查看更多>>摘要：The composition-dependent pseudo-binary (PB) interdiffusion coefficients and the main intrinsic diffusion coefficients of all the components at the near equiatomic composition of NiCoFeCr system are estimated following the PB diffusion couple method. These are otherwise impossible to estimate directly following the conventional method. Subsequently, a physics-informed machine learning based numerical inverse method is used to optimize the diffusion parameters in two steps. Initially, optimization is done by developing a good match with the diffusion profiles and estimated interdiffusion coefficients over whole composition range of the diffusion couples. However, a mismatch was found in the extracted intrinsic diffusion coefficients. Therefore, the second level of optimization is done with estimated intrinsic diffusion coefficients at the Kirkendall plane as constraints demonstrating the need for these diffusion parameters for generating a reliable mobility database. The direct estimation and optimization of diffusion coefficients without using thermodynamic details is an added advantage, especially in multicomponent alloy systems.
查看更多>>摘要：Quench-induced S(Al2CuMg) phases are generally formed in Al-Zn-Mg-Cu alloys. The precipitation and relative crystallographic relationships of eta-type (MgZn2) precipitates at the interfaces between the quench-induced S phases and Al matrix were studied in an Al-Zn-Mg-Cu alloy by coupling Cs-corrected scanning transmission electron microscopy (STEM) with scanning precession electron diffraction (SPED) technology. It was found that Zn segregation occurred at S-Al interfaces due to higher lattice strain energy, which induced the heterogeneous nucleation of nanosized eta' precipitates at these interfaces. Crystallographic orientation relationships (ORs) between the S phases and eta'/eta precipitates were firstly reported and discussed in Al-Zn-Mg-Cu alloy. With the coarsening of eta precipitates at S-Al interfaces, a new type of OR ([112]Al//[1210]eta, (111)Al//(1013)eta) between the interfacial eta precipitates and Al matrix was identified, which was different from their non-interfacial counterparts in Al matrix reported to date.
查看更多>>摘要：The ground state structure of NiTi martensite in experiments and existing theoretical calculations is the focus of ongoing disagreements. Based on Waitz et al.'s (2004, 2007) experiments, we use the first principle calculations to investigate the effect of (001) twin interface and thickness on the stability of NiTi martensite. Moreover, we determine the interface of the (001) martensitic twins observed in the experiment as the interface of twinned supercell-1 (TSC-1), in which the lattice parameters of individual unit cells are close to the experimental measurements of B19 & PRIME;. Furthermore, the energy per atom for TSC-1 is always between that of B19 & PRIME; and B33 and does not vary with the twin thickness. Considering the structural similarity of TSC-1 and B33, an energy barrier between TSC-1 and B33 via the minimum enthalpy pathways was demonstrated. The influence of the (001) twin interface could proves the rationality of the existence of B19 & PRIME; in experiments.
查看更多>>摘要：This work revealed the causes of embrittlement and anisotropy in the mechanical properties of H13 steel fabricated by selective laser melting (SLM). It was found that the low mechanical stability of the carbon-enriched retained gamma (austenite) films amongst martensite blocks transferred to high carbon twin martensite through stress induced martensitic transformation upon plastic deformation, leading to a high susceptibility to cracking. Moreover, owing to the directional solidification nature in SLM, the majority of these retained gamma films was aligned with the building direction (i.e. longitudinal direction). This significantly impaired the ductility of the steel when the load was perpendicular to these gamma films (i.e. transverse loading condition).
Prohinig, Jennifer M.Huetner, JohannaReichmann, KlausBigl, Stephan...
6页
查看更多>>摘要：Electrostatic force microscopy (EFM) was used to directly image the impact of SiO2 content variations on the grain boundary potential barriers in semiconducting BaTiO3-based ceramics. The grain boundary barriers were shown to be significantly thinner and more pronounced as the amount of SiO2 was increased from 0 to 5 mol%. The EFM results were confirmed by capacitance-voltage (C-V) measurements which proofs the accuracy of both methods and highlights their importance for gaining a better understanding of the interrelations between material composition and electrical properties.
