Influence of Processing Method on the Grain Boundary Character Distribution and Network Connectivity Page: 3 of 14
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INFLUENCE OF PROCESSING METHOD ON THE GRAIN BOUNDARY
CHARACTER DISTRIBUTION AND NETWORK CONNECTIVITY
ADAM J. SCHWARTZ, MUKUL KUMAR, AND WAYNE E. KING
University of California, Lawrence Livermore National Laboratory, Chemistry and Materials
Science Directorate, Livermore, CA 94550, USA, firstname.lastname@example.org
There exists a growing body of literature that correlates the fraction of "special" boundaries
in a microstructure, as described by the Coincident Site Lattice Model, to properties such as
corrosion resistance, intergranular stress corrosion cracking, creep, etc. Several studies suggest
that the grain boundary character distribution (GBCD), which is defined in terms of the relative
fractions of "special" and "random" grain boundaries, can be manipulated through
thermomechanical processing. This investigation evaluates the influence of specific
thermomechanical processing methods on the resulting GBCD in FCC materials such as oxygen-
free electronic (ofe) copper and Inconel 600. We also demonstrate that the primary effect of
thermomechanical processing is to reduce or break the connectivity of the random grain
boundary network. Samples of ofe Cu were subjected to a minimum of three different
deformation paths to evaluate the influence of deformation path on the resulting GBCD. These
include: rolling to 82% reduction in thickness, compression to 82% strain, repeated compression
to 20% strain followed by annealing. In addition, the influence of annealing temperature was
probed by applying, for each of the processes, three different annealing temperatures of 400, 560,
and 800 C. The observations obtained from automated electron backscatter diffraction (EBSD)
characterization of the microstructure are discussed in terms of deformation path, annealing
temperature, and processing method. Results are compared to previous reports on strain-
annealed ofe Cu and sequential processed Inconel 600. These results demonstrate that among
the processes considered, sequential processing is the most effective method to disrupt the
random grain boundary network and improve the GBCD.
Watanabe first discussed "grain boundary design and control" in reference to the
manipulation of the relative fractions of "special" and "random" boundaries in order to improve
certain bulk materials properties . Since that time, such manipulations have become known as
grain boundary engineering. Grain boundary engineering has been demonstrated to be a viable
means of improving certain properties of low to medium stacking fault energy FCC materials
such as austenitic stainless and microalloyed steels [2,3], nickel and nickel-based alloys [2, 4-
15], and lead alloys [16-18]. The susceptible properties are typically grain boundary controlled,
such as corrosion and stress corrosion cracking [2, 4-18], creep and cavitation [19-22], and
Recent advances in grain boundary engineering have resulted from a number of factors. One
of the most significant is the commercialization of a scanning electron microscopy (SEM) based
technique to accurately and rapidly characterize crystal misorientations between grains in order
to determine the GBCD [24-26]. Less than a decade ago, these misorientations were determined
through time consuming transmission electron microscopy (TEM) or electron channeling within
the SEM [27,28]. With automated EBSD hardware and software, it is now possible to acquire
approximately 10,000 data points per hour, thus allowing characterization of a statistically
significant number of grain boundaries in a reasonable time frame. Additional factors
contributing to the recent advances in grain boundary engineering are reports by Palumbo et al.
[2-13, 16-18] of the optimization of the GBCD through practical thermomechanical processing
schedules and the recognition that improvements in the special fraction can play a crucial role in
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Kumar, M & King, W.E. Influence of Processing Method on the Grain Boundary Character Distribution and Network Connectivity, article, December 20, 1999; California. (digital.library.unt.edu/ark:/67531/metadc742066/m1/3/: accessed August 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.