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Hydrogen Accumulating Alloys

#G-1434


Elaboration of Iron Based Hydrogen Accumulating Alloys

Tech Area / Field

  • MAT-ALL/High Performance Metals and Alloys/Materials
  • MAT-SYN/Materials Synthesis and Processing/Materials

Status
3 Approved without Funding

Registration date
26.06.2006

Leading Institute
Georgian Technical University, Georgia, Tbilisi

Collaborators

  • New Mexico Institute of Mining and Technology / Mechanical Engineering Department, USA, NM, Socorro\nTU Bergakademie Freiberg / Institut für Maschinenbau, Germany, Freiburg

Project summary

The goal of the project is elaboration of competitive, inexpensive and safety iron based hydrogen accumulating alloys (HAA) using original methodology.

HAA materials are intermetallic compounds consisting of hydride-forming metal atoms A(Ti, Mg, Zr, P3M, etc.) and transition metals B (Ni, Cr, Fe, Mn, etc.) which have catalytic properties. For improving of HAA mechanical properties partial replacement of elements with other ones (alloying) may be used. To HAA materials belong also those which do not form hydrides but at comparatively low pressures and temperatures form hydrogen rich phases-solid solutions, easily giving off hydrogen when environmental conditions are changed.

The research involves following idea. Basically, for storing of hydrogen "containers"' of Fe-C-Si alloys with optimum content of residual austenite are used. Natural, as well as artificial hydrogen saturation of metals is planned. In the second version it is assumed that vacancies of fcc lattice as well as hydride forming ability of silicon and other alloying elements will be used. The idea is based on under mentioned facts..

Having analysed available data and the results of our own investigations scientific hypothesis was proposed. There is silicon threshold (Si 0,50%) in "Fe-Si" system and Fe-C alloys (e.g. in bainitic alloys). Reducing lattice parameter of iron apparently down to 0,50%, Si is used for compensation of 4 uncompensated spins on 3d6(10) subshell of iron atoms and drives the system to energy cone of the attractor. Further increase of Si content (Si 0,50%) in Fe-C bainitic alloys causes self-organized phenomena: sudden increase of hydrogen solubility and amount of residual austenite in the alloy after γ→B transformation, formation of two supersaturated solid solutions <α + γr>, "rejuvenation” and its reverse process (after heating above AC3 and then cooling). New bifurcations appear in Fe-C bainitic alloys.

In common conditions bainitic transformation in some extent fixes high temperature state when carbon and hydrogen supersaturated solid solutions – B[α (C,H) + γr(C,H)], so called "brittle bainite", are obtained. While weathering of metal, "rejuvenation", hydrogen diffuses in residual austenite and relaxed bainite is obtained – B[α (C) + γr (C,H+H)]. Mechanical tests indicate that mechanical properties, particularly those of plasticity, are improved. When heating above AC3 austenite γ (C,H) is obtained again. Further γ→B transformation is ended with formation of "brittle" bainite again – B[α (C,H) + γr (C,H)], etc.

Pairing of two influencing factors – silicon and subzero temperature – is scientifically proved. They decrease lattice parameter of iron and give the same result – iron embrittles, KCU=0. Rapprochement of iron atoms when Si 0,50%, seemingly, causes appearance of new covalent forces where uncompensated electrons of 3d subshell are involved and it provokes synergetic phenomena. New covalent forces between iron atoms "free" silicon atoms. After that silicon itself becomes a getter of hydrogen using vacancies (14) of 3Pd subshell and it results in sudden increase of hydrogen solubility in metal. Paralelly, chemical activity of iron is sharply decreased and as a result carbon is "released” and its redistribution is speeded up. The latter controls bainitic transformation and after γB ensures creation of supersaturated solid solutions

< α γr >, so called “brittle bainite", etc.

Presented scientific hypothesis explains available experimental facts (influence of silicon and hydrogen on properties of bainitic alloys, changing of mechanical properties after weathering of metal – steels: graphitization and weldability processes, forming of flakes, reaching high strength, etc.) in a new manner, making significant corrections in theoretical and practical materials science and gives real opportunity for creating of new branches in many fields, e.g. iron based HAA.

