Defect Grain Research Articles

Enhanced Ultrasonic Imaging and Non-Destructive Evaluation Using Angle-of-Arrival Estimation in Dimension-Reduced Beam Space

Abstract Robust defect detection in the presence of grain noise originating from material microstructures is a challenging yet essential problem in ultrasonic non-destructive evaluation (NDE). In this paper, a novel method is proposed to suppress the gain noise and enhance the defect detection and imaging. The defect echo and grain noise are distinguished through analyzing the spatial location where the echo is originating from. This is achieved by estimation of the angle of arrival (AOA) of the returned echo and evaluation of the likelihood that the echo is reflected from the point where the array is focused or otherwise from the random reflectors like the grain boundaries. The method explicitly addresses the statistical models of the defect echoes and the spatial noise across the array aperture, as well as the correlation between the flaw signal and the interfering echoes; estimates the AOA and the likelihood in a dimension-reduced beam space via a linear transformation; and determines a weighting factor based on the mean likelihood. The factors are then normalized and utilized to correct and weigh the NDE images. Experiments on industrial samples of austenitic stainless steel and INCONEL Alloy 617 are conducted with a 5 MHz transducer array, and the results demonstrate that the grain noise is reduced by about 20 dB while the defect reflection is well retained, thus the great benefits of the method on enhanced defect detection and imaging in ultrasonic NDE are validated.

Effect of Annealing Temperature on Cube Texture Formation in Ni7W/Ni12W/Ni7W Compound Substrate

This study is to fabricate a composite substrate (Ni7W/Ni12W/Ni7W) with weak magnetization, strong reinforcement, and improved cube texture via Rolling Assisted Biaxially Textured Substrates (RABiTS) route. The formation of cube texture with reduction in twin boundaries due to recrystallization annealing was investigated thoroughly. The optimized recrystallization annealing process revealed 97.4% of cube texture and 83.9% of small angle grain boundaries at an angle of (<10°). Higher W content and presence of defects (holes, dislocations, and grain boundaries) within inner layer of the substrate restricted the formation of cube texture along the normal direction (ND), as compared to rolling direction (RD). Furthermore, significant improvement in mechanical strength (σ0.2 = 205 ± 2 MPa) and saturation magnetization (2.6 emu/g) was found for Ni7W/Ni12W/Ni7W as compared to Ni7.5W substrates.

Enhancing the spin Seebeck effect by controlling interface condition in Pt/polycrystalline nickel ferrite slabs

The spin Seebeck effect (SSE) is an emergent thermoelectric phenomenon, which enables a thermal-to-electrical energy conversion via the thermal injection of spin currents from a ferromagnet (FM) into an attached paramagnetic metal (PM). Recent studies have revealed that the SSE is very sensitive to the PM/FM interface condition, suggesting a potential way to enhance the SSE by controlling the interface condition. However, most of the previous studies are limited to conventional Pt/bulk single-crystal or thin-film YIG systems, lacking consideration for mesoscale surface defects such as pores and grain grooves, which frequently exist in more prevalent bulk polycrystalline magnets. Here, we investigate the effect of interface condition on the longitudinal SSE (LSSE) in a Pt/polycrystalline NiFe2O4 (NFO) slab system. Different interface conditions are induced by treating the surface of NFO slabs with varying combinations of polishing force (Fp) and post-annealing temperature (Ta) before the Pt deposition. The resultant LSSE signals show strong correlations with different interface parameters. In particular, we find that mesoscale surface defects (cracks, pores, and grain grooves) and the surface roughness play a crucial role in determining the magnitude of LSSE signals and demonstrate that those parameters can be deliberately controlled by properly choosing Fp and Ta. We report one sample with a spin Seebeck coefficient of 0.58 μV/K, which is significantly larger than that of bulk polycrystalline magnets reported thus far.

Synthesis of a Hybrid Nanostructure of ZnO-Decorated MoS2 by Atomic Layer Deposition.

