Conical indentation methods to determine residual stress are proposed by examining the finite element solutions based on the incremental plasticity theory. We first note that hardness depends on the magnitude and sign of residual stress and material properties and can change by up to 20% over a specific range of elastic tensile and compressive residual stress, although some prior indentation studies reported that hardness is hardly affected by residual stress. By analyzing the characteristics of conical indentation, we then select some normalized indentation parameters, which are free from the effect of indenter tip rounding. Adopting dimensional analysis, we present practical conical indentation methods for the evaluation of elastic/plastic equi- and nonequi-biaxial residual stresses. The validity of developed approaches is confirmed by applying them to the experimental evaluation of four-point bending stress.

The resurgence of nuclear power as a strategy for reducing greenhouse gas (GHG) emissions has, in parallel, revived interest in the environmental impact of actinides. Just as GHG emissions are the main environmental impact of the combustion of fossil fuels, the fate of actinides, consumed and produced by nuclear reactions, determines whether nuclear power is viewed as an environmentally “friendly” source of energy. In this article, we summarize the sources of actinides in the nuclear fuel cycle, how actinides are separated by chemical processing, the development of actinide-bearing materials, and the behavior of actinides in the environment. At each stage, actinides present a unique and complicated behavior because of the 5f electronic configurations.

Mg-based metallic glass interpenetrating phase composites (IPCs) containing 30–70 vol% titanium was fabricated in this study. The effects of reinforced phase volume fraction and interspace on the mechanical properties were investigated systematically. With increasing the volume fraction of titanium, the fracture strength and strain increased up to 1860 MPa and 44%, respectively. The results showed that the critical volume fraction (around 40%) of Ti metal should be required for significantly improving plasticity of IPC. Decreasing the interspace of the titanium phase could lead to enhancement of yield and fracture strength. The deformation behavior and strengthening mechanisms were discussed in detail.

In this study, Ti-based metallic glass matrix composites with high plasticity have been developed by controlling characteristic and volume fraction of primary phase embedded in the glass matrix. By careful alloy design procedure, the compositions of β/glass phases, which are in metastable equilibrium have been properly selected, therefore the mechanical properties can be tailored by selecting the alloy compositions between the composition of β and glass phases. The relation between the compressive yield strength and volume fraction of β phase is well described using the rule of mixtures.

In our previous paper, the expanding cavity model (ECM) and Lamé solution were used to obtain an analytical expression for the scale ratio between hardness (H) to reduced modulus (Er) and unloading work (Wu) to total work (Wt) of indentation for elastic-perfectly plastic materials. In this paper, the more general work-hardening (linear and power-law) materials are studied. Our previous conclusions that this ratio depends mainly on the conical angle of indenter, holds not only for elastic perfectly-plastic materials, but also for work-hardening materials. These results were also verified by numerical simulations.

Lead barium niobate (PBN or PbxBa1–xNb2O6) is a promising tungsten bronze ceramic system that has a morphotropic phase boundary between the orthorhombic and tetragonal phases at x ≈ 0.63, where the spontaneous polarization (Ps ≈ 60–70 μC/cm2) and other ferroelectric properties are known to be higher. However, even textured PBN60 ceramics have low Ps (∼23.9 μC/cm2) and piezoelectric charge coefficient (d33 ≈ 236 pC/N) as compared to the single crystal counterparts. The aim of this study is to control powder processing, green body formation, and sintering conditions to enhance both densification and electrical properties. Therefore, samples were prepared by tape casting methods using single phase PBN60 and reactive mixture of PbNb2O6 and BaNb2O6 powders. Three wt% excess PbO was found to be necessary for densification. Our results showed that undoped PBN60 ceramics reached Ps = 33 μC/cm2, d33 = 305 pC/N, and had a Tc = 340–350 °C. These results are much higher than the reported values in the literature, which can be attributed to the careful ceramic processing such as tape casting (e.g., homogenous green structure), annealing (e.g., control of excess grain boundary phase), and liquid phase sintering (e.g., higher densification).

Advanced spectroscopic techniques provide new and unique tools for unraveling the nature of the electronic structure of actinide materials. Inelastic neutron scattering experiments, which address temporal aspects of lattice and magnetic fluctuations, probe electromagnetic multipole interactions and the coupling between electronic and vibrational degrees of freedom. Nuclear magnetic resonance clearly demonstrates different magnetic ground states at low temperature. Photoemission spectroscopy provides information on the occupied part of the electronic density of states and has been used to investigate the momentum-resolved electronic structure and the topology of the Fermi surface in a variety of actinide compounds. Furthermore, x-ray absorption and electron energy-loss spectroscopy have been used to probe the relativistic nature, occupation number, and degree of localization of 5f electrons across the actinide series. More recently, element- and edge-specific resonant and non-resonant inelastic x-ray scattering experiments have provided the opportunity of measuring elementary electronic excitations with higher resolution than traditional absorption techniques. Here, we will discuss results from these spectroscopic techniques and what they tell us of the electronic and magnetic properties of selected actinide materials.

