Thermodynamic and mechanical properties of copper precipitates inα-iron from atomistic simulations (original) (raw)
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Hardening due to copper precipitates in α-iron studied by atomic-scale modelling
Journal of Nuclear Materials, 2004
We present results of a large-scale atomic-level study of dislocation-precipitate interaction. We have considered a 1 2 AE1 1 1ae edge dislocation gliding in a-iron containing coherent copper precipitates of size from 0.7 to 6 nm over a temperature range from 0 to 450 K. The results demonstrate that some features are qualitatively consistent with earlier theoretical conclusions, e.g. the critical resolved shear stress (CRSS) is proportional to L À1 and lnðDÞ, where L and D are precipitate spacing and diameter. Other features, which are intrinsic to the atomic-level nature of the dislocationprecipitate interaction, include strong dependence of the CRSS on temperature, dislocation climb and precipitate phase transformation.
Hardening due to copper precipitates in alpha-iron studied by atomic-scale modelling
J Nucl Mater, 2004
We present results of a large-scale atomic-level study of dislocation-precipitate interaction. We have considered a 1 2 AE1 1 1ae edge dislocation gliding in a-iron containing coherent copper precipitates of size from 0.7 to 6 nm over a temperature range from 0 to 450 K. The results demonstrate that some features are qualitatively consistent with earlier theoretical conclusions, e.g. the critical resolved shear stress (CRSS) is proportional to L À1 and lnðDÞ, where L and D are precipitate spacing and diameter. Other features, which are intrinsic to the atomic-level nature of the dislocationprecipitate interaction, include strong dependence of the CRSS on temperature, dislocation climb and precipitate phase transformation.
Embedded atom potential for Fe-Cu interactions and simulations of precipitate-matrix interfaces
Modelling and Simulation in Materials Science and Engineering, 1998
A new empirical interatomic potential of the embedded atom type is developed for the Fe-Cu system. The potential for the alloy system was constructed to reproduce known physical parameters of the alloy, such as the heat of solution of Cu in Fe and the binding energy of a vacancy and a Cu atom in the α-Fe matrix. The potential also reproduces first-principle calculations of the properties of metastable phases in the system. This atomic interaction model was used in simulation studies of the interface of small coherent Cu precipitates in α-Fe and of dislocation core structure. The phase stability of the body-centred cubic Cu precipitates was also analysed.
Revealing the atomistic nature of dislocation-precipitate interactions in Al-Cu alloys
Journal of Alloys and Compounds, 2019
Despite significant gains on understanding strengthening mechanisms in precipitate strengthened materials, such as aluminum alloys, there persists a sizeable gap in the atomistic understanding of how different precipitate types and their morphology along with dislocation character affects the hardening mechanisms. Toward this, the paper examines nature of precipitation strengthening behavior observed in the Al-Cu alloys using atomistic simulations. Specifically, the critical resolved shear stress is quantified across a wide range of dislocationprecipitate interactions scenarios for both θ' and θ phase of Al2Cu. Overall, the simulations reveal that the dislocation character (edge or screw) plays a key role in determining the predominant hardening mechanism (shearing vs. Orowan looping) employed to overcome the θ' Al2Cu precipitate. Furthermore, the critical shear stress and mechanism to overcome the precipitate is sensitivity to the position of the glide plane with respect to the precipitate and its orientation. Interestingly in our findings, the θ Al2Cu precipitate conventionally regarded as unshearable particle was overcome by shear cutting mechanism for small equivalent precipitate radius, which agrees with recent TEM observations. These findings provide necessary information for the development of atomistically informed precipitate hardening models for the traditional continuum scale modeling efforts.
