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Mineral replacement reactions are one of the most important phenomena controlling the geochemical cycle of elements on Earth. In the early years, solid-state diffusion was proposed as the main mechanism for mineral replacement reactions, but over the past 20 years the importance of the coupled dissolution-reprecipitation (CDR) mechanism has been recognized. In the presence of a fluid phase and at low temperatures (e.g.

This study investigated the activation energy and kinetic characteristics of silicon nitride (Si3N4) composite ceramics produced using different preparation methods. The effects of the linear shrinkage, expansion ratio, and heating rate on the sintering process were analysed in detail. The obtained results reveal that the finer particle size produced using the urea homogeneous precipitation method obviously enhanced the densification rate and reduced the atomic diffusion distance. Moreover, the densification sintering process was carried out efficiently, and the largest densification rate was achieved in advance. According to the Arrhenius curve, the activation energy of the Si3N4 composite ceramics calculated using the urea homogeneous precipitation method (310.94 kJ/mol) was lower than that achieved using the mechanical ball-milling method (365.11 kJ/mol). Additionally, the flexural strength and hardness of the Si3N4 composite ceramic prepared using the urea homogeneous precipitation method were 740 ± 42 MPa and 16.20 ± 30 GPa, respectively, which is attributed to this composite ceramic's higher diffusion rate and small grain size.

Cu/Al clad sheets with a 304 stainless steel foil (SUS304) interlayer are successfully fabricated by the powder-in-tube method. The influence of SUS304 thickness on the interfacial structure, elemental diffusion, and peeling strength of the clad sheets is studied. Experimental results indicate that the initial Cu/Al interface is partially transformed into a Cu/SUS304/Al interface after introducing the SUS304 interlayer. The proportion of SUS304 fragments at the bonding interface is shown to increase with thickness of the SUS304 interlayer. Differences in deformability between SUS304 interlayer and Cu/Al matrix promote the occurrence of shear deformation at the bonding interface via the cladding process, enhancing atomic diffusion at the Cu/SUS304/Al interface. Peeling tests reveal that interfacial cracks in clad sheets with an SUS304 interlayer propagate along the Cu/SUS304 and Cu/Al interfaces. Under combined effects of interfacial transfer and large shear strain, the interfacial strength of clad sheets is apparently improved. Clad sheets with the thickest SUS304 interlayer (30 μm) exhibit highest peeling strength (30.9 N/mm), demonstrating 73.6% improvement over clad sheets without an interlayer. These findings provide novel insights into the innovative design of clad sheets possessing extraordinary interfacial strength.

The chain-like prior particle boundaries (PPBs) as a kind of stubborn harmful precipitate will hinder atomic diffusion and particle connection. They can only be broken into nanoscale through thermal deformation (1160–1200 °C). Here, treated by the pulsed electric current at 800 °C, PPBs were dissolved quickly as a result of the interaction between the pulsed electric current and the chain-like structure. According to the electromigration theory and the calculation results, the high current density regions will be mainly produced at the gaps due to the conductivity difference between the precipitates and the matrix. The atomic diffusion flux caused by the pulsed electric current is proportional to the current density. Therefore, the existence of a large number of gaps in the chain-like PPBs will make the high current density regions play a more positive role in fast-dissolution.

A bulk (Hf0.2Ta0.2Zr0.2Nb0.2Ti0.2)C high-entropy ceramic (HEC) with a high density was prepared by hot pressing (HP), and through a robust joining technique, large-sized piece was fabricated. A hot-pressed carbide HEC with a single-phase and homogeneous composition was obtained at the sintering temperatures from 1800 to 1950 °C for 30 min under a pressure of 30 MPa. The influence of sintering temperature on the mechanical properties of the HEC was investigated, and the flexural and compressive strengths were reported. Additionally, the feasibility of active brazing of this HEC was studied and solid joints with high shear strength were obtained by atomic diffusion and chemical reaction at the interface, providing a key approach to fabricate complex components of HECs.

In this work, the titanium germanosilicide (TiSiGex) superlattice (SL) has been successfully fabricated. A monolayer of silicon atoms and bilayer of inversed titanium silicide constructed this novel superlattice periodically. A localized strain field has been found as a crucial factor via high resolution Annular Dark Field Scanning Transmission Electron Microscope (ADF-STEM) images, being generated by gradual segregation of germanium atoms. Germanium atoms would be excluded during the formation of the transition silicide. This phenomenon could be interpreted by thermodynamic preference. There was a substitution reaction between silicon and germanium, resulting from similar atomic volumes of both. In other words, germanium segregation pathway was based on where substitution occurred. Eventually, the excluded germanium atoms tended to accumulate at the boundary of TiSiGex-SL, contributing to a discontinuous thin film layer.

Sintering of advanced thermal barrier coatings (TBCs) at high temperatures is key challenge as it can adversely affect service performance and thermal fatigue resistance of TBCs. In this study, sintering behavior of pyrochlore-type La2(Zr0.7Ce0.3)2O7 (LZ7C3) was investigated using experiments and molecular dynamics. Meanwhile, the corresponding dynamic process and behind mechanism were uncovered. Results showed that novel LZ7C3 exhibited significantly higher sintering resistance than host La2Zr2O7 (LZ) and typical 8 wt% yttria-stabilized zirconia (8YSZ) at temperature up to 1773 K, which indicated that pyrochlore-type LZ7C3 is a promising TBC candidate to replace conventional 8YSZ at high temperatures. Further study also revealed that initial stage played crucial role in sintering process, and the sintering mainly occurred at grain boundary (GB) region. Intrinsic sintering activation energy of LZ7C3 GB (695.248 J mol−1) is larger than that of LZ GB (384.171 J mol−1) and 8YSZ GB (173.303 J mol−1), which resulted in outstanding sintering resistance for LZ7C3. Furthermore, no obvious enrichment of second phase was observed at the GB of LZ7C3. This study thus concluded that hindering the atomic diffusion of GB, as well as introducing foreign atom with larger mass and bond energy may act as effective strategy to enhance the sintering resistance of TBCs materials.

