Coarse Grain Research Articles

Soil diversity at Jezero crater and Comparison to Gale crater, Mars

The martian soil is of particular interest as it can help us understand the different processes that have occurred on Mars by studying the chemistry and mineralogy of its constituents as a function of grain size. The fine-grained martian soil is thought to be homogeneous across the planet and thus to represent a global component. In this study we report on the soil targets analysed by the SuperCam instrument aboard the Perseverance rover, which is currently exploring Jezero crater. A total of 343 targets were analysed. Their grain size distribution confirms the sparsity of 250–900 Âμm particles in the martian soil, although both smaller and larger grains are present. We found that the local components, due to erosion of the local bedrock, are present not only in the very coarse grains or larger gravels of the soil, but also in the very fine ones (¡250 Âμm). We detected some very coarse grains enriched in olivine, pyroxene and carbonate in both the crater floor and the delta front locations, whereas phyllosilicate-rich grains have been encountered only in the delta front. We have compared the Jezero fine-grained soil targets with those of Gale crater using ChemCam data. We found that those at Jezero show no evidence of Mg sulfates, in contrast to the observation at Gale. In addition, the fine-grained soil at Jezero is more hydrated than that at Gale, probably due to its higher specific surface area.

Achieving excellent bond strength and tensile strength synergy of ultrafine-grained Al/Cu bimetallic sheets developed by an innovative hybrid manufacturing process

In the present work, two new parameters that influence the bond strength and tensile strength of Al/Cu bimetallic sheets are explored using an innovative hybrid manufacturing process. The innovative hybrid manufacturing process includes engineering of four different microstructures, 1. Ultrafine grained (UFG); 2. Bimodal grained (BM); 3. Fine grained (FG) and 4. Coarse grained (CG) in parent Cu and Al via integration of cryogenic based thermo-mechanical treatment followed by an unique tailored criss-cross surface pattern generation and high deformation roll bonding to develop high performance Al/Cu engineered sheets with four microstructural combinations: UFG‐Al + UFG-Cu, UFG‐Al + BM-Cu, UFG‐Al + FG-Cu and CG‐Al + CG-Cu. The criss-cross pattern aids in initiation of crack at the junctions and fissure formations at cross paths during the roll bonding process. This kind of pattern develops mechanical bond in the form of nugget bunches, which result in enhancement of bond strength in all the microstructural combinations of Al/Cu bimetallic sheets. The ascending order of increase in bond strength-tensile strength synergy of all four engineered microstructural combinations is: CG‐Al + CG-Cu, UFG‐Al + FG-Cu, UFG‐Al + BM-Cu and UFG‐Al + UFG-Cu. The UFG‐Al + UFG-Cu combination has achieved an extraordinary bond strength of 18 N/mm, which is almost 1.6 times the bond strength of its conventional coarse grained counterpart CG‐Al + CG-Cu combination (10 N/mm). Similarly, the UFG‐Al + UFG-Cu combination showed excellent tensile strength of 323 MPa which is around 25 % higher than that of CG‐Al + CG-Cu combination (258 MPa). The engineered UFG microstructure in Al and Cu samples promote the dynamic recrystallization and partial diffusion kinetics at the interface region and established the mechanical and metallurgical bonding between Al/Cu bimetallic sheets during roll bonding process. The adopted surface pattern and the engineered microstructure have enhanced the bond strength and tensile strength of Al/Cu bimetallic sheets both at macro and micro levels. The underlying scientific knowhow for obtaining excellent bond strength-mechanical property synergy in the engineered Al/Cu bimetallic sheets are established.

