Simulation of Mechanical Behaviour of Martensites using Multicore Technology

The martensite-austenite phase transformation is one of the most important in metallurgy, existing in many materials. Typically, it involves a symmetry-breaking from a high temperature, ductile (austenite) phase to a low temperature, hard (martensite) phase. The transformation involves strain, and in practical applications such as steels and superelastic shape memory alloys both phases coexist.The transformation process is fast, and the microstructures are nanoscaled, so molecular dynamics study is appropriate. However, strain affects phase stability, and there are irrational interfaces between transforming phases (habit plane) so flexible initial and boundary conditions are required. Elegant mathematical analysis assuming perfectly rigid boundaries concluded that the structure is determined by minimising boundary energy. However, our preliminary simulations shows this to be an artifact of the boundary conditions: if the soft austenite is allowed to deform to accommodate the growing martensite very different results occur.Describing adequate surrounding material to match both elasticity and atomistic detail, makes these simulations very computationally intense. A parallel supercomputer is an option, but a far more cost-effective solution is becoming available through dedicated multicore processors, the standard desktop hardware coming into our group over the next few years. Fully utilising a shared-memory multicore machine requires considerable modification to the code: information needs to be transferred between processors, and doing this efficiently requiresparallel coding expertise. Parallelisation strategies also vary withthe type of interatomic potential. Metals are best described by many-body, short ranged interactions which call for a different strategy from potentials involving fixed bonds or ionic forces.We propose to re-engineer a simulation code suitable for study of how martensites transform, to understand what structure the interfaces between austenite and martensite takes, and how this is affected by material parameter. To do so we will use our experience in parallel coding, molecular dynamics and potential design.