Diffusion Rate Of Atoms Research Articles

Dislocation density evolution and related model construction of Ti60 alloy under multi-physical field coupling

Electrically-assisted forming (EAF) is a novel process that has shown the potential to reduce stress, improve formability, and accelerate recrystallization. However, the lack of a suitable physical coupling model due to the imperfect response mechanism of pulse current to dislocation density limits subsequent EAF finite element simulation. In this study, Ti60 alloy is subjected to periodic electro-assisted tensile (EAT) tests. The effects of current densities and pulse periods on dislocation density are expounded, and a physical coupling model based on dislocation density is established. The results are as follows: pulse current can promote the diffraction peak (001) to shift to a lower angle, and enhance the collision between electrons and atoms, elevating the rate of atomic diffusion. The phenomenon of recrystallization and grain growth leads to a decrease of dislocation density. After necking, the velocity of dislocation motion and annihilation is several times higher than that before necking, causing significant changes in flow stress. The modified Johnson-Cook (JC) model, which considers only temperature (T) and current density (J), exhibits a larger EAARE value after necking. Modified dislocation density (MDD) is a physical coupling model based on dislocation density (ρ), supplemented by current density (J) and temperature (T). The response of this model to flow stress is instantaneous, which can not only reflect the remarkable characteristics of the EAT process but also greatly improve the prediction accuracy after necking.

Influence of Bonding Temperature on Microstructure and Mechanical Properties of AZ31/Zn/Sn/5083 Diffusion Joint.

Diffusion bonding with an interlayer is considered an effective means of obtaining Mg/Al dissimilar alloy joints. However, at low temperatures, it is often impossible to simultaneously achieve joints between the interlayer and Mg/Al under the same bonding parameters. For this reason, the interlayer is usually prefabricated on the substrate, followed by conducting diffusion bonding. Due to the higher diffusion rate of atoms in the liquid phase compared to atoms in the solid phase, creating a liquid phase field in diffusion bonding to reduce diffusion resistance and thus omitting the step of prefabricating the interlayer is a feasible approach. In this study, solid-state diffusion bonding and TLP (transient liquid phase) diffusion bonding were combined. The low-temperature diffusion bonding of the Mg/Al alloy was achieved under the same parameters using a Zn/Sn composite interlayer, utilizing the formation of a Zn-Sn eutectic liquid phase and the complete melting of Sn during heating without requiring a prefabricated interlayer. Unlike conventional composite interlayers used in diffusion bonding, the Sn layer of the Zn/Sn composite interlayer completely melts into liquid and is squeezed out of the bonding interface at the bonding temperature. The Mg/Zn interface was bonded by solid-state diffusion bonding, while the Al/Zn interface was joined through TLP diffusion bonding. Research on the bonding temperature showed that the bonding temperature range was narrow and that variation in the bonding temperature had a significant impact on the microstructure of the joints.

Influence and mechanism of ultrafast laser-textured Cu substrate on wetting behavior of SAC305 solder

Periodic arrays of grids, micro-cones, and grooves were successfully fabricated on Cu substrate using ultrafast laser technology. The wetting behavior of SAC305 solder on micro-nano structured Cu substrates was investigated, and the influence mechanism of superficial micro-nano structure was discussed using classical wetting model and molecular dynamics (MD) simulation. The results indicate that compared to polished surface, all the superficial micro-nano structures on Cu substrate improve the wettability and wetting kinetics of SAC305 solder. Especially, grid structure shows the most significant improvement, and the effect is further enhanced with the increase of processing depth. When the processing depth of grid structure is 25 μm, the smallest wetting angle of 15.1° and wetting equilibrium time of 29 s were achieved. The wetting process of SAC305 solder on Cu substrate is composed of rapid reaction stage, stable diffusion state, and equilibrium stage. Rn ∼ t relationship curve reveals that the influence of micro-nano structure on wetting kinetics mainly occurs in the rapid reaction stage. The enhancement of wettability and wetting kinetics from superficial micro-nano structure can be attributed to the introduced extra capillary force and the improved atomic diffusion rate on the wetting interface.

