Precipitation Of Phase Research Articles

Exsolved Ru-mediated stabilization of MoO2-Ni4Mo electrocatalysts for anion exchange membrane water electrolysis and unbiased solar-driven saline water splitting

Molybdenum-based electrocatalysts remain the exclusive and practical option for anion exchange membrane water electrolysis (AEMWE) due to their exceptional catalytic activity in the alkaline hydrogen evolution reaction (HER). However, they are limited by low electrochemical stability resulting from the dissolution into MoO42- ions in alkaline conditions, leading to secondary phase precipitation that hinders the surface reaction. Here, we demonstrate Ru-mediated electrochemical stabilization of MoO2-Ni4Mo electrocatalysts, which exhibit exceptionally enhanced durability as well as catalytic activity, enabling ampere-level current density water splitting in saline water. Theoretical calculations and ex-situ X-ray absorption spectroscopy reveal that exsolved Ru nanoclusters with a higher hydroxyl affinity significantly establish a local hydroxide-deficient environment, leading to the stabilization of MoO2. Consequently, Ru-MoO2-Ni4Mo exhibits outstanding hydrogen production with stable operation for over 300 h to achieve a current density of 1.0 A cm−2 and a record-high solar-to-hydrogen efficiency of 22.5 % in AEMWE and photovoltaic-assisted water splitting system, respectively.

Regulation of mechanical properties in vanadium-containing high-nitrogen austenitic stainless steel via nano-Sized precipitated phase control

Nitride precipitation in high-nitrogen austenitic stainless steels significantly affects the mechanical properties of said steels. In this study, vanadium microalloying was employed to prepare high-nitrogen austenitic stainless steel with excellent comprehensive mechanical performance. The characteristics of the different precipitated phases, precipitation and dissolution behaviors, and their effects on mechanical properties were investigated. The impact mechanism of the precipitated phases on the mechanical properties of stainless steel was also discussed. The results indicate that the Me2X-type precipitated phase in the vanadium-containing high-nitrogen stainless steel exhibits a hexagonal close-packed (HCP) structure, forming a incoherent relationship with the matrix. This leads to a significant reduction in ductility owing to the larger size of particles enriched at the grain boundaries with minimal strengthening effects. Conversely, the MeX-type precipitated phase exhibits a face-centered cubic (FCC) structure, maintaining a semi-coherent relationship with the matrix. This results in smaller particle sizes and a more dispersed distribution, leading to a pronounced strengthening effect without compromising plasticity. Effective control of the precipitated phase can be achieved by solution treatment at different temperatures. Specifically, stainless steel subjected to a 1100 °C solution treatment exhibits only fine, dispersed MeX-type precipitated phases, resulting in optimal comprehensive mechanical properties: yield and ultimate tensile strengths of 587 and 924 MPa, respectively, with an elongation of 55% and a strength-ductility product of 49.6 GPa·%.

Effect of metastable precipitate phase transformation on reheat cracking in SS347H welding

Reheat cracking occurred in the welded heat affected zone (HAZ) of the SS347H tube during high temperature applications of approximately 600 °C. The reheat cracks occur when the inside of the grain is strengthened, causing grain boundary embrittlement. In this study, the intra-granular strengthening phase transformation of the HAZ causing the reheat crack was analyzed using TEM.The hardness of SS 347H HAZ with cracks is measured to be 221HV on average, which is about 25HV higher than 196HV of HAZ without cracks. This intra-granular strengthening is due to the formation of intra-granular precipitate phases. The precipitated phase is ultimately NbC, but undergoes an intermediate phase transformation due to diffusion of Nb and C components. The phase transformation consists of the following steps: “(i) SA (solution annealing), (ii) Zone A, (iii) Zone B, and (iv) NbC precipitation.”This is a process in which Nb/C components diffuse and segregate at the reheating temperature from a solid solution state of Nb/C components, and NbC with a size of several tens of nanometers is precipitated. As metastable phases, Zones A and B exist in the intermediate process of precipitation, which is the strengthening stage where intra-granular hardness is maximized. Zone A and B in the pre-precipitation stage means that a new lattice plane is formed as the segregation of component elements forms coherency with the matrix. The relationship between the base and new lattice planes is confirmed by Double Diffraction in the TEM diffraction diagram.The root cause of reheat cracking in SS 347H HAZ is believed to be the intra-granular strengthening phase caused by zone A and zone B as a metastable phase transformation in an intermediate stage before NbC precipitation. In order to suppress reheat cracking, it is desirable to precipitate stable NbC from the metastable phases of Zones A and Zone B through stabilization heat treatment.