We introduce the synthesis of hybrid nanostructures comprised of ZnO nanocrystals (NCs) decorating nanosheets and nanowires (NWs) of MoS2 prepared by atomic layer deposition (ALD). The concentration, size, and surface-to-volume ratio of the ZnO NCs can be systematically engineered by controlling both the number of ZnO ALD cycles and the properties of the MoS2 substrates, which are prepared by sulfurizing ALD MoO3. Analysis of the chemical composition combined with electron microscopy and synchrotron X-ray techniques as a function of the number of ZnO ALD cycles, together with the results of quantum chemical calculations, help elucidate the ZnO growth mechanism and its dependence on the properties of the MoS2 substrate. The defect density and grain size of MoS2 nanosheets are controlled by the sulfurization temperature of ALD MoO3, and the ZnO NCs in turn nucleate selectively at defect sites on MoS2 surface and enlarge with increasing ALD cycle numbers. At higher ALD cycle numbers, the coalescence of ZnO NCs contributes to an increase in areal coverage and NC size. Additionally, the geometry of the hybrid structures can be tuned by changing the dimensionality of the MoS2, by employing vertical NWs of MoS2 as the substrate for ALD ZnO NCs, which leads to improvement of the relevant surface-to-volume ratio. Such materials are expected to find use in newly expanded applications, especially those such as sensors or photodevices based on a p-n heterojunction which relies on coupling transition-metal dichalcogenides with NCs.

The influence of AlN buffer layer on the growth of self-assembled GaN nanocolumns on graphene

GaN nanocolumns were synthesized on single-layer graphene via radio-frequency plasma-assisted molecular beam epitaxy, using a thin migration-enhanced epitaxy (MEE) AlN buffer layer as nucleation sites. Due to the weak nucleation on graphene, instead of an AlN thin-film we observe two distinguished AlN formations which affect the subsequent GaN nanocolumn growth: (i) AlN islands and (ii) AlN nanostructures grown along line defects (grain boundaries or wrinkles) of graphene. Structure (i) leads to the formation of vertical GaN nanocolumns regardless of the number of AlN MEE cycles, whereas (ii) can result in random orientation of the nanocolumns depending on the AlN morphology. Additionally, there is a limited amount of direct GaN nucleation on graphene, which induces non-vertical GaN nanocolumn growth. The GaN nanocolumn samples were characterized by means of scanning electron microscopy, transmission electron microscopy, high-resolution X-ray diffraction, room temperature micro-photoluminescence, and micro-Raman measurements. Surprisingly, the graphene with AlN buffer layer formed using less MEE cycles, thus resulting in lower AlN coverage, has a lower level of nitrogen plasma damage. The AlN buffer layer with lowest AlN coverage also provides the best result with respect to high-quality and vertically-aligned GaN nanocolumns.

Amorphous intergranular films mitigate radiation damage in nanocrystalline Cu-Zr

Nanocrystalline metals are promising radiation tolerant materials due to their large interfacial volume fraction, but irradiation-induced grain growth can eventually degrade any improvement in radiation tolerance. Therefore, methods to limit grain growth and simultaneously improve the radiation tolerance of nanocrystalline metals are needed. Amorphous intergranular films are unique grain boundary structures that are predicted to have improved sink efficiencies due to their increased thickness and amorphous structure, while also improving grain size stability. In this study, ball milled nanocrystalline Cu-Zr alloys are heat treated to either have only ordered grain boundaries or to contain amorphous intergranular films distributed within the grain boundary network, and are then subjected to in situ transmission electron microscopy irradiation and ex situ irradiation. Differences in defect density and grain growth due to grain boundary complexion type are then investigated. When amorphous intergranular films are incorporated within the material, fewer and smaller defect clusters are observed while grain growth is also limited, leading to nanocrystalline alloys with improved radiation tolerance.

Nanoscale pathways for human tooth decay – Central planar defect, organic-rich precipitate and high-angle grain boundary

Understanding the pathways and mechanisms of human tooth decay is central to the development of both prophylaxes and treatments, but only limited information is presently available about the initiation of caries at the nanoscale. By combining atom probe tomography and high-resolution electron microscopy, we have found three distinct initial sites for human dental enamel dissolution: a) along the central dark line (CDL) within carbonated apatite nanocrystals, b) at organic-rich precipitates and c) along high-angle grain boundaries.3D maps of the atoms within hydroxyapatite nanocrystallites in sound and naturally-decayed human dental enamel reveal a higher concentration of Mg and Na in the CDL. The CDL is therefore thought to provide a pathway for the exchange of ions during demineralization and remineralization. Mg and Na enrichment of the CDL also suggests that it is associated with the ribbon-like organic-rich precursor in amelogenesis. Organic-rich precipitates and high-angle grain boundaries were also shown to be more vulnerable to corrosion while low-angle grain boundaries remained intact. This is attributed to the lower crystallinity in these regions.

