Microstructures and Mechanical Properties of Nanostructured Copper-304 Stainless Steel Multilayers Synthesized by Magnetron Sputtering

Abstract

Nanostructured Cu/304 stainless steel (SS) multilayers were prepared by magnetron sputtering at room temperature. 304SS has a face-centered cubic (fcc) structure in bulk. However, in the Cu/304SS multilayers, the SS layers exhibited fcc structure for layer thickness of less than or equal to 5 nm. For 304SS layer thickness larger than 5nm, bcc 304SS grains were observed to grow on top of the initial z 5 nm of fcc SS. The maximum hardness of Cu/304SS multilayers was z 5.5 GPa (factor of two enhancement compared to rule of mixtures hardness) achieved at a layer thickness of 5nm, with a decrease in hardness with decreasing layer thickness below 5 nm. The hardness of fcc/fcc Cu/304SS multilayers (layer thickness < 5 nm) is compared with Cu/Ni, another fcc/fcc system, to gain insight on how the mismatch in physical properties such as lattice parameters and shear moduli of the constituent layers affect the peak hardness achieved in these nanoscale systems. IntroductionNanostructured multi layers are made up of alternating nanometer scale layers of two different materials. The layer thickness can be well controlled in the scale of nmm or less by physical vapor deposition (PVD). These nanostructured multilayers have novel mechanical, electrical, magnetic, and optical properties [1][2][3]. The mechanical properties of these multilayered composites are of particular interest since the strength of these multilayer composites can be significantly increased to about 1/3 of the theoretical strength limit [4]. In the jin to the sub-[tm length scale regime, the strengthening in these multilayers can be explained by the Hall-Petch model of dislocation pile-ups at interfaces or grain boundaries. The yield strength, a, is proportional to h-1/

Effect of Temperature on the Nano/Microstructure and Mechanical Behavior of Nanotwinned Ag Films

“…[1][2][3][4][5][6][7][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][13][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.…”

“…[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][13][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.…”