Microstructural Stability Research Articles

Enhancing Ω Phase Thermal Stability in Al Alloys through Interstitial Ordering.

Scandium (Sc) can orderly occupy interstitial sites within the Ω phase of aluminum alloys, forming a new phase that significantly enhances the thermal stability of the alloy. However, Sc is relatively expensive and rare. In this work, we employ first-principles calculations to delve into the physical essence interstitial ordering of Sc in enhancing thermal stability at the electronic level, thereby revealing the crucial factors responsible for this improvement. By computationally screening all potential metallic elements across the periodic table, we uncover that, in addition to Sc, a diverse range of elements including lithium (Li), calcium (Ca), strontium (Sr), and some of rare earth elements (Sm, Ce, Y), possess the potential to contribute to thermal stability enhancement through interstitial ordering mechanisms in aluminum alloys. This study deepens our understanding of microstructural thermal stability and offers novel strategies for designing improved thermally stable Al alloys.

A new methodology for investigating the weld joint microstructure and micro-hardness of the austenitic stainless steel clad plate made by SMAW/GTAW multi-pass welding process: part III – clad layer case study

In this study, the influence of repeated thermal cycling during multi-pass welding on the microstructural transformations and mechanical properties of austenitic stainless clad-steel plates (ASCSPs) was investigated, with a particular focus on the clad layer. A novel methodology was employed, involving the complete filling of the groove length and gradually shortening subsequent passes. Microstructural characterization of various zones within the welded joint was conducted using optical microscopy. The results demonstrated that repeated thermal cycles during multi-pass welding caused significant microstructural changes in the weld metal clad layer (WM-CL), including the transformation from columnar to equiaxed grains and the evolution of δ-ferrite morphology from dendritic to skeletal. Additionally, the ferrite number decreased from 8.5 ± 2 in the sixth pass to 2 ± 0.5 in the ninth pass, correlating with increased heat input (HI) from 15.5 kJ/cm to 25.8 kJ/cm and repeated thermal cycling. Furthermore, the heat-affected zone (HAZ) exhibited coarse-grained polygonal austenite near the fusion line, with recrystallization attributed to the high thermal input. Micro-hardness measurements showed a reduction from 320 HV in the sixth pass to 195 HV in the ninth pass, linked to alloying element diffusion and ferrite content reduction. The findings highlight the importance of controlling thermal cycles and HI during multi-pass welding to optimize the microstructural stability and mechanical properties of ASCSP welded joints. These results provide valuable insights for improving the performance of ASCSP in industrial applications.

Thermal stability of microstructure on heat treatment of friction stir welded AA2014-T651 aluminum joints

Исследовано влияние термической обработки на микроструктуру и механические свойства соединений из алюминиевого сплава AA2014-T651, полученных сваркой трением с перемешиванием. Сварка трением с перемешиванием выполняется с помощью треугольного инструмента при двух скоростях вращения: 1000 и 1400 об/мин. При этом сварка осуществлялась с постоянной скоростью 63 мм/мин при обеих скоростях вращения инструмента. Установлено, что сварка трением с перемешиванием приводит к значительному измельчению микроструктуры и частичному растворению упрочняющих включений. Сварные соединения подвергали термообработке при температурах 573, 673, 773 и 823 К в течение одного часа. При термообработке наблюдалось вторичное выделение и укрупнение включений в сварном шве. Показано, что увеличение скорости вращения инструмента значительно повышает термическую стабильность микроструктуры, практически не вызывая аномальный рост зерен в сварном шве.

Effects of pre-tension on the microstructural stability and mechanical properties of a near-alpha high temperature titanium alloy

Effects of pre-tension on the microstructural stability and mechanical properties of a near-alpha high temperature titanium alloy

Order phase transition of HIP nickel-based powder superalloy during isothermal aging

Nickel-based powder superalloys have become one of key materials for aerospace turbine engines due to their excellent comprehensive properties. The microstructure stability during long-term isothermal aging is closely related to mechanical properties. The correlation between order phase transition and mechanical properties of a HIP (hot isostatic pressing) nickel-based powder superalloy after long-term isothermal aging treatment was investigated. The results show that the decomposition of MC carbides and precipitation, growth and coarsening of γ' phases occur with duration of isothermal aging. Tertiary γ' phases precipitates by the way of element diffusion with γ' phases coarsening. In addition, strengthening mechanism is quantitatively calculated, and the relative contribution of γ' phases to yield strength is largest, and multi-mode size of γ' phases are favorable to yield strength and hardness of HIP nickel-based powder superalloy.