Dissimilar TC4 titanium alloy and 316L stainless steel were successfully joined utilizing thermoplastic bonding (TPB) with a Ti-based bulk metallic glass (BMG) as the filler. Good physical pre-bonding and metallurgical bonding were successively achieved through superplastic flowing in the superliquid region and solid-sate atomic diffusion and reaction. The experimental results indicated that the superplastic flow of BMG in the superliquid region greatly promoted void shrinkage in the interfaces. Hence, a compact contacting was obtained at temperature much lower than the melting point of the filler metal, which is beneficial to the atomic diffusion between the filler metal and base metals as temperature increased. After holding for some time below the melting point of the filler metal, three different reaction layers derived from the atomic diffusion and reaction between the base metal and filler metal were formed in the interfacial regions. A series of irregular bulky and small plate-shaped fine phases were formed and uniformly distributed in the interfacial regions and intermediate region. The shearing tests showed that a high strength of 225 MPa was obtained after diffusing at 695 °C for 60min. The fracture surface of the joint shifted from the 316L interface to then central crystallization layer as temperature increased.

The effect of thermal treatments on mechanical properties was systematically investigated in Ni/Mo multilayers with a constant modulation period (160 nm) prepared by magnetron sputtering deposition. A supermodulus effect was found in the annealed multilayers as compared to the as-deposited state. A large tensile stress development was observed in the multilayers. The evolution of grain-boundary (GB) wetting was observed at the interfaces of the multilayers, which results in an enhanced modulus based on the mechanism of GB-wetting-induced interfacial stress/strain. The GB wetting phenomenon was further supported by a thermodynamic calculation. The results not only bring clear evidence of the important role of interfacial structures in governing the elastic behavior of metallic multilayers, but also allow designing the multilayers with special properties through atomic diffusion and wetting at the interfaces based on the thermodynamic calculation.

A growing interest is observed in industry for metallic additive manufacturing. Atomic Diffusion Additive Manufacturing (ADAM) is a new extrusion-based process. The mechanical behavior of metallic materials obtained via ADAM has not been analyzed much. In the present work, a microscale experimental investigation was performed to study the behavior of 17-4PH stainless steel. The effect of heat treatment on the mechanical properties of the material was also examined.

Reliable joints of Ti3SiC2 ceramic and TC11 alloy were diffusion bonded with a 50 μm thick Cu interlayer. The typical interfacial structure of the diffusion boned joint, which was dependent on the interdiffusion and chemical reactions between Al, Si and Ti atoms from the base materials and Cu interlayer, was TC11/α-Ti + β-Ti + Ti2Cu + TiCu/Ti5Si4 + TiSiCu/Cu(s, s)/Ti3SiC2. The influence of bonding temperature and time on the interfacial structure and mechanical properties of Ti3SiC2/Cu/TC11 joint was analyzed. With the increase of bonding temperature and time, the joint shear strength was gradually increased due to enhanced atomic diffusion. However, the thickness of Ti5Si4 and TiSiCu layers with high microhardness increased for a long holding time, resulting in the reduction of bonding strength. The maximum shear strength of 251 ± 6 MPa was obtained for the joint diffusion bonded at 850 °C for 60 min, and fracture primarily occurred at the diffusion layer adjacent to the Ti3SiC2 substrate. This work provided an economical and convenient solution for broadening the engineering application of Ti3SiC2 ceramic.

In this work, electrical studies made on two orthochromite samples - HoCr0.9Fe0.1O3 and HoCr0.9Mn0.1O3 as a function of frequency in the range- 100 Hz to 1 MHz and temperature varying from room temperature up to a maximum of 650 K are presented. The two samples have been synthesized employing the solid state diffusion technique. Both the samples crystallize in orthorhombic perovskite structure belonging to space group Pnma. Frequency dependent measurements of real (Z') and imaginary (Z′′) parts of impedance are suggestive of samples bearing the negative temperature coefficient of resistance thereby reflecting the typical semiconducting behaviour of both the orthochromite samples. Z′′ for higher temperatures (≥323 K) show a peaking behaviour. With peak maximum shifting towards higher frequency with rising temperature, it owes to the existence of temperature dependent electrical relaxation phenomenon in both the samples.

The joining of liquid-phase sintered SiC (LPS-SiC) ceramics was conducted using spark plasma sintering (SPS), through solid state diffusion bonding, with Ti-metal foil as a joining interlayer. Samples were joined at 1400 °C, under applied pressures of either 10 or 30 MPa, and with different atmospheres (argon, Ar, vs. vacuum). It was demonstrated that the shear strength of the joints increased with an increase in the applied joining pressure. The joining atmosphere also affected on both the microstructure and shear strength of the SiC joints. The composition and microstructure of the interlayer were examined to understand the mechanism. As a result, a SiC-SiC joining with a good mechanical performance could be achieved under an Ar environment, which in turn could provide a cost-effective approach and greatly widen the applications of SiC ceramic components with complex shape.