Basic staff members of this project are high-professional scientists. They are highly competent in classical materials science and in physical-chemical processes this branch (bainitic transformations in iron alloys after which optimum amount of residual austenite γropt is obtained, artificial and natural hydrogen saturation of the alloys, etc.).

This scientific hypothesis based on the experimental data assures that chemical compositions of bainitic alloys will be elaborated competing with known samples of HAA by sorptional capacity, safety and cost. “Extra product” of the project will be series of bainitic alloys (steels and pig irons) with high mechanical properties.

The subject of the project meets the requirements of ISTC. Scientists having formerly worked on secret subjects will now contribute to solving urgent and peaceful energy problem of our planet.

1. Elaboration of iron based bainitic alloys with γropt for HAA (Working out and melting of experimental alloys, thorough investigation of the obtained metal. definition of γropt %).

1.1 Bainite obtained by isothermal hardening of steels after usual (tH>AC3) and intercrystallic (between A1 and A3) heating.
1.2 Bainitic steels.
1.3 Austempered ductile iron obtained after isothermal hardening (ADI).
1.4 Bainitic ductile iron.


2. Natural hydrogen permeation into alloys (Hydrogen permeation into metal while melting with so called "metallurgical" hydrogen. Hydrogen permeation into coupons used for mechanical tests and definition of limits of this method).

2.1 Definition of hydrogen amount in steels.
2.2 Monitoring of obtained data by mechanical properties.
2.3 Influence of boiling in water (tH = 100 °C) on hydrogen's "leaving" steel.
2.4 Optimization of chemical compositions of steels and their further treatment by % γr, silicon activity, alloying level.


3. Artificial hydrogen permeation into bainitic alloys (Hydrogen permeation into testing samples, "containers", in α, α+β, β areas. Definition of hydrogen permeation limit up to which monitoring of the process by the results of mechanical tests is possible. Methodology for cycling of hydrogen absorption - desorption processes).

3.1 Definition of hydrogen amount in steels on different levels (α, α+β, β) of hydrogen permeation.
3.2 Comparison of experimental data, obtained after natural and artificial hydrogen permeation into metal. Ascertainment of connection Δψ, % = f (H, %) – between loss of plasticity and hydrogen amount.
3.3 Investigation of hydrogen absorption – desorption process in the selected alloys.
3.4 Continuation of optimization process according to the point 2.4 taking into consideration mechanical properties of the alloys, cost, sorptional capacity, etc.


4. Final experiments (Serviceability of the containers made of selected alloys is defined at multiple repetition of hydrogen absorption – desorption process. Scientifically proved conclusion is made on this question on the basis of obtained data together with our collaborators).

4.1 Definition of serviceability and other working characteristics of containers at multiple repetition of hydrogen adsorption – desorption processes.
4.2 Comparative evaluation of obtained results taking into account demands for HAA.
4.3 Discussion of obtained results together with collaborators for making scientifically proved conclusion on the subject.
4.4 Preparation of available materials for drawing up a business-plan and demonstration of technology.


Basic experiments are carried out in the "Laboratory of properties of materials", GTU:
  1. Mechanical tests of metals covering wide range of properties (SK, σB, σT (σ0,2), σ0,05, δ(δ1 + δ2), ψ(ψ1 + ψ2), e, A, D; a0,25 (a1 + a2), a2-60°C, T50, J-integral, σ-1; macro- and microhardness);
  2. Metallographic, fractographic, X-ray analyses;
  3. Kinetic research of γ→α;
  4. Investigation of supersaturated solid solutions;
  5. Definition of chemical compositions of alloys – is absent. .
  6. Determination of hydrogen content in the alloys – installation of the equipment is accomplished.
  7. Methodology and base for natural hydrogen permeation into metal;
  8. Artificial hydrogen permeation into metal on the base of IMET of Georgia; creation of personal base for carrying out of hydrogen "absorption – desorption" processes in the alloys.

Complete and original definition of structural strength – metal durability (δ1, ψ1, al – statical and dynamical deformability); δ2, ψ2, a2, – deformability after beginning of fracture, T50 – cold brittleness threshold; J-integral – cracking resistance of material; σ-1 – fatigue, etc.) allows to control hydrogen permeation into metal.

Use of experimentally proved methods assists us in obtaining alloys with required composition (e.g. with γropt) which according to our suggestions will ensure success.


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