Continuous Grain Research Articles

Structure-property correlation for friction stir welded joints of 2219Al alloys microalloyed with Cd

Present study aimed at experimental investigation of microstructural evolution, microhardness profile, tensile and impact properties of friction stir welded (FSW) joints of 2219Al alloys microalloyed with varying (up to 0.1 wt%) Cd contents. FSW was performed on the cast and homogenized alloys. Microstructural analysis from weld line up to base metal, identified three sequential heat affected weld zones having separate grain morphologies, namely Weld Nugget Zone (WNZ), Thermo-Mechanical Affected Zone (TMAZ) and Heat Affected Zone (HAZ). Vickers microhardness value increased from weld line towards the WNZ, then decreased towards the TMAZ, and finally increased through HAZ towards the base metal, which exhibited higher hardness compared to all the heat affected weld zones. Microhardness, yield and tensile strengths of the FSW joint of 2219Al alloy increased, due to microalloying with 0.06 wt% of Cd contents, which was attributed to continuous grain refinement. While tensile ductility and toughness, and impact toughness of the welded joint reduced, resulting from trace additions of Cd. Investigated alloys retained significant mechanical strength, ductility and toughness, on the respective joints, following to the FSW operation. Cd was observed to be a potential microalloying element to control the microstructure, refine grain size and improve mechanical strength and hardness of the welded joint of 2219Al alloy. Present experimental results established a structure-property correlation, in order to validate potential application of FSW technique on investigated 2219Al alloys with trace additions of Cd, to attain desirable weld-quality avoiding welding imperfections.

Simulating Compaction and Cementation of Clay Grain Coated Sands in a Modern Marginal Marine Sedimentary System

Reservoir quality prediction in deeply buried reservoirs represents a complex challenge to geoscientists. In sandstones, reservoir quality is determined by the extent of compaction and cementation during burial. During compaction, porosity is lost through the rearrangement and fracture of rigid grains and the deformation of ductile grains. During cementation, porosity is predominantly lost through the growth of quartz cement, although carbonate and clay mineral growth can be locally important. The degree of quartz cementation is influenced by the surface area of quartz available for overgrowth nucleation and thermal history. Clay grain coats can significantly reduce the surface area of quartz available for overgrowth nucleation, preventing extensive cementation. Using a coupled-effect compaction and cementation model, we have forward-modelled porosity evolution of surface sediments from the modern Ravenglass Estuary under different maximum burial conditions, between 2000 and 5000 m depth, to aid the understanding of reservoir quality distribution in a marginal marine setting. Seven sand-dominated sub-depositional environments were subject to five burial models to assess porosity-preservation in sedimentary facies. Under relatively shallow burial conditions (<3000 m), modelled porosity is highest (34 to 36%) in medium to coarse-grained outer-estuary sediments due to moderate sorting and minimal fine-grained matrix material. Fine-grained tidal flat sediments (mixed flats) experience a higher degree of porosity loss due to elevated matrix volumes (20 to 31%). Sediments subjected to deep burial (>4000 m) experience a significant reduction in porosity due to extensive quartz cementation. Porosity is reduced to 1% in outer estuary sediments that lack grain-coating clays. However, in tidal flat sediments with continuous clay grain coats, porosity values of up to 30% are maintained due to quartz cement inhibition. The modelling approach powerfully emphasises the value of collecting quantitative data from modern analogue sedimentary environments to reveal how optimum reservoir quality is not always in the coarsest or cleanest clastic sediments.

Refinement of microstructure and improvement of mechanical properties of directed energy deposited titanium alloys by adding Fe

Elemental alloying is a validated strategy for enhancing the mechanical properties of directed energy deposited titanium alloys. However, it is still a challenge to obtain titanium alloys with both high strength and high ductility. In this work, to balance strength and ductility, the alloying element Fe was in-situ added to the TC4 melt pool during the directed energy deposited process and the effects of its content on the microstructure and mechanical performance of the TC4 alloy deposits were investigated. The results showed that the Fe additive ranging from 0.5 to 2.0wt.% were completely solid-solved in the retained β phase of TC4 alloys. Moreover, the primary β columnar grains were transformed into fully equiaxed grains. Meanwhile, the presence of Fe refined the α-laths, increased the proportion of the retained β phase, and the continuous grain boundary α (GB-α) became discontinuous. The tensile strength of the deposited alloys was continually improved with increasing Fe content, while the elongation had a peak value. When the Fe content was 1.0wt.%, the deposited alloy exhibited the best comprehensive performance, with an ultimate tensile strength of 1071MPa and an elongation of 9.3%. The enhancement of tensile strength was attributed to the solid solution strengthening and the refinement of α-laths and primary β grains. The increased proportion of retained β phase and the formation of discontinuous GB-α were beneficial for the alloy ductility. However, increased α/β interfaces inhibited dislocation movements, resulting in a decrease in ductility. The development of this alloy is important for aerospace and other fields that require high strength, high ductility and lightweight.

