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Super High Strength and Plasticity of Metals

#3484


Development of methods for production of ultrahigh strength materials basing on combined effect of severe plastic deformation and shock-wave loading

Tech Area / Field

  • MAT-ALL/High Performance Metals and Alloys/Materials
  • MAN-MPS/Manufacturing, Planning, Processing and Control/Manufacturing Technology
  • MAT-SYN/Materials Synthesis and Processing/Materials

Status
3 Approved without Funding

Registration date
14.03.2006

Leading Institute
VNIIEF, Russia, N. Novgorod reg., Sarov

Supporting institutes

  • Russian Academy of Sciences / Institute of Metals Superplasticity Problems, Russia, Bashkiria, Ufa

Collaborators

  • Ladish Co., USA, WI, Cudahy\nLos Alamos National Laboratory, USA, NM, Los-Alamos

Project summary

Experimental study of the behavior of materials under high pressures is of critical importance, both in gaining a better understanding of the fundamental mechanisms that are important in determining material behavior, and in answering any number of technical issues that may arise in specific engineering applications. Shock-wave loading is a unique method for providing these high-pressure conditions. In addition to being an excellent tool for studying the behavior of materials, shock wave loading may also be used as a method for altering material behavior (by affecting change on physical and mechanical properties, and in some cases by changing the fundamental structure of the material). It is well known, for example, that in some cases it is possible to use shock wave loading to modify material structure in such a way as to improve the material’s strength. It is also possible, in some cases, to take advantage of the high-rate plastic strain that is generated in a shock wave in order to improve material performance in some way. Electromagnetic and electrohydraulic forming are examples of manufacturing techniques that exploit high-rate plastic strain in procedures that result in materials possessing enhanced properties. Another manufacturing technique, which exploits this phenomenon, involves the use of high explosive (HE) loading with subsequent capture of the material in water. Despite the potential benefits offered through the use of shock wave loading in the manufacturing process, its use has not been widely adopted. Reasons for the limited use of shock wave loading in manufacturing include: (1) limited data availability, (2) questions remain concerning the optimal time-frame for loading (how do variations in loading conditions effect the material), (3) questions remain regarding both long and short-term stability (short term stability issues might arise, for example, with deformation localization and concomitant short-term heating effects), and (4) perhaps most importantly, mathematical models that provide accurate prediction of the resultant material properties for any arbitrary loading history, are not available at present.

The mechanical properties of ultra-fine-grain (UFG) and nano-structural materials differ, often significantly, from those of the more-common “large-grain” polycrystalline metals. For example, under quasistatic loading conditions, flow stress and ultimate strength increases have been observed that are several times greater than those for comparable large-grain materials. These observations have resulted in a great deal of interest in UFG and nano-structural materials. By applying shock wave loading to UFG and nano-structural materials, it is possible modify the structure of these materials, and to perhaps improve their properties in ways heretofore not observed through quasistatic procedures. Most importantly, it may be possible, through the use of shock wave preconditioning of UFG and nano-structural materials, to create “new materials” with specially designed properties. The potential for creating materials with mechanical properties specially tailored for specific engineering applications is enormous (somewhat analogous to that offered by composite materials).

The effect that a shock wave will have on a metal is a complicated matter, involving several different factors, many of which act simultaneously. These include the magnitude of the pressure in the shock wave, the strain rate (which can be quite high), the magnitude of any tensile stresses generated on unloading, and the rise in temperature associated with the passage of the shock wave.

At present, the influence of shock wave loading with peak pressures up to about 100 GPa has been extensively studied for “large-grain” metals. It has been observed that shock wave loading causes significant structural changes in these materials. For example, it has been observed that for shock pressures above a certain threshold value, heterogeneous deformation localization takes place within the grain. These heterogeneities tend to take on a band-like structure with a periodicity of 1-10 m. This phenomenon has been observed in shock wave loading of a number of materials (if it will manifest itself in all materials is an unanswered question). The nature of these heterogeneous structures can be controlled by controlling the loading conditions, and the effect of these structures on overall material performance can be significant. Whether such an effect will appear when UFG and nano-structural materials are subjected to shock loading, and whether it can be exploited in order to create specially designed materials with enhanced properties is an unanswered question, and is a primary motivation for the proposed work.

Because so little is known regarding the potential for exploiting the effects of shock wave loading on UFG and nano-structural materials, and because the potential for producing materials with enhanced properties is so great, a primary focus of the proposed work will be an exploration of this topic. In particular, it will be interesting to study the effects of strain rate (up to 106 and higher), temperature, and other physical parameters, which will have an effect on subsequent material properties for a variety of loading conditions. It will be interesting to apply a variety of loading scenarios to UFG and nano-structural materials that have been prepared using the usual methods. Shock wave loading of these materials will result in changes to the material structure. These changes may result in materials possessing unique mechanical properties (such as enhanced strength or flow stress characteristics).

Goal of Project: The development of methods for producing materials with enhanced properties (such as increased strength or flow stress characteristics), using shock wave loading and high-rate plastic strain.

Expected Results and their Application

Completion of the project will allow:

  • To reveal the influence of initial structure on mechanisms of plastic deformation of metals;
  • To develop physical models of metal behavior under the effect of intensive loading;
  • To develop methods for providing mechanical properties in metals.

The basic technical approach, which will be developed under the project framework, includes the development of methods for providing mechanical characteristics in metals with precisely controlled initial micro-structure by the application of shock wave loading.

The following activities are planned to be performed under the project frameworks:

  • Production of metals having various initial microstructures by the method of overall forging;
  • Study of strength properties of metals having various initial microstructures under static and dynamic loading conditions;
  • Study of the metal microstructure after testing;
  • Loading of samples having various initial microstructures by shock and quasi-isentropic compression waves of various intensities (samples are recovered);
  • Study of mechanisms of formation of various types of microstructure under plastic deformation and annealing, mechanisms of plastic deformation;
  • Study of strength properties of metals under static and dynamic loading conditions after shock-wave and quasi-isentropic pre-conditioning;
  • Preparation of final report and suggestions for industrial application of the developed techniques.

Role of Foreign Collaborators

During the project efforts, it is planned to exchange information with the collaborators and to consider their comments to technical reports. Parallel verification of results obtained under the project frameworks is also possible.


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