Solute clusters are one of the important mechanisms of irradiation embrittlement of ferritic steels. It is of great significance to study the stability of solute clusters in ferritic steels and their ...effects on the mechanical properties of the materials. Molecular dynamics was used to study the binding energy, defect energy, and interaction energy of 2 nm-diameter Cu-Ni clusters in the ferritic lattice, which have six categories of Cu-Ni clusters, such as the pure Cu cluster, the core–shell structural cluster with one layer to four layers of Ni atoms and the pure Ni cluster. It was found that Cu-Ni clusters have lower energy advantages than pure Ni clusters. Through shear strain simulation of the three clusters, the structure of 2 nm diameter clusters does not undergo phase transformation. The number of slip systems and the length of dislocation lines in the cluster system are positively correlated with the magnitude of the critical stress of material plastic deformation.
Heterogeneous nucleation interface structure of Al-Cu alloys was tuned through solute composition and substrate lattice structure in this study to achieve a sophisticated nucleation control. The ...tuning mechanism at atomic level was systematically investigated using high angle annular dark field scanning transmission electron microscopy (HAADF STEM) and electron energy loss spectroscopy (EELs) techniques. The results show that the solutal element and substrate both can be used to modify the lattice matching of the nucleation interface, where alloying element Cu was found to adsorb at the nucleation interface tuning the lattice matching between new crystal and substrate rather than embed in the matrix distorting the lattice structure of the matrix. The substrate structure can also affect the preferred crystal orientation of new crystals instead. A relationship between the nucleation potency (undercooling) of the alloys and the lattice misfit was further proved, which may lead to a quantitative approach for the nucleation control of Al.
Display omitted
Effect of Si on the growth behavior of the Fe
2
Al
5
phase formed at the Al-
x
Si
(liquid)
/Fe
(solid)
interface during holding was investigated by a synchrotron radiation real-time imaging ...technique. Results show that growth of the Fe
2
Al
5
phase is accompanied by its simultaneous dissolution into the melt. Addition of Si inhibits the growth of Fe
2
Al
5
to reduce its thickness and change its morphology. The growth and dissolution kinetics of the Fe
2
Al
5
phase are discussed.
Electron backscatter diffraction was used to reveal high- and low-angle grain boundaries (HAGBs, with misorientation ≥15 deg, and LAGBs, <15 deg) in pure titanium (ASTM grade 2) subjected to equal ...channel angular pressing. Comprehensive paradigms were developed to present relations of yield strength
vs
HAGB grain diameter, and LAGB contribution
vs
LAGB linear intercept. Incorporating grain orientations (against loading axis) into the Hall–Petch relation, we quantitatively investigated the strength contributions by HAGBs and LAGBs, respectively.
The growth of Inter-Metallic Compounds (IMCs) with dissolution was investigated on the liquid Al/solid Fe interconnection by using synchrotron radiation real-time imaging technology. At the initial ...stage of holding at 850°C, a layer of the η-Fe2Al5 phase formed at the interface, and tongue-like η grew into α-Fe. The tongue-like η phase had a stronger (001) texture than the layered phase. The coalescence of tongue-like η started at the bottom, followed by the dissolution of IMCs, which leads to a further increase in its growth rate. During solidification stage, the dotted, needle-like and flake θ-FeAl3 phases were sequentially formed.
Display omitted
•A layered and tongue-like η phase was in-situ observed by synchrotron radiation X-ray radiography.•The coalescence of η phase bottom resulted in dissolution, further increasing the growth rate.•The θ phase growth behavior with different morphologies during cooling was analyzed.