Investigation of the microstructural characteristics of laser-cladded Ti6Al4V titanium alloy and its corrosion behavior in simulated body fluid

Laser cladding technology has a wide range of potential industrial applications in the surface strengthening, repair and reuse of orthopedic implants. By employing this technique to conduct same-material surface restoration and enhancement on titanium alloys, it demonstrates significant developmental potential. However, the microstructure of laser additively manufactured titanium alloy differs significantly from that of traditional titanium alloys, which affects its corrosion resistance in human body fluids. To compare the corrosion resistance differences between the cladding layer and the substrate, this study investigates the microstructure of multi-pass laser cladding Ti6Al4V (TC4) titanium alloy and analyzes the corrosion morphology and corrosion products of the cladding layer in simulated body fluids (SBF). By comparing the electrochemical corrosion behavior of laser cladding with that of traditionally manufactured TC4, this research reveals the differences in corrosion resistance between the two titanium alloys. The research demonstrates that the microstructure of cladding primarily consists of prior-β grains and continuous grain boundary α phase, along with a complex basketweave structure composed of fine acicular α phase and lamellar α phase. Additionally, due to the complex thermal cycling process, the acicular α' colonies within the prior-β grains. These features enhance the cladding layer’s resistance to plastic deformation and increase microhardness, though with some uneven distribution. Interestingly, the TC4 cladding layer forms a porous passivation layer after corrosion, primarily composed of a TiO2 passivation film and deposits of hydroxyapatite and other phosphates. Due to the lower β-phase content, finer grains with higher energy states, and a greater proportion of high-angle grain boundaries (HAGBs) in the cladding layer, it exhibits higher electrochemical activity. As a result of these microstructural differences, the corrosion resistance of the TC4 cladding layer in SBF is inferior to that of TC4 manufactured using traditional techniques.

Effect of precipitate evolution on galvanic corrosion behavior of friction stir welded AA6061-T6 joint after post-weld aging

The microstructural transformation of FSW AA6061-T6 joint after post-weld T6 and its effects on the mechanical properties and corrosion behavior was investigated through electrochemical tests, immersion experiments and transmission electron microscopy (TEM) observation. The research results show that the joint efficiency and strength can be enhanced by post-welding aging. The hardness of SZ is recovered to a level close to that of matrix due to the sufficient precipitation of the effective strengthening phase β''. The main β' precipitate in over-aged HAZ coarsens during post-weld aging and cannot effectively restore strength, resulting in the lowest hardness in HAZ and limited tensile strength of the joint. The presence of macro-galvanic effects in the whole joint was confirmed. In SZ, the highest level of aging characteristics is caused by the highest aging drive due to fully solidified atoms, and is confirmed by the continuous grain boundary precipitates (GBPs) and dense matrix precipitates, which lead to the most positive potentials. Whereas, in HAZ, discrete GBPs and coarsened matrix precipitates indicate over-aged features, which lead to the most negative potentials. The potential difference between SZ and HAZ results in a macro-galvanic effect in the joint, where SZ is protected as the cathode and HAZ is corroded faster as the anode.

Effect of grain boundary ferrite morphologies on impact toughness of X80 girth weld

The X80 girth weld microstructure formed by high-strength acicular ferrite and low-strength grain boundary ferrite was studied to investigate the effect of grain boundary ferrite morphologies on impact toughness. The results show that due to the difference in direction of heat loss caused by the narrow groove, the grain boundary ferrite morphology of the weld metal center and the weld metal edge are continuous network structure and parallel layered structure, respectively. The continuous network structure grain boundary ferrite causes strain localization, resulting in the formation of a large number of secondary cracks in the crack propagation process, which seriously deteriorates the toughness.

