Mechanical Behavior of Nanotwinned Materials-Experimental and Computational Approaches

Nanotwinned materials exhibit high strength combined with excellent thermal stability, making them potentially attractive for numerous applications. When deposited on cold substrates at high rates, for example, silver films can be prepared with a high-density of growth twins with an average twin boundary spacing of less than 10 nm. These films show a very strong {111} texture, with the twin boundaries being perpendicular to the growth direction. The origins of superior mechanical and thermal properties of nanotwinned materials, however, are not yet fully understood and need further improvements. The aim of this research is to develop a connected experimental and theoretical/modeling study to elucidate the fundamental mechanisms that control the strength and stability of nanotwinned materials. To that end, we employed in-situ high-temperature nanoindentation to examine the mechanical behavior of nanotwinned materials. The hardness and strain rate were determined as a function of temperature, from which activation energies, activation volumes and strain rate sensitivities –which are fingerprints of dominant deformation mechanism- were determined. Furthermore, to better understand the physical phenomena that leads to their high strength, we have used the phase field dislocation dynamics (PFDD) model to study the effect of twin boundary spacing, grain size, applied stress on the stress driven emission and interaction of leading/trailing partial dislocations from grain boundary. Understanding both the mechanical properties of nanotwinned materials as well as how to control their structures will allow us to design better materials with desired properties

Bending Nanoindentation and Plasticity Noise in FCC Single and Polycrystals

Abstract: We present a high-throughput nanoindentation study of in situ bending effects on incipient plastic deformation behavior of polycrystalline and single-crystalline pure aluminum and pure copper at ultranano depths (\u3c 200 nm). We find that hardness displays a statistically inverse dependence on in-plane stress for indentation depths smaller than 10 nm, and the dependence disappears for larger indentation depths. In contrast, plastic noise in the nanoindentation force and displacement displays statistically robust noise features, independently of applied stresses. Our experimental results suggest the existence of a regime in Face Centered Cubic (FCC) crystals where ultranano hardness is sensitive to residual applied stresses, but plasticity pop-in noise is insensitive to it

Mechanical Behavior of Nanotwinned Materials-Experimental and Computational Approaches

Nanotwinned materials exhibit high strength combined with excellent thermal stability, making them potentially attractive for numerous applications. When deposited on cold substrates at high rates, for example, silver films can be prepared with a high-density of growth twins with an average twin boundary spacing of less than 10 nm. These films show a very strong {111} texture, with the twin boundaries being perpendicular to the growth direction. The origins of superior mechanical and thermal properties of nanotwinned materials, however, are not yet fully understood and need further improvements. The aim of this research is to develop a connected experimental and theoretical/modeling study to elucidate the fundamental mechanisms that control the strength and stability of nanotwinned materials. To that end, we employed in-situ high-temperature nanoindentation to examine the mechanical behavior of nanotwinned materials. The hardness and strain rate were determined as a function of temperature, from which activation energies, activation volumes and strain rate sensitivities –which are fingerprints of dominant deformation mechanism- were determined. Furthermore, to better understand the physical phenomena that leads to their high strength, we have used the phase field dislocation dynamics (PFDD) model to study the effect of twin boundary spacing, grain size, applied stress on the stress driven emission and interaction of leading/trailing partial dislocations from grain boundary. Understanding both the mechanical properties of nanotwinned materials as well as how to control their structures will allow us to design better materials with desired properties.</p

Development of a rapid-scan fiber-integrated terahertz spectrometer

Scientists in terahertz (THz) wave technologies have benefited from the recent developments in ultrafast laser technologies and RF technologies and applied these new gained techniques into characterizing a wide variety of phenomena. Undoubtedly, the most successful of these applications has been in the development of time-domain terahertz spectroscopic and imaging systems which has been utilized in the characterization of dielectrics and semiconductors. This pulsed technique has allowed users to characterize dynamical behavior inside materials under illumination with picosecond resolution. Typically pump/probe or similar dynamical measurements require the use of amplified pulses derived from free-space solid state lasers in the J-mJ range and since interferometric techniques are typically used in pulsed measurements the measurement time of a THz spectrum can last at least tens of minutes. Better systems can be realized based on fiber laser technologies. Here we discuss the advantages of a THz spectrometer driven by an ultrafast Ytterbium doped fiber laser whose repetition rate can be tuned rapidly allowing for rapid dynamical measurements. The efficient gain medium, robust operation and compact design of the system opens up the possibility of exploring rapid detection of various materials as well as studying dynamical behavior using the high brightness source

Discrete dislocation dynamics simulations of nanoindentation with pre-stress: Hardness and statistics of abrupt plastic events