Identifying the defects process in concurrent recrystallization and precipitation during aging a supersaturated solid solution is essential for understanding their interaction mechanisms and for manipulating the microstructure, but was rarely done at the atomic scale. Herein, the concurrent recrystallization and precipitation in the supersaturated hexagonal Sm(Co, Fe, Cu, Zr)7.5 alloys were studied through detailed transmission electron microscopy investigations, where the recrystallization, growth of recrystallized subgrains (cells) and precipitates stem from the gradual formation and dissociation of defects, including basal stacking faults (SFs), vacancies and excess interstitial atoms. The diffusion-controlled glides of -type partial dislocations associated with the SFs not only transform the matrix from the mixture of hexagonal Sm(Co, Fe, Cu, Zr)7 (1:7H) and Sm2(Co, Fe, Cu, Zr)17 (2:17H) to Sm-depleted rhombohedral Sm2(Co, Fe, Cu, Zr)17 (2:17R) cells but also provide continuous diffusion channels to reduce the point defects to form the Sm-enriched hexagonal Sm(Co, Fe, Cu, Zr)5 (1:5H) cell boundary precipitates and Zr-enriched rhombohedral (Sm, Zr)(Co, Fe, Cu)3 (1:3R) platelets. It indicates a diffusion-controlled displacive phase transformation mechanism, characterized by the composition-dependent 2:17R’ intermediate phase due to incomplete basal slip and incomplete solute partitioning. The growth velocities of both recrystallized cells and precipitates are closely related to the defects density, being faster due to the high defects density at early stage, and being slower due to the reduced defects density at later stage. A basal slip model is proposed to explain the formation and dissociation of defects along with the stacking period change and the simultaneous formation of continuous atomic diffusion channels. These new findings may yield a deep understanding of the interaction between recrystallization and precipitation.

The plate-shaped θ′ (Al2Cu) precipitate acts as one of the primary strengthening phases in Al-Cu alloys. The interface, especially the semicoherent interface, between Al-Cu solid solution (αAl) and θ′ phase contains a lot of clues about phase transformations. Thus, these interfacial structures in an Al-Cu alloy after high-temperature and longtime aging have been analyzed in detail using atomic-scale high-angle annular dark-field scanning transmission electron microscopy and first-principles calculations in this work. It was found that the lateral growth of θ' precipitates is subjected to a combination of several major mechanisms under this aging condition. Except for some common intermediate phases, two novel and striking structures were observed on the interface, which implies two alternative atomic diffusion mechanisms for θ′ precipitate growth. For one condition, the atomic diffusion from αAl to θ′ phase transformation adopts an interstitialcy mechanism based on additional Al atoms. For the other condition, the diffusion is carried out through Al atoms. Both mechanisms are distinctly different from the previous theory based on direct diffusion of Cu atoms. The first-principle calculations also confirm that these newfound diffusion processes are energetically favored.

Silicon (Si) as an anode material for lithium-ion batteries exhibits the highest theoretical capacity. However, huge volume expansion ~400% attributes to high intercalation stress followed by pulverization and fracture. Numerous research outcomes on the hollow Si nanosphere have been extensively studied to establish the optimum way to accommodate volume expansion and reduced inter-particle stress for better cyclability. It has also been shown that the nanosphere geometry leads to density reduction which can impart the structure of a metal-like character and improve the fracture toughness. The density reduction can either be accommodated inside the cavity within the hollow nanosphere or at the glass interfaces. In this work, we carried out classical molecular dynamics (CMD) and Density Functional Theory (DFT) based simulation study to elucidate the role of density reduction due to atomic diffusion inside the cavity is higher than that at the Si inter-particle interfaces to improve the aforesaid inadequacies. The simulated structures would further explain the in-depth analysis of the electronic structure.

Bound Powder Extrusion (BPE) is increasingly gaining popularity and makes metal additive manufacturing easier and more accessible for industrial production. The Markforged-Metal X technology with debinding and sintering, also called Atomic Diffusion Additive Manufacturing (ADAM), is a newcomer in the field of extrusion additive manufacturing. The main objective of this work is to investigate the mechanical properties of 17-4PH stainless steel samples produced by ADAM. Moreover, the effects of a mechanical post-treatment (SMAT) on surface and mechanical properties are also analyzed. The macroscopic tensile response and superficial residual stresses of as-fabricated and SMATed samples are compared.

Summary Calendering is a crucial manufacturing process in the optimization of battery performance and lifetime due to its significant effect on the 3D electrode microstructure. By conducting an in situ calendering experiment on lithium-ion battery cathodes using X-ray nano-computed tomography, here we show that the electrodes composed of large particles with a broad size distribution experience heterogeneous microstructural self-arrangement. At high C-rates, the performance is predominantly restricted by sluggish solid-state diffusion, which is exacerbated by calendering due to the increased microstructural and lithiation heterogeneity, leading to active material underutilization. In contrast, electrodes consisting of small particles are structurally stable with more homogeneous deformation and a lower tortuosity, showing a much higher rated capacity that is less sensitive to calendering densification. Finally, the dependence of performance on the dual variation of both porosity and electrode thickness is investigated to provide new insights into the microstructural optimization for different applications in electrode manufacturing.

The 93W and Mo1 refractory metals were bonded with different Cu1-xNix coating interlayers of various Ni content using plasma-activated sintering at 700 °C. The effects of the Ni content in the Cu1-xNix coating interlayer on the interfacial microstructure evolution and mechanical properties of the W/Mo joints were studied. The maximum average shear strength of the W/Mo joint was 316.5 MPa when the Ni content of the Cu1-xNix coating interlayer was 25 %. When the Ni content of the Cu1-xNix coating interlayer was below 50 %, the atomic diffusion at the W/Mo joint interface was adequate without the formation of intermetallic compounds, as demonstrated by the High Resolution Transmission Electron Microscope analyses of the joints. The presence of Ni in Cu1-xNix promoted diffusion bonding at the interface, which contributed to the high mechanical properties of the W/Mo joint. With an increase in the Ni content of the Cu1-xNix coating interlayer, the MoNi intermetallic compound (IMC) nucleated and grew at the Cu1-xNix coating/Mo1 interface. When the Ni content of the Cu1-xNix coating interlayer was above 50 %, the generation of a brittle MoNi IMC weakened the shear strength of the W/Mo joint dramatically.