The nucleation pathway plays an important role in vitrification, preparation of glass-ceramic composites and synthesis of metastable materials. In this paper, we studied the nucleation pathway of a ...novel ferroelectric BaTi
O
(BT2) during crystallization from undercooled liquid by aerodynamic levitation (ADL) containerless processing and structural analysis. An interesting polymorphic transition of BT2 regulated by the undercooling was observed during the crystallization process: the ferroelectric monoclinic phase (γ-BT2) was fabricated at low undercoolings and the paraelectric orthorhombic metastable phase (β-BT2) was obtained from hypercooled liquid. This polymorphic transition phenomenon corresponds to a non-classical nucleation pathway: metastable β-BT2 preferentially nucleates from undercooled melt and γ-BT2 is generated from β phase by solid-state phase transition. The two-step nucleation pathway stems from the structural heredity between the undercooled liquid and crystals. A stronger structural homology exists between the undercooled melt and β-BT2 than γ-BT2 based on diffraction data and atomic configurations analysis. This structural homology coupled with nucleation barrier calculation was used to elucidate the non-classical nucleation pathway of BT2 crystallization: the similarity of the structural unit (Ti-O polyhedra) between the undercooled liquid and the metastable β-BT2 reduces the nucleation barrier and contributes to the preferential precipitation of β-like clusters. This work reveals the formation route of BT2 from cooling melt, which not only benefits the synthesis and application of this novel functional material but also provides a guideline of the crystallization process of titanates from melt at atomic level.
The liquid/solid (L/S) interface of dissimilar metals is critical to the microstructure, mechanical strength, and structural integrity of interconnects in many important applications such as ...electronics, automotive, aeronautics, and astronautics, and therefore has drawn increasing research interests. To design preferential microstructure and optimize mechanical properties of the interconnects, it is crucial to understand the formation and growth mechanisms of diversified structures at the L/S interface during interconnecting.
In situ
synchrotron radiation or tube-generated X-ray radiography and tomography technologies make it possible to observe the evolution of the L/S interface directly and therefore have greatly propelled the research in this field. Here, we review the recent progress in understanding the L/S interface behaviors using advanced in situ X-ray imaging techniques with a particular focus on the following two issues: (1) interface behaviors in the solder joints for microelectronic packaging including the intermetallic compounds (IMCs) during reflow, Sn dendrites, and IMCs during solidification and reflow porosities and (2) growth characteristics and morphological transition of IMCs in the interconnect of dissimilar metals at high temperature. Furthermore, the main achievements and future research perspectives in terms of metallurgical bonding mechanisms under complex conditions with improved X-ray sources and detectors are remarked and discussed.
The growth mechanisms of single- and variant-flake Al
3
Ni phases at the liquid Al/solid Ni interface during solidification were investigated by synchrotron radiography and 3D tomography. The ...single-flake Al
3
Ni in the form of an elongated diamond rod evolves from one needle-like grain. The variant-flake Al
3
Ni is formed by coalescence of several needle-like Al
3
Ni grains, and its growth is dominated by the creation and propagation of a pair or groups of screw dislocations with opposite signs.
Electrochemical nitrate reduction to ammonia is an efficient strategy for nitrate removal and ammonia production in ambient conditions. TiO2 is a promising electrocatalyst for such a reaction, but ...chemical doping is still needed to further improve the electrocatalytic properties of TiO2. Here, we investigated the effect of Zr-doping on the nitrate reduction reaction processes on the (101) surface of anatase TiO2 using first-principles calculations. Two models with different Zr-doping levels were built. The reaction pathways and the potential-determining steps were established based on a thorough investigation of the variation in Gibbs free energy of each possible elementary step. The results show that a high level of Zr doping was effective to lower the Gibbs free energy for nitrate adsorption; however, Zr doping may promote the competing hydrogen evolution reaction (HER) by reducing the adsorption Gibbs free energy of H. Moreover, Zr doping also increases the adsorption Gibbs free energies for the intermediate products NO2 and NO, which may result in an earlier termination of the reaction, by releasing the intermediates as the final products without producing ammonia. Therefore, Zr doping may decrease the Faradaic efficiency and selectivity of TiO2 for the reaction and should be treated with caution experimentally.
PDF
