Soiree

TYC Soiree: "The role of interfacial diffusion in the creep of Ni superalloys" and "Atomistic Simulation of Crystalline Defects (A Numerical Analysis Perspective)"

Prof. Vikram Deshpande, University of Cambridge
and
Prof. Christoph
Ortner, University of Warwick

Thursday 19th July 2018
Time: 5-7 pm
Venue: K4U.12, King's Building, Strand Campus, King's College London. WC2R 2LS
Contact: Jemma Trick

Directions to room K4U.12 - http://www.modelsofauthority.ac.uk/blog/directions-to-k4u12/


The role of interfacial diffusion in the creep of Ni superalloys

Prof. Vikram Deshpande

Cambridge University Department of Engineering, UK.

We present a discrete dislocation plasticity analysis of the creep of Ni superalloys with an emphasis on the role of interfacial diffusion at the  interfaces. First a methodology for modelling the climb-enabled glide motion of dislocations coupled to vacancy diffusion will be presented. This framework for the deformation of the  phase is then coupled to an interfacial diffusion model to investigate the effect of stress-driven inter-diffusion of Al in Ni3Al at the  interfaces. This modelling scheme, combined with a temporal scaling algorithm, allows the modelling of the creep of Ni superalloys on realistic time scales (i.e. on the order of 1000 hours). The experimentally observed continuously increasing creep strain rate of Ni superalloys will be shown to be an outcome of this discrete dislocation model with interfacial diffusion playing a critical role. In particular, consistent with observations, the model predicts that interfacial diffusion results in the formation of wavy interfaces. This in turn initiates the formation of dislocation cell structures in the  phase that ultimately soften the alloy. The calculations can be used to gain insight into the of role heavy elements such Re that reduce creep rates by segregating to the  interfaces.

 

Atomistic Simulation of Crystalline Defects (A Numerical Analysis Perspective)

Prof. Christoph Ortner

Mathematics Institute, University of Warwick, UK. 

A common problem of atomistic materials modelling is to determine properties of crystalline defects, such as structure, energetics, or mobility, from which meso-scopic material properties or coarse-grained models (e.g., Kinetic Monte-Carlo, Discrete Dislocation Dynamics, Griffith-type fracture laws) can be derived. In this lecture I will focus on one of the most basic tasks: computing the equilibrium configuration of a crystalline defect. If time permits and/or there is sufficient interest I may also comment on transition rates and on free energy). A wide range of numerical schemes, both classical and multi-scale such as Green's function methods, atomistic/continuum coupling and QM/MM schemes, can be interpreted as Galerkin discretisations with variational crimes, for an infinite-dimensional nonlinear variational problem. This point of view is effective to study properties of ``exact solutions'', identify approximation parameters, derive rigorous error bounds, optimise and construct novel schemes with superior error/cost. In some cases we can even show that certain  classical schemes diverge.

 

 

 

  • Vikram Deshpande and Christoph Ortner
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