Significant developments in the microstructural characterization of superplasticity have been achieved in the 2010s, which can be attributed to advanced electron microscopy and well-controlled mechanical experiments. The objective of this overview is to describe the scientific advances in the microscopic to nanoscopic mechanisms of superplasticity. The particular emphasis is placed on the accommodation mechanisms (i.e. atomic diffusion and/or dislocation activities) associated with grain boundary sliding (GBS) in quasi-single phase materials during superplastic (region II) and near-superplastic (regions II/III ~ III) flows. Superplasticity in region II is attributed to the cooperative process between GBS and grain boundary diffusion, which play the straining and accommodating roles, respectively. On the other hand, near-superplastic flow in regions II/III ~ III is typically attributed to shear strain propagation between GBS and dislocation slip in mantle regions (i.e. Gifkins’ core–mantle model, 1976) and across grain interiors (i.e. Ball and Hutchison's transgranular model, 1969) with increasing strain rate. These accommodation mechanisms lead to dynamic microstructural evolutions as represented by continuous dynamic recrystallization during the near-superplastic flow.

A 0.66 mm-diameter AZ31 alloy wire with ultimate tensile strength of 400 MPa and elongation of 28.5% was successfully prepared via the combination of cold-drawing and electropulsing treatment processing (EPT). Microstructure observation showed that the grain size of EPTed samples was refined to about 1 μm and the basal texture strength with maxima texture index was weakened to 7.18. EPT can significantly accelerate recrystallization by enhancing the mobility of dislocation and atomic diffusion due to the coupling of the thermal and athermal effects. Finally, uniform ultrafine-grained structure was obtained in the EPTed samples by static recrystallization completed in a very short time (30 s) at relatively low temperature (433 K).

In steel processing, electric field present at the interface between molten iron and refractory materials has important influence on erosion and clogging of the submerged entry nozzle. In this study, a voltage was applied between a droplet of molten iron and several nozzle constituent materials, while measuring the liquid/solid contact angle to quantify the effect of the voltage on interfacial wetting. At 0 V the contact angles between molten iron and graphite, Al2O3–C, and ZrO2–C substrates are 130°, 136°, and 128°, respectively. The contact angles are reduced to 85°, 88°, and 103° when a potential of 3 V is applied. Also, it was found that silicon atoms in the molten iron diffuse and aggregate at the interface of the two phases under an external electric field, and that the electric field promotes chemical reactions between the two phases. Mass transfer, atomic diffusion, and dissolution at solid-liquid interface are promoted by interfacial electric field, which is partially responsible for the improvement in wetting. These results provide kinetic conditions related to erosion and clogging of refractory material.

This work explores mechanical properties, structural evolution, and mechanism of creep-life enhancement for widely used P9 heat-resistant steel. The 17-year-on-site used P9 alloy exhibit a higher tensile strength and a smaller elongation than the new P9 alloy from room temperature to 700 °C. The P9 alloy also displays a typical ductile feature with a significantly necking profile. The P9 alloy shows phase transformation sequences of α-Fe (bcc) → A c 1 ∼ 858 ° C α + γ -Fe (bcc + fcc) → A c 3 ∼ 894 ° C γ-Fe (fcc) upon heating and γ-Fe (fcc) → M s ∼ 352 ° C martensite (bct) → M f ∼ 300 ° C martensite (bct) upon cooling. The new P9-alloy tube mainly contains ∼73.5% ferrite phase (α-Fe) and ∼26.5% carbide M3C. However, the used P9-alloy tube shows four crystalline phases including ∼45.9% ferrite, ∼14.5% martensite, ∼37.5% cementite (M3C) and ∼2.7% carbide M23C6. The creep test indicates that the used P9-alloy tube has a longer creep-life (or better anti-creep ability) than the new tube. Activation energies of atomic diffusion for the new and used tubes are respectively 252.45 and 345.87 kJ/mol, indicating a decreased diffusion capability in the used tube. This work suggests that martensite laths, lath boundaries, and precipitates (such as carbides) play important roles to inhibit creep-deformation in the P9-alloy steel.

Herein, porous calcium hexaluminate ceramics that contain pores exhibiting multiple morphologies were fabricated via in situ reaction sintering using α-Al2O3 powders and pre-fired CaO/Al2O3 pellets. The results indicated that the composition of the pre-fired CaO/Al2O3 pellets significantly affected the pore morphology, reaction-diffusion mechanisms, sintering behaviour and properties of the porous CA6 ceramics. For the specimens containing low CaO/Al2O3-ratio (0.37) pellets, the main reaction occurred by solid state diffusion, i.e. ion diffusion through the solid reactant phase, which resulted in a slow process and low CA6 formation rate at an elevated sintering temperature. With higher CaO/Al2O3-ratio (0.57) pellets, large-sized pores were observed because of transient liquid phase diffusion during the sintering process. The transient liquid phase diffusion effect increased the porosity of the porous ceramics and promoted the formation of a large number of plate-like CA6 grains in the walls of the pores, enhancing their mechanical properties and high-temperature performance. The porous CA6 ceramics containing high CaO/Al2O3-ratio (0.57) pellets sintered at 1700 °C exhibited high open porosity (55.88%), low thermal conductivity and excellent high-temperature performance.