Orientation-related and temperature-dependent continuous grain boundary migration in multi-principal element alloys

Grain boundaries (GBs) significantly affect the mechanical properties of metals and alloys. In this study, we investigated using molecular dynamic simulations the migration behavior of Σ25 (710), Σ5 (310), and Σ37 (750) [001] symmetric tilt GBs in CoCrCuFeNi multi-principal element alloy (MPEA) and Cu samples subjected to shear deformation. In Cu, the migration of the GBs exhibits a coupled migration pattern, consistent with the Cahn model; while in MPEA, the migration pattern varies with GB angle and temperature. Both Σ25 (710) and Σ37 (750) GBs, along with higher temperatures, induce GB roughening and continuous migration in the MPEA samples. Further investigation to the effects of GB angle and temperature was conducted through microstructure evolution tracing and quantitative analysis. A model was developed to describe the temperature-dependent continuous GB migration and average flow stress in MPEA samples with Σ25 (710) or Σ37 (750) GBs. This work can help understand the mechanical behavior of GB in MPEA and provide valuable insights for the development of high-performance materials.

Constructing a three-dimensional continuous grain boundary with lithium ion conductivity and electron blocking property in LLZO to suppress lithium dendrites

Li7La3Zr2O12 (LLZO) stands out as a promising material for solid-state batteries due to its superior performance. However, the lithium dendrite growth in LLZO significantly affects battery performance due to high electronic conduction of LLZO. Herein, amorphous Li3BO3 (ALBO) is introduced into LLZO to construct a three-dimensional continuous grain boundary with lithium ion conductivity and electron-blocking property to suppress lithium dendrites. The symmetric cells of ALBO-LLZO achieved a high critical current density (CCD) of 1.1 mA·cm−2 and cycled stably for 2000 h at 0.3 mA·cm−2. The capacity retention of LFP/1 ALBO-LLZO/Li battery retains 84.6 % after 200 cycles at 0.2 C, room temperature. This research offers a potential solution to enhance the performance of the garnet electrolyte for ASSBs.

Screen printing Ag2Se/carbon nanocomposite films for flexible thermoelectric applications

Flexible thermoelectric generators offer the possibility of harvesting waste heat from the human body. However, intrinsic brittleness and the high production cost of bulk thermoelectric materials limit their applications in flexible thermoelectric generators. Herein, flexible Ag2Se/carbon nanocomposite films on polyimide substrates are prepared by scalable screen-printing followed by facial heat treatment. An optimal film shows a maximum power factor of 1617 μW m−1 K−2 at room temperature and good flexibility. The film consists of mainly Ag2Se grains with a preferred (00Ɩ)-orientation and a small amount of carbon. Microstructure observations reveal that the Ag2Se grains with sizes of nano to micrometers have coherent or continuous grain boundaries, and the carbon is mainly amorphous with slight graphitization. A flexible thermoelectric device assembled with the optimal film exhibits a power density of 29.1 W/m2 at a temperature gradient of 35.4 K. This work demonstrates a cost-effective route to high-performance flexible thermoelectric films.

High Power Factor Flexible Ag2Te Film on Nylon by a Wet Chemical Method for Power Generator.

Herein, we develop a facile wet chemical method for the synthesis of Ag2Te powders at room temperature and flexible Ag2Te/nylon thermoelectric (TE) films are prepared by vacuum-assisted filtration of the synthesized Ag2Te powders and then hot pressing. Because of the good crystallinity of Ag2Te grains and continuous grain boundaries, an optimized film exhibits a power factor of 513 μW m-1 K-2 at 300 K, which stands among the highest values reported for Ag2Te-based films to date. In addition, the film also has good flexibility. A four-leg flexible TE device assembled with the film generates a power density of 5.46 W m-2 at a temperature gradient of 31.8 K. This work provides a facile and environmentally friendly method for preparing flexible Ag2Te films.

