B06 – Investigating Grain Boundary Phases and Mechanism-Property Relationships in Ni and Ni-X (X=Cu, Au, Nb) Solid Solutions

PI(s): Prof. Gerhard Dehm and Dr. Ramachandramoorthy (MPIE, Düsseldorf)                                                           

SFB researchers: Dr. Saba Ahmad (MPIE, Düsseldorf)

The intricate complexity of grain boundaries (GBs) at the atomic scale, encompassing both structural and chemical aspects, is widespread across materials, exerting a significant impact on their properties and behaviour. Through the integration of experimental characterization, computational simulations, and in situ mechanical testing, this project endeavours to offer comprehensive insights into GB phases and their mechanical responses within both pure Ni and Ni-X (X=Cu, Au, Nb) solid solutions. The outcomes of this research will contribute to the development of mechanism-property diagrams, guiding material design and optimization strategies for various applications.

The experimental characterization involves utilizing scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), focused ion beam (FIB), and advanced scanning transmission electron microscopy (S/TEM). In the first approach, these methods will be applied to investigate and analyse [111] tilt GBs across different length scales in pure Ni. Concurrently, computational techniques, including density functional theory (DFT) calculations and molecular dynamics (MD) simulations, will be employed within the SFB to explore defect phases and associated mechanisms at the atomic level. Moreover, the project seeks to understand the impact of alloying elements such as Cu, Au, and Nb on Ni GB phases. Through detailed examination, it aims to elucidate how these elements alter the atomic structure of GBs and affect their mechanical properties. An additional crucial aspect of this project involves the analysis of secondary defects within GBs, as they can significantly influence material properties. These defects, including dislocations, disconnections and steps, are critical for GB related phenomena such as GB migration, shear coupled GB motion and GB cohesion etc.

Furthermore, to obtain insights into the mechanical properties, in situ tensile testing will be conducted, correlating GB phases with mechanical behaviour. A novel mesoscale push-to-pull device will be designed and fabricated using additive micro-manufacturing, employing localized electrodeposition in liquid. This device will enable in-situ SEM and TEM analysis of Ni and Ni-Au GBs, subjected to tensile testing with strain rates ranging from 0.001 s−1 to 1000 s−