Grain size dependence of the martensitic transformation in a nano-grained Fe–Ni polycrystal – A molecular dynamics study

Martensitic transformation (MT) in Fe–Ni binary alloys shows grain size dependence, which is an unresolved issue. Experimental results of MT in nano particles or nano-grained polycrystals are somehow controversial. Alternatively, computer simulation, e.g. molecular dynamics (MD) is becoming an important way which may give insight into the kinetics of phase transformations. Here MD simulation is applied to the study on grain size dependence of MT in nano-grained Vorononi construction polycrystalline systems by means of rapid quenching process in the constant temperature and stress (NPT) ensemble. Results show that the decrease of grain size would restrain MT in Fe(1−x)Nix (x = 0.35, 0.25 and 0.15) alloy with the grain size from 5 to 15 nm. The possible mechanism of grain size dependence is discussed based on both experimental and theoretical results.

► As the grain size decreases, there are several regulations.
► The martensitic transformation temperature decreases.
► The fraction of martensite decreases at low temperature.
► The temperature range for martensitic transformation widens.
► The possibility of martensite nucleation at grain boundary increases.