High strength and elongation of Mg-Gd-Nd-Zr alloy obtained by synergistic action of high-speed extrusion and short-time aging treatment

Magnesium–gadolinium (Mg–Gd)-based alloys have excellent high-temperature properties and the addition of two heterogeneous rare earth (RE) elements may promote the formation of secondary phase for better-strengthened properties. Herein, novel Mg-7Gd-2Nd-0.5Zr (wt%) alloys were prepared by synergistic reaction induced by high-speed extrusion (EX) and short-time aging treatment (AT). The microstructures, textures, and mechanical properties of the resulting alloys were then comprehensively studied by various analytical methods. The result reveals that the as-cast Mg-7Gd-2Nd-0.5Zr (wt%) alloy is composed of α-Mg matrix and Mg5(Gd,Nd) phase with bony and continuous networks at grain boundaries. The microstructure presents coarse deformed grains and fine recrystallized grains after high-speed EX, and formation of typical (0001)∥ ED extruded fiber texture and [1¯21¯1] RE texture is observed. The EX22 sample exhibits more Mg5(Gd,Nd) precipitated phases, fuller DRXed grains, and shorter peak aging times than the EX9 sample. After the AT at 250 °C, the proportion of deformed grains decreases due to static recrystallization, which leads to a reduction in the average grain size and weakening of the texture intensity. Therefore, combined effect of all strengthening mechanisms aids in achieving balance of high-strength and high-elongation for Mg-7Gd-2Nd-0.5Zr (wt%) alloy. The values of yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of EX22-A sample at room temperature are found to be 292.5 MPa, 350.6 MPa, and 24.3%, respectively. Overall, this study provides relevant experimental basis and theoretical guidance for the development of high-strength Mg-RE alloys, which are useful for future consideration.

Microstructural and mechanical characterization of electron beam welded low-nickel nitrogen-strengthened austenitic stainless steel

In this paper, the Electron Beam Welding (EBW) was used to join thin plates of low-nickel nitrogen-strengthened austenitic stainless steel (LNiASS), a material valued for its superior mechanical properties and cost-effectiveness. Traditional welding techniques often lead to issues such as hot cracking, reduced toughness, and undesirable microstructures. The objective was to address these challenges using EB·W., which offers precise control, minimal heat input, and deeper penetration.Methodology included joining LNiASS plates with E.B.W. and analyzing the resulting microstructures and mechanical properties through optical microscopy, tensile testing, microhardness testing, and scanning electron microscopy (SEM). The findings indicated the presence of various ferrite morphologies without significant precipitation of deleterious phases like carbides and sigma phase. The weldment strength was ∼90 % of the base alloy, with fractures occurring near the weld cord due to nitrogen loss and grain coarsening in the (HAZ). Microhardness increased by ∼12.9 %, attributed to microstructural evolution and a fine-grained structure. Impact testing in Charpy V-Notch (CVN) configuration showed the weld absorbed ∼50 % more impact energy than the base material, due to refined Microstructure and enhanced hardness. Longitudinal residual stress analysis indicated compressive nature below mid-thickness, resulting from thermal expansion and contraction during welding. These results demonstrated E.B·W.'s effectiveness in preserving mechanical properties and enhancing the performance of nitrogen-strengthened stainless steel welds.

Effect of MgO content and CaO/Al2O3 ratio on melting temperature and viscosity of CaF2–CaO–Al2O3–MgO slag for electroslag remelting

