The thermal stability of nanocrystalline Au–Cu alloys

Abstract

Grain refinement to the nanocrystalline scale is known to enhance physical properties as strength and surface hardness. For the case of Au-Cu alloys, development of the pulsed electroplating has led to the functional control of nanocrystalline grain size in the as-deposited condition. The thermal aging of Au-Cu electrodeposits is now investigated to assess the stability of the nanocrystalline grain structure and the difference between two diffusion mechanisms. The mobility of grain boundaries, dominant at low temperatures, leads to coarsening of grain size whereas at high temperature the process of bulk diffusion dominates. Although the kinetics of bulk diffusion are slow below 500 K at 10 -20 cm 2 ·sec, the kinetics of grain boundary diffusion are faster at 10 -16 cm 2 ·sec. The diffusivity values indicate that the grain boundaries of the asdeposited nanocrystalline Au-Cu are mobile and sensitive to low-temperature anneal treatments affecting the grain size, hence the strength of the material.

Characterization of Strain-Rate Sensitivity and Grain Boundary Structure in Nanocrystalline Gold-Copper Alloys

“…The synthesis method to produce and measure the grain size of the nanocrystalline foils has been described [4][5][6] in great detail. The synthesis approach by electrodeposition is based [5] on the regulation of a pulsed current through a cyanoalkaline solution to produce preselected grain sizes in a fully dense deposit.…”

“…Surface defects and flaws internal to the bulk nanostructure are intrinsic to nanocrystalline alloys synthesized by methods such as pulsed electrodeposition. [4][5][6] Under uniaxial tension, these defects often lead to premature failure through stress concentration evidenced by highly localized deformation. The result can be a significant variation [7][8][9] in the measurement of tensile strength.…”

“…The result can be a significant variation [7][8][9] in the measurement of tensile strength. Recently, similar nanocrystalline, gold-copper alloy specimens have been tensile tested and shown [6,8] to exhibit ultrahigh strength. These specimens follow a Hall-Petch strengthening behavior with a reduction in grain size (d g ) down to just a few nanometers.…”

Interdiffusion at Room Temperature in Cu-Ni(Fe) Nanolaminates

“…As such, additional mechanisms for diffusion are now considered that are much faster than found in the bulk at lower temperatures. For example, a transition in diffusion behavior can be observed below half the melt point where a much faster rate of nano-micro-polycrystalline grain growth occurs [33,34] than would correspond to bulk diffusion. The higher diffusion rates become prevalent, often, though the transport of atoms along paths that short circuit [35,36] the bulk diffusion process.…”

Grain boundary networks in nanocrystalline alloys from atom probe tomography quantization and autocorrelation mapping

“…Reducing the grain size in metals to the nanoscale results in a high density of grain boundaries, which strengthens the metals but renders them susceptible to coarsening [1][2][3][4][5][6][7][8]. Doping these metals produces nanocrystalline alloys that are additionally strengthened by solute atoms [9][10][11][12][13] and are stablized by solute segregation to grain boundaries [4,8,14].…”