Structure and properties of bulk nanostructured alloys synthesized by flux-melting |
| |
Authors: | T D Shen X Zhang K Han C A Davy D Aujla P N Kalu R B Schwarz |
| |
Affiliation: | (1) Materials Science and Technology Division, Los Alamos National Laboratory, Mail Stop G755, Los Alamos, NM 87545, USA;(2) Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123, USA;(3) National High Magnetic Field Laboratory, 1800 E Paul Dirac Dr., Tallahassee, FL 32310, USA |
| |
Abstract: | Nanomaterials can easily be prepared as thin films and powders, but are much harder to prepare in bulk form. Nanostructured
materials are prepared mainly by consolidation, electrodeposition, and deformation. These processing techniques have problems
such as porosity, contamination, high cost, and limitations in refining the grain size. Since most bulk engineering metals
are initially prepared by casting, we developed a casting technique, flux-melting and melt-solidification, to prepare bulk
nanostructured alloys. The casting technique has such advantages as simplicity, low cost, and full density. In our method,
Ag–Cu alloys were melted in B2O3 flux, which removed most of the impurities, mainly oxides, in the melts. Upon solidifying the melt at a relatively slow cooling
rate on the order of 101–102 K/s a large undercooling of ∼0.25 T
m (where T
m is the melting temperature) was achieved. This large undercooling leads to the formation of bulk nanostructured Ag–Cu alloys
composed of alternative Ag/Cu lamella and nanocrystals, both ∼50 nm in dimension. Our liquid-processed alloys are fully dense
and relatively free from contamination. The nanostructured Ag–Cu alloys have similar yield strength in tension and in compression.
The as-quenched alloys have yield strength of 400 MPa, ultimate tensile strength (UTS) of 550 MPa, and plastic elongation
of ∼8%. The UTS was further increased to ∼830 MPa after the as-quenched alloy rod was cold drawn to a strain of ∼2. The nanostructured
Ag–Cu alloys show a high electrical conductivity (∼80% that of International Annealed Copper Standard), a slight strain hardening
(strain-hardening coefficient of 0.10), and a high thermal stability up to a reduced temperature of 2/3 T
m. Some of these behaviors are different than those found in previous bulk nanostructured materials synthesized by solid state
methods, and are explained based on the unique nanostructures achieved by our flux-melting and melt-solidification technique. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|