Binary solid solution alloys that show class A alloy (CAA) behaviour with low stress exponents, absence of substructure and reduced normal or inverted primary creep are analysed. These characteristics are referred to as the class A state (CAS). Basic dislocation climb based models are used to compute properties of Al-Mg and Al-Zn alloys. It is demonstrated that a single climb based model can accurately represent the creep strain rate versus stress. It is no longer necessary to consider a transition from climb to glide and back to climb again. The absence of substructure in CAS is allotted to the recovery of screw dislocations by cross-slip. An expression for the rate of this type of recovery is derived. The presence of inverted primary creep is believed to be due to a significant initial dislocation density. This is consistent with simulated primary creep curves.

Creep experiments on 304 austenitic steels at high temperatures and low stresses (750°C, 2–15 MPa), conducted by Kombaiah et al. (Acta Materialia 121137, 2025), reported a stress exponent close to 1 and attributed the mechanism to diffusional creep. It has recently been found that diffusional creep and primary dislocation creep are competing mechanisms in the high-temperature, low-stress regime with a stress exponent of approximately 1. For this reason, the data of Kombaiah et al. are reanalysed in this note. Their data show a distinct primary creep stage, which is well-described by the ϕ (phi) model. Moreover, the primary creep curve and associated creep rates are successfully predicted by a basic dislocation model. These findings provide strong evidence that primary dislocation creep is the controlling creep mechanism. Furthermore, the Coble grain boundary diffusional creep model significantly overestimates the observed creep rates in austenitic stainless steels, further challenging the diffusional creep interpretation.

Reliable long-term creep rupture life prediction of high-temperature materials demands a deep understanding of rupture-controlling mechanisms. Conventional analytical models for creep rupture extrapolation rely heavily on experimental data and adjustable parameters, potentially neglecting the critical failure mechanisms. This study employs fundamental creep models for HR3C(25Cr20NiNbN) austenitic steels, incorporating ductile and brittle creep mechanisms with well-defined physical parameters and no adjustable parameters. The ductile creep models account for dislocation hardening, precipitation hardening, solid solution hardening, and stacking faults, while the brittle creep models in addition consider creep cavitation along sliding grain boundaries. Key physical parameters are derived as follows: precipitate evolution is simulated using thermodynamic computations and validated against experiments, while high-temperature elastic properties and atomic-size misfit are determined through first-principles calculations, with lattice vibrations incorporated via the quasi-harmonic Debye model. By combining first-principles and thermodynamic calculations, the mechanism-based fundamental models successfully predict the creep rupture strength of HR3C quantitatively.

In recent years, a number of models for creep properties have been derived based on physical principles and avoiding adjustable parameters (APs). They are referred to as basic models and have, for example, been formulated for primary, secondary, and tertiary creep. The purpose of the basic models is that they should have general applicability and that they can allow extrapolation of results to a much greater extent than empirical models with APs. This has also been verified for a number of the models such as for the primary and secondary creep. Basic models are excellent to safely identify operating mechanisms. The purpose of this review is to give a summary of methods for deriving basic models for creep including the role of substructures and different applications of grain boundary sliding. It is hoped that this will assist more researches to use and to develop them further. Many aspects of creep have still not been handled with basic models.

Dispersion strengthened (DS) alloys are used in critical high temperature applications due to their excellent creep strength. Finer particles than in precipitation hardened (PH) alloys can be used due to the thermal stability of the dispersoids. During recent years, models for the creep strength in PH-alloys have been developed. They have successfully been able to describe the creep strength of austenitic stainless steels and copper alloys. These models are referred to as time controlled climb (TCC) because the time it takes a dislocation to climb across a particle plays a crucial role. In the paper, TCC is applied to DS-alloys for the first time. A copper alloy and a ferritic steel are considered. Many DS-alloy are associated with a threshold stress. It is demonstrated it can be computed from a dislocation density that is generated during the creep process. The commonly used Rösler-Arzt (RA) model (1990) is analyzed. Several proposals are made to allow the RA-model to be applied to a wider spectrum of applications.