(Invited) Morphology-Engineered Hematite for Addressing Short Hole-Diffusion Lengths

This study addresses challenges in photoelectrochemical (PEC) water oxidation on hematite photoanodes, with a focus on overcoming the limited hole diffusion length (~4 nm) and poor electrical properties. To achieve this, an efficient overlayer is integrated onto the branched structure, generating a highly porous architecture by leveraging additional reaction interfaces exploiting the Kirkendall effect. This phenomenon occurs during high-temperature annealing, particularly at the interface of the overlayer and Ti-FeOOH (hematite precursor), utilizing distinct diffusion rates of metal atoms. By introducing additional interfaces on the hematite precursor surface, porosity and pore size are effectively controlled, resulting in a highly nanoporous structure. Through morphological engineering, the overlayer facilitates heteroatom diffusion (doping) into the hematite lattice, thereby promoting facile charge transport. The overlayer material selection is guided by density functional theory calculations. The resulting optimized photoanode, combined with an efficient cocatalyst (NiFe(OH)x), exhibits a maximum photocurrent density of 5.1 mA cm-2 at 1.23 V vs. RHE, marking a 3.2-fold increase compared to the reference hematite photoanode. This enhancement is attributed to the highly nanoporous structure and optimal doping. Thus, this study represents a significant advancement in enhancing the PEC performance of hematite-based photoanodes for future applications.

Early Stages of High‐Temperature Oxidation Behavior and Its Phase Evolution of 9% Ni Steel

Herein, the effects of oxygen partial pressure (5–20%) and oxidation time (0.5–6 h) on the growth behavior and phase structure of 9% Ni steel oxide layer are studied by means of high‐temperature oxidation experiment, scanning electron microscopy, and X‐ray diffraction. The results show that the inner and outer oxide layers of 9% Ni steel grow opposite to each other along the initial surface direction of the vertical matrix during the high‐temperature oxidation process. From the perspective of the phase, the phase transition of Fe2O3→Fe3O4→FeO mainly undergoes from the outside and the inside, the results of thermodynamic calculations show that <<<0, and the main factor affecting the phase transition is the diffusion concentration of free O and Fe atoms. During the high‐temperature oxidation process of 9% Ni steel, the diffusion of O and Fe atoms along grain boundaries promotes preferential oxidation at these boundaries. The columnar structure formed in the outer oxide layer of 9% Ni steel may be related to the uneven diffusion rate of Fe atoms at different positions at the interface between the inner and outer oxide layers.

500 μm heavy micro-alloyed Cu wire for IGBT application: The study on microstructure characteristics, electrical fatigue fracture mechanism and bonding reliability

In this study, we introduced trace amounts of silver and nickel into 500 μm diameter copper wires to form micro-alloyed copper wires used in insulated gate bipolar transistors (IGBT). The addition of silver and nickel enhanced the mechanical properties of the conductors and suppressed the work hardening effect, significantly improving the power cyclic lifetime. Additionally, this study conducted chlorination and high-temperature oxidation test to compare the application characteristics of the heavy micro-alloyed copper wires with pure copper wires, through tensile and bending test, as well as electrical property comparisons. Finally, Cu50Ni (50 ppm Ni) wires were selected and nickel ceramic substrates for wire bonding to evaluate module electrical properties and bonding reliability.In the chloride test, there was no significant pitting corrosion observed in copper wire, and the micro-alloyed copper wire outperformed the pure copper wires in terms of bending lifetime and power cycling performance. In the high-temperature oxidation test, an oxide layer of cuprous oxide formed on the surface of all wires. The pure copper wire exhibited a significant increase in resistance. Notably, the micro-alloyed copper wires had better resistance to oxidation. Regarding wire bonding, the use of Cu50Ni wires and nickel ceramic substrates reduced the diffusion rate of nickel atoms from the substrate to the copper wire, forming a thinner alloy diffusion layer. This prevented electrical degradation and achieved high bonding reliability, especially under higher bonding forces. These findings confirm that micro-alloyed copper wires are suitable for high-power applications.

Synergistic optimization of microstructure and mechanical properties of AISI 430 ferritic stainless steel via dual-phase zone annealing process

This study systematically evaluated the impact of dual-phase zone annealing on the microstructure and mechanical properties of cold-rolled 430 Ferritic Stainless Steel (FSS), focusing on the phase transformation process from ferrite to austenite and the dissolution and precipitation behavior of the M23C6 phase. The annealing process significantly affects the microstructural characteristics of ferrite and martensite, including grain size, the distribution of grains of various sizes, aspect ratio, and phase content. The amount of martensite first increased and then decreased with rising annealing temperatures. The sample annealed at 1050 °C exhibited the highest martensite content of 29.5%. The variation in martensite content reflects the complex interplay between phase transformation kinetics and thermodynamic equilibrium. As the annealing time increased or temperature rose, the M23C6 phase at ferrite grain boundaries gradually dissolved and re-precipitated at higher temperatures. At lower temperatures, the M23C6 phase precipitated within martensite, but as the temperature increased, the precipitated phase diminished until it disappeared. Temperature changes affect the solubility of precipitates, atomic diffusion rates, and the uniform distribution of atoms across different phases. Appropriately increasing annealing temperature or extending annealing duration enhances the strength and hardness of 430 FSS. However, excessively high annealing temperatures lead to a decline in mechanical properties. The sample annealed at 1000 °C demonstrated the best mechanical properties, achieving a tensile strength of 783 MPa and an elongation of 16.0%. Furthermore, the analysis of fracture morphology and yield behavior in stress-strain curves further elucidated the macroscopic mechanical performance of the material.

