Non-homogeneous Microstructures Research Articles

Three-Dimensional Columnar Microstructure Representation Using 2D Electron Backscatter Diffraction Data for Additive-Manufactured Haynes®282®.

This study provides a methodology for exploring the microstructural and mechanical properties of the Haynes®282® alloy produced via the Powder Bed Fusion-Electron Beam (PBF-EB) process. Employing 2D Electron Backscatter Diffraction (EBSD) data, we have successfully generated 3D representations of columnar microstructures using the Representative Volume Element (RVE) method. This methodology allowed for the validation of elastic properties through Crystal Elasticity Finite Element (CEFE) computational homogenization, revealing critical insights into the material behavior. This study highlights the importance of accurately representing the grain morphology and crystallographic texture of the material. Our findings demonstrate that created virtual models can predict directional elastic properties with a high level of accuracy, showing a maximum error of only ~5% compared to the experimental results. This precision underscores the potential of our approach for predictive modeling in Additive Manufacturing (AM), specifically for materials with complex, non-homogeneous microstructures. It can be concluded that the results uncover the intricate link between microstructural features and mechanical properties, underscoring both the challenges encountered and the critical need for the accurate representation of grain data, as well as the significance of achieving a balance in EBSD area selection, including the presence of anomalies in strongly textured microstructures.

Preparation and Characterization of Novel Green Seaweed Films from Ulva rigida.

Ulva rigida green seaweed is an abundant biomass consisting of polysaccharides and protein mixtures and a potential bioresource for bioplastic food packaging. This research prepared and characterized novel biodegradable films from Ulva rigida extracts. The water-soluble fraction of Ulva rigida was extracted and prepared into bioplastic films. 1H nuclear magnetic resonance indicated the presence of rhamnose, glucuronic and sulfate polysaccharides, while major amino acid components determined via high-performance liquid chromatography (HPLC) were aspartic acid, glutamic acid, alanine and glycine. Seaweed extracts were formulated with glycerol and triethyl citrate (20% and 30%) and prepared into films. Ulva rigida films showed non-homogeneous microstructures, as determined via scanning electron microscopy, due to immiscible crystalline component mixtures. X-ray diffraction also indicated modified crystalline morphology due to different plasticizers, while infrared spectra suggested interaction between plasticizers and Ulva rigida polymers via hydrogen bonding. The addition of glycerol decreased the glass transition temperature of the films from -36 °C for control films to -62 °C for films with 30% glycerol, indicating better plasticization. Water vapor and oxygen permeability were retained at up to 20% plasticizer content, and further addition of plasticizers increased the water permeability up to 6.5 g·mm/m2·day·KPa, while oxygen permeability decreased below 20 mL·mm/m2·day·atm when blending plasticizers at 30%. Adding glycerol efficiently improved tensile stress and strain by up to 4- and 3-fold, respectively. Glycerol-plasticized Ulva rigida extract films were produced as novel bio-based materials that supported sustainable food packaging.

