Void nucleation at elevated temperatures under cascade-damage irradiation (original) (raw)
Related papers
Journal of Nuclear Materials, 1994
The effect of stochastic fluctuations in the point-defect concentrations on the microstructure development in a fully annealed metal at low irradiation doses is investigated. It is found that the appearance of an order structure consists of segregated vacancy-rich and interstitial-rich regions may be understood as a noise-induced transition. This occurs through the nonlinear coupling between the microstructure evolution at low dose and the fluctuations in the point-defect concentrations resulting from the random nature of cascade initiation and the point-defect migratory jumps. Unlike in the conventional mean field rate theory where concentrations of point defects are taken to be homogeneous, the appearance of an ordered structure in the form of vacancy-rich and interstitial-rich regions does not require the actual long-range transport of point defects in the present investigation. The swelling rate in the void growth regions and the sizes of these regions are calculated and found to be in agreement with experimental results.
Defect accumulation in pure fcc metals in the transient regime: a review
Journal of Nuclear Materials, 1993
Over the years, a considerable amount of experimental results have been reported on defect accumulation in low-dose neutron irradiated pure fee metals. In an effort to further the understanding of the processes involved in the defect accumulation in the transient regime, the experimental results are compiled and the salient features of these results are pointed out. Experimental results in pure aluminium, copper and nickel are chosen for this review. The dose dependence of the experimentally measured parameters makes it abundantly clear that the rate of build-up of cluster density, cavity density and the void swelling reaches a maximum at very low doses (I 0.1 dpa). There is no experimental evidence for the formation of a well defined dislocation network during irradiation of pure metals at temperatures in the void swelling regime up to a dose level of _ 1 dpa. The experimental results allow us to identify three significant aspects of the defect accumulation behaviour under cascade damage conditions: (a) evolution of cavity microstructure in a spatially heterogeneous and segregated fashion, (b) high swelling rates at very low doses when the dislocation density is negligibly low and Cc) enhanced vacancy accumulation in the vicinity of grain or subgrain boundaries. It is pointed out that these features cannot be rationalized in terms of conventional mean-field approach using chemical rate equations and dislocation bias as the only driving force. These features can be explained, however, by taking into considerations the specific nature of the cascade damage, namely, the intracascade recombination and clustering of interstitials and vacancies during the cooling down phase of a multidisplacement cascade.
A sharp interface model for void growth in irradiated materials
Philosophical Magazine, 2015
A thermodynamic formalism for the interaction of point defects with free surfaces in single component solids has been developed and applied to the problem of void growth by absorption of point defects in irradiated metals. This formalism consists of two parts, a detailed description of the dynamics of defects within the non-equilibrium thermodynamic frame, and the application of the second law of thermodynamics to provide closure relations for all kinetic equations. Enforcing the principle of non-negative entropy production showed that the description of the problem of void evolution under irradiation must include a relationship between the normal fluxes of defects into the void surface and the driving thermodynamic forces for the void surface motion; these thermodynamic forces are identified for both vacancies and interstitials and the relationships between these forces and the normal point defect fluxes are established using the concepts of transition state theory. The latter theory implies that the defect accommodation into the surface is a thermally activated process. Numerical examples are given to illustrate void growth dynamics in this new formalism and to investigate the effect of the surface energy barriers on void growth. Consequences for phase field models of void growth are discussed.
Journal of Nuclear Materials, 1996
The consequences of displacement damage produced by energetic particles on physical and mechanical properties of metals and alloys have been investigated both experimentally and theoretically for several decades. Over the years, a number of theoretical models have been proposed to rationalize the rate and magnitude of defect accumulation under different irradiation conditions. In recent years, significant advances have been made in understanding the nature of the damage produced in this form of multi-displacement cascades. The new knowledge regarding the intra-cascade recombination and clustering of self-interstitial atoms and vacancies during the cooling-down phase of cascades makes it necessary to reexamine the appropriateness of the available models for describing the accumulation of damage under cascade damage conditions. In this paper, recent advances in the understanding of damage production and its consequences are reviewed. A historic perspective is adopted. A comprehensive analysis of the effects of temperature, dose rate and particle type on multi-phenomena (swelling, creep, growth, microstructure evolution, RED, RIS) is presented to discuss the strength and weakness of various models, as they have evolved with the understanding of the damage processes. It has been shown that the irradiation damage modeling has progressed from the standard rate theory model to the BEK model to the production bias model with an increasing degree of sophistication as increasingly more realistic features of the irradiation damage production process were incorporated. It is shown that the newly proposed production bias model uniquely includes the necessary features of cascade damage production in its treatment of the damage accumulation.