To study the crystallization kinetics of β-Si3N4 in Si–B–C–N polymer-derived ceramics, the amorphous ceramics with composition SiC1.6N1.0B0.4 were synthesized and then isothermally annealed at 1700, 1775 and 1850 °C. The integrated intensities of β-Si3N4 x-ray diffraction (XRD) patterns were used to examine the course of crystallization. The average size of the Si3N4 nanocrystallites was analyzed by means of the XRD measurements and energy-filtering transmission electron microscopy. It was realized that the nanocrystallite dimensions change insignificantly within the time period of crystallization; however, they depend significantly on the temperature. Subsequently, the kinetics of the β-Si3N4 crystallization was analyzed. Consequently, large activation energy in the range of 11.5 eV was estimated. Moreover, continuous nucleation and diffusion-controlled growth have been concluded as the main mechanisms of the crystallization process. Further analysis points at the crucial role of the nucleation rate in the crystallization kinetics of β-Si3N4.

Polymer electrolyte fuel cells (PEFCs) are drawing attention as energy conversion devices for next generations because of their highly efficient, environmentally benign, and portable features. In the last five decades, three distinguishable innovations were achieved in terms of proton conductive membranes and electrodes: introduction of perfluorinated membranes into PEFCs, adoption of ionomers for electrodes, and increased toughness of membranes by reinforced membranes. The efficiency, cost, and durability achieved from the past three innovations are still not enough to replace competing technologies such as combustion engines. In this review, the authors would elucidate the three different methods based on nanotechnology to overcome the limits: nanoporous carbon-supported catalysts, nanocomposite membranes, and nanostructured membrane electrode assemblies, which will bring the fourth innovation to PEFCs. With the innovation, PEFCs will fulfill the goals of being clean-energy conversion devices in the major applications of stationary, portable, and vehicle markets.

Hierarchically structured zinc oxide was prepared from zinc acetylacetonate by a microwave-assisted process. The zinc oxide formed nanoparticles that are packed in substructured spherical agglomerates with a diameter of 0.5 μm. Nitrogen adsorption, x-ray diffraction, and dilatometry were used to investigate the densification. Ion beam method was applied to prepare cross sections and enable microstructural analysis. Three regimes of microstructural evolution were identified on different scales during sintering. In the first regime, nanoparticles changed morphology and densification occurred only in the interiors of the agglomerates. In the second regime, agglomerates became hollow and built necks. Simultaneously, densification set in on the macroscopic scale. A drastic homogenization of the microstructure was observed that marked the beginning of the third regime, where densification and grain growth occurred.

Actinide materials, which are the backbone of nuclear energy, are being examined with growing interest due to the pressing need for carbon-free energy production. Prospects for advanced fuels for next-generation reactors demand a solid understanding of the physical properties of actinide materials, including thermodynamics and quantum mechanics. In this issue of MRS Bulletin, six articles give a broad overview of the current state of actinide science, illustrating current advances and emerging areas of interest in this class of materials, and how this fundamental understanding supports nuclear energy.

A modified plastic damage model that accounts for tensile damage and compressive plasticity as well as interactions among them is adopted to simulate the indentation-induced cracking of silicon under Berkovich, cube corner, and Vickers indenters. Simulations with this model capture not only the well-known cracking geometries in indented ceramics, such as radial, median, lateral, and half penny (Vickers indenter) cracks, but also the recent experimentally discovered quarter penny cracks under Berkovich and cube corner pyramidal indenters. The quarter penny cracks are found to be formed by the coalescence of radial and median cracks for the first time in the simulation. Loads at which radial and half penny cracks are initiated in silicon are generally close to the experimental values reported in the literature, and the crack lengths on the sample surface agree well with both the current experimental measurements and analytical results by fracture mechanics.

The parallel nano-scanning calorimeter (PnSC) is a silicon-based micromachined device for calorimetric measurement of nanoscale materials in a high-throughput methodology. The device contains an array of nanocalorimeters. Each nanocalorimeter consists of a silicon nitride membrane and a tungsten heating element that also serves as a temperature gauge. The small mass of the individual nanocalorimeters enables measurements on samples as small as a few hundred nanograms at heating rates up to 104 K/s. The sensitivity of the device is demonstrated through the analysis of the melting transformation of a 25-nm indium film. To demonstrate the combinatorial capabilities, the device is used to analyze a Ni–Ti–Zr sample library. The as-deposited amorphous samples are crystallized by local heating in a process that lasts just tens of milliseconds. The martensite–austenite transformation in the Ni–Ti–Zr shape memory alloy system is analyzed and the dependence of transformation temperature and specific heat on composition is revealed.

CaF2:Yb3+,Er3+ upconversion (UC) luminescence nanoparticles have been synthesized using mesoporous silica (SBA-15) as a hard template. The samples were characterized by x-ray diffraction, Fourier transform infrared spectra, field-emission scanning electron microscopy, transmission electron microscopy, and UC emission spectra, respectively. Highly crystalline cubic phase CaF2:Yb3+,Er3+ nanoparticles are uniformly distributed with an average diameter of about 40–50 nm, and the formation process is also demonstrated. The UC fluorescence has been realized in the as-prepared CaF2:Yb3+,Er3+ nanoparticles on 980-nm excitation. The UC emission transitions for 4F9/2–4I15/2 (red), 2H11/2–4I15/2 (green), 4S3/2–4I15/2 (green), and 2H9/2–4I15/2 (violet) in the Yb3+/Er3+ codoped CaF2 nanoparticles depending on pumping power and temperature have been discussed. The UC mechanism, especially the origin on the temperature-dependent UC emission intensities ratio between 2H11/2 and 4S3/2 levels, have been proposed.