查看更多>>摘要：The performance of the material can be significantly improved by introducing stacking faults and nanotwins. However, introducing high-density stacking faults and twins into Al remains difficult due to its ultrahigh stacking-fault energy. In this study, it was discovered for the first time that the addition of Ce promotes the formation of stacking faults in Al. The broadening of stacking faults is attributed to the extremely low content of Ce in Al and the local stress concentration during the rolling process. The solubility at eutectic temperature was determined to be 0.0084at.%. The solid solution of Ce has a great influence on the stacking fault energy of Al, which is attributed to the solute Ce disturbing the lattice orientation and electronic environment of the matrix atoms. The local stress concentration in Al matrix near the eutectic Al11Ce3 phase also provides a favorable condition for the formation of stacking faults.
查看更多>>摘要：A simple and versatile strategy, denominated Slip Trace - Modified Lattice Rotation Analysis (ST-MLRA), is presented to enable the identification of the active slip systems in polycrystalline alloys from surface information. The slip plane trace orientation is used to define the potential active slip planes while the actual slip direction within the active slip plane is obtained from the grain rotation, as indicated by the stretching of the trace of the grain orientation in the pole figure as a result of deformation. Examples of application of the strategy in a HCP Mg alloy are presented for illustration. They show that the strategy is simple to implement and allows to identify the active slip system(s) in each grain.
查看更多>>摘要：Developing cost-effective and high-performance conversion/alloying anode materials in lithium-ion batteries (LIBs) depend on the exquisite design of nanostructure that can efficiently improve volume change and enhance lithium storage capability of active materials. Herein, taking the typical SnO2 as an example, a universal strategy has been proposed to solve many difficulties faced by these electrode materials, i.e. in situ encapsulating hollow SnO2 nanospheres into sack-like reduced oxide graphene nanosheets (SnO2@RGO). This simple and ingenious design combines the flexibility of external graphene and the hollow characteristics of internal SnO2, thus providing more insertion sites and greatly avoiding the occurrence of structural collapse caused by large volume changes upon cycling. As expected, the SnO2@RGO electrode shows a larger initial discharge capacity, better capacity retention and more remarkable rate capability as compared to pristine SnO2 nanospheres electrode when used as advanced anode for LIBs.
查看更多>>摘要：The energetics of various extended interstitial (I) defects in crystalline Si is examined by constructing an artificial-neural-network (ANN) potential trained with density-functional-theory (DFT) data, enabling us to perform accurate large-scale simulations and to obtain well-converged formation energies (E-f). By varying the number of interstitials n to around 1,000, E-f & nbsp;is calculated for the compact cluster, I-12-like, (001)-plane, (311)-rod-like and Frank-loop defects. For n <=& nbsp;36, the compact cluster or (311)-rod-like defect is found to be most stable, depending on n. This trend strongly depends on simulation cell sizes, suggesting the importance of sufficiently large cells. For 36 < n ?& nbsp;860, the (311)-rod-like defect is most stable whereas the Frank-loop defect becomes most stable for larger n. The ANN potential is demonstrated to outperform empirical potentials in prediction of E-f and defect structures. Furthermore, ANN values of E-f are fitted to analytic functions with the aim of refining macroscopic simulations for device manufacturing processes.
查看更多>>摘要：Morphological variations of grain boundary (GB) allotriomorphs and widmanstatten sideplates (WS) of alpha pre-cipitate in a beta titanium alloy, have been systematically investigated by combining three-dimensional (3D) phase-field simulations, 3D experimental characterization and crystallographic orientation analysis. The inclination angle, theta, between the habit plane of the GB alpha and the hosting GB plane is found to dictate the morphologies of GB precipitates. For the first time, three distinct regimes of alpha morphology at a beta GB, separated by two critical angles (theta(1)(c) , theta(2)(c)) are observed: theta <= theta(1)(c), GB alpha alone decorates the GB as a continuous layer; theta 1c < theta <= theta(2)(c), alpha precipitate appears as a mixture of GB alpha and a WS emanating from it; theta > theta(2)(c), WS alone grows directly from bare beta GBs. The dramatic morphological variation owes its origin to the dynamic interplay between the spreading along GBP and the intragranular growth of the GB precipitate, and its dependence on theta.
NSTL
Elsevier