Motion Of Interstitial Clusters Research Articles

Radiation-induced glide motion of interstitial clusters in concentrated alloys

We propose a mechanism for glide motion, i.e. one-dimensional (1D) migration, of interstitial clusters in concentrated alloys driven by high-energy particle irradiation. Interstitial clusters are fundamentally mobile on their respective 1D migration tracks, but in concentrated random alloys they are stationary at the position where the fluctuating formation energy achieves a local minimum. Irradiation changes the microscopic distribution of solute atoms through atomic displacement and recovery of the produced Frenkel pairs, which causes cluster 1D migration into a new stable position. In molecular dynamics simulations of interstitial clusters up to 217i in Fe–Cu alloys, stepwise 1D migration was observed under interatomic mixing or shrinkage of the cluster: a single 1D migration was induced by two exchanges per atom or cluster radius change by two interatomic distances. The 1D migration distance ranged up to several nanometers. We compared the frequency and distance of 1D migration with those for in situ observation using high-voltage electron microscopy, allowing for the extremely large rate of interatomic mixing and cluster shrinkage in the present simulation.

Temperature dependence of one-dimensional motion of interstitial clusters in Fe and Ni

The temperature dependence of one-dimensional (1-D) motion of interstitial clusters and void growth in Fe and Ni was studied to a dose of 0.3 dpa. Two criteria were applied to detect the 1-D motion of interstitial clusters. One is the formation of interstitial type dislocation loops near the dilatational side of edge dislocations. The other is no formation of interstitial type dislocation loops near grain boundaries. In neutron irradiated Ni with improved temperature control at 573 K, the 1-D motion of interstitial clusters existed. However no evidence of 1-D motion was found for a conventional temperature controlled irradiation, where the specimen temperature changed with reactor power. This suggested that there was little 1-D motion of interstitial clusters at lower temperatures during the start-up of the reactor. In neutron irradiated Fe, the 1-D motion of interstitial clusters occurred at 473 K and 623 K, judging from the criteria. A good correlation existed between the 1-D motion of interstitial clusters and void growth. These results are discussed based on the temperature dependence of the interaction between impurities and interstitial clusters.

One dimensional motion of interstitial clusters and void growth in Ni and Ni alloys

One dimensional (1-D) motion of interstitial clusters is important for the microstructural evolution in metals. In this paper, the effect of 2 at.% alloying with elements Si (volume size factor to Ni: −5.81%), Cu (7.18%), Ge (14.76%) and Sn (74.08%) in Ni on 1-D motion of interstitial clusters and void growth was studied. In neutron irradiated pure Ni, Ni–Cu and Ni–Ge, well developed dislocation networks and voids in the matrix, and no defects near grain boundaries were observed at 573 K to a dose of 0.4 dpa by transmission electron microscopy. No voids were formed and only interstitial type dislocation loops were observed near grain boundaries in Ni–Si and Ni–Sn. The reaction kinetics analysis which included the point defect flow into planar sink revealed the existence of 1-D motion of interstitial clusters in Ni, Ni–Cu and Ni–Ge, and lack of such motion in Ni–Si and Ni–Sn. In Ni–Sn and Ni–Si, the alloying elements will trap interstitial clusters and thereby reduce the cluster mobility, which lead to the reduction in void growth.

Thermal friction and Brownian motion of interstitial defects in irradiated materials

We investigate the origin of long-range correlated jumps observed in molecular-dynamics simulations of Brownian motion of interstitial clusters in irradiated crystalline materials. We show that the presence of long jumps is associated with low thermal friction experienced by a cluster propagating through the crystal lattice in the presence of thermal fluctuations. Using the equation for the friction coefficient, we estimate the length of ballistic trajectories of clusters ejected from high-energy cascades and analyse implications of our findings for understanding the nature of the long-range effect observed in experiments on ion implantation in fcc and bcc metals, and the connection between this effect and the stability of metals under irradiation.