Carmoisine azo dye-modified Al/p-Si junction

This study investigates the impact of a Carmoisine azo dye layer on electronic transport at the p-silicon/Al interface. The morphology of the Carmoisine azo layer is characterized using atomic force microscopy (AFM). Various spectroscopic measurements, including nuclear magnetic resonance (NMR), ultraviolet–visible (UV–Vis), and Fourier transform infrared (FTIR) spectroscopy, are employed to analyze the Carmoisine dye molecule. The direct and indirect band gap values of the Carmoisine dye molecule, prepared in methanol solvent, are determined to be Eg,1 = 2.15 eV and 2.06 eV (D band) and Eg,2 = 3.54 eV and 3.35 eV (C band), respectively. Results indicate that the Carmoisine film on a glass slide consists of non-homogeneous microstructures, with a surface roughness of 16.76 nm. A spin coater is used to form an Al/Carmoisine/p-Si device, which is a cost-effective and readily scalable approach for creating semiconductor films. The basic contact parameters of the Al/p-Si and Al/Carmoisine/p-Si contacts are measured using current-voltage (IV) and capacitance-voltage (CV) techniques. The Al/Carmoisine/p-Si device exhibits good rectifying behaviour, with an ideality factor value of 1.547, indicating that the Carmoisine azo dye used as the interface material enhances the junction's performance and reduces the ideality factor. Barrier height (BH) parameters are calculated to be 0.770 eV, 0.733 eV, and 0.799 eV using the lnI-V, Cheung, and Norde techniques, respectively. The interfacial dipole created by passivation of the film causes the Carmoisine interlayer to raise the BH, resulting in an improved interface region for Al/p-Si structures. The extracted interfacial level concentration (Nss) of the Al/Carmoisine/p-Si junction is lower than that of the Al/p-Si contact, indicating that the Carmoisine dye molecule reduces the Nss value. Furthermore, the reverse bias 1/C2-V characteristic is employed to analyze the barrier height values and compare the findings to those from the IV method. The results show that the thin Carmoisine azo dye layer decreases leakage current and defect-trapped charge density, enhancing the reliability and performance of the devices. This study contributes a new organic electronic material, Carmoisine dye, to the literature on semiconductor devices.

Polyesters Incorporating Gallic Acid as Oxygen Scavenger in Biodegradable Packaging.

Biodegradable polyesters polybutylene succinate (PBS) and polybutylene adipate-co-terephthalate (PBAT) were blended with gallic acid (GA) via cast extrusion to produce oxygen scavenging polymers. The effects of polyesters and GA contents (5 to 15%) on polymer/package properties were investigated. Increasing GA formed non-homogeneous microstructures and surface roughness due to immiscibility. GA had favorable interaction with PBAT than PBS, giving more homogeneous microstructures, reduced mechanical relaxation temperature, and modified X-ray diffraction and crystalline morphology of PBAT polymers. Non-homogenous dispersion of GA reduced mechanical properties and increased water vapor and oxygen permeability by two and seven folds, respectively. Increasing amounts of GA and higher humidity enhanced oxygen absorption capacity, which also depended on the dispersion characteristics of GA in the matrices. PBAT gave higher oxygen absorption than PBS due to better dispersion and higher reactive surface area. GA blended with PBAT and PBS increased oxygen scavenging activity as sustainable active food packaging using functional biodegradable polymers.

Dynamic Recrystallization and Its Effect on Superior Plasticity of Cold-Rolled Bioabsorbable Zinc-Copper Alloys.

High plasticity of bioabsorbable stents, either cardiac or ureteral, is of great importance in terms of implants’ fabrication and positioning. Zn-Cu constitutes a promising group of materials in terms of feasible deformation since the superplastic effect has been observed in them, yet its origin remains poorly understood. Therefore, it is crucial to inspect the microstructural evolution of processed material to gain an insight into the mechanisms leading to such an extraordinary property. Within the present study, cold-rolled Zn-Cu alloys, i.e., Zn with addition of 1 wt.% and 5 wt.% of Cu, have been extensively investigated using scanning electron microscopy as well as transmission electron microscopy, so as to find out the possible explanation of superior plasticity of the Zn-Cu alloys. It has been stated that the continuous dynamic recrystallization has a tremendous impact on superior plasticity reported for Zn-1Cu alloy processed by rolling to 90% of reduction rate. The effect might be supported by static recrystallization, provoking grain growth and thereby yielding non-homogeneous microstructures. Such heterogeneous microstructure enables better formability since it increases the mean free path for dislocation movement.