Microstructure evolution and mechanical property response via 3D printing parameter development of Al–Sc alloy

ABSTRACT Three-dimensional (3D) printed Sc-modified Al alloy by powder bed fusion (PBF) provides significant strength and ductility without hot tearing during the process. This kind of 3D-printable high specific strength materials exhibits great potential in lightweight applications. Due to the lesser design limitation through the 3D printing process, the degree of lightweight is greatly affected by the specific strength of the materials. Hence, to further improve the mechanical properties of the material through process optimisation or post-treatment is of great importance. Microstructure feature variations due to different processing parameters are well known for traditional processes and materials. This study explores the parameter–microstructure–performance relationship of 3D printed Sc-modified Al alloys from the perspective of melt pool interactions. According to the stress concentration effect and Hall–Petch effect, the mechanical properties of the 3D printed materials vary greatly depending on the difference in defect size, shape and grain size.

Forming-Free SiGeOx/TiOy Resistive Random Access Memories Featuring Large Current Distribution Windows

Optimal device integrity was achieved in Ni/SiGeOx/TiOy/TaN resistive memory by using a forming-free switch with a low switching power of 790 μW, stable endurance of 104 cycles, optimal retention time of 105 s, resistance window of at least 1150×, and tight current distributions at 85 °C. These characteristics are attributed to the low current switching obtained using SiGeOx with a high oxygen vacancy density and highly defective TiOy grain boundaries.

Influence of cooling path after rolling on sulfide stress cracking behavior for casing steel

Interrupted accelerated cooling (IAC) in comparison with normal air cooling after rolling is introduced into the production of the API-5CT-C110 casing steel. Sulfide stress cracking (SSC) resistance is improved by IAC processing without compromising strength. Multiple characterizations combined with hydrogen permeation tests are performed to reveal the mechanism of SSC behavior with respect to hydrogen interactions with metallurgical defects (grain boundaries, dislocations and precipitates). The results indicate a low dislocation density and increased amount of irreversible traps are responsible for the superior SSC resistance of the IAC specimen. A model of local hydrogen concentration is proposed to illustrate SSC susceptibility.

Stress Localization Resulting from Grain Boundary Dislocation Interactions in Relaxed and Defective Grain Boundaries

Large-scale molecular dynamics simulations are used to study strain and stress localization in atomistic polycrystalline FCC digital samples in a thin-film configuration, deformed in tension. Special focus is placed on the effects of additional grain boundary disorder on the dislocation–grain boundary interaction. The development of the localized stress and strain regions is studied as dislocations are emitted from and arrive at grain boundaries. Digital samples with two different degrees of disorder in the grain boundaries but otherwise identical microstructures are compared in order to understand the effects of additional defects on the stress concentration that develops at the grain boundaries. Localization phenomena are found to depend on the details of the grain boundary defect structure and relaxation state. The results clearly show that the samples with more disordered grain boundaries are more prone to strain and stress localization, with a higher fraction of atoms experiencing extreme deformation. The simulation results are validated by comparison with the predictions of continuum theories and experimental measurements of localized stress performed in austenitic stainless steel.

Effect of intrinsic defects on the thermal conductivity of PbTe from classical molecular dynamics simulations

Despite being the archetypal thermoelectric material, still today some of the most exciting advances in the efficiency of these materials are being achieved by tuning the properties of PbTe. Its inherently low lattice thermal conductivity can be lowered to its fundamental limit by designing a structure capable of scattering phonons over a wide range of length scales. Intrinsic defects, such as vacancies or grain boundaries, can and do play the role of these scattering sites. Here we assess the effect of these defects by means of molecular dynamics simulations. For this we purposely parametrize a Buckingham potential that provides an excellent description of the thermal conductivity of this material over a wide temperature range. Our results show that intrinsic point defects and grain boundaries can reduce the lattice conductivity of PbTe down to a quarter of its bulk value. By studying the size dependence we also show that typical defect concentrations and grain sizes realized in experiments normally correspond to the bulk lattice conductivity of pristine PbTe.