During electroslag remelting (ESR), high MgO contents are typically added to CaF2–CaO–Al2O3 slag to control magnesium content in iron- and nickel-based alloys. The melting temperature and viscosity of ESR slag are pivotal for energy consumption, production efficiency, smooth operation, and ingot quality. However, there is currently a notable scarcity of research on the melting temperature and viscosity of CaF2–CaO–Al2O3–MgO slag with high MgO levels. Thus, the melting temperatures and viscosity of CaF2–CaO–Al2O3–MgO slags with varying MgO contents and CaO/Al2O3 (C/A) ratios were investigated. The results show that as the MgO content increases from 7.83 % to 13.18 %, the final precipitation content of the MgO phase significantly increases, resulting in an increase in the melting temperature from 1306 °C to 1319 °C. With the increase in the C/A ratio from 0.86 to 1.16, the precipitation completion temperatures of the Ca12Al14F2O32 and MgO phases significantly decrease and the MgAl2O4 phase transforms into the CaO phase. Hence, the melting temperature decreases from 1329 °C to 1314 °C. Further increasing the C/A ratio to 1.40, the final precipitation content of the CaO phase increases, resulting in a decrease in the melting temperature from 1314 °C to 1282 °C. Moreover, as the MgO content and C/A ratio increase, the slag viscosity exhibits different change trends within various temperature ranges. This depends on which of the depolymerization of the slag structure and the precipitation and clustering of the MgO phase has a greater effect on the slag viscosity.

Influence of SiC particles on the microstructure and mechanical behaviors of AlMgScZr alloy processed by laser powder bed fusion

Laser powder bed fusion (LPBF) of AlMgScZr alloy has garnered significant attention as a high-strength aluminum alloy. However, its low modulus, Portevin-Le Chatelier (PLC) behavior, and weak strain hardening capability restrict its application in the aerospace sector. In this study, SiC/AlMgScZr composites with different SiC content have been successfully fabricated using LPBF. The inherent bimodal grain structure of AlMgScZr alloy was not completely altered by the addition of SiC particles. However, with increasing SiC content, heat accumulation increased, and the solidification cooling rate decreased. This led to an increase in the size of α-Al grains in the 5 wt% SiC/AlMgScZr composites. Meanwhile, movable dislocations can be efficiently preserved inside the grains, where they effectively accumulate and become entangled. Consequently, the strain hardening capability of the 5 wt% SiC/AlMgScZr composites improved by approximately 58 % compared to AlMgScZr alloy, with a strain hardening index (n) reaching 0.29. Additionally, the addition of SiC particles led to an increase in the elastic modulus (81.0 GPa). Furthermore, the reaction between Mg atoms and SiC particles resulted in the formation of Mg2Si, which altered the distribution of Mg elements and initiated the reactive precipitation of a Mg-rich phase. There is no competition between the diffusive migration of solute atoms and the motion of movable dislocations within the composites. The additional SiC particles effectively eliminated the PLC effect in the LPBF of AlMgScZr alloy. This work provides essential guidance for developing high-strength and high-stiffness aluminum matrix composites with excellent processing properties in LPBF technology.

Effect of aging on the structure and mechanical properties of austenite stainless steel N50 alloyed with nitrogen, niobium and vanadium

In this study, the austenitic, corrosion-resistant N50 steel alloyed with different nitrogen, niobium and vanadium content was investigated. This steel is used in the production of high-strength, cryogenic pipes. The production process for these pipes involves aging at 650 °C–665 °C for 50–100 h. Therefore, steels were examined in their as-delivered state, after aging at 650 °C, 100 h and after solid solution heat treatment. The structure of the steel was analyzed using optical and scanning microscopy, tensile and impact strength tests were conducted at room temperature and at −196 °C. It was found that the total volume fraction of the precipitated phase after aging is more dependent on the total concentration of nitride-forming elements—Nb and V, than on nitrogen. Aging does not affect the basic operational properties at room temperature, but it can significantly affect toughness at −196 °C.

Influence of non-valve metal phase on growth behavior and performance of PEO coating on Mg–Zn–Mn alloys with high Mn content

The influence of pure metal phases (precipitation or reinforcement phases) on the PEO discharge and coating growth in Mg alloys remains underexplored. This study investigated the effects of the α-Mn phase on voltage evolution, coating morphology, phase composition, and corrosion resistance by subjecting Mg–4Zn-xMn (x = 0, 0.6, 1.2, 2.4 wt%) alloys to PEO treatment in alkaline silicate-based electrolyte. Results indicate that the presence of α-Mn does not prevent spark discharge. However, an increase in α-Mn content leads to a downward shift in the voltage-time curve. The α-Mn phase significantly slows down the voltage ascent rate and prolongs the duration of Stages I to III of PEO process. Electrochemical oxidation of the surrounding Mg matrix by the α-Mn phase induces the formation of pits and porous local morphologies, exacerbating coating unevenness. With the increasing in Mn content, the thickness and porosity of PEO coatings gradually decrease for the same treatment time. The coated Mg–4Zn-1.2Mn alloy exhibits the highest corrosion resistance. The differences in oxidizability between the α-Mn phase and the Mg matrix, as well as the stability and dielectric properties of the oxide products may be the underlying reasons for these effects. Despite Mn oxides' instability under alkaline conditions at high potentials, reaction products with the electrolyte offset this drawback. This study enhances understanding of pure metal phases' influence on Mg alloy PEO and contributes to research on PEO processes for Mg-based materials containing pure metal phases.

