Uncovering the Properties of Grain Boundary Triple Junctions (Advanced Metallic Systems CDT)

In a polycrystalline material the interfaces between pairs of crystal grains of different orientations are known as grain boundaries - two-dimensional defects in the material. These grain boundaries themselves intersect one another along lines defining one-dimensional defects called triple junctions. Whilst many open questions remain about grain boundaries, we know even less about triple junctions.

Despite this neglect, triple junctions are very important. They constrain the topology of the grain boundary network and, via their energetics, determine the locally relaxed grain structure. Motion of grain boundaries necessarily involves the motion of triple junctions. The mobility of triple junctions thus plays an important role in controlling the evolution of grain structure during processing and service of polycrystalline materials. In addition to this, triple junctions are lines of high energy and high local lattice disorder and so can act as focal points for chemical attack and mechanical failure and provide pathways for enhanced solid-state diffusion.

To fully understand the evolution of grain structure in polycrystals, we must understand the structures, energies and mobilities of triple junctions and how they depend on the local grain boundary network.

Systematic experimental study of triple junction behaviour is very difficult, but we can also study triple junctions with atomistic computer simulations. Such simulations offer enhanced control over the systems under study and allow us to determine the dependence of triple junction properties on local grain structure.

This project will use atomistic simulation to make a detailed exploration of grain boundary triple junction properties. It will examine the variation of the energy of the junctions as a function of the geometries and energies of the boundaries that meet there and look for simple, physically motivated models to capture these relationships.

Advanced Metallic Systems CDT
The Advanced Metallic Systems CDT is a 4 year programme hosted jointly by the universities of Manchester and Sheffield building on their complimentary expertise and international reputations in materials science and engineering research. In year 1, students from a range of disciplinary backgrounds undertake taught courses in core materials topics. PhD research begins after 6 months. Our transferable skills and personal development programme leads to a Diploma in Professional Skills. Visit our website for more information www.metallicsCDT.co.uk.