Temperature Dependent Growth Kinetics of Pd Nanocrystals: Insights from Liquid Cell Transmission Electron Microscopy.

Quantifying the role of experimental parameters on the growth of metal nanocrystals is crucial when designing synthesis protocols that yield specific structures. Here, the effect of temperature on the growth kinetics of radiolytically-formed branched palladium (Pd) nanocrystals is investigated by tracking their evolution using liquid cell transmission electron microscopy (TEM) and applying a temperature-dependent radiolysis model. At early times, kinetics consistent with growth limited is measured by the surface reaction rate, and it is found that the growth rate increases with temperature. After a transition time, kinetics consistent with growth limited by Pd atom supply is measured, which depends on the diffusion rate of Pd ions and atoms and the formation rate of Pd atoms by reduction of Pd ions by hydrated electrons. Growth in this regime is not strongly temperature-dependent, which is attributed to a balance between changes in the reducing agent concentration and the Pd ion diffusion rate. The observations suggest that branched rough surfaces, generally attributed to diffusion-limited growth, can form under surface reaction-limited kinetics. It is further shown that the combination of liquid cell TEM and radiolysis calculations can help identify the processes that determine crystal growth, with prospects for strategies for control during the synthesis of complex nanocrystals.

High performance Cu/SAC305 solder low temperature bonding using Ti3C2 MXene interlayer

Ti3C2 MXene (MX) was introduced as the interlayer between the Cu film and Sn-3.0Ag-0.5Cu (SAC) solder to inhibit the overgrowth of intermetallic compounds (IMCs) at the bonding interface of Cu and SAC solder. The Cu-MX-SAC bonding was fabricated at 160 °C for 6 mins under a load of 10 MPa. Compared with Cu-SAC bonding, after 72 h aging, the average thickness of the IMCs layer in the Cu-MX-SAC structure is about 47 % thinner. As aging time increases, the diffusion rate of Cu atoms is limited due to the introduction of MXene interlayer, and the growth of IMCs in the Cu-MX-SAC structure is controlled by volume diffusion. For the Cu-MX-SAC solder bonding, after prolonged aging, the shear strength increases, and contact resistance at the bonding interface is almost no change compared with Cu-SAC solder bonding.

Investigation on interfacial compound growth kinetics in Sn-0.7Cu/Cu solder joint and mechanism analysis: Experiments and molecular dynamics simulations

Herein, the interfacial compound growth kinetics and corresponding mechanisms in Sn-0.7Cu/Cu solder joint at aging stage were investigated using both experiments and molecular dynamics simulations. The research results indicate that, the growth rates of interfacial IMCs (Cu6Sn5 IMC and Cu3Sn IMC) are affected by the aging temperature severely, the higher aging temperature leads to the larger growth kinetics for both Cu6Sn5 IMC and Cu3Sn IMC. At aging stage, Cu substrate continuously supplies Cu3Sn IMC with Cu atoms. Those Cu atoms diffuse across Cu3Sn IMC to the Cu3Sn/Cu6Sn5 interface and react with Sn atoms diffused from the Sn-based solder to form new Cu3Sn grains growing towards Cu6Sn5 IMC, and the main crystal orientations are (100), (42–1), and (3−10). As the grain boundary diffusion rate of Cu atoms in Cu3Sn IMC determines the CuSn reaction rate (new Cu3Sn grains formation rate) on Cu3Sn/Cu6Sn5 interface, the growth of Cu3Sn IMC is driven by grain boundary diffusion, which is manifested by a growth index n near to 0.3. Meanwhile, the rod-like Cu6Sn5 IMC preferentially grows into Sn-based solder attributed to the large number of Cu atoms provided by Cu3Sn IMC, which can diffuse to the top of Cu6Sn5 IMC and reacts with Sn-based solder. While when Cu6Sn5 IMC is thick enough, Cu atoms cannot reach to the top of Cu6Sn5 IMC anymore, but diffuse laterally within the Cu6Sn5 grains, resulting in the widening of scallop-like Cu6Sn5 IMCs. As the thickening of Cu6Sn5 IMC is caused by the growth of the existing Cu6Sn5 grains, the diffusion of Cu and Sn atoms in Cu6Sn5 grains plays a decisive role. Therefore, the growth of Cu6Sn5 IMC is driven by bulk diffusion, which is manifested by a growth index n near to 0.5.