Microstructure evolution and composite strengthening mechanism during solid solution and aging treatment for Cu-Ni-Co-Si sheet

A type of Cu-Ni-Co-Si alloy was designed and conducted by solid solution and aging treatments. Meanwhile its microstructure evolution and performance evolution were also studied. The characteristics of precipitated phases after aging treatment, and the strengthening mechanism of the process have been thoroughly studied. The results indicate that the optimal process for Cu-Ni-Co-Si alloy is solid solution at 900 °C for 120 min and aging at 500 °C for 240 min, respectively. At peak aging, the alloy reached tensile strength and conductivity of 631 MPa and 41.3 % IACS, respectively. The grain orientation of the aged alloy is complex; besides it is equiaxed; and there are a large number of twins and dislocation lines in the crystal. The matrix contains both Co2Si large-grained precipitated phases and orthorhombic, nanoscale precipitated phases of (Ni,Co)2Si; with sizes in the range of 5–8 nm. (Ni,Co)2Si is the main strengthening phase of the alloy after aging treatment due to its fineness and diffuseness. Solid solution and aging treatment improve microstructure and comprehensive properties of materials, and validated the theoretical guidance and feasibility in practical applications through high-precision quantitative calculations.

Quantitative Microstructure Prediction of Powder High-Temperature Alloy during Solution Heat Treatment and Its Validation

Heat treatment, particularly solution heat treatment, is a critical process in the preparation of powder metallurgy superalloys, where the cooling process significantly impacts the microstructure. This study, based on thermodynamic and kinetic databases as well as the precipitation mechanism of strengthening phases, delves into the influence of cooling process, especially the cooling path, on the material’s microstructure. The results indicate that under slow cooling rates, the precipitated phases are more likely to exhibit a multimodal size distribution, while under rapid cooling rates, a unimodal distribution may form. The average cooling rate does not consistently accurately reflect the growth of the precipitated phases; even with the same average cooling rate, different cooling paths can lead to significant differences in the size of the precipitates. To accurately predict the size of the precipitates, it is necessary to consider the specific cooling process. Constant cooling rate experiments designed for the study and the dissection testing of full-size turbine discs produced in manufacturing validated the calculated results of the precipitates. Therefore, optimizing cooling through simulation calculations can effectively and accurately control the precipitates, thereby obtaining a microstructure that can meet performance requirements.

Microstructure evolution and strengthening mechanism of Al–Cu–Li–Mg–Ag VPPA welded joint during local three-stage and natural aging treatment

Local three-stage (LTA) and natural aging (NA) treatments were proposed to address the challenges associated with the aging treatment of Al–Li alloy fuel tanks and improve the mechanical properties of VPPA welded joints. The microstructure evolution and mechanical properties of aging welded joints were investigated, followed by a discussion of strengthening mechanisms. The results demonstrated that LTA treatment significantly improved the mechanical properties of VPPA welded joints, with an elongation of 6.8 % and a tensile strength of 501 MPa, representing 88.6 % of the base metal. Following the local double-stage solution (LDS) treatment, the eutectic phases in the welded joints dissolved. During the LTA treatment, there was a consistent decrease in elongation. Initially, the θ'' phase precipitated, followed by the T1(Al2CuLi), σ(Al6Cu5Mg2), and S′(Al2CuMg) phases. With increasing aging time, some θ'' phases transformed into θ′(Al2Cu) phases, while others combined with Mg and Ag to form Ω phases. The precipitated phases continued to grow, increasing the precipitation-free zone (PFZ) width. After 30 h of aging, three types of <110> twinned dendrites were observed in the weld zone (WZ) with (111) twinned planes. The improvement in performance was credited to the elimination of eutectic segregation, as well as the enhanced solid solution and precipitation-strengthening effects. The increase in strength of the LDS state welded joints was primarily due to solid solution strengthening. The strength of the precipitated phase was mainly achieved through the bypass mechanism. The eutectic phases did not dissolve after NA treatment, which resulted in limited strength increment and unchanged elongation (EL). Numerous T1 phases precipitated contributed to the precipitation-strengthening effect.