High density lath twins lead to high thermoelectric conversion efficiency in Bi2Te3 modules.

Thermoelectric (TE) generators based on bismuth telluride (Bi2Te3) are recognized as a credible solution for low-grade heat harvesting. In this study, an combinative doping strategy of both the donor (Ag) and the acceptor (Ga) in Ag9GaTe6 as dopants is developed to modulate the microstructure and improve the ZT value of p-type Bi0.4Sb1.6Te3. Specifically, the distribution of Ag and Ga in the matrix synergistically introduces multiple phonon scattering centers including lath twins, triple junction boundaries, and Sb-rich nanoprecipitates, leading to an obviously suppressed lattice thermal conductivity of 0.50 W m-1 K-1 at 300 K. At the same time, such unique microstructures of lath twins synergistically enhance the room-temperature power factor to 48.8 μW cm-1 K-2 and improve the Vickers hardness to 0.90 GPa. Consequently, a high ZT of 1.40 at 350 K and ZTave of 1.24 (300-500 K) are achieved in the Bi0.4Sb1.6Te3 + 0.03 wt% Ag9GaTe6 sample. Based on that, a competitive conversion efficiency of 6.5% at ΔT = 200 K is obtained in the constructed 17-couple TE module, which exhibits no significant change in the output property after 30 thermal cycle tests benefiting from the stable microstructure.

Thermal stability of microstructure and properties of ingots and fine wires from Al–Zr alloys

The process of precipitation of Al3Zr particles in cast Al–(0.25–0.4) wt % Zr alloys manufactured by the induction casting method is studied. The effect of zirconium concentration on the microstructural parameters, hardness, and specific electrical resistance (SER) of cast alloys is investigated. The dependences of hardness and SER on the time of cast alloys annealing at 500°C are plotted. The parameters of the Johnson–Mehl–Avrami–Kolmogorov equation for alloys with different Zr content are determined. The optimal regimes of cast ingot aging are found. Fine wires with ∅ 0.3 mm are manufactured by the drawing method; their strength, SER, and hardness are studied in the initial state and after heat treatment. The tests of thermal stability of wires are carried out according to the state standard GOST R MEK 62004–2014.

Low Thermal Conductivity and Diffusivity at High Temperatures Using Stable High-Entropy Spinel Oxide Nanoparticles.

The realization of low thermal conductivity at high temperatures (0.11W m-1 K-1 800 °C) in ambient air in a porous solid thermal insulation material, using stable packed nanoparticles of high-entropy spinel oxide with 8 cations (HESO-8 NPs) with a relatively high packing density of ≈50%, is reported. The high-density HESO-8 NP pellets possess around 1000-fold lower thermal diffusivity than that of air, resulting in much slower heat propagation when subjected to a transient heat flux. The low thermal conductivity and diffusivity are realized by suppressing all three modes of heat transfer, namely solid conduction, gas conduction, and thermal radiation, via stable nanoconstriction and infrared-absorbing nature of the HESO-8 NPs, which are enabled by remarkable microstructural stability against coarsening at high temperatures due to the high entropy. This work can elucidate the design of the next-generation high-temperature thermal insulation materials using high-entropy ceramic nanostructures.