Highly Sensitive, Fast Response Perovskite Photodetectors Demonstrated in Weak Light Detection Circuit and Visible Light Communication System

Organic-inorganic hybrid perovskite (OIHP) photodetectors have presented unprecedented device performance mainly owing to outstanding material properties. However, the solution-processed OIHP polycrystalline thin films with defective surface and grain boundaries always impair the key parameter of photodetectors. Herein, a nonfullerene passivation layer exhibits more efficient passivation for OIHP materials to dramatically reduce the trap density of state, yielding a dark current as low as 2.6 × 10-8 A cm-2 under -0.1 V. In addition, the strong absorption in near-infrared (NIR) region of nonfullerene/C60 heterojunction broadens the detectable range to over 900 nm by effective charge transport, ultimately leading to a specific detectivity of 1.45 × 1012 and 7.37 × 1011 cm Hz1/2 W-1 at 650 and 820 nm, respectively. Encouragingly, the response speed of 27 ns is obtained at 0.6 mm2 of device area by removing constrain from the resistance-capacitance constant. Moreover, the prominent practical application of the photodetector is demonstrated in a weak light detection circuit and a visible light communication system. It is believed that the OIHP photodetectors with high sensitivity, NIR photoresponse, and ultrafast speed would pave the way to commercial applications.

Effects of annealing under fixed temperature and cyclic temperature on strength and microstructure of Al–Mg–Mn-Sc-Zr alloy

Fractures sometimes are located at heat affected zone rather than weld zone in weldments. This phenomenon may be related with the thermal shock which impacts the heat affected zone. In order to study this mechanism, the Al–Mg–Mn-Sc-Zr alloy plates were processed by different heat treatment methods. One method is persevering the samples at 550 °C and the other is heating the samples to 550 °C then cooling to room temperature and recycling this process to simulate welding thermal shock. The results show that tensile properties of the samples under fixed temperature (FT) decrease only a little at first. However, the strength of the samples under cyclic temperature (CT) decrease dramatically after just one cycle. This is different from traditional perception. Generally, dislocations would move and be polygonised at high temperature, which accords to the microstructure of FT sample. But in CT sample, the phenomenon of polygonization is not uniform. The dislocations tend to aggregate at the place where particle number is high, like tiny defects in grain cutting the continuity of fiber texture. Therefore, the strength decreases a lot.

Improving the surface hardness number of subsoil plow chisel using water-jet preening

This study discusses the effects of pressure in waterjet peening (WJP) of subsoil plow chise. It was made from austenitic stainless steel 301 JIS standard S30100. Analysis of surface integrity and change of surface hardness number is used to evaluate the performance of various parameters in the WJP process. The article summarizes information about austenitic stainless steel physically-mechanical of subsoil plow chisel that is most useful for soil tillage. The subsoil chisel was given surface treatment WJP process with a variation of pressure and time. The physical properties of subsoil plow chisel from various pressure and time of WJP are analyzed. The findings of this study indicated that surface treatment with waterjet peening could increase the surface hardness number and the hardening layer fromaustenitic stainless steel 301 (material of subsoil plow chisel).Treats the surface with WJP pressure 250 MPa and time 3 hours results in a higher increase in surface hardness number up to 41% and 151% greater than the raw material respectively. Also, a deeper hardening layer to depth 250 and 500 μm each produced. Next, the cross-sectional micro structure shows the density is higher than the slip band in the defective grain of specimens that have undergone the WJP process at the time and higher pressure. However, the number of slip bands in grain defects decreases with the pressure drop.

Pyrophosphate-fructose 6-phosphate 1-phosphotransferase (PFP1) regulates starch biosynthesis and seed development via heterotetramer formation in rice (Oryza sativa L.).