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The medium-entropy alloy (NbTa)0.67\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{0.67}$$\\end{document}(HfZr)0.33\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{0.33}$$\\end{document} and the high-entropy alloy (NbTa)0.67\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{0.67}$$\\end{document}(HfZrTi)0.33\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{0.33}$$\\end{document} were prepared by mechanical alloying using high-energy planetary ball mill. The results of X-ray diffraction, scanning electron microscopy, and positron annihilation lifetime spectroscopy measurements suggest that both as-prepared powders are multicomponent alloys in amorphous (or highly disordered) state. The magnetic and thermodynamic results obtained for these powders undoubtedly prove that bulk superconductivity is not observed at temperatures exceeding 2 K. Thermal treatment of both studied materials leads to decomposition of the amorphous phase and precipitation of several crystalline phases. In both annealed samples, the structure of the main crystalline phase was identified as body-centered cubic (bcc), and in this phase, bulk superconductivity was observed below 6.5 K.

Selective laser melting of the ternary NiTi+3Cu shape memory alloys with excellent properties via microstructural tailoring

The ternary NiTi+3Cu parts were produced using selective laser melting (SLM) with the addition of 3 wt% Cu nanoparticles. The incorporation of Cu nanoparticles resulted in the precipitation of nano-sized Ti2Cu second phase, the refinement of B2 matrix, the elimination of texture, and a transition from columnar to equiaxed grains. The SLM-fabricated NiTi+3Cu parts exhibited excellent antibacterial properties, achieving an antibacterial rate of 70.83 % due to the persistent release of Cu ions. The NiTi+3Cu deposits demonstrated stable tensile performance in both the transverse and longitudinal directions, and they performed better than their NiTi counterparts, primarily due to the effects of B2 grain refinement and the presence of nano-sized Ti2Cu precipitates. As the B2 phases transformed from columnar to equiaxed grains, the anisotropic rate of ultimate tensile strength and elongation to fracture was reduced from 16.3 % to 1.64 % and 16.1–3.07 %, respectively. Furthermore, the wear resistance was also enhanced by the incorporation of Cu nanoparticles, and the wear mechanism shifted from abrasive to delamination wear. These findings indicate that the crack-free ternary NiTi+3Cu shape memory alloys can be fabricated using SLM, synchronously achieving excellent antibacterial, mechanical, and wear properties through microstructural tailoring.

Development of a Versatile Nanostructured Lipid Carrier (NLC) Using Design of Experiments (DoE)-Part II: Incorporation and Stability of Butamben with Different Surfactants.

Nanostructured lipid carriers (NLCs) are typically composed of liquid lipids, solid lipids, and surfactants, enabling the encapsulation of lipophilic drugs. Butamben is a Class II anesthetic drug, according to the Biopharmaceutical Classification System (BCS); it has a log P of 2.87 and is considered a 'brick dust' (poorly water-soluble and poorly lipid-soluble) drug. This characteristic poses a challenge for the development of NLCs, as they are not soluble in the liquid lipid present in the NLC core. In a previous study, we developed an NLC core consisting of a solid lipid (CrodamolTM CP), a lipophilic liquid with medium polarity (SRTM Lauryl lactate), and a hydrophilic excipient (SRTM DMI) that allowed the solubilization of 'brick dust' types of drugs, including butamben. In this study, starting from the NLC core formulation previously developed we carried out an optimization of the surfactant system and evaluated their performance in aqueous medium. Three different surfactants (CrodasolTM HS HP, SynperonicTM PE/F68, and CroduretTM 40) were studied and, for each of them, a 23 factorial design was stablished, with total lipids, % surfactant, and sonication time (min) as the input variables and particle size (nm), polydispersity index (PDI), and zeta potential (mV) as the response variables. Stable NLCs were obtained using CrodasolTM HS HP and SynperonicTM PE/F68 as surfactants. Through a comparison between NLCs developed with and without SRTM DMI, it was observed that besides helping the solubilization of butamben in the NLC core, this excipient helped in stabilizing the system and decreasing particle size. NLCs containing CrodasolTM HS HP and SynperonicTM PE/F68 presented particle size values in the nanometric scale, PDI values lower than 0.3, and zeta potentials above |10|mV. Concerning NLCs' stability, SBTB-NLC with SynperonicTM PE/F68 and butamben demonstrated stability over a 3-month period in aqueous medium. The remaining NLCs showed phase separation or precipitation during the 3-month analysis. Nevertheless, these formulations could be freeze-dried after preparation, which would avoid precipitation in an aqueous medium.