Nanoindentation of crystalline materials has been thought as a primarily surface-driven technique that is not able to probe bulk mechanical properties directly, such as material yield strength or bulk plastic flow rates. We elucidate this question through extensive discrete dislocation plasticity simulations of nanoindentation on a single crystal. We consider the competition between nanoindentation and tensile loading (pre-stress) towards crystal plasticity. For this purpose, we study a two-dimensional discrete dislocation model where indentation is performed by using cylindrical indentation with varying radius under both displacement and load control. We focus on the behavior of the hardness and pop-in event statistics during nanoindentation under various pre-stress levels and we correlate them to the spatially correlated dislocation microstructure behavior. At small indentation depths (relative to other microstructural or tip length scales), we find that the hardness is inversely dependent on the plastic strain/dislocation density induced by the applied tensile pre-stress; consequently, we argue that small-depth indentation may be useful for identifying bulk plastic yielding behavior prior to indentation. In contrast, for larger indentation depths, pre-stress has no effect on hardness. However, effect of pre-stress can be revealed through plastic events statistics, both in load and displacement controlled protocols. Moreover, post-indentation surface morphology clearly shows the effect of the pre-stress

Novel debittering process of green table olives: application of β-glucosidase bound onto superparamagnetic nanoparticles

In this work, the olive β-glucosidase (β-glu) enzyme was immobilized onto superparamagnetic nanoparticles (SPMNs). Moreover, immobilized enzyme was also used for the debittering process for natural edible olives from Edremit, Turkey. Owing to SPMNs, the system can be easily removed by a simple magnet and reused many times for debittering process. The free olive β-glucosidase (E), β-glucosidase bound SPMNs (IE), free commercial β-glucosidase (CE), and commercial β-glucosidase bound SPMNs (ICE) were comparatively studied for oleuropein removal. In 6 h, the treatment of E, IE, and ICE hydrolyzed the 15.8%, 56.4%, and 80.0% of the oleuropein for 1000 g of olives, respectively, and further treatment showed that the IE and ICE reached the 100% after 22 h treatment. The results revealed that the IE and ICE with biocompatible properties of SPMNs have the economical, fast, and reusable properties for the industrial debittering process in the table olive production

Bending Nanoindentation and Plasticity Noise in FCC Single and Polycrystals

We present a high-throughput nanoindentation study of in situ bending effects on incipient plastic deformation behavior of polycrystalline and single-crystalline pure aluminum and pure copper at ultranano depths (&lt; 200 nm). We find that hardness displays a statistically inverse dependence on in-plane stress for indentation depths smaller than 10 nm, and the dependence disappears for larger indentation depths. In contrast, plastic noise in the nanoindentation force and displacement displays statistically robust noise features, independently of applied stresses. Our experimental results suggest the existence of a regime in Face Centered Cubic (FCC) crystals where ultranano hardness is sensitive to residual applied stresses, but plasticity pop-in noise is insensitive to it

Deep insight into the photoluminescent monocrystalline particles : Heat-treatment, structure, mechanisms and mechanics

The red light emitting down-converting Ag@Y2O3:Eu3+ phosphor particles were synthesized by one-step ultrasonic spray pyrolysis and exposed further to the heat treatment at 1000°C (12h). A detailed investigation on structural and functional properties of the as-prepared and heat treated particles was conducted in a comparative manner. High-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRPD) and focus ion beam milling (FIB) revealed in a great consistency the poorly crystallized and porous nature of the as-prepared particles. Well-crystallized coarser primary nanocrystals of Y2O3:Eu3+and Ag, which are hierarchically organized in dense spherical Ag@Y2O3:Eu3+ phosphor particles, were obtained through the heat treatment. Along with the change of structural properties, down conversion (red luminescence at 612nm owing to the Eu3+5D0→7F2 electric dipole transition) and mechanical endurance were enhanced 4-fold and 5-fold via heat treatment, respectively. This comparative study implies a good correlation between mechanical and luminescence behavior of phosphors, both strongly influenced by the particles structural properties

A parametric study on processing of scratch resistant hybrid sol-gel silica coatings on polycarbonate

Scratch resistant silica-based hybrid coatings on polycarbonate substrates were formed by dip-coating of acid-catalyzed tetramethyl ortohosilicate (TMOS): diethylenetriamine (DETA): H2O:2-propanol sols. The sol formulation and dip-coating process parameters on microstructural and performance properties-here optical transmittance and scratch resistance-of the coatings were evaluated. The effect of water quantity, total aqueous component (H2O + 2-propanol) amount and relative proportion of TMOS: DETA on film formation behavior and on performance properties have been investigated in a systematic way. It was found that an effectively polymerized hybrid coating rich in silica content, as realized for high TMOS or abundant water containing sols, resulted in defective films with microcracking and adhesion problems. High 2-propanol content on the other hand led to incomplete film coverage. It was shown that 5 +/- 1 mu m-thick, scratch resistant and pristine coatings exhibiting a visible transmittance of 86-88% can be formed with a single deposition process using an optimized sol formulation of TMOS: DETA: H2O: 2-propanol of 30: 30: 20: 20 in wt.%. Meanwhile, the hardness of the PC has increased from an initial value of 13.9 +/- 2 to 70 +/- 25 (Vickers hardness, HV1) upon coating. A surface hardness approaching to 250 HV1 can be attained by for the thicker coatings (8 +/- 1 mu m) deposited at higher withdrawal speeds. However, such films suffered from non-uniform coverage and poor surface/optical quality. The transmittance values reduced by a factor of 20-30% for thicker coatings