Influence of thermal conductivity on evolution of grain morphology during laser-based directed energy deposition of CoCrxFeNi high entropy alloys

A model CoCrxFeNi high entropy alloy system was chosen to investigate the effect of thermal conductivity on the evolution of spatial orientation of columnar grain morphology during laser directed energy deposition. The thermal conductivity of the alloy was varied by tuning the chromium content in CoCrxFeNi alloys. CoCrxFeNi alloys with chromium content ranging between 0 and 24 at% were produced under identical processing conditions of laser direct energy deposition method. Electron back scattered diffraction images of the cross-sections revealed that the spatial orientation of grain morphology transitioned from zigzag columnar grains from layer-to-layer to near-continuous columnar grains across multiple layers with increased content of chromium in CoCrxFeNi. A multi-scale multi-physics finite element based thermo-kinetic model with consideration to multi-track multi-layer nature of the laser direct energy deposition technique was adopted to correlate the process thermo-kinetics with the evolution of microstructure. The computation calculations revealed that the decrease in thermal conductivity from 36 W/m.K (CoFeNi) to 26 W/m.K (CoCr24FeNi) at the melting point reduced the cooling rate from 3.3 ×104 °C/s to 1.3 ×104 °C/s in CoFeNi and CoCr24FeNi alloys, respectively. This subsequently evolved into increased degree of remelting of previously deposited layers and caused the direction of resultant thermal gradient to reorient towards the build direction. Such reorientation in resultant thermal gradient contributed to transition of spatial orientation of grain morphology from columnar zigzag microstructures from layer-to-layer to near continuous columnar grains across multiple layers. The present observation was verified compared with other reported metallic systems exhibiting zigzag and continuous columnar grains, and a unified mechanism underlining the role of thermal conductivity on microstructure evolution was proposed.

Numerical simulation of continuous microwave drying of rice grains

AbstractTo comprehensively understand temperature and moisture changes in a continuous microwave rice grain drying system, this study proposes a simulation strategy that facilitates the continuous movement of rice grains. The study establishes a three‐dimensional model concerning multiple physical fields, including electromagnetism, heat, and mass transfer. It examines the effects of rice grain layer thickness and microwave intensity on the moisture and temperature of rice grains. The results indicate that the drying rate is negatively correlated with material thickness but positively correlated with temperature. The optimal thickness for the rice grain layer is 8 mm. Furthermore, both the microwave drying rate and temperature increase with microwave intensity. These findings contribute to a deeper understanding of the hydrothermal change mechanisms in rice grains during microwave drying.Practical applicationsMicrowave drying, as an emergent drying technology, has garnered widespread attention for its selective heating, efficient drying, energy savings, and environmental protection. Nevertheless, enhancing uniformity during the microwave heating process constitutes an important research topic in scientific research and technological applications. Numerical simulation methods can visually analyze electric field distribution, thereby optimizing microwave heating uniformity and improving drying effects. This article aims to accurately predict the continuous microwave drying time of paddy and maximize energy usage by optimizing drying thickness and microwave power parameters establishing a mathematical model for the process. The study not only provides a solid theoretical basis for microwave dryer design but also scientifically guides the continuous microwave drying of rice and other food crops.

Pigs, planners, and potato peels: the Soviet Scheme to feed pigs with urban food waste as a waste regime under Stalin, Khrushchev, and Brezhnev

ABSTRACT In this article, I study why and how Soviet planners organized a scheme to collect food waste from Soviet residential buildings and food service establishments in Moscow and other cities and utilize it as a feedstock for pork production. By relying on sociologist Zsuzsa Gille’s “waste regime” concept and a great variety of primary sources, I analyze the Soviet “garbage feeding scheme” as a social institution that patterned the social behavior of actors who engaged with food waste in the USSR from the early 1930s until the beginning of the 1980s. I argue that Soviet planners, informed by zootechnics, perceived garbage feeding as a way to reconcile their goal to increase meat production with the reality of continuous grain shortages. As such, they imparted food waste with the economic meaning that it could be turned into other commodities – wheat and meat. I demonstrate that the Soviet garbage feeding scheme never became a success, as the collection of food waste that laid dispersed across many locations in cities posed too big of an organizational challenge for the USSR’s centralized bureaucracy, and because planners did not succeed at integrating Soviet citizens into its scheme.

