Effect of grain boundaries on shock-induced phase transformation in iron bicrystals

Non-equilibrium molecular-dynamic simulations with a modified analytic embedded-atom model potential have been performed to investigate the effect of three kinds of grain boundaries (GBs) on the martensitic transformation in iron bicrystals with three different GBs under shock loadings. Our results show that the phase transition was influenced by the GBs. All three GBs provide a nucleation site for the alpha -> epsilon transformation in samples shock-loaded with u(p) - 0.5 km/s, and in particular, the elastic wave can induce the phase transformation at Sigma 3 < 110 > twist GB, which indicates that the phase transformation can occur at Sigma 3 < 110 > twist GB with a much lower pressure. The effect of GBs on the stress assisted transformation (SAT) mechanisms is discussed. All variants nucleating at the vicinity of these GBs meet the maximum strain work (MSW) criterion. Moreover, all of the variants with the MSW nucleate at Sigma 5 h001i twist GB and Sigma 3 < 110 > tilt GB, but only part of them nucleate at Sigma 3 < 110 > twist GB. This is because the coincident planes between both sides of the GB would affect the slip process, which is the second stage of the martensitic transformation and influences the selection of variant. We also find that the martensitic transformation at the front end of the bicrystals would give rise to stress attenuation in samples shock-loaded with u(p) - 0.6 km/s, which makes the GBs seem to be unfavorable to the martensitic transformation. Our findings have the potential to affect the interface engineering and material design under high pressure conditions. Published by AIP Publishing.