We directly observed the atomic diffusion process of bilayered Fe/ZnO transforming into a Fe3O4/ZnO heterostructure. Significantly, we suggested a unique two-step route in which Fe diffused along [0001]ZnO via boundaries of ZnO and then reacted along [ 1 ¯ 2 1 ¯ 0]ZnO. The specific orientation relationship of [0001]ZnO//[11 1 ¯ ]Fe3O4 could be precisely controlled. In addition, the formation of a ZnO/Fe3O4 heterostructure can be tuned in terms of reaction depth by controlling the annealing time. This study provided a novel nanofabricated method to produce oriented metal oxide heterostructures while visualizing the atomic mechanism of metal oxide formation, which allows for further investigation of promising devices.

Laser welding of TC4 Titanium (Ti) alloy to 304 stainless steel (SS) has been applied using Ag73-Cu16-Zn11 alloy as filler metal. A new welding process for SS-Ti alloy joint was introduced on the basis of the controlling the formation of Ti-Fe intermetallics in the joint. One pass welding involving creation of a joint with one fusion weld and one diffusion weld separated by remaining unmelted SS. When laser beam on the SS side was 1.5 mm, SS would not be completely melted in joint. Through heat conduction of unmelted SS, the atomic diffusion occurred at the SS-Ti alloy interface. A diffusion weld was formed at the SS-Ti alloy interface with the main microstructure of γ-Fe + Fe3Zn2, AgZn3 + Cu5Zn8 and α-Ti + Ti2Cu. The joint fractured at the diffusion weld with the maximum tensile strength of 129 MPa. Keywords: TC4 Ti alloy, 304 stainless steel, Laser welding, Diffusion welding, Microstructure, Filler metal

Energy-resolved neutron imaging is employed for in-situ measurements of dopant transport in a simple experiment performed before the crystal growth of the scintillator BaBrCl:5%Eu via a vertical gradient freeze technique. During a stabilization period preceding growth, we observed the diffusion of Eu from the solid phase into the melt over a period of approximately 4 hours. Comparing the measured centerline concentration profile with a mathematical model for the system, we estimate the solid-state diffusivity of Eu in BaBrCl as D 1 = 1.9 × 10 − 10 m2/s and an upper limit for the liquid-phase diffusivity of Eu in the melt as D 2 * = 2.5 × 10 − 10 m2/s, at temperatures near the melting point. We compare this experiment, where diffusion is driven by a concentration discontinuity arising from segregation, to the classical diffusion couple technique. Suggestions are offered on how this segregation-driven couple might be improved as a tool for measuring diffusion coefficients, and we draw attention to the great promise of neutron imaging for in-situ measurements of the distribution of elements, with sufficiently high neutron attenuation coefficients, in difficult environments.

This study deals with the mechanical characterization of materials resulting from Markforged Atomic Diffusion Additive Manufacturing (ADAM) process. 17-4PH stainless steel fabricated by ADAM was investigated by exploring the microstructure generated by this manufacturing process, then analysing the effect of the microstructure on the deformation of such materials. Single Edge Notch Tensile (SENT) 17-4PH samples were fabricated in order to highlight microstructure effects in in-situ tensile tests. Then, a microscale experimental method coupled with digital images correlation (DIC) was used to measure kinematic fields of the sample surface. The effect of the deposited layer thickness on the material deformation was investigated by testing two samples fabricated with the same printing parameters except the layer thickness (i.e., 50 µm and 125 µm filament diameter). The results show that the layer thickness is an important printing parameter for such process since it affects the measured kinematic fields.

A mass diffusion model is developed to describe the growth kinetics of Cu6Sn5 intermetallic compounds (IMC) in the Cu-Sn-Cu sandwich structure. The proposed model is based on the local interfacial mass conversation law where interfacial Cu/Sn reactions and atomic diffusion are considered. Theoretical analysis shows that the IMC thickness growth is proportional to the square root of the product of the diffusion coefficient and time. The proposed model can explain the polarity effect of electromigration on kinetics of IMC growth where all the parameters have clear physical meaning. The theoretical predictions are compared with experimental results and show reasonable accuracy. Keywords: Intermetallic compounds, Polarity effect, Electromigration, Diffusion, Size effect

In this study, microstructures and electrochemical properties of a Zr-based AB2-type metal hydride alloy (Ti12.1Zr21.3V10.5Cr7.5Mn8.1Co8.0Ni31.7Al0.8) doped with 6 wt% LiH by solid-state diffusion at different temperatures were investigated and compared with those of the base alloy sintered at the same conditions. Structural study by x-ray diffraction analysis exhibited a lattice expansion in the main C14 phase of the Li-doped alloys with a relatively low sintering temperature, indicating that Li incorporated into the C14 Laves phase but was evaporated at higher sintering temperatures. Addition of Li deteriorated both the electrochemical capacity and activation easiness; however, it improved the high-rate dischargeability (HRD). The benefit of Li addition on HRD can be associated with the increase in amount of metallic nickel clusters embedded in the surface oxide (estimated by the saturated magnetic susceptibility) and was a strong function of sintering temperature. As the sintering temperature increased, HRD increased due to the increase in amount of surface catalytic metallic nickel.

Due to its excellent resistance to high temperature oxidation and steam corrosion, FeCrAl alloys have received much attention recently as a highly potential candidate cladding material for light water reactors. However, under the effect of thermal aging and neutron irradiation applied in reactor, the nanoscale brittle precipitates will occur in the ferritic FeCrAl alloys after spinodal decomposition due to the presence of Cr, which greatly increase the hardness and reduce the toughness of the material, thus seriously affecting the operation of the nuclear reactor. In this work, the alloy after heat aging was treated by pulsed electric current at room temperature. The micro-hardness and electrical properties of the aged alloy are greatly restored. In addition, compared with the heat treatment at the same temperature, the dissolution time of precipitates in aged alloys into the matrix is reduced by 10 times by electropulsing treatment with higher parameters. In comparison to the ex-situ conventional annealing treatment, this in-situ pulsed treatment can be used as a novel efficient and convenient method to repair the performance degradation of aged materials. Based on the thermodynamic and kinetics, electric pulses reduces the thermodynamic barrier for precipitation dissolution and increases the atomic diffusion rate.

