CA1225572A - HIGH ENERGY BEAM THERMAL PROCESSING OF .alpha. ZIRCONIUM ALLOYS AND THE RESULTING ARTICLES - Google Patents

Abstract

29 48,331 ABSTRACT OF THE DISCLOSURE
Described herein are alpha zirconium alloy fabrication methods and resultant products exhibiting improved high temperature, high pressure steam corrosion resistance. The process, according to one aspect of this invention, utilizes a high energy beam thermal treatment to provide a layer of beta treated microstructure on an alpha zirconium alloy intermediate product. The treated product is then alpha worked to final size. According to another aspect of the invention, high energy beam thermal treatment is used to produce an alpha annealed microstruc-ture in a Zircaloy alloy intermediate size or final size component. The resultant products are suitable for use in pressurized water and boiling water reactors.

Description

1 48,331 HIGH ENERGY BEAM THERMAL PROCESSING OF ALPHA
ZIRCONIUM ALLOYS AND THE RESULTING ARTICLES
CROSS-REFERENCE TO RELATED APPLICATION
Zircaloy alloy fabrication methods and resultant products which also exhibit improved high temperature, high pressure steam corrosion resistance are described in related Canadian Application Serial No. 419,843, assigned to the same assignee. This related application describes a process in which a conventional beta treatment is followed by reduced temperature alpha working and annealing to provide an alpha worked product having reduced precipitate size, as well as enhanced high temperature, high pressure steam corrosion resistance.
BACKGROUND OF THE INVENTION
The present invention relates to alpha zirconium alloy intermediate and final products, and processes for their fabrication. More particularly, this invention is especially concerned with Zircaloy ~ alloys having a particular microstructure, and the method of producing this microstructure through the use of high energy beam heat treatments, such that the material has improved long term corrosion resistance in a high temperature steam environment.
The Zircaloy alloys were initially developed as cladding materials for nuclear components used within a i~, ~ "

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2 48,331 high temperature pressurized water reactor environment (U.S. Patent No. 2,772,964). A Zircaloy-2 alloy is an alloy of zirconium comprising about 1.2 to 1.7 weight percent tin, about 0.07 to 0.20 weight percent iron, about 0.05 to 0.15 weight percent chromium, and about 0.03 to 0.08 weight percent nickel. A Zircaloy-4 alloy is an alloy of zirconium comprising about 1.2 to 1.7 weight percent tin, about 0.12 to 0.18 weight percent iron, and about 0.05 to 0.15 weight percent chromium (see U.S.
Patent No. 3,148,055).
In addition variations upon these alloys have been made by varying the above listed alloying elements and/or the addition of amounts of other elements. For example, in some cases it may be desirable to add silicon to the Zircaloy-2 alloy composition as taught in U.S.
Patent No. 3,097,094. In addition oxygen is sometimes considered as an alloying element rather than an impurity, since it is a solid solution strengthener of zirconium.
Nuclear grade Zircaloy-2 or Zircaloy-4 alloys are made by repeated vacuum consumable electrode melting to produce a final ingot having a diameter typically between about 16 and 25 inches. The ingot is then condi-tioned to remove surface contamination, heated into the beta, alpha + beta phase or high temperature alpha phase and then worked to some intermediate sized and shaped billet. This primary ingot breakdown may be performed by forging, rolling, extruding or combinations of these methods. The intermediate billet is then beta solution treated by heating above the alpha + beta/beta transus temperature and then held in the beta phase for a speci-fied period of time and then quenched in water. After this step it is further thermomechanically worked to a final desired shape at a temperature typically below the alpha/ alpha + beta transus temperature.
For Zircaloy alloy material that is to be used as tubular cladding for fuel pellets, the intermediate billet may be beta treated by heating to approximately . .

