DE1521506A1 - Process for producing high corrosion resistance - Google Patents

Description

SIEMENS SCIIUCKERTWERKE Erlangen, 1 July 1, 1966

Aktiengesellschaft Werner-von-Siemens-Str.

PLA 66/1492

Process for producing high corrosion resistance

Depending on the intended use, the material of Workpieces placed special requirements. Such are e.g. high mechanical strength, elasticity, or corrosion resistance also, as occurs particularly in reactor technology, lower Neutron absorption cross section. These requirements already largely limit the selection of the workpieces in Question coming materials. As long as only one of these requirements must be fulfilled, the choice of material does not prepare any major ones Trouble. But as soon as several requirements are to be met at the same time, this problem begins to be difficult

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will. For example, it is not necessarily the case that materials of high strength also have a high level of corrosion resistance to water or other corrosive media. If there is a further requirement, such as that of the low neutron absorption cross-section, it is often only possible to meet all three requirements in the form of a compromise . This means that under certain circumstances a material must be taken which does not have the otherwise attainable maximum strength. The consequences of this are, for example, the need for greater material wall thicknesses, which, however , have disadvantages from the point of view of neutron absorption . These disadvantages are exacerbated by the fact that, according to the prior art, in most cases it is necessary to distribute an alloy element or several alloy elements over the entire cross-section of the workpiece, since protective layers only applied to the surface are known to lose their effect as soon as they are are destroyed by corrosion.

The present invention reduces these previous corrosion protection methods Adhering disadvantages to a large extent! »and refers to a method for producing high corrosion resistance, or to reduce the diffusion of harmful substances. This can also be higher on finished / machined parts mechanical strength can be applied. According to the invention, only the layers of these workpieces close to the surface are subject to corrosion enriched inhibiting elements, which do not or only to a small extent in the corresponding corrosion products, but

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rather in not yet corroded surface repairs of the work pieces diffuse in and retain their effectiveness. The elements inhibiting the corrosion also retain their effectiveness when the outer layers of the workpiece, in which these elements were originally located, are destroyed by corrosion. the Workpieces are thereby processed according to methods known per se, such as e.g.

by electroplating, vapor deposition, deposition from the gas phase, spraying or dipping with a corrosion-inhibiting element or an alloy containing the element to a thickness <100 yu coated. Through a subsequent annealing treatment, which also includes the normal operation of these workpieces can be given, a diffusion of these elements into the layers near the surface of the work piece »accomplished. Before using such workpieces So, under certain circumstances, only the process step of coating with the corrosion-inhibiting layers is necessary, the second process step of diffusion then takes place during operation of these workpieces, e.g. inside a nuclear reactor. Not unmentioned should remain that this diffusion of the corrosion-inhibiting legal elements even without prior coating, e.g. by a diffusion annealing in melts from these .Elementen or their Connections or by direct diffusion from the gas phase can be carried out. However, it is also possible to use the workpiece made of a composite material, the outer layer of which has already been enriched with the corrosion-inhibiting elements made of clad sheet metal or tubular composite materials, for example.

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In cases where the anti-corrosion element becomes a Part passes into the corrosion product and only partially in the metal ' remains, it may be necessary to replace the loss of corrosion-inhibiting elements in the event of prolonged corrosion, This can be done by manufacturing the workpiece from an alloy which contains the corrosion-inhibiting elements in such an alloy Quantity that includes the loss of these elements in whole or in part can complement. In this case, too, the invention still has advantages, since the total amount of the corrosion-inhibiting elements can be kept smaller than if these elements are in the amount required to inhibit corrosion evenly the cross-section of the workpiece would be distributed.

As already mentioned at the beginning, such corrosion protection processes have It is particularly important in reactor technology, since the aspect of low neutron absorption is a decisive factor here Role play. A possible material is e.g. the metal zircon or its alloys Zircaloy 2 or Zircaloy 4. These have a relatively low neutron absorption cross section and also have good mechanical properties. It has already been proposed to increase the corrosion resistance to add copper to the zirconium. However, this in turn brings with it an increased neutron absorption, which affects the neutron economy a nuclear reactor influenced in an unfavorable sense. It is precisely here that the particular advantage of the proposed one becomes apparent Process in which only a relatively thin layer, the thickness of which is generally less than 100 μm, but often less than 10 μm.

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gen, is made of a zirconium copper alloy with a higher copper content on the finished workpiece made of zirconium or Zircaloy. The methods already mentioned can be used for application purposes. A subsequent annealing process at approx. 500 to 1000 ⁰ G causes the copper to diffuse into the outer layers of the base material, which - as already mentioned - can also be achieved during the reactor operation itself - that is, without a special process. In addition to copper, other metals that are more noble than zirconium, such as nickel, silver and platinum, can also be used for this purpose. These all have slightly larger absorption cross-sections than zircon, but are of little use because of the relatively small amount.

Another great advantage of the invention is that, in addition to reducing corrosion, there is also oxygen diffusion is slowed down in the metal. This is particularly important because the life of workpieces made of zirconium alloys is due to oxygen diffusion is limited from the oxide phase.

In addition to other structural elements of nuclear reactors, this process is particularly important for protecting fuel rod cladding from corrosion. These cladding tubes are expediently bandaged from the inside and outside, since oxygen is released from the cleavage tablets during operation of the reactor and on the eae |

The inside of the cladding tubes can also be protected from attack . Of course, corrosion protection generally applies

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mine and not only against the effect of oxygen. In addition to this example from reactor technology , other materials are also conceivable that can be protected from corrosive attack by analogous methods.

From these explanations it becomes clear that with the help of this corrosion protection method it is possible to use base materials of e.g. to use the highest strength and / or the lowest neutron absorption and at the same time maximum protection

to have against corrosion. It is also particularly advantageous that this corrosion protection method is applied to finished workpieces Can be applied, so that it has no repercussions whatsoever on the machinability of the workpieces are possible, as might be the case if the entire workpiece were made through and through a corrosion-resistant alloy would be made.

5 claims

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Claims (5)

PLA 66/1492 claims 1. ^ Process for generating high corrosion resistance on workpieces / i> EW. damaging for the reduction of diffusion Substances, characterized in that the near-surface layers of these work pieces are enriched with the corrosion-causing elements, which are not or only slightly Has passed into corresponding corrosion products, but rather diffuse into not yet corroded surface layers of the workpieces and thus retain their effectiveness. 2. A method for producing high corrosion resistance according to claim 1, characterized in that the Werkstück.nach an known methods, such as galvanizing, vapor deposition, Deposition from the gas phase, spraying on or immersion with a corrosion-inhibiting element or one of this element containing alloy in a pick. 100 / u are coated and with a subsequent annealing treatment the normal operation of these workpieces can be given, a diffusion of these elements into the near-surface Layers of the material is accomplished. 3. A method for producing high corrosion resistance according to claim 1, characterized in that the workpieces from e.g. made of plate or tubular composite materials Mü / Or 9098A $ / 033t BATH ORIGINAL PLA 66/1492 whose outer layer is already enriched with the corrosion-inhibiting elements. 4. Use of this method according to claim 1 to 4, for the corrosion protection of components in nuclear reactor technology, in particular those made of zirconium alloys, with elements that are more noble than zirconium as corrosion-inhibiting substances, for example Copper, nickel or platinum, are possible. 5. Use of the method according to claims 1 and 2 for corrosion protection, in particular the cladding tubes of nuclear reactor fuel rods, on their outside and inside. SAD ORIGINAL Mü / Or 909845/0331