26 research outputs found
Data associated with publication: "Separating geometric and diffusive contributions to the surface nucleation of dislocations in nanoparticles" by R. Ding, S. Azadehranjbar, I.M. Padilla Espinosa, A. Martini, and T.D.B. Jacobs, published in ACS Nano, 2024
No full textData associated with publication: "Separating geometric and diffusive contributions to the surface nucleation of dislocations in nanoparticles" by R. Ding, S. Azadehranjbar, I.M. Padilla Espinosa, A. Martini, and T.D.B. Jacobs, published in ACS Nano, 202
Anomalous Eutectic and Nanolaminated Composites of Mg-Al Alloys: Microstructure and In-Situ Compression Test
No full textEutectic alloys demonstrate excellent casting behavior and composite properties. Their morphologies are characterized by the simultaneous growth of at least two solid phases from the liquid phase. Besides, the solidification condition can affect the final morphology. Under a non-equilibrium condition, a transition from the regular to anomalous eutectic can occur. However, the formation mechanisms of the anomalous eutectic are still debated. In this study, melt spinning was applied to rapidly solidify Mg-33.3%Al eutectic alloy at different wheel speeds from 5 to 50 m/s. Four distinct anomalous eutectic microstructures were identified, and their corresponding formation mechanisms were determined using scanning electron microscopy (SEM), scanning/transmission electron microscopy (S/TEM), and high resolution TEM (HRTEM) analyses. Owing to their low density and high strength-to-weight ratio, Mg alloys are one of the most potential alloys to replace aluminum, zinc, and steel for automotive and aerospace applications. However, the current use of magnesium in the industry is limited because of low strength and poor formability at ambient temperatures. These limitations are due to the insufficient independent deformation modes in Mg. To achieve a good combination of strength and ductility, microstructural engineering was applied and Mg-Al in-situ composites were fabricated by melt spinning considering that the nanolaminated composites exhibit outstanding mechanical properties depending on the layer thickness and interface structure. Two different morphologies of Mg-Al nanocomposites were examined by the in-situ SEM microcompression test; the layered and fibrous eutectics. It was shown that the combination of mechanical properties of nanolaminated composite was superior to that of fibrous eutectic and pure Mg. The reason was attributed to the high interfacial area and the effect of α layers in restricting the shear propagation. The investigation of orientation relationship between the layers demonstrated weak interphase interfaces. The dislocation entrapment by the weak interfaces improved the strength of nanolaminated composites. Moreover, the enhanced activity of dislocations in the β phase and suppressing the propagation of deformation instabilities by the α phase resulted in the increase of ductility
Deformation Mechanisms in Mg–Al Nanocomposite
No full textMagnesium is the lightest engineering metal. Replacing steel with Mg based materials in automotive applications would lead to more than 40% weight reduction which significantly boost fuel efficiency. However, conventional Mg alloys typically suffer from low strength and poor deformability due to very few slip systems and easy twinning. Alloying Mg with other materials and microstructural engineering are promising approaches to increase ductility and strength of Mg According to Wang et al. interfaces with low energy and high coherency may effectively constrict the nucleation of twins in Mg In this work, the microstructure of Mg nano layers and nano rods were examined after deformation to determine the dominant deformation mechanism
Anomalous Eutectic Microstructures in Mg-Al Structural Alloy Prepared by Rapid Solidification
No full textMagnesium is the lightest engineering metal 1 However, conventional Mg alloys typically suffer from low strength and poor deformability due to very few slip systems and easy twinning 3 Alloying Mg with other materials and microstructural engineering are promising approaches to increase ductility and strength of Mg In the current work, non equilibrium solidification conditions were applied to induce a transition from regular to anomalous eutectic in Mg Al eutectic alloy such that four distinguished microstructures were acquired and the corresponding formation mechanisms were investigate
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Separating Geometric and Diffusive Contributions to the Surface Nucleation of Dislocations in Nanoparticles
No full textWhile metal nanoparticles are widely used, their small size makes them mechanically unstable. Extensive prior research has demonstrated that nanoparticles with sizes in the range of 10-50 nm fail by the surface nucleation of dislocations, which is a thermally activated process. Two different contributions have been suggested to cause the weakening of smaller particles: first, geometric effects such as increased surface curvature reduce the barrier for dislocation nucleation; second, surface diffusion happens faster on smaller particles, thus accelerating the formation of surface kinks which nucleate dislocations. These two factors are difficult to disentangle. Here we use in situ compression testing inside a transmission electron microscope to measure the strength and deformation behavior of platinum particles in three groups: 12 nm bare particles, 16 nm bare particles, and 12 nm silica-coated particles. Thermodynamics calculations show that, if surface diffusion were the dominant factor, the last two groups would show equal strengthening. Our experimental results refute this, instead demonstrating a 100% increase in mean yield strength with increased particle size and no statistically significant increase in strength due to the addition of a coating. A separate analysis of stable plastic flow corroborates the findings, showing an order-of-magnitude increase in the rate of dislocation nucleation with a change in particle size and no change with coating. Taken together, these results demonstrate that surface diffusion plays a far smaller role in the failure of nanoparticles by dislocations as compared to geometric factors that reduce the energy barrier for dislocation nucleation
Making Light-weight Mg-Metal Laminated Nanocomposites
No full textMagnesium is the lightest of all the engineering metals. Replacing steel structural materials with Mg-based materials in automotive applications would boost fuel. However, conventional Mg alloys typically suffer from low strength and poor deformability due to very few slip systems and easy twinning. Alloying Mg with other materials and microstructural engineering are promising approaches to increase ductility and strength of Mg. According to Wang et al., interfaces with low energy and high coherency may effectively constrict the nucleation of twins in Mg. In this work, Mg-metal multilayered nanocomposites will be produced by melt spinning procedure and the layers’ mechanical properties will be examined by picoindentation. Meanwhile, plastic co-deformation of the layers can be designed by crystallographic theory and multiscale modelling to achieve fine nanolaminate microstructure in bulk Mg alloys
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Size-Dependent Role of Surfaces in the Deformation of Platinum Nanoparticles
No full textThe mechanical behavior of nanostructures is known to transition from a Hall-Petch-like "smaller-is-stronger" trend, explained by dislocation starvation, to an inverse Hall-Petch "smaller-is-weaker" trend, typically attributed to the effect of surface diffusion. Yet recent work on platinum nanowires demonstrated the persistence of the smaller-is-stronger behavior down to few-nanometer diameters. Here, we used in situ nanomechanical testing inside of a transmission electron microscope (TEM) to study the strength and deformation mechanisms of platinum nanoparticles, revealing the prominent and size-dependent role of surfaces. For larger particles with diameters from 41 nm down to approximately 9 nm, deformation was predominantly displacive yet still showed the smaller-is-weaker trend, suggesting a key role of surface curvature on dislocation nucleation. For particles below 9 nm, the weakening saturated to a constant value and particles deformed homogeneously, with shape recovery after load removal. Our high-resolution TEM videos revealed the role of surface atom migration in shape change during and after loading. During compression, the deformation was accommodated by atomic motion from lower-energy facets to higher-energy facets, which may indicate that it was governed by a confined-geometry equilibration; when the compression was removed, atom migration was reversed, and the original stress-free equilibrium shape was recovered
Separating Geometric and Diffusive Contributions to the Surface Nucleation of Dislocations in Nanoparticles
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