Philosophical Magazine, 2012
Early experimental data on void swelling in electron-irradiated materials disagree with the dislocation bias models based on the dislocation-point defect elastic interactions. Later, this became one of the factors that prompted the development of models based on production bias (PBM) as the main driver for swelling, which assumed that the dislocation bias was much lower than that predicted by theoretical analyses of dislocation bias. However, the PBM in its present form fails to account for important and common observations, namely, the indefinite void growth often observed under cascade irradiation and the swelling saturation observed under high-dose irradiation and in void lattices. In this paper, we show that these contradictions can be naturally resolved in the framework of the rate theory that accounts for the radiation-induced vacancy emission from extended defects, such as voids, dislocations and grain boundaries. This modification introduces a new bias type in the theory, namely, the emission bias. This modified rate theory agrees well with the experimental data and demonstrates that the original dislocation bias should be used in rate theory models along with the emission bias in different irradiation environments. The modified theory predictions include, but are not limited to, the radiation-induced annealing of voids, swelling saturation under high-dose irradiation, generally, and in void lattices, in particular.
Classical nucleation theory of microstructure development under cascade-damage irradiation
Journal of Nuclear Materials, 2003
Cascade irradiation produces a significant fraction of the damage in the form of small mobile and immobile vacancy and interstitial clusters. This has led to the introduction of the Woo-Singh production bias theory. In the pursuant studies, the predominant effort that has been spent is in investigating the validity of the concept, and in its usefulness in complementing the traditional theory based on the concept of sink bias. Although plenty of theoretical and experimental results supports the concept, relatively little attention has been paid to the important area of microstructure nucleation. Within the framework of the classical theory of nucleation of overcritical precipitates from small subcritical nuclei, the nucleation processes at elevated temperatures of both voids and interstitial loops from the primary clusters are similar, and can be similarly treated. Recognizing the importance of stochastic fluctuations in the evolution of small embryos, a single-component nucleation theory is formulated using the Fokker-Planck equation, to take into account the stochastic effects of the fluxes of mobile defects, arising from the random nature of diffusion jumps and cascade initiation. Analytic solutions for the separate cases of voids and Frank loops are obtained, and the corresponding effects on the evolution of the microstructure are discussed.
Fluctuations of point-defect fluxes to sinks under cascade damage irradiation
Journal of Nuclear Materials, 1996
The arrival rates of point defects at sinks are not deterministic, but probabilistic and fluctuate with time because of the random nature of diffusing jumps and cascade occurrence. The influence of such fluctuations on the evolution of different sink types is analyzed, and discussed in comparison with literature. The 'diffusion coefficients' of the size-distribution function for several sink types (voids, interstitial and vacancy loops and clusters) are derived from first principles. The "diffusion coefficient' for the fluctuations of the climb rate of network dislocations is also calculated. The application of the present formalism to the evolution of the primary clusters of point defects generated during cascade damage is also discussed.
Diffusion anisotropy and void development under cascade irradiation
Applied Physics A, 2008
Cascade irradiation of metals gives rise to swelling as a result of the creation of voids and the evolution of the void ensemble. Under suitable circumstances, the originally disordered void distribution transforms into to a void lattice. As demonstrated previously, the understanding of the evolution and the unique features of the void ensemble requires a difference in the anisotropy of the diffusion (DAD) of vacancies and self-interstitial atoms (SIAs), which is achieved by one-dimensional diffusion of the SIAs. On the other hand, void swelling has been successfully modeled in terms of three-dimensional diffusion of both vacancies and SIAs. In the present paper it is shown that these seemingly contradicting interpretations and all related observations can be quantitatively reconciled by a small DAD created by only ∼1% of SIAs diffusing one-dimensionally. It is also demonstrated that at the initial stage of void-lattice formation, ordering occurs mainly on close-packed crystal planes, which is in contrast to the naïve expectation that one-The paper is dedicated to Professor Dr. Dr. h. c. Alfred Seeger on the occasion of his 80th birthday.
Heterogeneous void swelling near grain boundaries in irradiated materials
Physical Review B, 2003
We found that by assuming that the density of dislocations in an irradiated material varies as a function of the distance to grain boundaries and that mobile interstitial defect clusters perform three-dimensional diffusional motion it is possible to achieve significantly better agreement with experimental observations of profiles of heterogeneous void swelling than in the model where defects diffuse purely one-dimensionally. This approach explains the origin of several distinct features characterising the effect of heterogeneous void swelling, including the variation of the shape of swelling profiles as a function of irradiation dose, the formation of peaks of swelling and void denuded zones, and the occurrence of anomalously large voids in the regions adjacent to grain boundaries.