The roles of geometry and viscosity in the mobilization of coarse sediment by finer sediment

In rivers, the addition of finer sediment to a coarser riverbed is known to increase the mobility of the coarser fraction. Two mechanisms have been suggested for this: a geometric mechanism whereby smaller sizes smooth the bed, increasing near-bed velocity and thus mobility of the larger sizes, and a viscous mechanism whereby a transitionally smooth turbulent boundary layer forms, rendering the coarser grains more mobile. Here, we report on experiments using two sediment mixtures to better understand these proposed mechanisms. In Mixture 1, we used 0.5 and 5 mm grains, and in Mixture 2, we used 2 and 20 mm grains. If the entrainment of coarse gravel by finer sediment is a purely geometric effect, then the addition of finer material should produce the same effect on the mobility of the coarser material for both mixtures because they have the same size ratio. We show that addition of finer material has a different effect on the two mixtures. We observed an increase in the mobility of the coarse fraction for both mixtures, but the increase in coarse fraction mobility for Mixture 1 was almost twice that for Mixture 2. Our experiments show that in addition to the geometric effect, enhancement of coarse gravel transport by finer sediment is also driven by a viscous effect.

Coarse-Graining Conformational Dynamics with Multidimensional Generalized Langevin Equation: How, When, and Why.

A data-driven ab initio generalized Langevin equation (AIGLE) approach is developed to learn and simulate high-dimensional, heterogeneous, coarse-grained (CG) conformational dynamics. Constrained by the fluctuation-dissipation theorem, the approach can build CG models in dynamical consistency (DC) with all-atom molecular dynamics. We also propose practical criteria for AIGLE to enforce long-term DC. Case studies of a toy polymer, with 20 CG sites, and the alanine dipeptide, with two dihedral angles, elucidate why one should adopt AIGLE or its Markovian limit for modeling CG conformational dynamics in practice.

A strategy for simultaneously enhancing the strength and ductility of metastable β titanium alloys: Coupling heterogeneous structure and TRIP effects

The applicability of metastable β titanium alloys is frequently constrained by their relatively low yield strength. This study has successfully designed a metastable β titanium alloy with heterogeneous microstructures (HS) comprising both deformed and recrystallized grains, achieved through simple cold rolling followed by short-term annealing. Compared to traditionally coarse-grained (CG) specimen that is entirely crystallized and equiaxed, the HS specimen exhibit not only a postponed initiation of double yielding but also superior yield strength (enhanced by 27.8 %) and ductility (enhanced by 7 %). The delayed double yielding and enhanced strength in the HS specimen are ascribed to the restriction of dislocation motion by α" martensite and the heterogeneous deformation induced (HDI) strengthening mechanisms. The ductility of the HS specimen exceeds that of the CG specimen, owing to the combined effect of HDI hardening and the transformation-induced plasticity (TRIP) effects. The more pronounced TRIP effect in the HS specimens results from the synergistic effect of the elevated HDI stress and the applied external stress, which promotes the occurrence of stress-induced martensitic phase transformation. This study offers a novel strategy for the development of high-performance metastable β titanium alloys.

Synergistic enhancement of strength and ductility of Mg-12.8Gd-3.8Y-1.9Zn-0.5Zr alloy by low-temperature solid solution treatment during forging process

Forging and low-temperature solid solution treatment to regulate Mg-12.8Gd-3.8Y-1.9Zn-0.5Zr (wt%) alloy were investigated in this paper, which exhibited a heterogeneous microstructure. The alloy demonstrated a yield strength (YS) of 266.68 MPa, an ultimate tensile strength (UTS) of 337.01 MPa, and elongation (EL) of 8.98 %. It was shown that the strength and ductility of the Mg-12.8Gd-3.8Y-1.9Zn-0.5Zr (wt%) alloy were synergistically enhanced. This enhancement can be attributed to the alteration of the second phase particles through low-temperature solid solution treatment, as well as the hardening effect induced by hetero-deformation. The low-temperature solid solution treatment allowed the large-sized brittle Mg5RE phase to be dissolved, while the deformation-induced dislocation tangle in the coarse grains (CGs) promotes the co-segregation of Gd and Zn elements, resulting in the precipitation-strengthened γ′ phase. The presence of dynamically precipitated phases within the dynamic recrystallized (DRXed) zone enhanced the strain regulation ability in different regions and inhibited crack propagation. Furthermore, the hetero-deformation induced (HDI) hardening effect, arising from the interaction between CGs and fine grains (FGs) in the heterogeneous microstructure, effectively prevented necking and improved ductility.