Active meat packaging from thermoplastic cassava starch containing sappan and cinnamon herbal extracts via LLDPE blown-film extrusion

• Active packaging from conventional blown extrusion of herb compounding TPS/LLDPE. • Films with sappan and cinnamon gave antimicrobial and preserved redness of beef. • Cinnamon gave higher compatible nano- and micro-structures between starch and LLDPE. Compounding of starch and herbal extracts containing antimicrobial functions possibly produces active packaging to preserve food quality. Active meat packaging was developed from thermoplastic starch (TPS) containing herbal extracts namely sappan or cinnamon powders via LLDPE blown-film extrusion. Higher TPS and herbal contents caused dispersion of clumps within film matrices, giving decreased mechanical properties (60–80 % for tensile strength and 30–90 % for elongation at break) due to non-homogeneous microstructures. Surface topography indicated increased roughness by 2.0–4.0 times with addition of TPS and herbal extracts and revealed nanovoids in films containing high sappan contents. Infrared spectra indicated hydrogen bonding between starch and herbal extracts which limited disruptions of starch granules during extrusion. Increased TPS raised water vapor permeability (WVP) but decreased oxygen permeability (OP) due to increased hydrophilicity of the film matrices. Cinnamon gave higher WVP (1.7–2.0 times) than sappan but similar OP. Increased herbal contents at 2 times increased OP by 1.8–2.9 times due to the formation of microvoids. Furthermore, films were used as minced beef packaging (direct contact) and determined for meat appearance and microbial counts. Films containing ≥ 8.6 % sappan and ≥ 6.7 % cinnamon showed preserved redness of packaged minced beef due to phenolic interaction. Moreover, films containing ≥ 3.3 % herbal extracts (sappan and cinnamon) gave lower total microbial counts in packaged meat due to antimicrobial capacity of sappan and cinnamon extracts, prolonging the shelf-life of minced beef. TPS films containing sappan and cinnamon extracts effectively preserved redness and delayed microbial growth, producing active packaging.

Microstructure development in Laser Metal Deposition of Ti-5553

Laser Metal Deposition (LMD) is promoting increased interest with regard to manufacturing parts of complex geometry. It is especially important with respect to manufacturing cost reductions for relatively expensive Titanium alloys. The rapid and directional cooling processes inherent with LMD produce nonhomogeneous microstructures and large residual stresses. Knowledge of the LMD process to optimise deposited microstructures is in high demand. The high-strength β-Titanium alloy, Ti-5Al-5Mo-5V-3Cr (Ti-5553), was deposited using LMD on to a heat-treated substrate of the same alloy. Two blocks of 15 x 15 x 6.4 mm3 were made with different laser power to powder feed rate ratios followed by microstructural analyses. Both blocks have almost identical geometry and density. Low ratios of laser power to powder feed rate resulted in pure β phase in the deposited layers and the re-melted material in the substrate. High ratios resulted in larger columnar β grains, the precipitation of nano-scaled α, and a pronounced increase in microhardness ≈1 mm above and below the substrate interface. This could be detrimental to the mechanical properties of the substrate and highlights the importance of the optimisation of LMD parameters.

Wire-arc additive manufacturing H13 part: 3D pore distribution, microstructural evolution, and mechanical performances

The crack-free H13 block was deposited through additive manufacturing with the cold metal transfer technology. The internal 3D pore distribution, the microstructural evolution, and the mechanical performances were explored. A negligible porosity with dispersive-distribution and spherical-shape below 0.001% guaranteed a sound metallurgical bonding within the as-deposited part. The martensite laths growth direction varied dramatically with a very short position variation, as well as the block-like size-inconsistent δ-ferrite presence in the overlap zone, which were mainly generated by the thermal flux direction from the center to margin within a single arc track. Massive second-phase particles with morphology-diversity and size-nonuniformity were precipitated, indicating a strong dependency with the intrinsic heating treatment. The enhanced microhardness in the body zone was attributed to the martensite strengthening mechanism, while slightly low hardness was produced due to the soft δ-ferrite formation. When compared with the other zones, the enhanced ultimate tensile strength was obtained in the body zone at the expense of tensile ductility, revealing a positive relationship with the rise of hard martensite percentage. This work demonstrated that a crack-free H13 block with limited porosity and desirable mechanical properties was deposited using the present technology, despite the nonhomogeneous microstructures.

