU Template and Buried Charcoal, Forming SiC Whiskers that Filled Hollow Voids within the SiC Struts. Additionally, Catalyst Ferric Nitrate Was Added to the Si Slurry to Promote the Generation and Growth of SiC Whiskers. as a Result, When Compared to the Untreated SiC Reticulated Porous Ceramic, the SiC Reticulated Porous Ceramic Pre-Coated with Si Layers Exhibited Significant Improvements in Mechanical Strength and Thermal Shock Resistance, Despite Minor Differences in Porosity. Furthermore, an Industrial Test Conducted in the Copper Smelting Industry Showed that the Structure of SiC Reticulated Porous Ceramic, Prepared in This Study and Used as Filters, Remained Intact Even after 7 Days of Continuous Use. Meanwhile, a Significant Number of Inclusions Was Adhered to the Surfaces of the Filters. Therefore, the Processes Combined with In-Situ Generation of SiC Whiskers is an Ideal and Low-Cost Method for Fabricating SiC Filters with Excellent Properties

Microstructure, Mechanical Properties and Oxidation Behavior of Refractory Multi-Principal Element Alloys by Laser Remelting and Conventional Manufacturing

Refractory Multi-Principal Element Alloys (RMPEAs), HfNbTaTiZr, (HfNbTaTiZr)9Cr, and (HfNbTaTiZr)9Al, Were Manufactured using Vacuum Arc Melting Followed by Laser Remelting to Mimic Additive Manufacturing. the Microhardness of the As-Cast HfNbTaTiZr, (HfNbTaTiZr)9Cr, and (HfNbTaTiZr)9Al Samples after Arc Melting Was Measured as 6.20, 7.63, and 6.89 Gpa, respectively. after Laser Remelting and Re-Solidification, the Hardness Increased by ~ 30% for Each Composition; the Hardest Was (HfNbTaTiZr)9Cr Measured at 9.60 GPa, While the Softest Was HfNbTaTiZr with a Hardness of 8.42 GPa, Which Was Still Harder Compared to All the Other Samples. the Addition of Al and Cr Led to Enhanced Oxidation Resistance for the Respective RMPEA Systems. the Al-Containing Composition Showed the Best Oxidation Resistance for the Samples; However, after Laser Remelting, the Cr-Containing RMPEA Had the Best overall Oxidation Resistance, and the Increase in Weight after Oxidation Dropped by 42% When compared to that for the As-Cast Alloy. Laser Remelting the RMPEAs Led to an Improvement in Mechanical Properties; It Also Resulted in Enhanced Oxidation Resistance for (HfNbTaTiZr)9Cr. However, Laser Remelting Barely Changed the Oxidation Resistance for (HfNbTaTiZr)9Al, and It Decreased the Oxidation Resistance for HfNbTaTiZr. These Phenomena Are Related to Microstructure Changes Induced by the Laser Remelting/additive Manufacturing Compared to Conventional Casting-Based Manufacturing