Thermal Stability of Residual Stress, Microstructure, and Mechanical Property in Shot-Peened CNT/Al-Cu-Mg Composites

To investigate the thermal stability of a shot-peened specimen and ensure the reliability operation under high temperatures, CNT/Al-Cu-Mg composites were treated by shot peening (SP) and the isothermal aging treatment. The heating temperatures were 100, 150, 200, and 250 °C. Changes in surface residual stress and the distribution along the depth were investigated. The microstructure changes were analyzed by XRD and observed by TEM. Changes in mechanical properties were characterized by microhardness. The results show that the compressive residual stress (CRS) release and the microstructure changes mainly occurred at the initial stage of heating treatment. After 128 min of isothermal aging treatment at 250 °C, the surface CRS released 91.9% and the maximum CRS released 80.9%, the surface domain size increased by 222%, and the microstrain and microhardness decreased by 49% and 27.3%, respectively. The reinforcement effect introduced by SP basically disappeared. A large number of second-phase particles, such as CNT, Al2Cu, and Al4C3, were anchored at grain boundaries, hindering dislocation movement and enhancing the thermal stability of the material. Isothermal aging treatment at 100 °C and 150 °C for a duration of 32 min is a reliable circumstance for maintaining SP reinforcement.

Efficient Ethanol Sensor Based on Vertically Aligned ZnO Nanorods on Radio Frequency Sputtered ZnO/Pt/SiO2/Si Substrate

The volatile organic compounds (VOCs) sensing device is developed by using hydrothermally grown vertically aligned 1D ZnO nanorods (ZnO NRs) on radio frequency sputtered ZnO/Pt/SiO2/Si substrate. Before the fabrication of the sensor device, the microstructure, morphology, and temperature stability of the NRs are characterized using x‐ray diffraction, absorption and emission spectrum, field emission scanning electron microscopy, and thermal gravimetric analysis. Observation shows the formation of well‐vertically aligned, temperature‐stable (up to 900 °C) ZnO NRs with a hexagonal wurzite phase. The NRs show enhanced defects, vacancies, and interstitial‐related green emission (503 nm) and red emission (655 nm) with a bandgap of ≈3.74 eV. The observed Raman active E1 and A1 modes are prominent for such NRs. The sensing device exhibits a selective response to ethanol as compared with other VOCs (e.g., methanol, ethanol, and 2‐propanol). The oxygen‐vacancy‐rich ZnO NRs show enhanced ethanol sensing with a speedy response time (87–97 s) and recovery characteristics time (66–169 s). The device shows a lower detection limit for ethanol ≈4.5 ppm. The ethanol sensing mechanism and the advantages of the as‐grown vertically aligned ZnO NRs structure as sensing material are also discussed. The device shows excellent long‐term stability (≈20 weeks) and reproducing capability for ethanol.

Microstructural Suitability and Stability of AlSi10Mg–Sn Plasma Coatings for Thermal Energy Storage Purposes

The study explored the possibility of producing thick coatings of fully metallic composite phase change materials with suitable microstructure for thermal energy storage or thermal energy management purposes. The composite materials are based on Al-Si-based alloys with Sn additions, potentially obtainable from scraps. This leads to an Sn-rich low-melting phase which is able to store/release heat when it melts/solidifies. The material can thus be considered as a composite phase change material (C-PCM). A thick coating was deposited on an Al alloy substrate by plasma spray, mixing AlSi10Mg and Sn powders in a 60:40% mass ratio. Optical scanning microscopy and X-ray diffraction revealed a microstructure suitable for a C-PCM, presenting Sn basins interrupted by a matrix made up of primary Al and Al–Si eutectic. Preliminary investigation into the reliability of the coating was conducted by performing up to 10 heat cycles across the melting temperature of the low-melting phase, simulating service in TES/TEM devices. No significant changes in its coating microstructure were observed. Minor surface leakage of molten Sn occurred, mainly during the first heat cycle. No detachment of the coating or cracks formed within the coating were observed, which could have been expected due to the mismatch in the coefficients of thermal expansion of the main phases and to the expansion/shrinkage due to Sn melting/solidification.