Exploring mechanical behavior at interfaces of laser powder bed fusion (LPBF) deposits on wrought Inconel 718: an indentation-based approach

PurposeThis study used an indentation-based mechanical testing framework for the mechanical characterization of laser powder bed fusion (LPBF) processed Inconel 718 on a wrought Inconel 718 substrate. The purpose of the paper is to investigate the effectiveness of the indentation-based approach for localized mechanical evaluation.Design/methodology/approachThe LPBF-processed wrought substrate was sectioned into three sections for microstructural and mechanical characterization. A 3D heat source model was used for the thermal analysis of the interface region. The developed interface region is probed using the Knoop hardness indenter in different orientations to determine the textural anisotropy and mechanical behavior of the region.FindingsLPBF process develops a melted interface zone (MIZ) at the deposition-substrate interface. The MIZ exhibited a coarse grain structure region along with a larger primary dendritic arm spacing (PDAS), signifying a slower cooling rate. FE modeling of the LPBF process reveals heat accumulation in the substrate along with intrinsic heat treatment (IHT) induced due to layer-wise processing. The obtained yield locus shows strong anisotropy in the deposition region, whereas reduced anisotropy with a nearly uniform ellipse locus for the MIZ regions. This reduced anisotropy is attributable to IHT and heat accumulation in the substrate.Originality/valueAn alternative localized mechanical characterization tool has been investigated in this work. The approach proved sensitive to thermal variations during LPBF processing in an isolated region which extends its suitability to variable geometry parts. Moreover, the approach could serve as a screening tool for parts made from dissimilar metals.

Polymyxin B1 in the Escherichia coli inner membrane: A complex story of protein and lipopolysaccharide-mediated insertion

The rise in multi-drug resistant Gram-negative bacterial infections has led to an increased need for 'last-resort' antibiotics such as polymyxins. However, the emergence of polymyxin-resistant strains threatens to bring about a post-antibiotic era. Thus, there is a need to develop new polymyxin-based antibiotics, but a lack of knowledge of the mechanism of action of polymyxins hinders such efforts. It has recently been suggested that polymyxins induce cell lysis of the Gram-negative bacterial inner membrane (IM) by targeting trace amounts of lipopolysaccharide (LPS) localized there. We use multiscale molecular dynamics (MD) including long-timescale coarse-grained (CG) and all-atom (AA) simulations to investigate the interactions of polymyxin B1 (PMB1) with bacterial IM models containing phospholipids (PLs), small quantities of LPS, and IM proteins. LPS was observed to (transiently) phase separate from PLs at multiple LPS concentrations, and associate with proteins in the IM. PMB1 spontaneously inserted into the IM and localized at the LPS-PL interface, where it cross-linked lipid headgroups via hydrogen bonds, sampling a wide range of interfacial environments. In the presence of membrane proteins, a small number of PMB1 molecules formed interactions with them, in a manner that was modulated by local LPS molecules. Electroporation-driven translocation of PMB1 via water-filled pores was favored at the protein-PL interface, supporting the 'destabilizing' role proteins may have within the IM. Overall, this in-depth characterization of PMB1 modes of interaction reveals how small amounts of mislocalized LPS may play a role in pre-lytic targeting and provides insights that may facilitate rational improvement of polymyxin-based antibiotics.

A pH-Dependent Coarse-Grained Model for Disordered Proteins: Histidine Interactions Modulate Conformational Ensembles.

Histidine (His) presents a unique challenge for modeling disordered protein conformations, as it is versatile and occurs in both the neutral (His0) and positively charged (His+) states. These His charge states, which are enabled by its imidazole side chain, influence the electrostatic and short-range interactions of His residues, which potentially engage in cation-π, π-π, and charge-charge interactions. Existing coarse-grained (CG) models often simplify His representation by assigning it an average charge, thereby neglecting these potential short-range interactions. To address this gap, we developed a model for intrinsically disordered proteins (IDPs) that accounts for the properties of histidine (H). The resulting IDPH model is a 21-amino acid CG model incorporating both His charge states. We show that interactions involving previously neglected His0 are critical for accurate modeling at high pH, where they significantly influence the compaction of His-rich IDPs such as Histatin-5 and CPEB4. These interactions contribute to structural stabilizations primarily via His0-His0 and His0-Arg interactions, which are overlooked in models focusing solely on the charged His+ state.

