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Nanocrystalline Alloys with Enhanced Properties

#1922


The Creation of Scientific Basis for Development of Technology for Manufacturing Sheets and Strips of Fe- and Cu-based Alloys with Nanocrystalline Structure with Enhanced Strength, Electric Conductivity and Damping Properties

Tech Area / Field

  • MAT-ALL/High Performance Metals and Alloys/Materials

Status
3 Approved without Funding

Registration date
10.07.2000

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

Supporting institutes

  • VNIITF, Russia, Chelyabinsk reg., Snezhinsk\nNational Nuclear Center of the Republic of Kazakstan / Institute of Atomic Energy (1), Kazakstan, Almaty\nInstitute of Solid State Physics, Russia, Moscow reg., Chernogolovka

Collaborators

  • Osterreichisch Akademie der Wissenschaftem, Austria, Vienna\nGeneral Electric Company / Global Research Center, USA, NY, Niskayuna\nUniversita' Degli Studi Di Ancona / Dipartimento di Meccanica, Italy, Ancona\nUniversity of Idacho / Institute for Materials and Advanced Processes, USA, ID, Moscow

Project summary

The State of the Art in the Field and the Impact of the Proposed Project on the Progress in the Field.

his proposed ISTC Project is the research work relating to the development of technologies for processing materials and their alloys.

The ever increasing demands to modern technique dictate the necessity for application of materials with high specific characteristics. Application of such materials allows to decrease weight of machines and mechanisms and improve their operational reliability.

Reliability of machines depends, to a large measure, on a damping ability of metallic materials: it is well known that about 80% breakdowns and failures of machines and mechanisms are due to the insufficient relaxing ability of materials used for their production under vibration and cyclic loads. Traditional solution to tackle this problem by means of equipping machines with vibration damping units leads to increased dimensions, complicated design, and, finally, to high cost of these machines. Other approaches to solve the problems of enhancing the set of physical and mechanical properties of alloys that are responsible for long-term serviceability of machines and mechanisms by means of creating new materials, including the stages of development, production and certification, require, as a rule, large investments. Besides, new principal difficulties sometimes emerge when these approaches are applied. Thus for example, the development of high damping materials by means of correcting alloys composition or using alloys with magneto-mechanical dispersion of energy is often accompanied by unwanted decrease in their strength or other physical properties, such as electric conductivity.

The authors of the present Project suggest that the existing problems should be solved by means of developing special technologies which provide the generation in commercially produced alloys of submicrocrystalline (SMC) or nanocrystalline (NC) structures with an average grain size of about 100 nm and less, with non-equilibrium state of grain boundaries. In tackling this problem it is proposed to employ two alternative approaches. One of those, which is simpler and less costly, involves the exposure of commercially produced alloys to directional thermomechanical processing in order to produce the qualitative change of their structure and properties. Another approach uses consolidation of nanomonocrystalline powders (an average size of particles being 10-50 nm) of pure metals in order to produce massive practically pore-less material with a grain size close to the average size of particles in the starting powder material.

The results obtained by the authors of the present Project during preliminary investigations show that the state of the generated structure contributes to the attainment of unique properties: high strength, enhanced ductility and toughness, lowered temperature of ductile-brittle transition, improved resistance to wear and corrosion, and high damping capacity.

Though the interest to these materials all over the world is increasing every year, the generation of SMC and NC structures in massive intermediate products still remains a very serious problem. Methods used for production of such materials are unique and costly, and, when applied, allow to generate SMC structure only in small samples, with volumes of only several tens of cubic millimeters, the use of which for study of the most important characteristics of materials structural strength (deformation behaviour, physical magnitudes, fracture toughness etc.) is problematic or impossible. On the basis of the accumulated experience the scientists of the Institute for Metals Superplasticity Problems and the Institute of Solid State Physics have confirmed that it is possible to generate SMC structure in massive billets by methods of pressure shaping using the effect of superplasticity. The principle of the specified approach is in thermomechanical treatment which includes super high plastic deformation within the temperature range 0.2 - 0.4 Tmelt. The second approach chosen by the authors of the present Project is in formation of a fine grain size and the required quality of boundaries between these grains by means of consolidation of nanomonocrystalline powders (an average size of particles being 10-50 nm) of pure metals in order to produce massive material the porosity value of which is close to zero, and with a grain size close to an average size of particles in the starting powder material. The above approaches make possible the production of samples the dimensions of which are sufficient for carrying out systematic studies of structural strength characteristics of SMC materials, and, in future, could be applied as a basis for production of intermediate products with specified set of properties, radical updating of technologies for production of various intermediate (semi-finished) products and parts from different materials.