Precipitation behavior of G-phase and its effect on mechanical properties of 30Cr2Ni4MoV steel

Precipitation behavior of G-phase and its effect on mechanical properties of 30Cr2Ni4MoV steel during thermal aging at 350–600 °C for 0–10,000 h are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atom probe tomography (APT), hardness and impact tests. Aging at 500 °C, the martensitic matrix of 30Cr2Ni4MoV steel basically keeps stable. With the lath width almost remaining unchanged, carbides coarsen to a slight degree, but G-phase will precipitate at grain boundary (GB). The G-phase is Ni16Mn6Si7 and its “nose” temperature is around 500–550 °C. Due to relatively high enrichment level of forming elements including Ni, Mn and Si at GB, the G-phase can nucleate at triple junction or adjacent to M23C6 at GB. Subsequently, the G-phase grows along GB until contacts with M23C6, and then coarsens along the width direction, which results in alternating distribution morphology of G-phase and M23C6 at GB. The Vickers hardness results show that the hardness remains stable due to the relatively stable microstructure after aging. After aging for 10,000 h, the hardness undergoes little decrease due to the slight coarsening of M23C6 and G-phase. Interestingly, the impact energy drops obviously after the precipitation of G-phase. The reason is that the G-phase at GB promotes the initiation and propagation of cracks during the impact process, leading to intergranular fracture (IGF).

Investigation the Effect of Hydrothermal Aging on the Microstructural, Physical, and Color Stability of Different Dental Ceramics. (An in vitro Study)

Рurроse: To evaluate the influence of thermocycling on the microstructural, physical, and color stability of three CAD/CAM ceramic materials. Materials and Method: In total, 93 specimens (7×5×1.5mm) were prepared from lithium disilicate glass ceramic (IPS e.max CAD), Extra translucent zirconia (VITA YZ), and resin nanoceramic (Cerasmart 270). All the materials was A2 or equivalent shades. The samples were obtained as directed by the manufacturer. these were samples exposed to thermocycling at 5 to 55 C in distilled water for (10.000 cycles). Color stainability, surface roughness, microhardness and surface microstructure were measured and assessed prior and after thermocycling. The Statistical analysis were performed with a Wilcoxon Signed Ranks Test, independent Kruskal-wallis test and Pearsons’s correlation analysis. The significant level was set at P ≤ 0.05. Results: prior and after hydrothermal aging Cerasmart presented the lowest hardness value . VITA XT exhibited the highest hardness value . The surface roughness had the maximum level of exhibition in VITA XT group . lithium disilicate exhibited the lowest surface roughness values . Cerasmart showed the highest color changes values (∆E) after hydrothermal aging , lithium disilicate showed the lowest (∆E) values . after the hydrothermal aging the hardness of VITA XT increased significantly . surface roughness of lithium disilicate increased significantly after aging . for stain ability all the materials used in this study was within the clinically accepted threshold < 3.3 . Conclusion: Cerasmart showed least degree of hardness before and after aging and highest stainability after aging . Before and after aging, VITA XT showed the highest levels of hardness and surface roughness. lithium disilicate presented the lowest stainability , lowest surface roughness prior and after aging .

Investigation of thermal stability of residual stresses and microstructure of dual shot peened TC17 titanium alloy

Investigation of thermal stability of residual stresses and microstructure of dual shot peened TC17 titanium alloy

Microstructural design opportunities and phase stability in the spray-formed AlCoCr0.75Cu0.5FeNi high entropy alloy

Designing a microstructure with controlled morphology is one of the determining factors for the optimum performance of a material. High entropy alloys (HEAs) have gained significant attention due to their enhanced mechanical and functional properties compared to conventional alloys, particularly based on opportunities for microstructural design. In this fast-developing field, varied thermal treatments can be applied to engineer a material as per the requirements. In the present work, we have studied the effect of thermal treatment on the microstructural modifications in the spray-formed AlCoCr0.75Cu0.5FeNi HEA. The alloy was characterized by using a light microscope, scanning electron microscope equipped with EDS detector and electron probe micro analyzer (EPMA). The elemental distribution and microstructural evolution of the alloy were studied by giving the heat treatments at different time-temperature spaces. The evolution of phases and their composition were correlated with the CALPHAD predicted property diagram and phase composition. It is observed that at a higher temperature of 1300°C, the alloy shows the simple solid solution phases to be more stable due to the high entropy effect, which brings down the Gibbs free energy of the system. The formation of the disordered BCC, FCC and their derivatives along with the sigma phase were observed in the temperature range of 600-1000°C. This work also draws attention to why understanding the microstructural evolution and solidification behaviour is important in designing the HEAs to meet the industrial promises and the role of entropy, enthalpy and slow diffusion kinetics are discussed.