All-Atom Membrane Builder via Multiscale Simulation.

I present an automated and flexible tool designed for constructing bilayer membranes at all-atom (AA) resolution. The builder initiates the construction and equilibration of bilayer membranes at Martini coarse-grained (CG) resolution, followed by resolution enhancement to the atomic level using the accompanying backmapping tool. Notably, this tool enables users to create bilayer membranes with user-defined lipid compositions and protein structures, while also offering the flexibility to accommodate new lipid types. To assess the simplicity and robustness of the tool, I demonstrate the construction of several membranes incorporating protein structures. The tool is freely available at github.com/ksy141/mstool.

Graph neural network coarse-grain force field for the molecular crystal RDX

Condense phase molecular systems organize in wide range of distinct molecular configurations, including amorphous melt and glass as well as crystals often exhibiting polymorphism, that originate from their intricate intra- and intermolecular forces. While accurate coarse-grain (CG) models for these materials are critical to understand phenomena beyond the reach of all-atom simulations, current models cannot capture the diversity of molecular structures. We introduce a generally applicable approach to develop CG force fields for molecular crystals combining graph neural networks (GNN) and data from an all-atom simulations and apply it to the high-energy density material RDX. We address the challenge of expanding the training data with relevant configurations via an iterative procedure that performs CG molecular dynamics of processes of interest and reconstructs the atomistic configurations using a pre-trained neural network decoder. The multi-site CG model uses a GNN architecture constructed to satisfy translational invariance and rotational covariance for forces. The resulting model captures both crystalline and amorphous states for a wide range of temperatures and densities.

Numerical Simulation and Microstructure Analysis of 30CrMnMoRe High-Strength Steel Welding.

Welding experiments were conducted under different currents for single-pass butt welding of high-strength steel flat plates. The microstructure of welded joints was characterized using OM, SEM, and EBSD, and the welding process was numerically simulated using a finite element method. According to the grain size obtained by electron microscope characterization and the temperature data obtained by simulation, the microstructure and mechanical properties of coarse grain and fine grain areas of the heat-affected zone were predicted by using the material microstructure and property simulation software. Finally, the results of mechanical properties simulation were verified through mechanical property testing.

Role of terminal beads in fracture of topological gels: A coarse-grained molecular dynamics study

Topological gels feature movable cross-linking sites which yield great deformation capability, but we show that their long-term performance would be undesirable. Because a long backbone chain has only 2 terminal beads to restrict sliding of rings, the entire chain would fail by just a small debonding. Chain segmentation by adding terminal beads is a promising strategy to improve durability. In this work, we develop a coarse-grained (CG) model of topological gels based on MARTINI force field, to simulate tensile behaviors of the gel. The developed CG model accurately predicts elastic modulus of typical topological gels with different crosslinking densities. Based on the model, we show that adding terminal beads to the chain can effectively improve mechanical properties of topological gels after initial debonding. With analyses on distribution of ring molecules along the chain and effective load-bearing chains during tensile deformation, mechanism of the improvement on durability is discussed.

Laser powder bed fusion of Fex(CoCrMnNi)100-x medium-entropy ferrous alloys: Processability, microstructure and dynamic deformation mechanism

In this work, Fex(CoCrMnNi)100-x (x = 40, 60 and 80 at.%) medium-entropy ferrous alloys (MEFAs) were fabricated through laser powder bed fusion (LPBF) of mixed powders composed of FeCoCrNiMn and Fe powders, and the dynamic compressive properties and deformation mechanisms were studied with combination of experiment and molecular dynamics simulation. The results demonstrate that all MEFAs exhibit good processability.The Fe40 and Fe60 samples were predominantly composed of FCC phase with coarse grains, while the Fe80 mainly consisted of BCC phase with a smaller grain size. When subjected to quasi-static and dynamic compression at 3000/s, the yield strengths of Fe40, Fe60 and Fe80 increases by 131, 220 and 256 MPa, respectively, illustrating the positive strain rate sensitivity and influence of Fe on the mechanical properties of MEFAs. Further, both the single-crystal and the polycrystalline models suggested that the incompatibility between the BCC and FCC phases is responsible for the enhancement of strength. Therefore, it is more likely to produce deformation twins, dislocations and thus stress concentration around the BCC phase, which is consistent with the TEM observations.