Eliminating Cu-Cu Bonding Interfaces Using Electroplated Copper and (111)-Oriented Nanotwinned Copper.

Cu-Cu joints have been adopted for ultra-high-density packaging for high-end devices. However, the atomic diffusion rate is notably low at the preferred processing temperature, resulting in clear and distinct weak bonding interfaces, which, in turn, lead to reliability issues. In this study, a new method for eliminating the bonding interfaces using two types of Cu films in Cu-Cu bonding is proposed. The difference in grain size was utilized as the primary driving force for the migration of bonding interfaces/interfacial grain boundaries. Additionally, the columnar nanotwinned Cu structure acted as a secondary driving force, making the migration more significant. When bonded at 300 °C, the grains from one side grew and extended to the bottom, eliminating the bonding interfaces. A mechanism for the evolution of the Cu bonding interfaces/interfacial grain boundaries is proposed.

Heterostructure mediated high strength and large ductility in novel medium-Mn steels with low Mn content

Medium-Mn steels (MMnS) exhibit superior strength and ductility via the transformation-induced plasticity (TRIP) of retained austenite. However, to realize the partitioning of Mn atoms into retained austenite for thermal stability optimization, long-term intercritical annealing is required. In addition, the high Mn content of MMnS also causes other issues, e.g., high cost, welding, etc. In this work, instead of utilizing the TRIP effect of retained austenite, heterostructure consisting of alternatively distributed lamellar martensite zones and lamellar ultrafine dual-phase (martensite + ferrite) zones was engineered in a MMnS with low Mn content by a conventional rolling and short-term intercritical annealing process. The formation of the heterostructure was attributed to the heterogeneous distribution of Mn, the formation of highly dispersed martensite-austenite (MA) islands in Mn-poor zones and the low diffusion rate of Mn atoms at the intercritical annealing temperature. Tensile test results show that the steel exhibits superb synergy of a high ultimate tensile strength of 1452 MPa, a large ductility of 17 % and a high work hardening capability. The high work hardening capability and large ductility were mainly attributed to the apparent microhardness difference between the lamellar martensite zones and the ultrafine dual-phase zones that caused a strong hetero-deformation induced (HDI) strengthening effect. This study proposes a novel approach to developing high-performance steels, which provides an effective paradigm for addressing the long-established conflicts between mechanical performance, high Mn content and long intercritical annealing period of MMnS.

Enhanced Copper Bonding Interfaces by Quenching to Form Wrinkled Surfaces

For decades, Moore’s Law has been approaching its limits, posing a huge challenge for further downsizing to nanometer dimensions. A promising avenue to replace Moore’s Law lies in three-dimensional integrated circuits, where Cu–Cu bonding plays a critical role. However, the atomic diffusion rate is notably low at temperatures below 300 °C, resulting in a distinct weak bonding interface, which leads to reliability issues. In this study, a quenching treatment of the Cu film surface was investigated. During the quenching treatment, strain energy was induced due to the variation in thermal expansion coefficients between the Si substrate and the Cu film, resulting in a wrinkled surface morphology on the Cu film. Grain growth was observed at the Cu–Cu bonding interface following bonding at 300 °C for 2 and 4 h. Remarkably, these procedures effectively eliminated the bonding interface.

