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SCRIPTA

Nucleation of crystalline defects such as dislocations lies at the heart of mechanical deformation. Here, we demonstrate a technique for observing the nucleation of individual dislocations during in situ transmission electron microscopy (TEM) tensile testing and measuring fundamental parameters relevant for plasticity from the individual events. Our method relies on systematic detection of dislocation slip traces with automated image analysis in an oriented single crystal Ni sample. Using the identification of individual defect traces from in situ testing, a cumulative probabilistic function is applied to correlate the relationship between a dislocation nucleation event and the corresponding stress level. Our analysis allows for the extrapolation of the activation parameters for individual dislocation nucleation events using the data on one sample in one tensile test. Precise and quantitative correlation of activation parameters for dislocation nucleation from in situ TEM nanomechanical testing can provide direct quantitative measurements useful for computational models of plasticity.

SCRIPTA

The mechanical response of macroscale metallic samples is typically determined using the uniaxial tensile test, which provides a direct measure of critical properties such as Young's modulus and yield strength. However, due to experimental challenges, uniaxial tensile tests have seldom been used for studying the mechanical behavior of metallic nanolaminates. Here, we use a custom-made MEMS device to study the quasi-static, uniaxial tensile behavior of Cu-Co nanolaminates with four different layer thicknesses (h = 2, 4, 8 and 16 nm). Our experiments reveal a peak in the yield strength at h = 4 nm, while the Young's modulus is independent of h. Surprisingly, the nanolaminates recover significant amount (> 60%) of inelastic deformation during and after unloading, and this recovery is enhanced by an increase in temperature. Possible mechanisms for this unusual strain recovery in Cu-Co nanolaminates are discussed.

SCRIPTA

12Cr-1MoWV (wt.%) ferritic/martensitic (F/M) steel is a candidate material for fuel cladding in advanced nuclear reactors. As such, understanding the relationship between microstructure and mechanical properties in the context of irradiation environments for these steels is critical. Here we reveal the presence of ultrafine scale (2-5 nm), intralath V(C,N) precipitates in conventionally heat treated 12Cr-1MoWV steel for the first time. Lower N content results in finer intralath precipitates, whereas higher N content results in larger, elongated disks or needles. N content significantly alters the strength, but not the strain hardening behavior, by its impact on precipitate characteristics. Finer precipitates could have an impact on irradiated behavior, specifically their capacity as defect sinks. The presence of ultrafine scale V(C,N) precipitates in conventionally heat treated 12Cr-1MoWV steel, controlled by N variations, provides a new means for tailoring the strength and irradiation response of F/M steels for nuclear applications.

SCRIPTA

Assessing the local residual stress and orientation with nanometer resolution within embedded steel grains has remained challenging. Here we use an advanced synchrotron technique, dark field X-ray microscopy to map 3D lattice variations, including both the crystallographic orientation and lattice strain, within two pro-eutectoid ferrite grains in pearlitic steel. We found an orientation variation up to 0.5° and compressive elastic strain up to 1.8 × 10^-3 are present in the as-manufactured sample. There is no direct correlation between the measured compressive strain and lattice orientation. The origin of the variations and their influence on the manufacturing process and mechanical properties are discussed.

SCRIPTA

Determining non-metallic inclusions (NMIs) are essential to engineer ultra-high-strength steel as they play decisive role on performance and critical to probe via conventional techniques. Herein, advanced Synchrotron X-ray absorption coupled with photoemission electron microscopy and first-principles calculations are employed to provide the structure, local bonding structure and electronic properties of several NMI model systems and their interaction mechanism within and the steel matrix. B K-, N K-, Ca L_2,3- and Ti L_2,3-edge spectra show that the additional B prefers to result in h-BN exhibiting strong interaction with Ca²⁺. Such Ca²⁺-based phases also stabilize through TiN, revealing the irregular coordination of Ca²⁺. Observed intriguing no interaction between TiN and BN is further supported with the first-principles calculations, wherein unfavorable combination of TiN and h-BN and stabilization of bigger sized Ca²⁺-based inclusions have been found. These observations can help to optimize the interaction mechanism among various inclusions as well as steel matrix.

