Atomistic simulation of grain boundary diffusion mechanisms in B2 NiAl

Thermal anneal treatments are used to identify the temperature range of the two dominant diffusion mechanisms – bulk and grain boundary. To assess the transition between mechanisms, the low temperature range for bulk diffusion is established utilizing the decay of static concentration waves in composition-modulated nanolaminates. These multilayered structures are synthesized using vapor deposition methods as thermal evaporation and magnetron sputtering. However, at low temperature the kinetics of grain-boundary diffusion are much faster than bulk diffusion. The synthesis of Au-Cu alloys (0-20 wt.% Cu) with grain sizes as small as 5 nm is accomplished using pulsed electro-deposition. Since the nanocrystalline grain structure is thermally unstable, these structures are ideal for measuring the kinetics of grain boundary diffusion as measured by coarsening of grain size with low temperature anneal treatments. A transition in the dominant mechanism for grain growth from grain boundary to bulk diffusion is found with an increase in temperature. The activation energy for bulk diffusion is found to be 1.8 eV·atom-1 whereas that for grain growth at low temperatures is only 0.2 eV·atom-1. The temperature for transitioning from the dominant mechanism of grain boundary to bulk diffusion is found to be 57% of the alloy melt temperature and is dependent on composition.

Download Full-text

Grain Boundary Diffusion Mechanisms in Metals**This chapter is based on the 1982 Institute of Metals Lecture. American Institute of Mining, Metallurgical, and Petroleum Engineers.

Diffusion in Crystalline Solids ◽

10.1016/b978-0-12-522662-2.50011-x ◽

1984 ◽

pp. 319-377 ◽

Cited By ~ 20

Author(s):

R.W. BALLUFFI

Keyword(s):

Grain Boundary ◽

Boundary Diffusion ◽

Grain Boundary Diffusion ◽

American Institute ◽

Diffusion Mechanisms

Download Full-text

Atomistic Simulation of Stress-Induced Grain Boundary Diffusion: For Tin-Whisker Problem

Materials Science Forum ◽

10.4028/www.scientific.net/msf.706-709.1545 ◽

2012 ◽

Vol 706-709 ◽

pp. 1545-1549 ◽

Cited By ~ 1

Author(s):

Yoshitaka Umeno ◽

Jun Negami

Keyword(s):

Grain Boundary ◽

Atomistic Simulation ◽

Boundary Diffusion ◽

Interatomic Potential ◽

Grain Boundary Diffusion ◽

Boundary Structure ◽

Stress Effect ◽

Whisker Formation ◽

Tin Whisker ◽

Effect Of Impurities

The problem of whisker formation in tin (Sn) wiring in small electronic devices has become an important issue with the requirement of lead-free wiring, because doping of Pb to reduce whisker formation cannot be applied. It is therefore urged to better understand stress migration in tin, which is suspected to play a key role in whisker growth. We aim to study grain boundary diffusion in tin by atomistic simulation. After constructing an efficient interatomic potential suitable for diffusion of atoms using the genetic algorithm (GA), we perform molecular dynamics (MD) simulation of grain boundary diffusion in Sn under stress. We find that the magnitude of stress effect on diffusion depends on the boundary structure. Moreover, we examine the effect of impurities on vacancy migration by ab initio calculation to find atom doping that has potential to suppress diffusion.

Download Full-text