Numerical modelling of grain refinement around highly reactive interfaces in processing of nanocrystallised multilayered metallic materials by duplex technique

Microstructure evolution around highly reactive interfaces in processing of nanocrystallised multilayered metallic materials has been investigated and discussed in the present work. Conditions leading to grain refinement during co-rolling stage of the duplex processing technique are analysed using the multi-level finite element-based numerical model combined with three-dimensional frontal cellular automata. The model was capable to simulate development of grain boundaries and changes of the boundary disorientation angle within the metal structure taking into account crystal plasticity formulation. Appearance of a large number of structural elements, identified as dislocation cells, sub-grains and new grains, has been identified within the metal structure as a result of metal flow disturbance and consequently inhomogeneous deformation around oxide islets at the interfaces during the co-rolling stage. These areas corresponded to the locations of shear bands observed experimentally using SEM-EBSD analysis. The obtained results illustrate a significant potential of the proposed modelling approach for quantitative analysis and optimisation of the highly refined non-homogeneous microstructures formed around the oxidised interfaces during processing of such laminated materials.

Steel binder cermets processed by combination of colloidal processing and powder metallurgy

Cermets constituted by a high-speed steel matrix reinforced with 50 vol% Ti(C,N) present a great potential due to its combination of properties, such as high wear and oxidation resistance, together with high values of hardness and toughness. However, the consolidation of these materials by conventional powder metallurgy processing presents two main problems: The agglomeration of Ti(C,N) particles, leading to non-homogeneous microstructures, and the low compressibility of the blends due to the small size and morphology of the starting powders.In this work, colloidal techniques are proposed to overcome these issues. Aqueous suspensions of steel powders and Ti(C,N) particles are prepared followed by spray-dry to obtain spherical granules able to be processed by pressing and sintering, avoiding oxidation of powders. The agglomerates present higher compressibility than blends, and sintered materials show higher density and hardness.

Effects of Rare Earth Y Addition on Microstructural and Properties of Pure Copper

The effects of rare earth Y addition on microstructure and properties of pure copper were investigated. Mechanical test, electrical test, oxidation resistance test, metalloscope, scanning electronic microscope (SEM) and X-ray difffraction (XRD) were performed to study the properties, microstructure and constitution. The results showed that both the hardness and antioxidant properties obviously increased with the increase of Y, confirmed the successful refinement role of Y. A small amount of Y (less than 0.5 wt.%) could improve the electrical conductivity of pure copper. When the Y content reached 0.2 wt.%, pure coppers obtained optimum electrical conductivity which is 96.8% IACS. However, over-added Y (>0.5 wt.%) resulted in second phase of Cu7Y coarsening and non-homogeneous microstructures forming, which reduces the conductivity of copper. In addition, Y can effectively purify the organization of molten copper.

Correlation of local strain with microstructures around fusion zone of a Cr-Ni-Mo-V steel welded joint

In this paper, in-situ SEM images with both low and high resolution near fusion line of a Cr-Ni-Mo-V steel welded joint were taken during interrupted monotonic tensile tests, with which macro- and micro-strain were measured based on digital image correlation technique and correlated with microstructures. An error analysis of strain measurement indicated sufficient resolution for image correlation with intrinsic microstructures as speckles. Results from digital image correlation showed that base metal, heat-affected zone and weld metal of the welds exhibited different responses to external tensile loading with mismatched strain distribution. A transfer of strain localisation from tempered martensites at base metal to lathy bainites at weld metal was observed around the fusion zone, due to varied hardening capabilities among non-homogeneous microstructures. Micro-strain could be several times higher than macro-strain at the same strained area, implying severe non-uniform deformation at microstructural scale. The most straining zone around the fusion line was found to be localized at blocks of soft δ-ferrites.

