skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Relation Between the Defect Interactions and the Serration Dynamics in a Zr-Based Bulk Metallic Glass
For this study, the effects of thermal annealing and compressive strain rate on the complexity of the serration behavior in a Zr-based bulk metallic glass (BMG) was investigated. Here, as-cast and thermally-annealed (300 °C, 1 week) Zr52.5Cu17.9Ni14.6Al10Ti5 BMG underwent room-temperature compression tests in the unconstrained condition at strain rates of 2 × 10−5 s−1 and 2 × 10−4 s−1. The complexity of the serrated flow was determined, using the refined composite multiscale entropy technique. Nanoindentation testing and X-ray diffraction characterization were performed to assess the changes in the microstructure and mechanical properties of the BMG that occurred during annealing. The results indicated that the BMG did not crystallize during annealing in the prescribed heating condition. Nanoindentation tests revealed that annealing led to a significant increase in the depth-dependent nanoindentation hardness and Young’s modulus, which were attributed to the structural relaxation in the glass. Furthermore, both annealing and an increased strain rate resulted in a marked enhancement in the complexity of the serrated flow during compression. It was concluded that the increase in the sample entropy with increasing strain rate is related to an increase in the number of defect interactions during the serrated flow.  more » « less
Award ID(s):
1611180
PAR ID:
10186327
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Applied Sciences
Volume:
10
Issue:
11
ISSN:
2076-3417
Page Range / eLocation ID:
3892
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. (, Minerals, Metals and Materials Series: Light Metals 2020)
    Combining a retrogression heat treatment with simulta- neous warm forming can increase the formability of peak-aged, high-strength aluminum alloys while allowing peak-aged strength to be recovered through a single reaging heat treatment after forming. This process is termed retrogression-forming-and-reaging (RFRA). This study investigates the applicability of RFRA to AA6013- T6 sheet material. Elevated-temperature tensile tests were performed at temperatures from 230 to 250 °C and strain rates from 3.2  10 −3 to 10 −1 s −1 . Tensile tests were followed by reaging with a simulated paint-bake heat treatment. Flow stress at a true strain of 0.10 ranges from 230 MPa (250 °C and 3.2  10 −3 s −1 ) to 290 MPa (230 °C and 10 −1 s −1 ), significantly lower than the room-temperature yield strength of 360 MPa in the T6 condition. The average elongation to rupture and reduc- tion in area from elevated-temperature tests are 22% and 56%, respectively, which are similar to the room- temperature values for the T4 condition. Elevated- temperature testing reduced material hardness compared to the original T6 condition. Subsequent reaging with a simulated paint-bake raised hardness to 96% of the T6 condition in un-deformed material, but slightly decreased the hardness of the deformed material. Recommendations for implementing RFRA of AA6013-T6 are presented. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, Journal of Synchrotron Radiation)
    An experimental platform for dynamic diamond anvil cell (dDAC) research has been developed at the High Energy Density (HED) Instrument at the European X-ray Free Electron Laser (European XFEL). Advantage was taken of the high repetition rate of the European XFEL (up to 4.5 MHz) to collect pulse-resolved MHz X-ray diffraction data from samples as they are dynamically compressed at intermediate strain rates (≤103 s−1), where up to 352 diffraction images can be collected from a single pulse train. The set-up employs piezo-driven dDACs capable of compressing samples in ≥340 µs, compatible with the maximum length of the pulse train (550 µs). Results from rapid compression experiments on a wide range of sample systems with different X-ray scattering powers are presented. A maximum compression rate of 87 TPa s−1was observed during the fast compression of Au, while a strain rate of ∼1100 s−1was achieved during the rapid compression of N2at 23 TPa s−1. 