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3 48,331 1050C and subsequently water ~uenched to a temperaturebelow the alpha + beta to alpha transus temperature. This beta treatment serves to improve the chemical homogeneity of the billet and also produces a more isotropic texture in the material.
Depending upon the size and shape of the inter-mediate product at this stage of fabrication, the billet may first be alpha worked by hea~ing it to about 750C and then forging the hot billet to a size and shape appro-priate for extrusion. Once it has attained the desiredsize and shape (substantially round cross-section), the billet is prepared for extrusion. This preparation in-cludes drilling an axial hole along the center line of the billet, machining the outside diameter to desired dimen-sions, and applying a suitable lubricant to the surfacesof the billet. The billet diameter is then reduced by extrusion through a frustoconical die and over a mandrel at a temperature of about 700C or greater. The as-extruded cylinder may then be optionally annealed at about 700C. Before leaving the primary fabricator, the ex-truded billet may be cold worked by pilgering to further reduce its wall thickness and outside diameter. At this stage the intermediate product is known as a TREX (Tube Reduced Extrusion). The extrusion or TREX may then be sent to a tube mill for fabrication into the final product.
At the tube mill the extrusion or TREX qoes through several cold pilger steps with anneals at about 675-700 between each reduction step. After the final cold pilger step the material is given a final anneal which may be a full recrystallization anneal, partial recrystallization anneal, or stress relief anneal. The anneal may be performed at a temperature as high as 675-700C. Other tube forming methods such as sinking, rocking and drawing, may also completely or partially substitute for the pilgering method.

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4 48,331 Thin-walled members of Zircaloy-2 and Zircaloy-4 alloys, such as nuclear fuel cladding, processed by the above-described conventional techniques, have a resultant structure which is essentially single phase alpha with intermetallic particles (i.e. precipitates) containing Zr, Fe, and Cr, and including Ni in the Zircaloy-2 alloy. The precipitates for the most part are randomly distributed, through the alpha phase matrix, but bands or "stringers"
of precipitates are frequently observed. The larger precipitates are approximately 1 micron in diameter and the average particle si2e is approximately 0.3 microns (3000 angstroms) in diameter.
In addition, these members exhibit a strong anisotropy in their crystallographic texture which tends lS to preferentially align hydrides produced during exposure to high temperature and pressure steam in a circumferen-tial direction in the alpha matrix and helps to provide the required creep and tensile properties in the circum-ferential direction.
The alpha matrix itself may be characterized by a heavily cold worked or dislocated structure, a partially recrystallized structure or a fully recrystallized struc-ture, depending upon the type of final anneal given the material.
Where final material of a rectangular cross section is desired, the intermediate billet may be pro-cessed substantially as described above, with the excep-tion that the reductions after the beta solution treating process are typically performed by hot, warm and/or cold rolling the material at a temperature within the alpha ; phase or just above the alpha to alpha plus beta transus temperature. Alpha phase hot forging may also be per-formed. ~xamples of such processing techni~ues are des-cribed in U.S. Patent No. 3,645,800.
It has been reported that various properties of Zircaloy alloy components can be improved if beta treating is performed on the final size product or near final size ~55 7~

5 48,331 product, in addition to the conventional beta treatment that occurs early in the processing. Examples of such reports are as follows: United States Patent No.
3,865,635, United States Patent No. 4,238,251 and United States Patent No. 4,279,667. Included among these reports is the report that good Zircaloy-4 alloy corrosion proper-ties in high temperature steam environments can be achieved by retention of at least a substantial portion of the precipitate distribution in two dimensional arrays, especially in the alpha phase grain boundaries of the beta treated microstructure. This configuration of precipi-tates is quite distinct from the substantially random array of precipitates normally observed in alpha worked (i.e. below approximately 1450F) Zircaloy alloy final product where the beta treatment, if any, occurred much earlier in the breakdown of the ingot as described above.
The extensive alpha working of the material after the usual beta treatment serves to break up the two dimen-sional arrays of precipitates and distribute them in the random fashion typically observed in alpha-worked final product.
It has been found that conventionally processed, alpha worked Zircaloy alloy cladding (tubing) and channels (plate) when exposed to high temperature steam such as that found in a BWR (Boiling Water Reactor) or about 450 to 500C, 1500 psi steam autoclave test have a propensity to form thick oxide films with white nodules of spalling corrosion product, rather than the desirable thin contin-uous, and adherent substantially black corrosion product needed for long term reactor operation.
Where beta treating is performed on the final product in accordance with U.S. Patent 4,238,251 or U.S.
Patent 4,279,667, the crystallographic anisotropy of the alpha worked material so treated tends to be diminished and results in a higher proportion of the hydrides formed - in the material during exposure to high temperature, high pressure a~ueous environments being aligned substantially ~5572

