Influence of Grain Boundary Character and Annealing Time on Segregation in Commercially Pure Nickel

Shery L Welsh,Olivia D Underwood,Jeffrey L Evans,Richard L Martens,Gregory B Thompson,Monica Kapoor

doi:10.1155/2016/4597271

Abstract

Commercially pure nickel (Ni) was thermomechanically processed to promote an increase in Σ3 special grain boundaries. Engineering the character and chemistry of Σ3 grain boundaries in polycrystalline materials can help in improving physical, chemical, and mechanical properties leading to improved performance. Type-specific grain boundaries (special and random) were characterized using electron backscatter diffraction and the segregation behavior of elements such as Si, Al, C, O, P, Cr, Mg, Mn, B, and Fe, at the atomic level, was studied as a function of grain boundary character using atom probe tomography. These results showed that the random grain boundaries were enriched with impurities to include metal oxides, while Σ3 special grain boundaries showed little to no impurities at the grain boundaries. In addition, the influence of annealing time on the concentration of segregants on random grain boundaries was analyzed and showed clear evidence of increased concentration of segregants as annealing time was increased.

Highlights

Nickel is the major alloying element in some of the most advanced alloys used today in applications ranging from nuclear power plant components to high temperature aircraft engine components [1, 2]
It can be noted that, qualitatively, the special grain boundaries (SGBs) is more difficult to identify than the random grain boundaries (RGBs) if the segregation itself is used as a visual aid
As is seen in the SGB, figures are more reflective of the grain boundary mismatch versus actual segregation to the grain boundary except in the case of Si

Summary

Introduction

Nickel is the major alloying element in some of the most advanced alloys used today in applications ranging from nuclear power plant components to high temperature aircraft engine components [1, 2]. Studying the character and chemistry of grain boundaries in commercially pure nickel, known as Nickel 200, could help elucidate various fundamental microstructure-property relationships of these materials. Engineering the character and chemistry of grain boundaries in polycrystalline materials can help in improving physical, chemical, and mechanical properties leading to improved performance [3]. GB structure, as compared to the bulk structure, is very different and exhibits its own unique environment, structure, composition, and energy levels at the atomic level [6]. This GB structure serves to either attract or repel segregants [7]. Preferential interactions exist between the segregants themselves which can affect segregation behavior [4]

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Conclusion