Grain boundary sliding (GBS) significantly influences the mechanical properties of polycrystalline metals and alloys. A comprehensive set of GBS data spanning 70 years and encompassing 12 material classes under various deformation conditions has been compiled. Analysis identifies strain (ε) and grain size (dg) as the primary factors influencing GBS displacement in agreement with a previously developed basic model, revealing a linear dependence of GBS displacement on strain and grain size. A major factor in the model is the strain enhancement factor, i.e., the ratio between the creep strain due to GBS and the total creep strain. Utilizing the average strain enhancement factor from the GBS data (0.2), the model demonstrates predictive capabilities across various materials (Fe, ferritic steels, austenitic steels, Al, Mg, Cu, Zn, and their respective alloys), grain sizes (nanometers to micrometers), and strain levels (0.1–161 %) without significant loss in statistical accuracy. Application to creep cavitation further illustrates the usefulness of the model.

The microstructure, grain size and grain boundary (GB) structure of copper in canisters for encapsulation of spent nuclear fuel have been characterized. Coincident site lattice (CSL) GBs were found to be more common than random high angle GBs. Apart from Σ3, the Σ9 and Σ27 GBs show a higher frequency of occurrence than the other CSL GBs. This effect is more pronounced for the material in the canister lid that is slightly deformed. The high fraction of CSL boundaries of 60–65% is of the same order as for grain boundary engineered material. One critical property for the canister is the creep ductility that is improved by the addition of phosphorus (P) to the copper (Cu-OFP). The structure and segregation energies for P onto CSL boundaries have been determined with quantum mechanical calculations. In comparison to a previous study where literature data for the frequency of occurrence of CSL GBs was used, the absolute values of the segregation energies and the occupancy of P at GBs are significantly increased when using data for the canister copper. The presence of P reduces the amount of creep cavitation, which controls the ductility during brittle creep rupture. The creation of cavities and creep ductility are predicted. The computed creep ductility is slightly higher than in a previous study mainly due to the frequent occurrence of the Σ9 GB, which leads to strong segregation of P. The influence of grain size on the creep ductility has also been analysed. A large reduction in ductility with grain size is found for Cu without P which agrees with observations. For Cu-OFP a reduction in creep ductility for grain sizes up to 300 µm is also predicted, but no further reduction is obtained for still larger grain sizes.

There are excellent methods for modelling physical and elastic properties, for example, those based on ab initio atomistic procedures. For mechanical properties that are controlled by the motion of the dislocations, such methods have not been available in the past. One has been forced to resort to fitting the experimental data with empirical methods by involving a number of adjustable parameters. However, in recent years, methods based on physical principles have been developed for a number of mechanical properties. These methods can predict properties accurately without the use of fitting parameters. A review of such methods will be given, for example, for the modelling of creep deformation in metallic materials. It will be demonstrated that some properties can be described over a wide range of temperatures and strain rates. The advantage of these new methods is that they can be used for prediction, identification of mechanisms and extrapolation of results for new conditions.

Cavitation is of great technical importance. Nucleated cavities grow and link to form cracks that can cause rupture. During creep, cavities are initiated in the grain boundaries. The nucleation takes place at particles or at subboundary—grain boundary junctions. The main mechanism is believed to be grain boundary sliding (GBS), Chap. 9. According to the double ledge model, cavities are formed when the particles or subboundaries meet other subboundaries. With this assumption quantitative models for cavity nucleation can be derived. They show that the nucleated number of cavities is proportional to the creep strain in good accordance with observations. Cavities can grow by diffusion or by straining. It is important to take into account that cavities cannot grow faster than the surrounding creeping matrix, which is referred to as constrained growth. Otherwise the growth rate can be significantly overestimated. Models both for diffusion and strain controlled growth have been available for a long time. A recently developed model for strain controlled growth is presented based on GBS. It has the advantage that is associated with a well-defined initiation size of cavities and that constrained growth is automatically taken into account, features that some previous strain controlled models miss.

In almost all metals and alloys, dislocations are concentrated to narrow regions after plastic deformation that divide the material into cells or subgrains. The cell walls consist of tangles whereas the subgrains are surrounded by thin regular networks of dislocations. The cells are transferred to subgrains with increasing temperature. Although these substructures have been analyzed for many years, basic models of their development have only appeared recently. Models for substructures are presented for plastic deformation at constant stress and at constant strain rate. During straining the dislocations can move in opposite directions creating a polarized structure, where the possibility for recovery of dislocations is reduced. This can be expressed in term of a back stress. Its presence explains why creep curves at near ambient temperatures could have an appearance that is similar to that at elevated temperatures. It is also the basis for the effect of cold work on creep. The models can quantitatively describe why the creep rate can be reduced by up to six orders of magnitude for Cu after cold work.