High-temperature mechanical properties and thermal shock resistance of an alumina-fiber-reinforced alumina ceramic matrix composite

An alumina-fiber-reinforced alumina ceramic matrix (Al2O3/Al2O3) composite is fabricated by a slurry infiltration process in this study. The slurry contains Al2O3 powders with broad particle size distribution (d10=0.35 μm, d50=0.57 μm, d90=1.90 μm). The resultant Al2O3/Al2O3 composite exhibits a density of 2.95 ± 0.02 g/cm3 and porosity of 25 ± 1%. Mechanical properties are assessed via three-point flexural tests, revealing a high flexural strength of 400 ± 8 MPa at room temperature. The high-temperature mechanical properties and thermal shock resistance are further examined. The flexural strength remains stable from room temperature to 1100°C, while temperatures up to 1200°C induces superplastic behavior. After thermal shock tests (5, 10 and 20 cycles at 1100°C), the composite maintains a stable microstructure and flexural strength. The Al2O3 powders with broad particle size distribution are beneficial to the high-temperature mechanical properties and thermal shock resistance of the Al2O3/Al2O3 composite.

Enhancing thermal stability of laser powder bed fusion fabricated 60NiTi alloy via Nb alloying

60NiTi (Ni55Ti45) alloy has a unique microstructure composed of a B2 NiTi matrix with supersaturated Ni atoms and numerous nanoscale Ni4Ti3 precipitates, resulting in excellent strength, hardness, and superelasticity. However, these characteristics make it challenging to directly form complex components. In addition, significant decrease in Ni saturation degree and coarsening of Ni4Ti3 precipitates lead to performance degradation of 60NiTi alloy during prolonged service. In this study, a 60NiTi-Nb (Ni55Ti40Nb5) alloy was successfully designed and fabricated using Laser Powder Bed Fusion (LPBF), which exhibits complex geometry and superior thermal stability. Particularly, after a heat-treatment at 500 °C for 5 h, the size of precipitates Ni4Ti3 in the Ni55Ti40Nb5 alloy increases by just over 10 nm, maintaining a hardness above 620 HV, whereas the Ni55Ti45 alloy experiences a precipitate size increase close to 200 nm, leading to a hardness decrease of 100 HV. The superior thermal stability is primarily attributed to the enrichment of Nb surrounding the Ni4Ti3 precipitates, which reduces the growth rate of the Ni4Ti3 precipitates, and the coexistence of spinodal decomposition and ordering in the matrix, thus enhancing microstructural stability. This study provides valuable insights for the development of 60NiTi complex structural components with high thermal stability, thereby promoting the application of 60NiTi alloys.

Microstructural stability enhancement and mechanical reinforcement of TLP-bonded Cu/Sn-3.5Ag/Cu microbumps under multiple reflow cycles through Zn Alloying and Ni substrate integration

The transient liquid phase (TLP) bonding process is effective for constructing stacked structures in advanced packaging, as it allows for multiple reflow cycles without remelting. However, the various reflows can cause phase transformations, leading to internal stress-induced voids. Thus, the stability of IMC phases is particularly challenged in 3D stacking structures. Common configurations include Cu/Sn/Cu and Cu/Ni/Sn/Cu. Although Ni improves the stability of the Cu6Sn5 phase, phase transformation to Cu3Sn can still occur, compromising reliability. This study investigates microstructure stability by doping Zn into the Cu/Sn-3.5Ag/Ni system across five reflow cycles. Results demonstrate that Cu-15Zn/Sn-3.5Ag/Ni microbumps reduce void formation and ensuring the phase stability of the (Cu,Ni)6(Sn,Zn)5 to maintain the microstructure stability. The Zn addition inhibits the Cu3Sn layer, while optimizing grain size and orientation of (Cu,Ni)6(Sn,Zn)5. (Cu,Ni)6(Sn,Zn)5 also exhibits increased hardness and reduced modulus (Er). These findings provide critical insights for designing sub-10-μm scale TLP-bonded microbumps in advanced packaging.