Contribution of oxygen vacancies to phase transition and ferroelectricity of Al:HfO2 films

We investigate the effects of oxygen vacancies on the ferroelectric behavior of Al:HfO2 films annealed in O2 and N2 atmosphere. X-ray photoelectron spectroscopy results showed that the O/Hf atomic ratio was 1.88 for N2-annealed samples and 1.96 for O2-annealed samples, implying a neutralization of oxygen vacancies during O2 atmosphere annealing. The O2-annealed films exhibited an increasing remanent polarization from 23 μC cm−2 to 28 μC cm−2 after 104 cycles, with a negligible leakage current density of ∼2 μA cm−2, while the remanent polarization decreased from 29 μC cm−2 to 20 μC cm−2 after cycling in the N2-annealed films, with its severe leakage current density decreasing from ∼1200 μA cm−2 to ∼300 μA cm−2. A phase transition from the metastable tetragonal (t) phase to the low-temperature stable orthorhombic (o) phase and monoclinic (m) phase was observed during annealing. As a result of the fierce· competition between the t-to-o transition and the t-to-m transition, clear grain boundaries of several ruleless atomic layers were formed in the N2-annealed samples. On the other hand, the transition from the t-phase to the low-temperature stable phase was found to be hindered by the neutralization of oxygen vacancies, with almost continuous grain boundaries observed. The results elucidate the phase transformation caused by oxygen vacancies in the Al:HfO2 films, which may be helpful for the preparation of HfO2-based films with excellent ferroelectricity.

Synergistic influence mechanism of B-Ga content on microstructures and magnetic properties of Nd-Fe-B ribbons

To understand the influence mechanism of B and Ga content on magnetic properties of NdFeB ribbons, Nd29.89FebalGayCo5.93Bx (wt%, x = 0.80–0.98, y = 0.24–1.04) alloys were prepared and magnetic properties, phase composition, coercivity mechanism, and microstructure of these alloys were investigated systematically. The melt-spun ribbons exhibited 2:14:1 phase grains with varying grain sizes and amorphous grain boundary phases at a wheel speed of 25 m/s. By reducing the B content within a specific range, grain refinement was achieved, resulting in narrower triangular grain boundaries, more uniform and continuous thin grain boundaries. Meanwhile, further increasing the Ga content, the grain shape changes from elongated to equiaxed, and the grain size is greatly refined. However, for x = 0.89, y = 0.84 strip, the coercivity is still reduced due to the large number of directly contacted grains. Consequently, an alloy composition of Nd29.89FebalGa0.64Co5.93B0.89 yielded excellent comprehensive magnetic properties, including a remanence of 8.5 kGs and a coercivity of 18.01 kOe. The corresponding magnetic properties enhancement mechanism is further discussed.

A novel strategy to enhance the interfacial bonding quality of CoCrFeMnNi high-entropy alloy joints produced by vacuum hot-compression bonding

The strain history of strain rate transient changes was introduced into the vacuum hot-compression bonding (VHCB) process of CoCrFeMnNi high-entropy alloy, which rapidly improved the interfacial bonding quality of the joint. The results of interfacial microstructure characterization indicated that the high-density dislocations generated in the interfacial region during the initial high strain rate stage not only promoted the nucleation of the interfacial recrystallized grains but also induced the transformation of the sub-boundaries and the interfacial grain boundaries (IGBs) to the high mobility twin boundaries (TBs). The accelerated discontinuous dynamic recrystallization process, the growth of TB-type continuous dynamic recrystallization grains, and the interfacial TB migration during the transient VHCB dramatically enhance the IGB migration level of the joints. This study provides an effective strategy for the interfacial regulation of high-quality VHCB joints.

Improvement of magnetic performance of Nd-Ce-Fe-B sintered magnets via Pr-Co-Ga grain boundary reconstruction

Grain boundary reconstruction is a commonly used method to improve the coercivity of Nd-Ce-Fe-B magnets but at the expense of a notable reduction in remanence. In this study, we present an effective approach to achieving a balance between remanence and coercivity of Nd-Ce-Fe-B magnets through Pr-Co-Ga grain boundary reconstruction. Compared to the original Nd0.7-Ce0.3-Fe-B magnet, the remanence of the magnet with 4 wt% Pr-Co-Ga addition decreased only from 13.09 kGs to 12.8 kGs, while the coercivity remarkably increased from 10.95 kOe to 14.84 kOe. Additionally, the coercivity temperature coefficient (20–150 °C) was improved from − 0.606 %/°C to − 0.547 %/°C, and the Curie temperature was increased from 278.4 °C to 285.1 °C, demonstrating excellent thermal stability. XRD refinement analysis showed a slight decrease in the main phase ratio, accompanied by a slight increase in orientation, resulting in a slight decrease in remanence. SEM and EPMA observations revealed that Pr preferentially replaced Ce on the grain surface, forming a “Pr-rich” shell with an enhanced anisotropy field. TEM analysis showed that the magnets with PCG addition exhibit a continuous Fe-lean grain boundary phase, weakening the exchange coupling of the adjacent grains. The synergistic effect of the “Pr-rich” shell formation and grain boundary optimization effectively enhanced the coercivity.