    more » « less
  3. ; ; ; ; ; (, Materials Science and Engineering: A)
    In a recent work, we have reported outstanding strength and work hardening exhibited by a metastable high entropy alloy (HEA), Fe42Mn28Co10Cr15Si5 (in at. %), undergoing the strain-induced martensitic transformation from metastable gamma austenite (γ) to stable epsilon martensite (ε). However, the alloy exhibited poor ductility, which was attributed to the presence of the brittle sigma (σ) phase in its microstructure. The present work reports the evolution of microstructure, strength, and ductility of a similar HEA, Fe38.5Mn20Co20Cr15Si5Cu1.5 (in at. %), designed to suppress the formation of σ phase. A cast and then rolled plate of the alloy was processed into four conditions by annealing for 10 and 30 min at 1100 °C and by friction stir processing (FSP) at tool rotation rates of 150 and 400 revolutions per minute (RPM) to facilitate detailed examinations of variable initial grain structures. Neutron diffraction and electron microscopy were employed to characterize the microstructure and texture evolution. The initial materials had variable grain size but nearly 100% γ structure. Diffusionless strain induced γ→ε phase transformation took place under compression with higher rate initially and slower rate at the later stages of deformation, independent on the initial grain size. The transformation facilitated part of plastic strain accommodation and rapid strain hardening owing to a transformation-induced dynamic Hall-Petch-type barrier effect, increase in dislocation density, and texture. The peak strength of nearly 2 GPa was achieved under compression using the structure created by double pass FSP (150 RPM followed by 150 RPM). Remarkably, the tensile elongation exhibited by the alloy was nearly 20% with fracture surfaces featuring a combination of ductile dimples and cleavage. 
    more » « less
  4. ; ; (, Materials science engineering)
    The softening effect of ultrasonic vibration on pure copper is studied from a new perspective with micro-tensile tests, where the gauge length of the specimen is one order of magnitude smaller than the ultrasonic wavelength. With this configuration, the amount of flow stress reduction increases linearly with vibration amplitude whereas the flow stress reduction is insensitive to the studied strain rate ranging from 0.06/s to 1/s. Temperature rise associated with ultrasonic vibration is minimal from infrared thermal imaging. In situ digital image correlation (DIC) analysis shows strain localization near ultrasonic source whereas uniform strain distribution was observed during conventional tensile test. Optical microstructure characterization shows that area fraction of annealing twins in the deformed copper reduced from 3.3% to 1.8% with ultrasonic vibration. This is possibly attributed to enhanced interaction of dislocation between twin boundaries which act as non-regenerative dislocation source. Electron backscatter diffraction (EBSD) results show that ultrasonic vibration promotes preferential grain re-orientation and reduces the misorientation within grains. 
    more » « less
  5. ; ; ; ; ; ; ; (, International Journal of Impact Engineering)
    This study provides an in-depth analysis of the mechanical behavior of rotating-square auxetic structures under various strain rates. The structures are fabricated using stereolithography additive manufacturing with a flexible resin. Mechanical tests performed on structures include quasi-static, intermediate, and high strain rate compression tests, supplemented by high-speed optical imaging and two-dimensional digital image correlation analyses. In quasi-static conditions (5 × 10–3 s-1), multiscale measurements reveal the correlation between local and global strains. It is shown that cell hinges play a significant role in structural deformation and load-bearing capacity. In drop tower impact conditions (intermediate strain rate of ca. 200 s-1), the auxetic structures display significant strain rate hardening compared to loading at quasi-static rates. The thin-hinge structures maintain a Poisson's ratio of approximately -0.8, showing higher auxeticity than slow-rate compression tests. High strain rate conditions (ca. 2000s-1) activate additional deformation mechanisms, including a delayed state of equilibrium exemplified by a heterogeneous distribution of lateral strains, possibly due to stress wave interactions and inertial stresses. The study further reveals nonlinear correlations between Poisson's ratio, strain, and strain rate, indicating reduced auxeticity at higher strain rates. These observations are discussed in terms of complex wave interactions and the strain rate hardening characteristics of the base polymer. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email