Influence of oxygen content on fatigue crack growth behavior of FGH96 superalloys

The fatigue crack growth (FCG) mechanism of FGH96 superalloys influenced by oxygen (O) was investigated in terms of grain structure and phase composition. The results reveal that the thinner powder oxide film process facilitates easier dissolution, and thus the fewer undissolved oxides as well as the movement of high-angle grain boundaries promote the generation of a uniform distributed small grains (SGs) within both the prior particle boundaries (PPB) interface and powder interior in the alloy with O content of 140 ppm. In contrast, the large number of undissolved oxide particles provides more recrystallization sites and thus the SGs clusters aggregate at the PPB interface in the alloy with O content of 340 ppm during sintering. A homogeneous distribution of SGs induces the uniform deformation of the alloy and thus stimulates the transgranular fracture of the coarse grains in alloy with O content of 140 ppm, in favor of a higher fatigue life. On the contrary, in the alloy with O content of 340 ppm, the SGs clusters forming on PPB interface results to the strain concentration at PPB, leading to the PPB fractured morphology and a serious reduction of the fatigue life. This study reveals that the generation of SGs is responsible for the FCG behavior and failure mechanism of the alloys, and suggests that regulating the uniform distribution of SGs or reducing the number of SGs during sintering plays an important role in improving the fatigue properties of powder metallurgy superalloys.

The Influence of Surface Nanocrystallization of TA2 Titanium Alloy on Its Corrosion Resistance

In this study, the surface nano treatment of TA2 titanium alloy was realized by means of surface mechanical wear treatment. The microstructure and electrochemical properties of the nanocrystalline layer were investigated by SEM, TEM, Electrochemical Impedance Spectroscopy, and Potentiodynamic Polarization, while the nucleation mechanism of the passivation film was discussed. The results indicate that the original coarse grains on the sample’s surface are transformed into randomly oriented nanocrystals by surface mechanical attrition treatment (SMAT). The corrosion current density of the surface nanocrystallized TA2 titanium alloy (9.2 nA·cm−2) experienced a reduction of two orders of magnitude compared to untreated TA2 titanium alloy (134.5 nA·cm−2) in 3.5 wt.% NaCl solution. The SMAT methods accelerates nucleation mechanism transitioning to continuous nucleation.

Optimization of gas metal arc welding parameters for dissimilar steel welds: A case study on duplex stainless steel 2205 and stainless steel 316L

The significance of welded connections in steel structures necessitates precise structural designs and processing adaptations to ensure robust mechanical strength and durability. Gas metal arc welding (GMAW) employing controlled curves presents advantages over conventional methods, offering enhanced weld bead properties, improved aesthetics, and reduced thermal inputs. This research investigates the impact of GMAW parameters using controlled curves on the microstructure and geometry of welds between dissimilar structural steels—duplex stainless steel 2205 and stainless steel 316L grade 50—commonly employed in construction. The aim is to optimize the GMAW welding process with controlled curves and surface tension transfer between these dissimilar steels. Through a 23-factorial experimental design encompassing feed speed (Va), arc focus (FC), and peak-to-base amplitude (APB), the study examines welding energy, geometry, deposition efficiency, microstructure, microhardness, tensile strength, and corrosion properties. Optimal welding energy fosters refined microstructures and uniform hardness, aiding in predicting weld throat area. Higher energy levels expand the heat-affected zone and coarse grains, while lower energies escalate variability. Predictive models facilitate fine-tuning welding energy and throat area for desirable properties and penetration while minimizing disruptions. This process optimization can be achieved by employing derived equations that limit welding energy and curve parameters, striking a desired balance between cost, structural integrity, and reliability.