X-ray nanodiffraction reveals stress distribution across an indented multilayered CrN–Cr thin film

In order to understand the indentation response of thin films with non-homogeneous microstructures, it is necessary to characterise local deformation fields and microstructural changes around the indenter imprint. In this work, residual stress fields across a wedge-indented nanocrystalline CrN–Cr thin film with a respective sublayer thickness of 500nm and 250nm and an overall thickness of 3μm on a steel substrate are characterised ex situ, using cross-sectional synchrotron X-ray nanodiffraction with a spatial resolution of 100nm. In the as-deposited multilayer, residual stresses of ∼−3.5 and −1GPa in the CrN and Cr sublayers, respectively, are found. After the indentation, a complex stress distribution across the film cross-section with stress peaks in the range from −10 to 2GPa was observed. In agreement with the results from a finite element model, the formation of the residual stresses can be interpreted by the plastic deformation of the Cr sublayers and the steel substrate in conjunction with a linear elastic response of CrN. During the indenter unloading, the plastically deformed materials hinder the full relaxation of the indentation-induced high compressive and tensile stresses in linear elastic deformed brittle regions and the stresses remain partly conserved. The ductile Cr sublayers serve as a fundamental stabilizing component, which ensures that the stress peaks do not cause the film rupture or delamination, but the damage remains arrested between the plastically deformed Cr sublayers and the substrate. The encapsulation of the highly stressed and damaged regions, enhanced by the excellent sublayer adhesion, serves as the decisive and stabilizing component to the multilayer mechanical integrity during and after the indentation.

Computation of the lower semicontinuous envelope of integral functionals and non-homogeneous microstructures

A numerical method is established for computing the weakly lower semicontinuous envelope of integral functionals with non-quasiconvex integrands. The convergence of the method is proved and it is shown that the method is capable of capturing curved and non-homogeneous microstructures. Numerical examples are given to show the effectiveness of the method for capturing curved and non-homogeneous laminated microstructures.

Effects of Ce on microstructure and mechanical properties of pure copper

The effects of Ce on microstructure and mechanical properties of pure copper were investigated using mechanical test, hardness test, metalloscope and scanning electronic microscope (SEM). The results confirmed that the strength and hardness decreases at first and then increases with increasing of Ce content. When the Ce content reaches 0.04%, pure coppers obtain fine microstructure and favorable comprehensive mechanical properties that the tensile strength, yield strength, and elongation after annealing are 251, 116 MPa, and 37.22%, respectively. Over-added Ce results in second phases coarsening and non-homogeneous microstructures forming. Also, the Ce content in samples was measured by plasma emissive spectrum (PES), and the absorptivity of Ce reduces with increasing its addition.

Role of material microstructure in plate stiffness with relevance to microcantilever sensors

This work examines the effect of microstructure upon microcantilever bending stiffness. An existing beam theory model, based upon an isotropic Hooke's law constitutive relationship, is compared to a model based upon a micropolar elasticity constitutive model. The micropolar approach introduces a bending stiffness relation which is a function of any two independent elastic constants of the Hooke's law model (e.g., the elastic modulus and the Poisson's ratio), and an additional material constant (called γ). A consequence of the additional material constant is the prediction of an increased bending stiffness as the cantilever thickness decreases—a stiffening due to the material microstructure which becomes measurable at micron-order thicknesses. Polypropylene microcantilevers, which have a non-homogeneous microstructure due to their semi-crystalline nature, were fabricated via injection molding. A nanoindenter was used to measure their stiffness. The nanoindenter-determined stiffness values, which include the effect of the additional micropolar material constant, are compared to stiffness values obtained from beam theory. The nanoindenter stiffness values are seen to be at least four times larger than the beam theory stiffness predictions. This stiffening effect has relevance in future MEMS applications which employ materials with non-homogeneous microstructures instead of the conventional MEMS materials (e.g., silicon, silicon nitride), which have a very uniform microstructure.