Mechanical process of Accumulative Roll Bonding (ARB) is one of the severe plastic deformation methods which can be contributed to produce ultrafine grind composites. In this research, multi-layered composite of stainless steel/aluminum/copper after five cycles of accumulative roll bonding has been produced. In order to examine the microstructure of the sample during the process of ARB, images of optical microscope (OM), and scanning electron microscope (SEM) of sample cross section were provided. Moreover, inter-diffusion of atoms of Steel, Al, and Cu has been examined through linear elemental analysis. In order for recognition of created phases in composite, X-Ray diffraction analysis (XRD) has been done. At the end, a test of hardness has been done on various layers of composite. The results showed that in the first and second cycle of the ARB, it has not been created any plastic instability in the layers. By increasing the number of the cycle of accumulative roll bonding up to the five, plastic instability (necking and fracturing) will be observed. According to the result of this study, during the process of ARB, proper connection has been created among the layers. By increasing the cycles up to the five, a composite of aluminum matrix, grinds reinforcing Cu, and steel will be produced. In addition, the investigation of atomic diffusion indicates that the diffusion of the atoms of Cu and Al is greater than Steel. Formation of intermetallic compound of Al2Cu through the ARB process in Stainless Steel/Al/Cu composite is another finding of the present study.

Accepted: 2019-06-26, 資料番号: SA1190047000

During deep space exploration, electronic devices will be inevitably exposed to cryogenic temperatures. The effects of cryogenic temperature storage on the interfacial microstructure and mechanical behaviors of Sn-3Ag-0.5Cu/Cu (SAC305/Cu) solder joints were systematically investigated. The thickness of interfacial intermetallic compounds (IMCs) in the joints stored at −196 °C and −100 °C was found to gradually increase with the prolonging of storage time, and the morphology of the interfacial IMCs transformed from scallop type to column type. The growth rate of interfacial IMCs in the joints stored at −196 °C was faster than that stored at −100 °C. The stress gradient in the solder joints induced by thermal expansion mismatch was the primary driving force for atomic diffusion and interfacial IMC growth at cryogenic temperatures. The stress gradient in solder joints stored at −196 °C was higher than that stored at −100 °C, leading to a faster growth rate of interfacial IMCs at −196 °C. During cryogenic temperature storage, the interfacial IMC growth caused a volume shrinkage and thus generated residual stresses around the interface. As a result, the shear strength of the solder joints stored at −196 °C and −100 °C declined and the fracture location shifted towards the solder/IMC layer interface with the increase of storage time.

Electrically assisted solid-state joining (or electrically assisted pressure joining, EAPJ) of dissimilar stainless steel 316L (SUS316L) and Inconel 718 (IN718) alloys is experimentally investigated. The specimen assembly for the experiment is comprised of two cylindrical solid specimens (SUS316L and IN718) with an identical geometry. In EAPJ, electric current and plastic compression are directly and simultaneously applied to the specimen assembly. The microstructural analysis confirms that crack/void-free joints are successfully fabricated by EAPJ in the selected dissimilar metal alloys without melting and solidification. An obvious atomic diffusion region at the joint interface is identified. The results of tensile tests show that all the joints fracture from the SUS316L side, which undergoes typical ductile fracture with large plastic deformation. The results of the present study confirm that the concept of EAPJ is applicable to solid state joining of dissimilar material combination.

An amorphous Zr58.6Al15.4Ni20Co6 foil was fabricated and applied as the filler metal to vacuum braze TiAl- and Ni-based alloys. The obtained joint has high strength both at room temperature (RT) and high temperature (HT). To investigate the effect of the brazing temperature and holding time on the joint strength, experiments were performed at different temperatures and held for different time. Five different regions derived from the interfacial atomic diffusion and crystallization of the amorphous filler metal were formed after brazing. The energy dispersive spectrometer (EDS) results indicated that sufficient interdiffusion occurred between the filler metal and base alloys after brazing. As a result, fine phases that were different from the base alloys were formed and dispersively distributed in the joint. Shear tests were performed at 30℃ and 600℃ and the results show that the joint strength first increased and then decreased with increases in holding time and heating temperature. The maximum shear strength of the joint at 30℃ and 600℃ were 353 MPa and 214 MPa respectively.

Using in-situ techniques, which couple energy dispersive spectroscopy mapping with a heated transmission electron microscope stage, solid-state diffusion of Ni-Al is studied in the temperature range 623–723 K with characteristic diffusion lengths of 1–100 nm. When the concentration profiles are analyzed using the Sauer-Freise method, and evaluated for 50 atomic percent Ni, the diffusion coefficients follow an Arrhenius temperature dependence: D N i → A l = 8.2 x 10 − 9 exp ( − 111 k J / R T ) m 2 / s . Additionally, the formation of Al-rich intermetallic phases (Al3Ni & Al3Ni2) is shown to occur within heating durations of a second at the studied temperatures.

A new Zr44Ti11Cu10Ni10Be25 (LM1B) bulk metallic glass (BMG) and AZ31B Mg alloy composites were prepared by hot stacking extrusion process based on the thermoplastic forming ability of LM1B BMG within the supercooled liquid range (SLR). The stacking extrusion tests were carried out at three different temperature of 430 °C, 440 °C and 450 °C, respectively, and the extrusion speed was 5 mm/min. Morphology and structure of the extruded samples were characterized by the different methods. The results indicated that the LM1B BMG and AZ31B magnesium alloy can be well bonded, and welding defects at the smooth and continuous interface were negligible. The bonding mode is mainly mechanical bonding, meanwhile, a few of metallurgical bonding does exists. Significant atomic diffusion was detected in the vicinity of the interface, while the nanocrystals and partial crystallization were produced in the LM1B BMG.