Exploring the impact of microstructure refinement on high temperature steam oxidation behavior of FeCrAl alloy

Microstructure refinement is an effective way to improve the mechanical properties and radiation resistance of FeCrAl alloy, which may also increase the susceptibility to high temperature steam oxidation (HTSO) due to the increased surface chemical activity. To investigate the microstructural effects on the HTSO behavior, a FeCrAl alloy was subjected to controlled annealing strategies to produce three types of microstructures: “fine sub-grains + fine precipitates”, “coarse grains + fine precipitates” and “coarse grains + coarse precipitates”. The three alloys were exposed to high temperature steam during a heating and holding procedure. Large oxide nodules and rough multilayer-structured oxide films were formed during heating, which subsequently evolved into a single α-Al2O3 layer during the isothermal oxidation. Microstructure refinement can promote the oxidation and slightly increase the weight gain. However, the variation of isothermal oxidation parabolic rate constants brought by the microstructure refinement is 1-2 orders of magnitude lower than that brought by alloying. Microstructure refinement can improve other service performance of FeCrAl alloy without significantly deteriorating the HTSO resistance, indicating its advantages for engineering applications.

Downstream change of luminescence sensitivity in sedimentary quartz and the rearrangement of optically stimulated luminescence (OSL) components along two large rivers

Recently, it has been proposed that the luminescence sensitivity of quartz grains, i.e. their luminescence response to unit dose, might be used for sediment fingerprinting. Sensitivity is determined both by the origin of quartz grains and the sedimentary processes they underwent. However, a more detailed understanding of the factors influencing sensitivity is essential in order to expand and specify the applicability of the parameter in sediment sourcing and geomorphological studies alike. In the present research, we examined the spatial changes of sensitivity parameters of coarse grain quartz in modern sediments of the largest rivers of the Carpathian Basin, Central Europe, to determine the role of source areas and transportation distance.Based on the luminescence analysis of 39 samples, quartz extracts with a Carpathian origin (catchment of the Tisza River have a significantly higher sensitivity, except the LM-OSL medium component, than those originating from the Alpine domain (catchment of the Danube River). No clear relationship could be identified between natural sensitisation and transportation distance. In terms of the Tisza the observed downstream increase of quartz sensitivity is due to high sensitivity quartz grains supplied by its tributaries. In the meantime, a recurring change was observed along the Danube, which can be attributed mostly to local erosional processes. Consequently, tributaries and erosion can overprint the potential downstream sensitisation of quartz grains in large rivers.Meanwhile, in terms of the Danube on sections where a significant downstream increase was detected in LM-OSL fast component sensitivity, LM-OSL medium component sensitivity systematically decreased. Additionally, during laboratory sensitization, the CW-OSL sensitivity of Danube samples increased considerably, whereas changes were more moderate in the case of Tisza samples. Moreover, in the case of Tisza-related quartz extracts, the 110°C TL sensitivity and the LM-OSL fast and medium components showed a strong correlation, indicating the stability of luminescence processes (trapping and recombination). Whereas, in the case of the Danube both LM-OSL components show a weak correlation with the 110°C TL intensity. All these indicate that Alpine-origin quartz grains are more susceptible to the rearrangement of electron traps and/or recombination centres, which can also be an indicator of sediment sources in Quaternary studies in the region.

Experimental and simulation study on mechanical properties of ZK60 magnesium alloy after accumulative roll bonding

Abstract The mechanical properties of two- and four-layered wrought ZK60 Mg alloy sheets after two passes of accumulative roll bonding (ARB) with different reduction were studied and the microstructure were analyzed. The four-layered ZK60 sheets after ARB with 50% reduction demonstrate better strength-ductility combinations with yield strength of 223 MPa, ultimate tensile strength of 327 MPa, and total elongation of 23.7%, compared with the initial ZK60 of 222 MPa, 291 MPa and 10.0%, respectively. The average grain size of four-layered ARB ZK60 sheet is reduced from 21.8 μm of the initial sample to 4.4 μm. Using a micromechanical finite element model, the strain hardening behavior of ZK60 sheet was successfully predicted. The predictions were in good agreement with the experimental results. The simulation results reveals that the high performance of ZK60 sheets may be contributed by the lamella structure formed by the fine and coarse grains, which can avoid the local stress concentration and inhibit initiation and propagation of the microcracks. These findings provide a theoretical basis for the structural optimization design of ZK60 Mg alloys.