6 48,331 parallel to the radial or thickness direction of the material. Hydrides aligned in this direction can act as stress raisers and adversely affect the mechanical perfor-mance of the component.
In addition the high temperatures utilized during a beta treatment process, especially such as that described in U.S. Patent 4,238,251, can create significant thermal distortion or warpage in the component. This is especially true for very thin cross-section components, such as fuel clad tubing.
Through the wall beta treating the component, before the last cold reduction step, as described in U.S.
Patent 3,865,635, may result in increased difficulty in meeting texture-related properties in the final product since only a limited amount of alpha working can be pro-vided in the last reduction step.
BRIEF SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention it has been found that the high temperature steam corrosion resistance of an alpha zirconium alloy body can be significantly improved by rapidly scanning the surface of the body with a high energy beam so as to cause at least partial recrystallization or partial dissolution of at least a portion of the precipitates.
Preferably the high energy beam employed is a laser beam and the alloys treated are selected from the groups of Zircaloy-2 alloys, Zircaloy-4 alloys and zircon-ium-niobium alloys. These materials are preferably in a cold worked condition at the time of treatment by the high energy beam and may also be further cold worked sub-sequently.
In accordance with the present invention inter-mediate as well as final products having the microstruc-tures resulting from the above high energy beam rapid scanning treatments are also a subject of the present invention and include, cylindrical, tubular, and rectang-ular cross-section material.

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7 48,331 In accordance with a second aspect of the present invention the high temperature, high pressure steam corrosion resistance of an alpha zirconium alloy body can also be improved by beta treating a first layer of the body which is beneath and adjacent to a first surface of said body so as to produce a Widmanstatten grain structure with two dimensional linear arrays of precipitates at the platelet boundaries in this first layer, while also forming a second layer containing alpha recrystallized grains beneath the first layer. The mater-ial so treated is then cold worked in one or more steps to final size, with intermediate alpha anneals between cold working steps.
Preferably any intermediate alpha or final alpha anneals performed after high energy beam beta treatment are performed at a temperature below approximately 600~C
to minimize precipitate coarsening. It has been found that Zircaloy bodies surface beta treated in accordance with this aspect of the invention are easily cold worked.
It has also been found that typically both the alpha recrystallized layer as well as the beta treated layer when processed in accordance with the present invention possess good high temperature, high pressure steam cor-rosion resistance.
Preferably the beta treating is performed by a rapidly scanning high energy beam such as a laser beam.
In one embodiment of this aspect of the invention, the degree of cold working after beta treating may be suffi-cient to redistribute the two dimensional linear arrays of precipitates in a substantially random manner while retain-ing good high temperature, high pressure steam corrosion resistance.
Beta treated and one-step cold worked alpha zirconium bodies in accordance with this second aspect of the invention are characterized by two microstructural layers. Both layers have anisotropic crystallographic textures; however, it is believed that the outermost .:~Z;ZS5 ~Z

8 48,331 layer, that is, the layer that received the beta treat-men~, is less anisotropic than the inner layer. This difference, however, diminishes as the number of cold working steps and intermediate anneals after beta treating increases.
These and other aspects of the present ir.vention will become more apparent upon review of the drawings in conjunction with the detailed description o~ the inven-tion.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1 and 2 show optical micrographs of micro-structures produced by laser treating Zircaloy-4 tubing in accordance with one embodiment of the present invention.
Figures 3A and 3B show optical micrographs of a Widmanstatten basket-weave structure produced by laser treating Zircaloy-4 tubing.
Figures 4A and 4B show transmission electron micrographs of typical microstructures found in the embodi-ment shown in Figures 1 and 2.
Figure 5 shows optical and scanning electron microscope micrographs of typical microstructures present in the as-laser treated tube according to ~he present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In one embodiment of the present invention it was found that scanning of final size Zircaloy-4 tubing by a high power laser beam would provide high temperature, high pressure steam corrGsion resistance even though a Widmanstatten basket-weave microstructure was not achieved.
It was found that material processed as described in the following examples could achieve high temperature, high pressure steam corrosion resistance even though optical metallographic examination of the material revealed it to have partially or fully recrystallized microstructural regions with a substantially uniform precipitate distribu-tion typical of that observed in conventionally alpha worked and annealed 2ircaloy tubing.