Induced Diffusion Effect Realizes Heterogeneous Separation/Aggregation for In Situ Fabrication of Heterostructure with Enhanced Catalytic Activity

AbstractSpace charge transfer, which can be provided by heterogeneous structure, is the key to efficient electrocatalytic processes. However, difficulty in controlling the relative atomic diffusion rates due to different atomic radii and affinity makes heterogeneous nanostructures difficult to be accurately designed. Herein, an induced diffusion strategy based on affinity differences between elements is proposed to direct the separation/aggregation of different components in the precursor. The key to strategy in this study is the different affinity of Cu and Co to S/P in the precursor of CuCo Prussian blue analogue (PBA). By controlling the molar ratio of S and P during the phosphorization/vulcanization process, induced diffusion can be achieved and leads to directional separation/aggregation of Cu and Co species. As a result, a heterogeneous yolk‐shell Cu2S@CoP2‐C‐N‐S structure is successfully synthesized with a reticular CoP2‐C‐N‐Cu‐S as the shell and a Cu2S nanocrystal as the core. The space charge effect of the semiconductor heterojunction resulting from component separation/aggregation significantly promotes oxygen evolution reaction, resulting in an ultralow overpotential of 180 mV at 10 mA·cm−2. This work not only provides a simple method for efficient separation of key components in gas‐solid systems but also provides a method for fine‐tuning the active site in an active‐site‐engineering approach.

Effects of Sb on the properties and interfacial evolution of SAC305-2Bi-xSb/Cu solder joints

This study investigated the influence of Sb addition on the microstructure, thermal behavior, mechanical properties, and interfacial evolution of SAC305-2Bi-xSb/Cu solder joints. Compared with the SAC305-2Bi alloy, the melting temperature and pasty range slightly increased with the increasing of Sb content from 0.2 to 2.0 wt.%, while the undercooling temperature decreased. The research revealed that with the addition of Sb element, the grain size of β-Sn is refined. When the content of Sb is 0.5 wt.%, the grain size of β-Sn reached minimum (19.91 μm). Compared to the SAC305-2Bi alloy, the ultimate tensile strength of SAC305-2Bi–2Sb alloy is increased by 30.10%, contributed to the Sb solid solution strengthening effect and the refinement of β-Sn. With the addition of Sb, the thickness and growth rate of the interface is reduced gradually. The uniform solution of Sb and Sn can significantly inhibit the diffusion rate of Cu atoms and Sn atoms at the interface. The SAC305-2Bi-xSb alloy system has low melting temperature, superior mechanical properties, and reliable solder joints for service. Therefore, it is a potentially reliable lead-free solder for high-stability connections in automotive electronics, communications electronics, and medical devices.

Enhanced Nanotwinned Copper Bonding through Epoxy-Induced Copper Surface Modification.

For decades, Moore's Law has neared its limits, posing significant challenges to further scaling it down. A promising avenue for extending Moore's Law lies in three-dimensional integrated circuits (3D ICs), wherein multiple interconnected device layers are vertically bonded using Cu-Cu bonding. The primary bonding mechanism involves Cu solid diffusion bonding. However, the atomic diffusion rate is notably low at temperatures below 300 °C, maintaining a clear and distinct weak bonding interface, which, in turn, gives rise to reliability issues. In this study, a new method of surface modification using epoxy resin to form fine grains on a nanotwinned Cu film was proposed. When bonded at 250 °C, the interfacial grains grew significantly into both sides of the Cu film. When bonded at 300 °C, the interfacial grains extended extensively, eventually eliminating the original bonding interface.

Quantitative study on dynamic instantaneous dissolution of precipitated phases in 2195-T6 Al-Li alloy based on characterizations with SANS and TEM

The kinetics of the dynamic instantaneous dissolution of the precipitated phases in 2195-T6 Al-Li alloy under high strain rate loading was firstly studied quantitatively by means of the small angle neutron scattering (SANS) and transmission electron microscopy (TEM) techniques, and the thermodynamics and transformation mechanism were also illustrated in this paper. The high strain rate loadings were performed by the split Hopkinson pressure bar. The maximum flow stresses increased but the pulse durations decreased with increasing strain rates. TEM observations indicated that the size and volume fraction of the T1 phases decreased. The SANS fitting results showed that the radius and volume fraction of the T1 phase decreased after loading. The dissolution activation energy (Qd) was calculated to be 28.4 kJ/mol by combining the Johnsone-Mehl-Avrami-Kolmogorov (JMAK) equation and the Arrhenius equation, indicating that the instantaneous dissolution of T1 phase was kinetically feasible. The T1 phase generated a larger distortion energy, and the surface energy as well as the internal pressure of T1 phase increased in dissolving during dynamic loading to increase the free energy difference (driving force for dissolving) between T1 phase and matrix, making the instantaneous dissolution of the T1 phases be thermodynamically feasible. The diffusion rates of Cu and Li atoms were significantly accelerated to promote the instantaneous dissolution of T1 phase particles. The results of the Vickers hardness values showed that the hardness increased after loadings, due to the high density of dislocations and only partial dissolution of the T1 phase particles.