The phase transformation and enhancing mechanical properties in high Zn/Mg ratio Al–Zn–Mg–Cu(-Si) alloys

Aging behavior and phase transformation of Al–5Zn–1Mg–1Cu(-Si) alloys under different isothermal temperatures were investigated using transmission electron microscope (TEM) and mechanical tests. The aging temperature and Si addition significantly influenced to the types of precipitated phases and mechanical properties of the Al–Zn–Mg–Cu alloys. Adding Si in this alloy changed the precipitated phases from T′ and η′ phases to the dual-sized η and GPB-II phases. With increasing isothermal aging temperature, more GPB-II phases formed in alloys with the same composition, effectively improving the microhardness and mechanical properties. When aging at 150 °C, 0.5 wt%Si-containing alloy reached the highest peak hardness of about 150HV and maintained stable hardness, while an alloy without Si only reached 120HV and later declined by 15HV. The tensile strength and yield strength of the 0.5 wt%Si-containing alloy were higher than those of non-Si alloy by 132 MPa and 165 MPa, increasing 51% and 90%, respectively. This result was due to the presence of fine and dispersed 4–8 nm GPB-II phases in 0.5 wt%Si-containing alloy. The GPB-II phase had a core-shell structure, with the core region mainly enriched in Mg and Si, and the shell region mainly enriched in Cu and Zn. Compared with the stability of T′ and η′ phases, this core-shell structure of GPB-II effectively inhibited its growth and beneficially maintained a smaller-sized GPB-II phase. The strengthening effect of GPB-II phase was better than that of η or T phases when aging at 150 °C or 200 °C. The mechanical properties of high Zn/Mg ratios Al–Zn–Mg–Cu alloys can enhanced by adding Si.

Microstructural Evolution and Mechanical Properties of Cast Al–2.6Li–2.8Mg–(0.5, 1.4)Cu–0.2Zr–0.2Sc Alloys during Heat Treatment

Cu is commonly used to improve the mechanical properties of Al–Li alloys, but its exact role in multicomponent Al–Li alloys is not fully understood. Herein, the microstructure and mechanical properties of two cast Al–2.6Li–2.8Mg–(0.5, 1.4)Cu–0.2Zr–0.2Sc (wt%) alloys aged at 165 °C are compared. The results show that Alloy 1.4Cu possesses finer grain size and better mechanical properties than Alloy 0.5Cu. The δ′ (Al3Li), Al3(Sc, Zr, Li) phases, and Guinier–Preston–Bagaryatsky zones are formed in both alloys. During the early stage of ageing (8 h), many dispersed S′ (Al2CuMg) phases precipitate only in Alloy 1.4Cu and coarsen continuously. Instead, many rod‐shaped S1 (Al2MgLi) phases start to precipitate in Alloy 0.5Cu up to ageing for 32 h and then coarsen continuously with ageing. Moreover, Alloy 1.4Cu shows narrower δ′‐precipitate‐free zones along grain boundaries than Alloy 0.5Cu. The higher strength and ductility with more uniform strain distribution for Alloy 1.4Cu than Alloy 0.5Cu is attributed to finer grain size and unique phase formation for the former.