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9 48,331 The laser treatments utilized in this illustra-tion of the present invention are shown in Table I. In all cases a 10.6 ~ wavelength, 5 kilowatt laser beam was rastered over an area of 0.2 in. x 0.4 in. (0.508 cm x 1.08 cm) of conventionally fabricated, stress relief annealed, final size Zircaloy-4 tubing, the tubing having a mechanically polished (400-600 grit) outer surface, was simultaneously rotated and translated through the beam area under the conditions shown in Table I. As the tube rotation and tube withdrawal rates decreased, more energy was transmitted to the specimen surace and higher tempera-tures were attained. This relationship of tube speed to energy is illustrated by the increase in specific surface energy (that is energy striking a square centimeter of the tube surface) with decreasing tube rotation and tube withdrawal rates as shown in Table I. ~lthough the treat-ment chamber was purged with argon at a rate of about 150 cubic feet/hour, most tubes were covered with a very light oxide coating upon exit from the chamber.
Representative sections of each treatment condi-tion were metallographically polished to identify any microstructural changes that had occurred. Results ob-tained from optical metallography are listed in Table II, where it can be seen that no obvious microstructural effects were discerned until the rotation speed had been reduced to below 285 rpm, at which recrystallization occurred (241 rpm). At the next slowest speed (196 rpm) the whole tube was transformed to a Widmanstatten basket-weave structure, Figure 3. Similar Widmanstatten struc-tures were also observed at a rotation speed of 147 rpm.
The structures produced at rotation speeds of 241 rpm and 285 rpm are shown in Figures 1 and 2, respectively. The only visible difference between the structures was that the 241 rpm sample had a fine recrystallized grain structure, whereas, the 285 rpm sample did not. Faster rotation speeds resulted in structures which were opti-cally indistinguishable from the 285 rpm sample. In no `12~557~
48,331 case was a beta treated structure produced solely in an outer layer of the tubing. Both the 196 rpm sample, as ,r.,'~ well as the 147 rpm sample, had Widmanst'atten basket-weave structures (Figures 3A and 3B~ extending through the wall thickness. Microhardness measurements performed on these specimens indicated that significant so~tening occurred only in samples where the rotation speed was less than 241 rpm.
Sections of the laser treated tubing were

10 pickled in 45% H20, 4S% HN03 and 10% XF to remove the oxide that had formed during the processing, and were subsequently corrosion tested in 454C (850F), 1500 psi steam to determine the effect of the various treatments on high temperature corrosion resistance. After five days corrosion exposure, all samples that had experienced rotation rates greater than 285 rpm had disintegrated, while those with comparable or slower rotation rates had black shiny oxide films. A summary of the corrosion data obtained after 30 days exposure in 45~C steam is pre-sented in Table III, as are data obtained on beta-annealed + water quenched Zircaloy-4 control coupons which were included in the exposures. It can be seen that the laser treated tubing generally had lower weight gains than the beta treated Zircaloy-4 control coupons. For comparison, conventionally processed cladding disintegrates after 5-10 days in the corrosion environment utilized.
Because beta-treated Zircaloy-4 with a Widman-statten microstructure has good corrosion resistance in 454C steam, it was anticipated, on the basis of optical metallography, that the laser treated specimens with the Widmanstatten structure (Figure 3) would also have good corrosion resistance. However, the change from cata-strophic corrosion behavior to excellent corrosion be-havior that occurred between rotation rates of 332 rpm and 2~5 rpm was not expected on the basis of optical metal-lography and forms the basis of this embodiment of the present invention. In order to determine what specific lZ~S572