The AA6061 and Ti6Al4V plates were joined by atomic diffusion and interfacial reactions. Layers of solid solution and intermetallic compound were both formed at the interface, and the interface thickness increased as the heat input increased. The intermetallic compound layer was found to be mainly composed of TiAl3. The shear strength of the friction stir lap AA6061-Ti6Al4V welds was found determined by the interfacial microstructure. The shear performance was promoted initially with the increase of interface thickness due to the formation of intermetallic compound. The maximum shear load of 4500 N was reached with a 7.5-μm-thick interface. When the thickness of interface further increased, the maximum shear load was found to decrease again because of the exorbitant residual stresses induced by the excessive intermetallic compounds. The fracture of the joints started with the micro-cracks formed at the intermetallic compounds and then leads to break during tensile shear test.

Nanocrystalline (NC) AgCu alloys have been attracted significant attention because of excellent electrical and mechanical properties. The microstructural evolution and deformation mechanisms are still challenging issues, and it is hard to observe directly by experimental methods. Accordingly, in this paper, atomic simulations are performed to investigate the tensile behavior of dual-phase equiaxial NC AgCu alloy (DPEA) at different strain rate (104-107 s−1), solute atomic concentration (5–20%) and temperature (300–600 K) using embedded atom method (EAM) potential. Relevant stress-strain curves and yield stress have been obtained. Result analysis reveals dislocation motion, atomic diffusion and grain boundary (GB) sliding are dominating deformation mechanisms. With the increase of strain rate and deformation, main deformation mechanisms are discovered to change from dislocation motion to GB sliding. Furthermore, the increase of solute atomic concentration (SAC) and temperature will promote the atomic diffusion and GB sliding. This work explains evolution process on deformation mechanisms of DPEA. It provides a qualitative analysis to design excellent mechanism property of DPEA by means of optimizing material structure parameters.

Reconstruction of heterogeneous catalysts during reaction, especially caused by the adsorption of reactants, is highly important for the structural evolution of nanoparticles (NPs) during activation and reaction processes. In this work, for the first time the CO-induced dynamic structure of Pd@Au core-shell NPs with different size and shape has been studied systemically using ab initio molecular dynamics. Our calculation has demonstrated that the thermostability of Pd@Au bimetallic NPs is decreased with increasing CO coverage. However, the kinetic stability can be enhanced when CO coverage is very high. With the adsorption of CO, the interaction between surface unoccupied atoms and nearby metal atoms at the second layer is strengthened, while the stress distribution in the second layer is significantly changed. The surface unoccupied metal atoms then migrate into the second layer, and metal atoms in the second layer move to surface in return. Such atomic diffusion between the top two layers leads to the atomic exchange in NPs interior layer by layer. Finally, Pd and Au atoms are redistributed in NPs, and Pd atoms accumulate at surface because of stronger CO adsorption. In a word, the segregation is dominated by the inward diffusion of surface unoccupied metal atoms. The great challenge in this work is how to establish the relationship between gas atmosphere and NP kinetic stability for determining the dynamic 3D bimetallic NPs.

The interface morphology and interdiffusion of the Al-Ni multilayers were studied by transmission electron microscopy (TEM) and atom probe tomography (APT). Asymmetric atomic diffusion and phase growth at the interfaces formed by Al atoms deposited on solid Ni (Al/Ni) and Ni deposited on Al (Ni/Al) were observed. Due to the blocking effect of interface, Ni diffused only into the upper Al layer after annealing at 573 K for 3 h leading to slow reaction rate. APT analysis further reveals that Al could diffuse across the Ni/Al interface into the inner Ni layers and distribute heterogeneously. Some Al atoms diffused into the particle and located on the same crystal plane with Ni, which helps to interpret spontaneous and rapid phase transformation of this nanostructured reactive multilayer.

In crystalline solids, to computationally determine atomic migration energy barrier is a highly time consuming challenge within the framework of Density Functional Theory (DFT). Through first-principle calculations, here we have proposed a simple, high-throughput formula to fast, effectively calculate atomic migration energy barrier for fcc metals through three basic parameters of materials, the equilibrium volume ( V 0 ), the bulk modulus ( B 0 ) and the Poisson's ratio (ν). This formula is useful not only for the ideal strain-free lattices but also for the uniaxially strained lattices. It has been further validated by a series of fcc metals when compared with both available experimental or theoretical data and DFT-derived data obtained by Nudged Elastic Band (NEB) method. Moreover, we have investigated the effect of uniaxial deformation on the diffusion behavior of vacancy in fcc metals. Our calculations revealed that in fcc metals under uniaxial tensile deformation, vacancy prefers to diffuse along the direction that is perpendicular to the uniaxial tensile deformation.

This paper investigates the influence of thermal annealing temperature on the periodic nanostructures and the thermoelectric properties of Sb2Te3/Au multilayer thin films fabricated by magnetron sputtering. The as-deposited amorphous periodic multilayer films (10 periods, 20 and 7 nm for the Sb2Te3 and Au layers, respectively) show regular and sharp interfaces between Sb2Te3 and Au layers. It was found that the interfaces of periodic films became a little fuzzy and some nanocrystallines could be observed after annealing at relatively lower temperature (373 K) due to atomic diffusion and crystallization. Additionally, obvious crystal grains appeared and the Au layers began to coarsen and even rupture when the annealing temperature was elevated to higher than 423 K. The evolution mechanism has been discussed in the view of grain boundary free energy and interfacial free energy. Furthermore, the experimental results suggest that the resistivity and Seebeck coefficient of the multilayer film sample have not exhibited distinct change until the annealing temperature was increased to as high as 473 K when the periodic nanostructures disappeared.

