Metal treatment – Stock – Chromium – molybdenum – or tungsten base
Reexamination Certificate
1999-02-01
2001-04-03
Sheehan, John (Department: 1742)
Metal treatment
Stock
Chromium, molybdenum, or tungsten base
C420S429000
Reexamination Certificate
active
06210497
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a Mo-based alloy and a method for its production, and more particularly to a super heat-resisting Mo-based alloy and a method for its production. These Mo-based alloys can be used as structural materials for handling high temperature liquid alkalis, structural materials for use in apparatuses for evaluating handling techniques of Na and Li, structural materials for Na or Li-cooled fast reactors, structural materials of portable reactors, electrode materials for use in solidifying nuclear fuel recycling wastes with glass, MOX sintered plates, structural materials for use in nuclear fuel reprocessing units, target materials of accelerators, and various other high temperature functional materials.
Ferrous alloys such as austenitic stainless steels and ferritic stainless steels have been used to fabricate fast reactors. However, there is a general tendency for the service temperature of liquid Na as a coolant to increase as performance and efficiency of the fast reactor increase. Furthermore, it is desirable to use liquid Li as a coolant for portable reactors which must be more efficient than other reactors. However, materials which can withstand such severe conditions have yet to be developed.
There is a desire for ultra high temperature materials such as electrodes for use in nuclear fuel recycling systems, and target materials of accelerators, which can achieve a longer service life as well as higher efficiency than ever in their performance. Due to recent remarkable developments in the energy and aerospace industries, the range of applications of high temperature materials is widening and the need therefor is increasing.
However, as mentioned above, there has been no material which can withstand such severe service conditions. There is a great need for the development of a new material for such needs.
Powder metallurgical methods have mainly been used to produce alloys for use in ultra high temperature materials. Powder metallurgical methods inevitably result in defects in its metallurgical phases of alloys, with adverse effects on various properties of the resulting alloy products. It is desirable, therefore, that structural materials be produced using a melting process.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an alloy material and a method of producing it, the material exhibiting improved resistance to a high temperature liquid alkali metal as well as improved mechanical properties at high temperatures.
More specifically, an object of the present invention is to provide an alloy having the above-mentioned properties and a method of producing the alloy, the alloy being produced by a melting process and not by a conventional powder metallurgical process.
An example of a material which can withstand such severe conditions is molybdenum, which is a refractory metal. Molybdenum has a melting point of 2623° C. and is expected to have a sufficient level of mechanical properties. Molybdenum, however, has problems with respect to its workability at room temperature. Namely, ductile-brittle transition temperature is usually higher than room temperature and a brittle intergranular fracture occurs at room temperature.
The corrosion resistance of molybdenum in liquid alkali metals, however, has not been investigated thoroughly. On the other hand, there is a great need for a molybdenum-based alloy with improved corrosion resistance in liquid alkali metals.
The inventors investigated heat resistance at 1200° C. as well as workability of a molybdenum-based alloy with an intention to provide a molybdenum-based alloy exhibiting improved heat resistance, i.e., high temperature creep strength, improved workability at room temperature, and improved corrosion resistance in high temperature liquid alkali metals.
Thus, the present invention is a method of producing a molybdenum-based alloy having a body-centered cubic, which comprises the steps of determining a bond order with molybdenum (Bo) as well as d-orbital energy level (Md) for two or more alloying elements by the DV−X&agr; cluster method, calculating a bond order and d-orbital energy level on average for an alloy composition based on the following formulas (1) and (2) to provide an average bond as well as an average d-orbital energy level and to determine the type and amount of the elements:
Average
Bo=&Sgr;Bo
i
×C
i
(1)
Average
Md=&Sgr;Md
i
×C
i
(2)
wherein, Bo
i
is the bond order of element “i”, Md
i
is the d-orbital energy level of element “i”, and C
i
is the atomic percent of element “i”.
In another aspect, the present invention is a super heat-resisting molybdenum-based alloy which includes two or more alloying elements, the type and amount of which are determined such that their average d-orbital energy level (average Md) and average bond order (average Bo) satisfy the following formula (3) and such that Tm is in the range of 2250-2700° C. in the following formula (4), the average Md and Bo are calculated by the before-mentioned formulas (1) and (2), and the bond order (Bo) with molybdenum and the d-orbital energy 25 level are determined by the DV−X&agr; cluster method.
1.718≦average
Md≦
1.881 (3)
Tm
(° C.)=(average
Bo−
0.165×average
Md−
4.899)/9.279×10
−5
(4)
According to a preferred embodiment of the present invention, a super heat-resisting molybdenum-based alloy is prepared by a melting process and consists essentially of 2-40 at % of Re, 0.01-1.0 at % of Zr, and a balance of Mo and incidental impurities. The alloying elements satisfy the above-mentioned formulas (3) and (4).
In the preferred embodiment above, the alloy may further contain Hf in an amount of 10 at % or less.
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Phys. Met. Metallogr., vol. 78, No. 1, '994, V.V. Manako et al., “Microstructure and Mechanical Properties of Internally Oxidized Mo-Re-Based Alloys”, pp. 105-111.
Study and Use of Rhenium Alloys, 1978, E.M. Savitskii et al., “Effect of Alloying on the Properties of MR47-VP Alloy”, pp. 175-182.
J. Phys. Condens. Matter, vol. 6, No. 27, Jul. 4, 1994, UK, S. Inoue et al., “Alloying Effect on the Electronic Structures of Nb and Mo”, pp. 5081-5096.
Furui Mitsuaki
Inoue Satoshi
Kano Shigeki
Morinaga Masahiko
Murata Yoshinori
Doryokuro Kakunenryo Kaihatsu Jigyodan
Sheehan John
Sughrue Mion Zinn Macpeak & Seas, PLLC
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