The formation of the above specified structural states in materials makes possible not only to sharply increase their operating characteristics in the region of their operating temperatures, but also to significantly increase their technological plasticity in the temperature region of mechanical working due to realization of low temperature or high rate superplasticity. The additional enhancement of strength in this case it turned to be due to a special state of grain boundaries in SMC and NC materials (thermodynamically non-equilibrium state).

The Project has very promising commercial potential since its results could be extended into various branches of civil industry during development of advanced technologies of double application thus stimulating the transition from the development of military technologies to the development of novel technologies for production of other products operating for long periods of time under conditions of high temperatures, cyclic loads, aggressive medium which are employed in gas and oil pumping stations, steam turbines, power and transportation vehicles.

The objective of this Project is to create scientific basis for development of technology for production of sheets and strips of Fe- and Cu-based alloys with nanocrystalline structures resulting in generation of enhanced strength, electric conductivity and damping properties.

For this purpose in view it is planned to carry out a wide complex of investigations using the existing unique facilities of IMSP and ISSP of RAS. The facilities available allow production of massive forged products up to 500 mm in size, rolled sections of 10-30 mm in cross-section and rolled sheets of 1-6 mm in thickness with SMC and NC structures by method of severe plastic deformation. Objects for scientific inquiry would be structural materials (stainless steels and copper based alloys) operating under conditions of alternate loads and aggressive mediums.

During development of technology for production of strips of nanomonocrystalline powders of metals and alloys the attention will be focused on the following topics: · production of high-uniform mixtures of nanomonocrystalline powders of metals and alloys of the specified size and composition;

· attainment of the required level of surface purity of particles of nanomonocrystalline powders of metals and alloys of the specified size and composition;

· development of the required conditions (pressure and temperature) for consolidation of nanomonocrystalline powders of metals and alloys of the specified size and composition.

During development of technology for production of strips with submicrocrystalline and nanomonocrystalline structures of massive intermediate products of Fe- and Cu-based alloys the attention will be focused on the matters pertaining to optimization of technological routes of thermomechanical treatment of billets under conditions of severe deformation.

Furthermore, it is also planned to carry out experiments on studying the peculiarities of heat release in during deformation of Cu-based alloys produced according to different technological routes: by consolidation of nanomonocrystalline powders of metals and alloys of the specified size and composition, or by means of severe deformation heat treatment of massive billets. These studies will contribute to optimization of technological routes for manufacturing nanocrystalline strips of alloys, as well as to the prediction of the behaviour of such materials under operating conditions responsible for elastic-plastic deformations.

Along with these activities, it is also provided that there would be conducted service tests for assessment of strength, damping, elastic, plastic, corrosion resistant properties, as well as heat resistance and electric conductivity in a wide range of temperatures (20° - 800°C), and also development of technical concept for design of equipment and means of technological provision for realization of integrated technology.

Expected Results and their Application

The Project realization will bring to reality the developed elements of pilot scale technology for production of strips and sheets with SMC and NC structures of structural materials of standard compositions (stainless steels of austenitic class and Cu-based alloys) operating under alternate loads and aggressive mediums. Production of sheets and strips according to the developed technologies will provide:

· increased ultimate strength and yield stress of stainless steels by factors of 2-3 and 3-4 times respectively with satisfactory ductile characteristics, increased resistance to general intercrystalline corrosion and corrosion cracking;

· increased amplitude-independent damping by factors of 3-4 times in the proposed alloys which will provide the decrease in noise level during operation of machines and mechanisms by the same factors of times, and will eliminate the necessity of using additional design elements in case of increasing damping if required;

· retention of electric conductivity properties of Cu-based alloys while their carrying capacity in critical structures being increased by factors of 3-5 times;

The application in various units of machines and mechanisms of sheets manufactured according to the new technologies will make possible the creation of unique equipment to be operated under conditions of great loads in combination with aggressive medium, such as, in marine and aircraft vehicles, offshore platforms, in food and chemical industries, in medicine, and also in space vehicles subjected to severe vibratory loads.

