Stock material or miscellaneous articles – All metal or with adjacent metals – Foil or filament smaller than 6 mils
Reexamination Certificate
2000-12-15
2002-10-08
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Foil or filament smaller than 6 mils
C148S403000, C148S427000, C148S538000, C148S555000, C148S675000, C420S422000, C420S580000, C420S588000
Reexamination Certificate
active
06461744
ABSTRACT:
The present invention relates to an article based on a metal alloy of nickel, chromium and metalloid elements including microcrystalline precipitates, and the relative preparation method.
It is known in the art that metal superalloys based on nickel allow performances characterized by an extremely high mechanical resistance at high temperatures; in fact, alloys based on nickel-chromium, for example, are used for the construction of blades in gas turbine rotors. The use of this group of alloys in resistors is also known, owing to the high resistivity with respect to conventional metal conductors, the low variation resistivity coefficient with temperature and the above-mentioned mechanical resistance at high temperature.
Furthermore, some particular compositions of these alloys (with respect to the Ni/Cr ratio) are used in the electro-technical field owing to their reduced or absence of magnetic susceptibility.
It is also known that the melting point of these alloys can be lowered by several hundreds of degrees, by adding metalloid elements such as phosphorous, boron or silicon. The alloys thus obtained are particularly suitable for the brazing of steel or other superalloys based on nickel, in particular in the form of fine sheets having a thickness of less than 50 &mgr;m, which are prepared by means of the rapid solidification technology, for example on a cooled rotating wheel (melt spinning or planar flow casting) (U.S. Pat. No. 4,148,973).
The presence of metalloids in the alloy and the high solidification rate cause the amorphization of the tapes or sheet thus produced, which have particularly high mechanical properties only below the crystallization temperature i.e. typically below 300-400° C. Over these temperatures the end-products thus obtained become fragile and it is therefore not possible to use them in applications which require a structural resistance at high temperatures.
This problem is known in particular and the state of the art (Tung S. K. et al., Scripta Materialia, 345, 1996) indicates that this fragility of superalloys containing metalloids, is due to the formation of intermetallic compounds which are formed in the above alloys. Efforts have consequently been made to solve this problem by introducing the minimum possible quantity of said metalloids, i.e. the absolute quantity necessary for amorphization. From what is specified above, it is evident that the use of superalloys in films or fine sheets, having a thickness of less than 50 &mgr;m, is extremely limited owing to the problems described above.
The present invention therefore proposes to overcome the drawbacks present in the known art.
It has been surprisingly found, in fact, that by using alloys based on nickel-chromium, with a low or no magnetic susceptibility (i.e. with a higher chromium content), containing metalloid elements, such as boron and silicon, in a higher quantity with respect to what is described in the known art, and by subjecting the above alloys to a particular thermal treatment after rapid solidification it is possible to produce tapes or filiform end-articles having interesting mechanical properties and resistance to oxidation, without the fragility typical of materials having a similar composition crystallized at temperatures only slightly higher than the glass transition temperature.
An object of the present invention therefore relates to an article based on a nickel-chromium-silicon metal alloy, including microcrystalline borides, obtained by the rapid solidification and subsequent thermal treatment , at a temperature ranging from 700° C. to 950° C. for a time which varies from 5 minutes, in the upper temperature limit, to 100 hours in the lower temperature limit, of a nickel-chromium-boron-silicon metal alloy comprising from 39.0 to 69.4 atom % of nickel, from 11.8 to 33.9 atom % of chromium, from 7.6 to 27.4 atom % of boron and from 7.6 to 17.5 atom % of silicon.
The thermal treatment is carried out within the range of 700 to 950° C., bearing in mind that below the lower temperature limit, the duration times are very long, over hundreds of hours and therefore of limited industrial interest, whereas over the upper temperature limit, coalescence phenomena of the precipitates arise, which reduce the mechanical properties. In the intermediate temperature range the treatment has an adequate duration, in the order of hours, with longer times at low temperatures and shorter times at high temperatures.
A further object of the present invention relates to a tape-form or filiform article having a thickness of less than 50 &mgr;m.
An additional object of the present invention relates to the use of articles in the form of non-magnetic tapes as substrates for the growth of superconductor oxides.
An object of the present invention also relates to the use of articles in tape, sheet or fiber form as a reinforcing element in composite materials with an organic, metallic or pyroceram matrix.
In particular, the tape-form or filiform article according to the present invention is characterized in that it has a thickness ranging from 5 to 40 &mgr;m.
The thermal treatment according to the present invention is preferably carried out in an inert gas or under vacuum, at a temperature preferably ranging from 750° C. to 880° C. and for a time which varies from about 30 minutes (at the upper limit of the temperature range) to about 15 hours (at the lower limit of the temperature range).
The very particular properties of the article according to the present invention are obtained as a result of the rapid solidification and subsequent thermal treatment to which the article is subjected.
This treatment, in fact, allows a structure to be obtained, which is characterized by the presence of microcrystals of nickel and chromium borides, precipitated in the metallic matrix of the nickel, chromium and silicon constituents. If the thermal treatment is carried out in air, the article, on oxidizing, has a nickel, chromium and silicon elemental composition of the matrix, which varies in the different parts of the article itself.
In particular, the use of articles in non-magnetic tape form as substrates for the growth of superconductor oxides, is especially interesting.
The possibility of obtaining superconductor tapes by deposition, with physical or chemical methods, of superconductor oxides on metallic substrates, is known, but the use of this metallic substrate has various problems.
The metallic substrate, in fact, must not only be non-magnetic (a necessary quality for guaranteeing low stream and/or varying magnetic field losses, in regime), but must also be extremely fine (a few tens of micrometers at the most), in order to obtain a high volumetric ratio between the fine superconductor film (in the order of micrometers) and the metallic substrate. In addition, the metallic substrate should not be reactive with the superconductor oxide at the high temperatures typical of its crystalline growth, i.e. at temperatures ranging from 800° C. to 900° C. In order to satisfy all the above conditions, the metallic substrates are generally produced by means of laborious rolling techniques and sophisticated deposition technologies of protective films, as regards both the oxidation of the substrate, and also with respect to the migration of metallic elements from the substrate to the superconductor oxide.
This use of the article according to the present invention is particularly advantageous in that the substrate in tape-form, which can be produced with the rapid solidification technique (by means of planar flow casting), can be obtained with a high productivity and with a particularly fine thickness. Furthermore, after the thermal treatment according to the present invention, it has high mechanical resistance properties and a limited reactivity under oxidative conditions, at the typical temperatures ranging from 800° C. to 900° C., at which the substrate must be maintained in the growth process of superconductor oxides.
In particular, an object of the present invention relates to the use of the end-articles in tape, sheet or fi
Ceresara Sergio
Giunchi Giovanni
Edison Termoelettrica S.p.A.
Koehler Robert R.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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