Enhancing Cesium Cation Exchange Efficiency Using Transition Metal-Based Core-Shell Prussian Blue Analogue-Carbon Nanofiber Composites

Electrochemical cation exchange processes are vital for diverse applications, including energy storage, catalysis, and environmental remediation. However, enhancing the efficiency of cation exchange with novel materials remains a challenge. Prussian blue (PB) is well-known to its excellent cation exchange properties, but improving its performance is necessary. To solve these problems, the use of various supporting matrices attach to PBA colloids has been reported such as zeolite, silica or carbon-based materials. In light of this, carbon-supported materials are particularly effective due to their unique microstructure and chemical stability, enabling rapid electron transfer. Among potential solutions, core-shell structured composites present a promising approach for enhancing electrochemical properties due to their unique architecture and synergistic effects.In this study, we propose a method for synthesizing core-shell structured Prussian blue analogue-carbon nanofiber (PBA-CNF) composites using various transition metals (Fe, Ni, Co, Cu, Mn) via electrodeposition and evaluated their effectiveness in cesium cation exchange via electrochemical adsorption/desorption processes. The prepared samples are characterized using SEM, TEM, and XRD measurements. Electrochemical characterization confirmed distinct adsorption and desorption behaviors for each transition metal-based composite. In particular, Fe, Ni, and Cu-based PBA-CNF composites exhibited enhanced efficiency in both cesium adsorption and desorption compared to other PBA-CNF composites. This suggests the potential for effectively removing cesium from contaminated water sources. This study highlights the significance of transition metal-based PBA composites in resolving challenges associated with cesium contamination through electrochemical applications

Phase-Structure-Property Relationships of Halide Coating Materials for Solid Composite Electrodes

Lithium-ion batteries (LIBs) have played a pivotal role in advancing energy storage technologies, enabling high-demand applications such as electric vehicles and renewable energy storage systems. Despite their widespread use, LIBs face significant challenges in terms of energy density and intrinsic safety issues. These challenges have spurred interest in all-solid-state batteries (ASSBs), which utilize solid electrolytes (SEs) to offer safe alternatives to conventional liquid electrolyte-based LIBs. Among the various types of SEs explored to date, halide SEs exhibit improved compatibility with high-voltage oxide cathodes, as compared with sulfide-based SEs. Thus, halide SEs may be utilized as cathode coating materials for ASSBs using sulfide SEs with high ionic conductivity. However, the specific material properties that determine the chemical/electrochemical characteristics of halide coatings have not been clearly studied yet.In this study, we synthesize lithium yttrium chloride (Li3YCl6, LYC) SEs using different methods (solid-state synthesis and ammonium-assisted liquid-phase synthesis) at various heat-treatment temperatures to control phase compositions and crystal structures. These allow us to systematically explore the phase-structure-property relationship of LYC SEs and their roles as coating materials for LiNi0.90Co0.05Mn0.05O2 (NCM). Our experimental findings reveal that the phase, crystal structure and crystallinity of LYC significantly influence the microstructure, ionic conductivity, interfacial compatibility, and thermal stability of LYC-coated NCM (NCM@LYC). The crystal structure and crystallinity of synthesized LYC SEs are explored by Rietveld refinement of X-ray diffraction patterns. Notably, LYC SEs prepared via wet synthesis under optimal heat-treatment conditions exhibit superior Li-ion transport kinetics due to the enhanced crystallinity of phase-pure LYC. This leads to the improved interfacial resistances of NCM@LYC, as evidenced by impedance analyses of NCM composite electrodes. Therefore, the NCM@LYC composite electrodes with the optimized LYC SE show significant improvement in rate capability and cycle lifetimes. This research elucidates the critical role of the synthesis conditions in controlling the properties of halide coating materials and thus in improving the interfacial kinetics and stability of composite cathodes of ASSBs. The insights gained from the phase-structure-property relationships provide valuable guidelines for the development of highly conductive and stable SEs for next-generation batteries.