Scope of activities

The Project is scheduled to last 24 calendar months and require 9000 person-days of former weapons specialists and materials science specialists and also by other support staff for the performance of the Project activities. Total amount of efforts of Weapon scientists - 210 person-months while the Project activities will spent 490 person-months.

The following activities will be performed in the course of realization of the submitted Project:

1. Creation of scientific basis for using the superplasticity effect in production of sheets and strips of Fe- and Cu-based alloys with nanocrystalline and submicrocrystalline structures which provide the attainment of high values of strength, plasticity / ductility and damping capacity, including:


a) development of processing schedule for production of intermediate blanks with homogeneous super fine grained microstructure in the above specified alloys;

b) investigation of the optimum values of temperature, strain and strain rates required for formation of submicrocrystalline and nanocrystalline structures with grain sizes of about 100 nm and less in pilot small-volume (amounting to several cubic centimeters) and medium-volume (amounting to several tens of cubic centimeters) samples of Fe- and Cu-based alloys under conditions of severe deformation and compacting of nanomonocrystalline powders;

c) Investigation of the structure, damping and mechanical and electric conductivity properties of sheets and strips of submicrocrystalline and nanocrystalline steels.


2. Development of design documentation and fabrication of special equipment and tooling for production of billets of Cu- and Fe-based alloys with specified structure under conditions of severe deformation and post deformation annealing operations.

3. Development of regimes for isothermal rolling of sheets of fine grained Fe- and Cu-based alloys blanks for formation of submicrocrystalline and nanocrystalline structures in these alloys followed by fabrication of a pilot lot of sheets (1 mm in thickness and not less than 50 x 200 mm2 in dimensions). Investigation of structure and mechanical properties of the rolled sheets.

Development of design documentation and fabrication of tooling will require the involvement of former weapons development specialists, as well as of those working in the field of materials science, and also some support personnel. Total labour content of the Project realization will amount to 9000 person-days .

While implementing the Project the following activities will be pursued :

1. Investigation of the nature of generation of high damping state in materials resulting from their processing using large plastic deformations.

2. Development of design documentation and fabrication of auxiliary accessories to isothermal rolling mill LIS-200 model and isothermal die stack unit UIShB-510 model for carrying out experiments on manufacturing medium size billets of austenitic stainless steel with submicrocrystalline and nanocrystalline structures.

3. Development of design documentation and fabrication of updated tooling for equal channel angular pressing of metals and alloys in order to produce copper alloys billets with specified structure under conditions of severe deformation and post deformation annealing.

4. Development of regimes for isothermal rolling of sheets of fine grained Fe- and Cu-based alloys for formation of submicrocrystalline and nanocrystalline structures in these alloys followed by fabrication of a pilot lot of sheets (1 mm in thickness and not less than 50 x 200 mm2 in dimensions). Investigation of structure and mechanical properties of the rolled sheets 3.

5. Development of technological regimes of superplastic forming of a model multilayer structure from sheets with submicrocrystalline and nanocrystalline structures of Fe-based alloys under conditions of combining diffusion bonding with superplastic forming including :


a) designing and fabrication of tooling;

b) investigation of formability and weldability of Fe-based alloys in solid state under superplasticity conditions;

c) fabrication of pilot structures from sheets of stainless austenitic steel with submicrocrystalline and nanocrystalline structures using superplastic forming combined with diffusion bonding.


6. Preparation of annual and final reports and a technology implementation plan to define the economic patterns of commercialization of the developed technology.


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