11 48,331 microstructural changes were responsible for this phenom-ena, transmission electron microscopy (TEM) samples were prepared from the 332-241 rpm tubing. The structures that are characteristic of these specimens are shown in Figures 4A and 4B. (The dark particles shown in these micrographs are not indigenous precipitates, but are oxides and hy-dride artifacts introduced during TEM specimen prepara-tion.) All of the samples had areas which were well polygonized (Figures 4A, area X) and/or recrystallized (Figure 4B). The structures were quite similar, in over-all appearance, to cold-worked Zircaloy-4 that had been subjected to a relatively severe stress relief anneal.
Precipitate structures were typical of those in normally processed Zircaloy-4 tubing, although many precipitates were more electron transparent than normally expected, indicating that partial dissolution may have occurred. No qualitatively discernible difference between the specimens which had poor corrosion resistance and good corrosion resistance was noted. It is however theorized that dis-solution of intermetallic compounds may result in enrich-ment of the matrix in Fe and/or Cr, thereby leading to the improved corrosion resistance observed.
In accordance with the present invention the above examples clearly illustrate that laser treating of Zircaloy-4 tubing so as to provide an incident specific surface energy at the treated surface of between approx-imately 288 and 488 joules per centimeter s~uared can produce Zircaloy-4 material which forms a thin, adherent and continuous oxide film upon exposure to high tempera-ture and high pressure steam. Based on these corrosiontest results it is believed that Zircaloy-4 material so treated will possess good corrosion resistance in boiling water reactor and pressurized water reactor environments.
While these materials in accordance with this invention possess the corrosion resistance of Zircaloy-4 having a Widmanstatten structure, it advantageously is believed to substantially retain the anisotropic texture SS7~

12 4~,331 produced in the alpha working of the material prior to laser treating, making it less susceptible to formation of hydrides in undesirable orientation with respect to the stresses seen by the component during service.
While the invention has been demonstrated using a laser beam, other high energy beams and methods of rapid heating and cooling may also be suitable.
The values of specific surface energy cited above in accordance with the invention may of course vary with the material composition and factors, such as section thickness and material surface condition and shape, which may affect the fraction of the incident specific surface energy absorbed by the component.
It is also believed that the subject treatments are also applicable to other alpha zirconium alloys such as Zircaloy-2 alloys and zirconium-niobium alloys. It is also believed that the excellent corrosion resistance obtained by the described high energy beam heat treatment can be retained after further cold working and low tempera-ture annealing of the material.
The material to be treated may be in a coldworked (with or without a stress relief anneal) or in a recrystallized condition prior to laser treatment.
In other embodiments of the present invention conventionally processed Zircaloy-2 and Zircaloy-4 tubes are scanned with a high energy laser beam which beta treats a first layer of tube material beneath and adjacent to the outer circumferential surface, producing a Widman-statten grain and precipitate morphology in this layer while forming a second layer of alpha recrystallized material beneath this first layer (see Figure 5) . The treated tubes are then cold worked to final size and have been found to have excellent high temperature, high pres-sure steam corrosion resistance. The following examples are provided to more fully illustrate the processes and products in accordance with these embodiments of the present invention.

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13 48,331 Note, as used in this application, the term scanning refers to relative motion between the beam and the workpiece, and either the beam or the workpiece may be actually moving. In all the examples the workpiece is moved past a stationary beam.
The laser surface treatments utilized in these illustrations of the present invention are shown in Table IV. In all cases a continuous wave CO2 laser emitting a 10.6 ~ wavelength, 12 kilowatt laser beam was utilized. An annular beam was substantially focused onto the outer diameter surface of the tubing and irradiated an arc encompassing about 330 of the tube circumference. The focused arc had a diameter equal to the tube diameter and a length of 0.1 inch. The materials were scanned by the laser by moving the tubes through the ring-like beam. While being treated in a chamber continually being purged with argon, the tubes were rotated at a speed of approximately 1500 revolutions per minute while also being translated at the various speeds shown in inches per minute (IPM) in Table IV, so as to attain laser scanning of the entire tube O.D.
surface. The variation in translation speeds or withdrawal or scanning speeds were used to provide the various levels of incident specific surface energy (in joules/centimeter squared) shown in Table IV. Under predetermined conditions of laser scanning, as the specific surface energy increases the maximum temperature seen by the tube surface and the maximum depth of the first layer of Widmanstatten structure, both increase. Rough estimates of the maximum surface temperature reached by the tube were made with an optical pyrometer and are also shown in Table IV. While these values are only rough estimates they can be used to compare one set of runs to another and they complement the calculated specific surface energy values since the latter are known to be effected by interference of the chamber atmospheric conditions on laser workpiece energy coupling.
The tubes treated included conventionally pro-cessed cold pilgered Zircaloy-2 and Zircaloy-4 tubes having a 0.65 inch diameter x 0.07 inch wall thickness, `l~

