The Effect of Microstructure Morphology on Indentation Response of Ta/Ti Nanocomposite Thin Films
- PDF / 3,241,840 Bytes
- 14 Pages / 593.972 x 792 pts Page_size
- 21 Downloads / 211 Views
UCTION
NANO-METALLIC materials (NMMs)—polycrystalline, porous, and composite metals with microstructural features below 100 nm—have been the subject of intensive research over the past decades.[1–5] This research has been driven largely by a desire to elucidate the effect of characteristic microstructure dimensions[6] and interface (or surface) area-to-volume ratios[7] on materials properties such as mechanical,[8–10] radiation response,[11,12] and electrochemical actuation.[13,14] However, the effect of microstructure morphology—i.e., the shape, orientation, and connectivity of microstructure elements—on these properties has not been investigated in comparable detail.[15] In this study, we investigate the effect of microstructure morphology on the mechanical properties of Ta/Ti nanocomposites, as characterized via nanoindentation. Thin films of these materials are synthesized by heat treating TaxTi1 x solid solutions vapor deposited by magnetron sputtering.[16] By changing initial alloy compositions and processing routes (times and temperatures of heat treatment), we synthesize nanocomposites with comparable characteristic dimensions of microstructure
features, but widely differing microstructure morphologies, ranging from particulate to interpenetrating bicontinuous. Despite these differences, all of the nanocomposites exhibit comparable enhancements in hardness over the original thin film and individual elemental constituents. However, microstructure morphology has a marked effect on indentation pileup height: pileups are largest for composites with connected, Ta networks and non-percolating Ti particles and lowest for highly connected, Ti networks and non-percolating Ta particles. Comparison of the as-synthesized and deformed microstructures leads us to hypothesize that these differences in pileup height are due to a marked influence of microstructure morphology on composite straining hardening behavior. Potential mechanisms of strain hardening in these materials are proposed. Our work suggests that strain hardening—and therefore flow uniformity—in NMMs may be tuned by altering their microstructure morphology without affecting strength.
II.
EXPERIMENTAL METHODS
A. Synthesis and Characterization of Thin-Film Samples IAN MCCUE is with the Department of Materials Science and Engineering, Texas A&M University, College Station, TX 77840 and also with the Research and Exploratory Development Department, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723. Contact e-mail: [email protected] SISI XIANG, KELVIN XIE and MICHAEL J. DEMKOWICZ are with the Department of Materials Science and Engineering, Texas A&M University. Manuscript submitted March 22, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
TaTi thin films were prepared by DC Magnetron co-sputtering Ta and Ti targets on 1-mm-thick, 2 9 2 inch2 polycrystalline Zr substrates using the ATC Orion Series Sputtering System at the Center for Integrated Nanotechnologies (CINT) at Los Alamos National Laboratory. The Zr substrates (99.2 wt pct) were cut from
Data Loading...
