Effect of Temperature on the Nano/Microstructure and Mechanical Behavior of Nanotwinned Ag Films
- PDF / 1,835,385 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 89 Downloads / 272 Views
TRODUCTION
NANOTWIN (NT) metals, with high strength, high strain rate sensitivity, and electric conductivity, are a leading material of interest for advanced electronics and other applications.[1–8] In recent years, NT metals (Cu and Ag) have been successfully synthesized with several techniques such as magnetron sputtering and pulsed electrodeposition methods.[3,9,10,11] Compared with coarse-grained and nanocrystalline metals, the NT structures exhibit outstanding thermal stability and enhanced mechanical strength due to the nano-scaled twin boundary spacings.[5,9,12–14] Lu et al. reported ultra-high strength for NT Cu,[1] while Anderoglu et al. have shown extremely high hardness with the remarkable thermal stability of sputter-deposited NT Cu film by using the ex situ annealing and indentation experiments.[15] Twin boundaries in face-centered cubic (fcc) metal can also function as barriers to dislocation climb due to their thermal stability at elevated temperatures.[7,16] Zhang et al. claimed the superior thermal stability of the CTBs is due to their order of magnitude lower energy stored compared to high-angle grain boundaries.[17] Bufford et al. proposed that the thermal stability of twin boundaries in NT silver have an orientation dependence, for which the coarsening and HUAN ZHANG, Postdoctoral Research Associate, JIE GENG, Postdoctoral Research Associate, RYAN T. OTT, Scientist I, MATTHEW F. BESSER, Assistant Scientist IV, and MATTHEW J. KRAMER, Director III, are with the Division of Materials Sciences and Engineering, Ames Laboratory, Iowa State University, Ames, IA 50011. Contact e-mail: [email protected] Manuscript submitted March 30, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
elimination of twin boundaries after annealing results in hardness reduction.[4] In situ TEM experiments’ results provide critical insight into the dislocation interactions with TBs and the effects on macroscopic mechanical behavior.[18] Besides the role of CTB as barriers to block the movement of dislocations, Li et al. used in situ TEM nanoindentation to show that CTBs can act as a source for multiplication of Shockley partial dislocation, for which the stress-induced ITB can lead to the de-twining of the NT structure.[19] Besides the experimental work, molecular dynamics (MD) simulation also revealed that CTBs in NT Cu can increase the thermal stability and yield stress due to the discontinuity of the slip systems across TBs.[17,20,21] In this paper, we report on the relationship between the mechanical properties and the thermal stability of NT Ag formed by magnetron sputtering. Specifically, the grain size, twin spacing, and dislocation density were examined by TEM at different annealing conditions for comparison with the bulk mechanical properties. In situ TEM heating experiments were used to examine the grain growth, twin boundary mobility, and dislocation diminution. Tensile tests on ex situ annealed NT Ag provided the correlation between the thermal stability of twin spacing, grain size, dislocation density, and the mech
Data Loading...