SCRIPTA

Cu protrusion phenomenon, one of the biggest challenges of the Cu through-silicon-via (TSV) technology, results from the thermal stress accumulation and the following plastic deformation during thermal annealing. Herein, we proposed an effective approach to inhibiting the detrimental Cu protrusion by introducing a highly (111)-oriented nanotwinned Cu to the TSV structure. The Cu nanotwin structure, in comparison with the normal Cu structure, gave rise to a 70.3% decrement of the protrusion height during thermal annealing at 250°C. The protrusion inhibition was attributed to the effective interaction of high-fraction coherent nanotwin boundaries with dislocations. The presence of low-energy coherent twin boundaries impeded dislocation glide, giving rise to the TSV strengthening and the significant protrusion inhibition. The electrodeposited nanotwinned Cu TSV exhibited great thermal stability under thermal annealing at 250°C for 2 h, as evidenced by the slight micro-hardness loss, 6.7%, based on the nanoindentation analysis.

SCRIPTA

Mechanical modelling using the level-cut Gaussian random field approach has been employed to simulate the effect of radiation induced amorphization on the Young´s modulus, Poisson´s ratio and hardness of zircon (ZrSiO₄). A good agreement with previous nanoindentation experiments has been achieved. Two percolation transitions occur at ~16% and ~84% amorphous volume fraction, leading to deviations from linearity in the evolution of the Young´s modulus. Interface regions between crystalline and amorphous areas stabilise the hardness for a considerable amount of amorphous fraction. The modelling approach is promising for predicting the intrinsic radiation damage related evolution of the mechanical properties of various materials.

SCRIPTA

We investigate a phase transformation in a Ni-Cr-Fe-based high-temperature alloy during the technologically important carburization process, with multi-length scale experimental techniques. The study focuses on the formation and stability of novel austenitic islands formed within carbide structures during the M₂₃C₆ to M₇C₃ phase-transformation. We demonstrate that the austenitic islands nucleate near the M₂₃C₆/M₇C₃ transformation front, from a supersaturation of metal atoms in the M₂₃C₆-carbide as M₇C₃ grows. After formation, the austenitic islands equilibrate their composition with the matrix temporally but remain relatively stable inside the carbides due to their large sizes (a few hundred nanometers in diameter) and a weak Gibbs-Thomson effect.

SCRIPTA

High entropy alloys with multi-principal elements have interested the research community due to the promising properties and tunable microstructure. In the current study, the multiphase alloy system with a mixture of solid solution and intermetallic (SS+IM) was predicted using a machine learning approach with a data set of 636 alloys. The Algorithms used are Logistic Regression, Decision Tree, Support Vector Machine (SVM) classifier, Random Forest, Gradient Boosting Classifier, and Artificial Neural Network (ANN). ANN has shown the best accuracy of more than 80% for the test data. The new alloys were prepared and characterized to verify the prediction and it is found that ANN is having more accurate prediction in the studied alloy system. Statistical analysis of the established data set reveals an overlapping boundary between the design parameters that hinders the successful prediction. Experimental data confirms the formation of new multiphase alloys.

SCRIPTA

As a feasible technological approach to promote the global energy transformation, hydrogen energy has gradually become a hot topic in the world's energy field. In order to solve the problem of the poor dehydrogenation kinetic performance in solid hydrogen storage materials, the effect of electropulsing treatment on the dehydrogenation kinetic performance of magnesium alloy was studied through the analysis of dehydrogenation amount, dehydrogenation rate, phase composition and microstructure. After electropulsing treatment, the initial dehydrogenation temperature was reduced by 39 °C, and the maximum dehydrogenation rate was increased from 7.48 wt.% H₂/h to 14.36 wt.% H₂/h. The electropulsing treatment provides a new idea and method for improving the dehydrogenation kinetic performance of hydrogen storage materials.