SummaryPyrophosphate‐fructose 6‐phosphate 1‐phosphotransferase (PFP1) reversibly converts fructose 6‐phosphate and pyrophosphate to fructose 1, 6‐bisphosphate and orthophosphate during glycolysis, and has diverse functions in plants. However, mechanisms underlying the regulation of starch metabolism by PFP1 remain elusive. This study addressed the function of PFP1 in rice floury endosperm and defective grain filling. Compared with the wild type, pfp1‐3 exhibited remarkably low grain weight and starch content, significantly increased protein and lipid content, and altered starch physicochemical properties and changes in embryo development. Map‐based cloning revealed that pfp1‐3 is a novel allele and encodes the regulatory β‐subunit of PFP1 (PFP1β). Measurement of nicotinamide adenine dinucleotide (NAD+) showed that mutation of PFP1β markedly decreased its enzyme activity. PFP1β and three of four putative catalytic α‐subunits of PFP1, PFP1α1, PFP1α2, and PFP1α4, interacted with each other to form a heterotetramer. Additionally, PFP1β, PFP1α1 and PFP1α2 also formed homodimers. Furthermore, transcriptome analysis revealed that mutation of PFP1β significantly altered expression of many essential enzymes in starch biosynthesis pathways. Concentrations of multiple lipid and glycolytic intermediates and trehalose metabolites were elevated in pfp1‐3 endosperm, indicating that PFP1 modulates endosperm metabolism, potentially through reversible adjustments to metabolic fluxes. Taken together, these findings provide new insights into seed endosperm development and starch biosynthesis and will help in the breeding of rice cultivars with higher grain yield and quality.

The Model of Decomposition of a Fe–Cu Alloy with Concentration-Depending Interatomic Interactions

The thermodynamics and kinetics of decomposition of a Fe–Cu alloy are investigated in the context of a simple ab initio parameterization model taking into account the concentration dependence of the magnetic contribution to the free energy. It is shown that taking into account a difference between the short-range and long-range magnetic orders near the Curie temperature is very important for calculating the solubility of copper in iron. The solubility of copper in bcc iron and the stability limit of a homogeneous state (physical spinodal) are evaluated via the kinetic Monte Carlo method. The impact of structural defects (dislocations and grain boundaries) on these curves, as well as on the kinetic time–temperature—transformation (TTT) diagram, is also discussed.

Distinct Catalytic Reactivity of Sn Substituted in Framework Locations and at Defect Grain Boundaries in Sn-Zeolites

Measurements of turnover rates of gas-phase bimolecular ethanol dehydration to diethyl ether (404–438 K) on a suite of hydrophobic and hydrophilic Sn-zeolites (Sn-Beta, Sn-BEC, Sn-MFI) of varying S...

Oligomeric Silica-Wrapped Perovskites Enable Synchronous Defect Passivation and Grain Stabilization for Efficient and Stable Perovskite Photovoltaics

The intrinsic instability of hybrid perovskite materials induced by defect states arises as one major challenge hampering the commercialization of perovskite solar cells (PSCs). Here, we report a f...

Effects of grain boundaries on conversion efficiencies of single-crystal-like GaAs thin-film solar cells on flexible metal tapes

We present a numerical simulation study of the effects of low-angle grain boundaries (GBs) in a single-crystal-like GaAs thin-film material on its photovoltaic performance. Here, 1D and 2D modeling are employed to simulate a solar-cell (SC) device based on the properties of single-crystal-like GaAs thin films grown on metal tape. Properties include minority carriers’ mobility, carrier lifetimes, and diffusion length. The 1D model, by incorporating a uniform biaxially textured GaAs compared to single crystal GaAs, predicts an efficiency ∼21% for average carrier lifetimes of 1 ns. This result is not consistent with an experimental results showing an efficiency of 4.3%. 1D simulation generally works well for the prediction of conventional crystalline SC I-V characteristics, but it fails for newly-developed single-crystal-like GaAs SC devices with different material properties and non-vertical device geometry. Hence, we develop a 2D model to study the effect of localized recombination centers in the material by defining different regions of defective low-angle grain boundaries and single crystalline intra-grains. The 2D model is comparable to the experimental results mainly due to its capability to consider localized material inhomogeneity and lateral carriers dynamic. The effect of grain boundary density on SC performance is studied by 2D modeling. Increasing the grain size of GaAs from 2 μm to 50 μm can improve efficiency from 4.8% to 12.3%. The open-circuit voltage (Voc) shows more sensitivity to varying grain boundary densities than other SC characteristic factors. The 2D model is also employed to study bulk passivation of GBs and suggests that an efficiency of ∼19.5% is achievable in the single-crystal-like GaAs SCs even with a small grain size of 2 μm, if effective grain boundary passivation is applied.