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Lecture

Observing the atomic structure of high angle [111] tilt grain boundaries in Al



Aluminum, being third most abundant element on earth crust, finds its use in various applications like construction, transportation and aerospace industry. However, various technically important aluminum alloys are highly susceptible to intergranular fracture, stress corrosion cracking and abnormal grain growth that depend on grain boundary type, structure, chemistry and their properties. Recent studies have shown that grain boundaries can be described as interface-stabilized 2 dimensional phases that exhibit transitions between different states. These transitions are characterized by discontinuous changes in grain boundary properties like mobility, cohesive strength and sliding resistance that are governed by the structure and chemistry of a grain boundary. Advances in transmission electron microscopy and other experimental techniques have provided strong evidence that grain boundary phase transitions play an important role for these phenomena. But, a detailed understanding of the atomic structure of GBs, their transitions and correlated GB properties is often lacking Therefore, understanding the structure of these interfaces and the way they influence material properties is key to advance novel alloys.


Due to the high complexity of grain boundaries, the observation of the local atomic structure is limited to special tilt grain boundaries. Therefore, epitaxial aluminum thin films were deposited on (0001) sapphire substrate by electron beam evaporation with different deposition parameters to establish a template based methodology for obtaining specific tilt GB types. EBSD measurements were employed to characterize the global GB structure, type and fractions present in the films. Cross-sectional view TEM samples from different films were prepared using plasma (Xe) focused ion beam (FIB) to systematically study the growth of aluminium on sapphire. Also, plan-view samples having ∑13b, ∑19b, and ∑7 GBs were extracted. First results of the local atomic structure of these GBs using advanced transmission electron microscopy techniques will be reported and discussed.


 

Speaker:
Saba Ahmad
Max-Planck-Institut für Eisenforschung GmbH
Additional Authors:
  • Dr. Christian H. Liebscher
    Max-Planck-Institut für Eisenforschung GmbH
  • Prof. Dr. Gerhard Dehm
    Max-Planck-Institut für Eisenforschung GmbH