Modeling the ductile-brittle transition behavior in thermomechanically controlled rolled steels

The Charpy impact transition temperature (ITT) is well modeled for hot-rolled or normalized steels having uniform grain size using empirical equations. However, the ITT of nonhomogeneous steel microstructures, such as duplex (mixed fine and coarse) grain sizes, and the scatter in experimental Charpy energy values, observed in the transition region, are not accurately modeled. This article describes research on the microstructure-fracture property relationship and the prediction of the ITT using a cellular automata finite element (CAFE) model in thermomechanically controlled rolled (TMCR) Nb-microalloyed steels. The ferrite grain size distributions for two TMCR steel plates were analyzed and used for the prediction of the local fracture stress (σ F ) values based upon the Griffith model. It was found that the coarse grain size distribution could be used to predict the range of σ F values observed. The CAFE model was used to predict the ITT using the predicted σ F distribution for a TMCR steel. Results showed that the CAFE model realistically predicted the Charpy ITT; in particular, it was able to reproduce the scatter in values in the transition region. Within the model, the percentage of brittle failure and the upper shelf ductile energy were predicted well. However, the lower shelf brittle energy was overestimated due to computational limitations in the commercial FE software used with the current CAFE model.

Ignition power in micropyretic synthesis

The influence of ignition power on stable and unstable micropyretic reactions is investigated numerically in this study. The numerical results show that a lower ignition power takes a longer time to ignite the specimens. Thus, the pre-heating zone at the ignition spot is lengthened. The changes in these parameters at the ignition spot may result in non-homogeneous microstructures and properties. The results also indicate that using a higher power to ignite the micropyretic reactions can reduce the ignition time and further prevent the heterogeneous structure from being formed at the ignition spot. However, higher heat loss occurs due to a high temperature gradient. The energy required to ignite the reaction is thus increased. In addition, the numerical results also show that the energy required for ignition is significantly enhanced for those reactions with a higher activation energy or higher heat capacity.

New approach for the quantification of microstructures in nonoriented electrical steels

An original method for the estimation of effective average grain size and effective aspect ratio in nonhomogeneous microstructures and a parameter describing the homogeneity of microstructure are presented. The principal types of microstructure for nonoriented electrical steels under investigation are defined. The coefficients of homogeneity for equiaxed and columnar microstructures are calculated. It is shown that the coefficient of homogeneity is independent of the shape of the grains. The effective average grain size of the nonhomogeneous microstructures is calculated as a weighted sum of the average grain sizes of homogeneous grain groups. The aspect ratio of the microstructure is also calculated by this weighted sum approach. A correlation is found between the mechanical properties and the proposed quantitative characterisation of the microstructure of the nonoriented electrical steel.

Three-dimensional X-ray structural microscopy with submicrometre resolution

Advanced materials and processing techniques are based largely on the generation and control of non-homogeneous microstructures, such as precipitates and grain boundaries. X-ray tomography can provide three-dimensional density and chemical distributions of such structures with submicrometre resolution; structural methods exist that give submicrometre resolution in two dimensions; and techniques are available for obtaining grain-centroid positions and grain-average strains in three dimensions. But non-destructive point-to-point three-dimensional structural probes have not hitherto been available for investigations at the critical mesoscopic length scales (tenths to hundreds of micrometres). As a result, investigations of three-dimensional mesoscale phenomena--such as grain growth, deformation, crumpling and strain-gradient effects--rely increasingly on computation and modelling without direct experimental input. Here we describe a three-dimensional X-ray microscopy technique that uses polychromatic synchrotron X-ray microbeams to probe local crystal structure, orientation and strain tensors with submicrometre spatial resolution. We demonstrate the utility of this approach with micrometre-resolution three-dimensional measurements of grain orientations and sizes in polycrystalline aluminium, and with micrometre depth-resolved measurements of elastic strain tensors in cylindrically bent silicon. This technique is applicable to single-crystal, polycrystalline, composite and functionally graded materials.