Diagenetic archives of the deeply-buried Cambrian Xiaoerbulake Formation microbialite reservoirs, Bachu-Tazhong area, Tarim Basin, China

The deep-burial Cambrian Xiaoerbulake Formation microbialites reservoir hosts significant hydrocarbon in the Tarim Basin. However, limited understandings of fluid-rock interactions from deposition to deep-burial regimes hamper petroleum exploration. Here, petrological observations, in-situ elemental contents and porosity-permeability analyses were performed to understand the complex interactions and the microbialites performance. Dolo-mudstone, crystalline dolostone, and four kinds of microbialites are distinguished as dolostones types. In the depositional stage, microbialites are characterized by (evaporated) seawater dolomitization with the mediation of microbial activity. The dolostone matrix shows seawater-like δ13C, δ18O and REY patterns. Thrombolitic and foam spongy dolostones from high-energy subtidal to intertidal zones show large framework pores compared to stratiform stromatolitic dolostones from low-energy intertidal zones. In near-surface settings, meteoric diagenesis generates secondary pores, while fine-crystalline dolomite cements partially fill pores. During the shallow to intermediate burial regimes, medium-to coarse-crystalline dolomite cements yield negative δ18O values and slightly flat REY patterns. The precipitation of this dolomite phase further decreases reservoir porosity. In deep burial settings, one type of saddle dolomite is likely to be formed by replacement from carbonate precursors, while the second type might be directly precipitated from hydrothermal fluids. These two types of saddle dolomites show different cathodoluminescent characteristics and geochemical data. Subsequently, two types of calcite cements are formed by the calcification of dolomite and yield significant negative δ13C values due to thermochemical sulfate reduction. Finally, the third calcite phase is likely to be a direct precipitate from burial brines. Hydrothermal activity and thermochemical sulfate reduction generate and/or re-distribute secondary pores. Based on the plethora of depositional environments and fluid-rock interactions, thrombolitic dolostone generally yields higher porosity-permeability than other types of microbialites. Thrombolite reservoir has high potential for petroleum exploration and is significant for those concerned with microbialite hydrocarbon fields.

The Atomic Atmosphere at the Antiphase Domain Boundary in Ni3Al: A Phase‐Field Study

The atomic atmosphere and formation mechanism of the antiphase domain boundary (APB) may depend on the environmental variables of the phase transformation for the L12‐structural Ni3Al phase, which is the first important precipitate phase for Ni‐based superalloys. Herein, a discrete phase field method is used to reproduce the complete formation process of an APB without preset restrictions. Numerical calculations are performed to classify the atomic atmosphere, and its formation mechanism is revealed by calculating and analyzing the functional properties of the driving force. The formation process shows that four types of antiphase domains survive to form the APB. The numerical calculation results demonstrate that the atomic atmosphere has the same temperature dependence for hypostoichiometric, stoichiometric, and hyperstoichiometric systems. However, Al plays two opposite roles in influencing the atomic atmosphere according to the changes in the alloy system. The positive and negative values of the driving force determine whether the atomic atmosphere is segregated or depleted, and the magnitude of the absolute value determines the atomic atmosphere level. This atomic‐scale study of nanoscale ordered domain boundaries can provide theoretical information for further understanding of these and similar interfaces in ordered precipitation‐strengthened phases.

Improved mechanical behavior of friction stir drilled 6082 aluminum alloy via T6 treatment

6082 Al-alloy underwent a friction stir drilling (FSD) processing. Subsequently, a two-stage post-heat treatment (PHT) procedure, i.e., solution treatment at 550 °C for 2 h, followed by artificial aging at 175 °C for 18 h, was implemented to significantly enhance microstructure and mechanical performance of the alloy. The microstructure was characterized by optical, laser, scanning electron and electron backscattered diffraction microscopes, while the mechanical behavior was assessed by a micro-indentation hardness tester, employing the indentation hardness (HIT) technique. Corrosion behavior of FSD as well as PHT specimens was investigated through electrochemical techniques.The microstructure of the base metal (BM) manifested an α-Al matrix with an average grain size of approximately 50 μm. FSD resulted in the creation of stirring zone (SZ) and thermo-mechanical affected zone (TMAZ), with respective widths of 400 ± 50 and 950 ± 100 μm. The SZ exhibited a very fine structure with an average grain size of 0.5 μm, thereby displaying increased hardness. The PHT microstructure displayed the formation of fine βʹ and βʺ second phase precipitate types, whereas the HIT hardness of the PHT α-aluminum matrix in the SZ, was lower than TMAZ and BM, due to reductions of βʹ in the SZ compared to TMAZ and BM. Moreover, the corrosion rate of the SZ decreased after the heat-treatment cycle, attributed to the recovery of strain energy induced during friction drilling and the increased solubility of solute atoms within the α-Al matrix.