Analyzing barrel surface damage in failed large caliber cannons

To elucidate the surface damage characteristics of artillery barrel bores, a dissected 155 mm failed barrel was analyzed. Utilizing macroscopic imaging, SEM and EBSD for characterization, distinct damage patterns were identified. The rifling and forcing cone regions predominantly exhibited fatigue crack patterns, while the mid-bore region also showed signs of fatigue cracks. Notably, the groove region demonstrated frictional wear features. Both the grooves and the lands region at the muzzle end were characterized by frictional wear. A significant finding was the presence of a heat-affected layer along the bore surface, extending from the breech end to the muzzle, with its thickness gradually decreasing. The radial hardness of the bore surface demonstrated a decreasing trend, with the hardness of the heat-affected layer being about double that of the matrix material. The formation of this layer was attributed to the high-energy impact loads the bore surface endures, involving a cycle of high temperature and rapid cooling. This process induces recrystallization, sub-grain structure formation, and continuous grain refinement alongside dislocation annihilation.

A cost-effective dual-layer grain boundary diffusion strategy to significantly enhance coercivity of sintered Nd-Ce-Fe-B magnets

In an attempt to obtain cost-effective sintered Nd-Ce-Fe-B magnet and overcome the coercivity-remanence trade-off challenge caused by heavy rare earth (HRE) diffusion, a novel dual-layer coating method has been proposed for the grain boundary diffusion process (GBDP). A high coercivity increment of 8.56 kOe is achieved by dual-layer coated DyHx/Pr80Al20 (DH/PA) diffusion with 0.8 wt% DyHx and a slight remanence reduction from 12.85 to 12.71 kG. Although the DyHx diffused magnet has a coercivity increment of 9.24 kOe, it consumes twice as much DyHx as the DH/PA diffused magnet at the great sacrifice of remanence. This can be attributed to the formation of continuous grain boundary phase and thin Dy-rich shell via microstructural observations. Further TEM characterization indicates that the amorphous triple junction grain boundary phase (TJP) gradually transforms into the crystalline Nd2O3 structure after GBDP. The coexistence of cubic-Nd2O3 phase and hexagonal-Nd2O3 phase found in the dual-layer coated Pr80Al20/DyHx (PA/DH) diffused magnet creates a more intricate grain boundary phase structure, hindering the diffusion of Dy. Comparably, the formation of single cubic-Nd2O3 (Ia3̅ structure) grain boundary phase in the DH/PA and DyHx diffused magnets is an important reason for the significant increase in coercivity. Based on the evaluation of magnetic performance and cost, the DH/PA diffused magnet achieves a higher price-performance ratio (PPR). This cost-effective bilayer grain boundary diffusion strategy provides a valuable reference for high PPR Nd-Ce-Fe-B magnet fabrication.

Self-organising phenomena in 2D complex plasma simulations withnon-mono dispersed dust size distributions

Complex plasma with a variety of continuous and discrete dust grain size distributions are simulated in 2D with molecular dynamics simulations with radial geometry to determine differences in self-organizing phenomena to more realistically represent the actual in situ variations in dust-size. The standard deviation of particle size σ(a) strongly correlates with phase separation and coupling parameter Γ for all distribution types. We observe local differences in bond order parameters and Voronoi diagrams for different size distributions, and our results suggest that phase transition is affected by continuous size distributions, particularly in the binary distribution case. Simulations with discrete size result in artifacts and discontinuities that are not found in the continuous distributions. The use of continuous distributions is observed to be beneficial both for more realistic approximation of complex plasma experiments and to study systems of strongly coupled particles in general.