Philosophical Magazine, 2007
Liverpool L69 3GH, UK ‡Computer Science and Mathematics Division, ORNL, Oak Ridge, TN 37831-6138, USA Copper-rich precipitates can nucleate and grow in ferritic steels containing small amounts of copper in solution and this affects mechanical properties. Growth kinetics, composition and structure of precipitates under irradiation are different from those under thermal ageing, and also vary with type of radiation. This implies that the interaction between radiation defects, i.e. vacancies, self-interstitial atoms (SIAs) and their clusters, and precipitates is influential. It is studied here by atomic-scale computer simulation. The results are compared with those of elasticity theory based on the size misfit of precipitates and defects, and the modulus difference between bcc iron and bcc copper. It is found that SIA defects are repelled by precipitates at large distance but, like vacancies, attracted at small distance. Copper precipitates in iron can therefore be sinks for both vacancy and interstitial defects and hence can act as recombination centres under irradiation conditions. A tentative explanation for the mixed Cu-Fe structure of precipitates observed in experiment and the absence of precipitate growth under neutron irradiation is given. More generally, agreement between the simulations and elasticity theory suggests that the results are not artefacts of the atomic model:
Acta Materialia, 2008
Atomistic simulations were carried out to study the interaction of dislocations with Cr precipitates in body-centered cubic Fe and Fe-10%Cr at 0 K. The results are compared with predictions of theoretical models accounting for precipitate strengthening based on different mechanisms. It is shown that solute hardening (in Fe-Cr matrix) and precipitate hardening can be considered, as a good approximation, to be additive effects.
Modelling and Simulation in Materials Science and Engineering, 2005
Classical molecular dynamics simulations of the interaction of edge dislocations with precipitates in a-iron are performed. The critical resolved shear stress (CRSS) is determined for various morphologies of precipitates: pure copper and nickel precipitates, ordered and unordered copper/nickel precipitates, copper and nickel precipitates with substitutional iron atoms, copper precipitates of ellipsoidal shape, and copper precipitates with nickel shells. The dependence of the CRSS on the nature of the precipitate is explained by considering the Burgers vector distribution within the precipitates. It is shown that, except for the ordered precipitates, chemical inhomogeneities of the precipitates lower the CRSS with respect to the precipitates consisting of the pure phases.
Atomistic computer simulation of the formation of Cu-precipitates in steels
Computational Materials Science, 2002
Thermal ageing of Cu-alloyed steels is a result of Cu-precipitates which arise above 300°C. Recently small angle neutron scattering was applied in order to analyse these precipitates in a defined initial state as well as in a thermally aged state. Atomistic computer simulations of the formation of precipitates can contribute to a deeper understanding of the mechanical behaviour of Cu-alloyed steels. A model is presented which is able to simulate the 'diffusion' of atoms by vacancy jumps . The underlying Monte Carlo method is presented and a binary system with components A and B is considered. Starting with a random distribution of atoms, the formation and growth of precipitates is simulated at a constant temperature of 600°C. In a second simulation, an initial temperature of 700°C is lowered to 400°C. At 700°C precipitates of radii between 1.1 and 1.7 nm are formed within seconds. At 400°C a part of the still dissolved atoms forms smaller precipitates while other atoms increase the size of the larger precipitates. At longer simulation times a significant decrease of the number of small precipitates and an increase of the averaged precipitate radius is found. The Russel-Brown theory is applied on the simulation results in order to calculate the increase of the yield stress in the thermally aged state. Ó
International Journal of Materials Research, 2008
The nucleation, growth, and coarsening kinetics of Cu-rich precipitates in a multicomponent Fe – Cu based steel, containing 1.17 at.% Cu, aged at 500 °C for up to 1024 h are investigated. The temporal evolution of the precipitate, heterophase interface, matrix compositions and precipitate morphology are presented. Coarsening temporal exponents are determined for mean radius, number density, and supersaturations, and are compared to the Lifshitz – Slyzov – Wagner model for coarsening, modified for multicomponent alloys by Umantsev and Olson. The experimental results indicate that the alloy does not strictly follow Umantsev – Olson model behavior. Additionally, we compare the results to an investigation of a similar multicomponent steel containing 1.82 at.% Cu and to results in the literature. Furthermore, we present a Thermo-Calc determined phase diagram.
Chinese Journal of Mechanical Engineering
High-dispersed nanoscale Cu precipitates often contribute to extremely high strength due to precipitation hardening, and whereas usually lead to degraded toughness for especially ferritic steels. Hence, it is important to understand the formation behaviors of the Cu precipitates. High-resolution transmission electron microscopy (TEM) is utilized to investigate the structure of Cu precipitates thermally formed in a high-strength low-alloy (HSLA) steel. The Cu precipitates were generally formed from solid solution and at the crystallographic defects such as martensite lath boundaries and dislocations. The Cu precipitates in the same aging condition have various structure of BCC, 9R and FCC, and the structural evolution does not greatly correlate with the actual sizes. The presence of different structures in an individual Cu precipitate is observed, which reflects the structural transformation occurring locally to relax the strain energy. The multiply additions in the steel possibly ma...