Overview of constitutive laws, kinematics, homogenization and multiscale methods in crystal plasticity finite-element modeling: Theory, experiments, applications

Rachinger grain boundary sliding is a characteristic of high temperature deformation in both creep when the grain size is large ( d > λ ) and superplasticity when the grain size is small ( d λ ), where d and λ are the grain size and the subgrain size, respectively. An analytical procedure is used to determine the rate equation for Rachinger sliding when d > λ . Data for superplastic metals are examined to give the rate equation for Rachinger sliding when d λ . A unified model is developed for Rachinger sliding at all grain sizes, where the rate of sliding is controlled by the rate of accomodation through intragranular slip. It is demonstrated that the predictions of this model are in good agreement with experimental data under both creep and superplastic conditions.

A unified approach to grain boundary sliding in creep and superplasticity

The ability to achieve a high tensile ductility in a polycrystalline material is of interest both from a scientific point of view and also because of potential applications in the materials forming industry. The superplasticity of conventional metallic alloys is now well-documented and understood reasonably well. However, the field of superplasticity has expanded recently beyond the traditional metallic alloys to include evidence of superplastic-like behavior in a very wide range of new and advanced materials. To date, superplasticity has been reported in mechanically alloyed metals, metal matrix composites, ceramics, ceramic matrix composites and intermetallic compounds. This review presents an overview of these new developments using the established behavior of conventional metallic alloys as a standard for comparison with the mechanical properties of these new materials. As well be demonstrated, the new materials often exhibit significant differences in their flow characteristics in comparison with the traditional superplastic metallic alloys. The successful utilization of superplastic materials in forming applications requires an understanding of the failure processes occurring in the materials in terms of both the localization of external flow and the accumulation of internal damage through the nucleation and growth of cavities. These problems are also addressed in this review.

Superplasticity in advanced materials

Strengthening mechanisms, deformation behavior, and anisotropic mechanical properties of Al-Li alloys: A review

On this seventy-fifth anniversary of the first scientific report of true superplastic flow, it is appropriate both to look back and examine the major developments that established the present understanding of superplasticity and to look to the future to the new opportunities that are made possible by new processing techniques, based on the application of severe plastic deformation, that permit the production of fully dense bulk materials with submicrometer or nanometer grain sizes. This review proposes a minor modification to the present definition of superplasticity, it provides an overview of the current understanding of the flow of superplastic metals and ceramics and then it examines, and gives examples of, the new possibilities that are now available for achieving exceptional superplastic behavior.

Seventy-five years of superplasticity: historic developments and new opportunities

Microscopic and macroscopic aspects of fracture in lithium-containing aluminum alloys

The role of matrix dislocations in the superplastic deformation of a copper alloy

In the present study, grain boundary dislocation (G.B.D.) structures, in a copper-base alloy, have been examined after deformation in each of the three regions of the strain-rate/stress flow behavior characteristic of superplastic deformation. The results show that GBDs are mobile in all three flow regions and that the same types of interaction, with the intergranular microstructure, may be seen in all three regions. Pile-ups of GBDs were seen at triple junctions and at the intersections of twin boundaries with grain boundaries. Intergranular precipitates also hindered the motion of GBDs and numerous examples of GBDs bowing between grain boundary precipitates were observed. A number of GBD sources have been observed and characterized.

P.R. Howell

Papers

Microscopic and macroscopic aspects of fracture in lithium-containing aluminum alloys

The role of matrix dislocations in the superplastic deformation of a copper alloy

The Role of Grain Boundary Dislocations in Superplastic Flow