In this work, the mechanism of WC formation during mechanical alloying and subsequent annealing of nickel, aluminum, tungsten, and graphite powder mixtures was investigated. X-ray diffraction was used to evaluate phase changes. Microstructural and morphological evaluations of the powders were examined by FESEM and TEM. The XRD results confirmed that phase changes occurred by increasing milling time. After 10 h of ball milling, NiAl and W2C phases formed and new tungsten carbides were synthesized by increasing of milling time. After 40 h, W was consumed completely and WC, WC1-x, W2C carbides along with NiAl were produced. After heat treatment of 40 h milled powder, W2C and WC1-x phases disappeared and NiAl/WC nanocomposite was formed. The results confirmed that the WC formation was a gradual reaction controlled by atomic diffusion.

Magnetocaloric properties of rare-earth-based materials often highly rely on the solidification microstructure. In this work, we employ the wedge-mold solidification technique as a high-throughput method to realize one-sample investigation of La-Fe-Si for its cooling rate-dependent microstructural evolution and magnetocaloric effect. Finite element simulations indicate that the cooling rate continuously varies in a large range of 270–3000 K/s along the axial direction of the sample. The non-stoichiometric La1.7Fe11.6Si1.4 keeps NaZn13-type La(Fe,Si)13 functional phase of about 80 vol% by cooling in 500–3000 K/s and subsequently annealing at 1323 K for just 5 min. This suggests that fast cooling after casting brings about quick atomic diffusion and shortened annealing time during the subsequent annealing. With the maximum cooling rate up to 3000 K/s, a large magnetic entropy change of 14 J/kg K at 2 T field has been achieved. In addition, by analyzing the elemental distribution in the same position, a needle-like phase was found to act as the diffusion channel of Si atoms for fast phase reaction. From this work, we have demonstrated the wedge mold casting technique as a simple and efficient method to study the microstructural dependency of magnetocaloric properties in cooling-rate sensitive materials.

The diffusivity of hydrogen is an important property of light water nuclear reactor (LWR) fuel cladding. LWR cladding absorbs hydrogen during normal operation, a contributing factor to embrittlement that decreases the lifetime of the fuel. Mass transport of hydrogen is dictated by an Arrhenius behavior typical of solid state diffusion and the associated activation energy is therefore a property relevant to LWR fuel performance. We have used incoherent quasi-elastic neutron scattering (QENS) to directly measure the diffusivity of hydrogen in recrystallized Zircaloy 2 with a hydrogen concentration of 170 μg/g. We rely upon the low-Q expansion for long-range diffusion to determine diffusivity as a function of temperature between 572 and 780 K. We find the diffusivity is given by D(T) = 0.0067 exp (-0.461 eV/kT) [cm2/s] below 670 K and by D(T) = 0.0012 exp (-0.36 eV/kT) [cm2/s] above 670 K. Our activation energy below 670 K agrees with the value typically used to assess hydrogen diffusivity in LWR cladding [Kearns, Journal of Nuclear Materials 43 (1972) 330], but is approximately 20% lower above 670 K. The two different activation barriers are attributed to impurity trapping of hydrogen solutes at lower temperature that ceases to influence diffusivity at higher temperature. The application of the Oriani model for diffusion with impurity trapping to our system demonstrates the plausibility of this hypothesis. We believe this mechanism may be responsible for historical discrepancies of measured hydrogen diffusivity in Zr-based alloys. The elastic intensity versus temperature in fixed window scans exhibit inflection points that are in good agreement with the published terminal solid solution solubility limits for hydrogen in Zircaloy 2.

This paper presents a systematic study of the differences in the microstructures and micro-mechanical properties of various Cu/Fe wave interfaces prepared by explosive welding. These wave interfaces, fabricated by different parameters, have been divided into four categories according to variations in their microstructures and the element distribution: vortex region, transition layer, interface without metal bonding, and interface with defects. In the wave interfaces, nanocrystalline areas filled with nano-copper and nano-iron grains (50 nm), medium-sized grains (300 nm), coarse grains (1 μm) and finer nanocrystals (5 nm) or amorphous phases in wave interfaces. The variations in the grain size contribute to the inhomogeneity of hardness distribution in the first kind of interface, the vortex region. In the second kind of interface, the transition layer, both EDS and TEM measurements reveal a gradient in the element contents due to atomic diffusion. This transition layer possesses rather higher and more uniformly distributed nano-hardness (up to 15.75 GPa) because of the combined effects of fine grain strengthening and work hardening. The third kind of interface with an abrupt change in element distribution does not form metal bonds at the boundaries. Additionally, a comprehensive analysis on these four kinds of interfaces suggests that the second type of interface (transition layer) is the ideal one.

The rare-earth-free hard magnetic L10-FeNi phase found in cosmic meteorites demonstrates potential as a next-generation permanent magnet. However, it is very difficult to artificially produce the L10-FeNi phase due to the low atomic diffusion coefficients of Fe and Ni near the order-disorder transition temperature (∼320 °C). Therefore, FeNiPC amorphous alloy systems exhibiting crystallization temperature (Tx) near the transition temperature were investigated. The amorphous alloys were annealed at Tx, resulting in high atomic diffusion. The structural and microstructural characterizations of annealed ribbons revealed the formation of L10-FeNi phase through observation of the superlattice peak. The magnetic property, such as coercivity (Hc), also indicated the formation of L10-FeNi phase, because the maximum Hc value is 641 Oe after the annealing process.