Regulating the microstructure and mechanical properties in cast Al–3Li–2Cu-0.15Zr alloy via Sn addition and heat treatment

The cast Al–3Li–2Cu-0.15Zr alloy is a promising material due to its high strength-to-weight ratio and stiffness. In this work, the Sn addition and heat treatment were employed to regulate its microstructure and mechanical properties. The results indicate that Sn exists in the matrix as Sn solute atoms and Sn-rich particles including Li5Sn2, Li13Sn5, Li7Sn2, and Li22Sn5. The number of these particles increases as the Sn content rises. The addition of Sn significantly enhances the grain refinement, reducing the average grain size to 50.2 μm when 0.3 wt% Sn is incorporated. During the aging process, the δ′ and δ'/β′ precipitates gradually grow and coarsen, while the T1 and θ′ precipitates nucleate and grow. Some δ′ precipitates attach to the board of θ′ to form sandwich-like phases, such as δ'/θ'/δ'. The addition of Sn promotes the nucleation of θ′ and T1 precipitates. This is achieved by leveraging the Sn-rich particles as nucleation sites and utilizing Sn solute atoms to decrease the interface energy between these precipitates and α-Al. Moreover, the addition of Sn with a high vacancy binding energy and the reduction of aging temperature can effectively decrease the diffusion rate of Li atoms and vacancies, thereby inhibiting the broadening of the δ′-PFZ. After a suitable heat treatment, the Sn-modified Al–Li alloy exhibits a microstructure characterized by fine and equiaxed grain, fine and uniform δ′ precipitates, and a narrow δ′-PFZ, contributing to excellent mechanical properties of the alloy. Significantly, the underlying mechanisms behind the aforementioned observations were discussed analytically.

Revealing the influence of in-situ formed LiCl on garnet/Li interface for dendrite-free solid-state batteries

Inadequate interfacial contact between lithium and solid-state electrolytes (SSEs) leads to elevated impedance and the growth of lithium dendrites, presenting significant obstacles to the practical viability of solid-state batteries (SSBs). To ameliorate interfacial contact, optimizing the surface treatment of SSEs has been widely adopted. However, the formation of LiCl through acid treatment, an equally crucial factor impacting SSB performance, has received limited attention, leaving its underlying mechanism unclear. Our study aims to shed light on SSE characteristics following LiCl formation and the removal of Li2CO3 through acid treatment. We seek to establish quantifiable links between SSE surface structure and SSB performance, focusing on interfacial resistance, current distribution, critical current density (CCD), and lithium deposition. The formation of LiCl, occurring as Li2CO3 is removed through acid treatment, effectively mitigates lithium dendrite formation on SSE surfaces. This action inhibits electron injection and reduces the diffusion rate of Li atoms. Simultaneously, acid treatment transforms the SSE surface into a lithiophilic state by eliminating surface Li2CO3. Consequently, the interfacial resistance between lithium and SSEs substantially decreases from 487.67 to 35.99 Ω cm2 at 25 °C. This leads to a notably high CCD of 1.3 mA cm−2 and a significantly extended cycle life of 1,000 h. Furthermore, in full SSBs incorporating LiCoO2 cathodes and acid-treated garnet SSEs, we observe exceptional cyclability and rate capability. Our findings highlight that acid treatment not only establishes a fundamental relationship between SSE surfaces and battery performance but also offers an effective strategy for addressing interfacial challenges in SSBs.

Effect of Al addition on Nb-rich phase precipitation behavior in ferritic stainless steel

The precipitation behavior of Nb-rich phase in Al-free and 1Al Nb-bearing ferritic stainless steels (FSSs) at 700 °C were investigated. The results show that Nb-bearing carbides and Laves phases with mutual transformation relationships are precipitated in both Al-free and 1Al Nb-bearing FSSs at the early stage of aging. At this stage, the coarsening rate of Laves phase is higher than that of Nb2C phase, and the addition of Al can promote the precipitation of Laves phase and weaken the precipitation of (Nb, Ti)2C phase. As the aging time extended to 60 min, the Nb-rich phase in the two experimental steels was mainly Laves phase, and the intragranular Laves phase showed feather like aggregation distribution. On the one hand, the added Al can be enriched in the Laves phase to produce a tailing morphology, on the other hand, it can reduce the diffusion rate of Nb atoms in the matrix, thereby weakening the aggregation state of the intragranular Laves phase. During the coarsening process of Laves phase, the addition of Al can reduce the coarsening rate of Laves phase by 7.45 times.