Interrelation between thermodynamics and elasticity in solid state precipitation in austenitic materials
This project wass dedicated
to the understanding of coherent precipitates
in shape memory alloys, and a more detailed
description of the findings is given below. This
project was completed at the end of 2010.
We have simulated small model systems of one, two and four Ni4Ti3 particles by the multi-phase field method. Simulation results provide a good description of the precipitation morphology as described in experimental work. In particular we found that external stress changes the thickness of the lenticular precipitates. Furthermore, two closely spaced Ni4Ti3 precipitates, which are coupled by diffusive and mechanical interactions, can promote the nucleation of a third particle. This rationalizes the experimentally observed autocatalytic nucleation and precipitation sequences.
This project was carried out in collaboration between Wei Guo, Ingo Steinbach, Christoph Somsen (LWW RUB) and Gunther Eggeler.
Calculated particle shape in comparison with experiment TEM micrograph. (a) and (b): Simulation results for 10800s aging at 823K (top and side view). (c) Experiment TEM image where a similar alloy was aged at 773K for 14400s. Four particle variants can be
Simulated and experimental results for Ni-concentration around a Ni4Ti3 particle. (a) Colour coded Ni-concentration map. (b) Ni-concentration fraction along the dashed vertical central line in Fig. 6a. (c) Experimental line.
Experimental and calculated images of special particle arrangements. (a) Rows of particles. (b) Side view of the simulation result. (c) Top view of the simulation result.