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14 48,331 and a 0.7 inch diameter x 0.07 inch wall thickness, respectively. The tubes had a mill pickled surface.
Ingot chemistries of the material used for the various runs are shown in Table V.
After the beta treatment the tubes were cold pilgered in one step and processed (e.g. centerless ground and pickled) to final size, 0.4~4 inch diameter x 0.0328 inch wall thickness, and 0.374 inch diameter x 0.023 inch wall thickness for the Zircaloy-2 and Zircaloy-4 heats, respectively.
Representative sections from various runs were then evaluated for microstructure, corrosion properties, and hydriding properties. Microstructural evaluation indicated that for the runs shown in Table IV the Widman-statten structure originally produced in the .070 inchwall typically extended inwardly from the surface to a depth of from 10 to 35 percent of the wall thickness, depending upon the beta treatment temperature. The abso-lute value of these` first layer depths, of course, de-creased significantly due to the reduction in wall thick-ness caused by the final cold pilgering.
Lengths of tubing from the various runs were then pickled and corrosion tested in high temperature, high pressure steam and the data are as shown in Tables VI
and VII. It will be noted that in all cases the samples processed in accordance with this invention had signifi-cantly lower weight gains than the conventionally alpha worked material included in the test standards. It was noted, however, that in some cases varying degrees of accelerated corrosion wer~ observed on the laser beta treated and cold worked samples (see Table VI 1120C, and 1270-1320C materials). These are believed to be an artifact of the experimental tube handling system used to move the tube under the laser beam which allowed some portions of tubes to vibrate excessively while being laser treated. These vibrations are believed to have caused portions of the tube to be improperly beta treated result-` ` i2;~5572 48,331ing in a high variability in the thickness of the beta treated layer around the tube circumference in the affected tube sections, causing the observed localized area~ of high corrosion. It is therefore believed that these incidents of accelerated corrosion are not inherent products of the present invention, which typically produces excellent corrosion resistance.
Oxide film thickness measurements performed on the corrosion-tested laser-treated and cold-worked Zircaloy-4 samples from the tests represented in Table VI surprisingly indicated that the inside diameter surface, as well as the outside diameter surface, both had equivalent corrosion rates. This was true for all the treatments represented in Table VI except for the 1120C treatment, where the inner wall surface had a thicker oxide film than the outer wall surface.
Based on the preceding high temperature, high pressure steam corrosion tests it is believed that these alpha Zirconium alloys will also have improved corrosion resistance in PWR and BWR environments.
The mechanical property characteristics and hydriding characteristics of the treated materials were found to be acceptable.
In this invention since only a surface layer of the intermediate tube is beta treated, it is believed that the crystallographic texture of the final product can be more easily tailored to provide desired final properties compared to the method disclosed in U.S. Patent No.
3,865,635. In this invention both the alpha working before and after the surface beta treatment can be used to form the desired texture in the inner layer of the tube.
Both good outside diameter and inside diameter corrosion properties have been achieved by laser surface treating and cold working according to this invention, without resort to the precipitate size control steps of Canadian Application Serial No. 419,843 prior to the laser treating step, as demonstrated by the 1'~2557~

16 48,331 preceding examples. However, in another embodiment of the present invention, the process of the copending applica-tion, utilizing reduced extrusion and intermediate anneal-ing temperature, may be practiced in conjunction with the high energy beam beta treatments of this invention. In this embodiment, the high energy beam surface treatment would be substituted for the intermediate anneal at step 5, 7 or 9, of the copending application. The intermediate product, in the surface beta treated condition, would have an outer layer having a Widmanstatten microstructure adjacent and beneath one surface, and an inner layer, beneath the outer layer, having recrystallized grain structure with the fine precipitate size of the copending application. Subsequent working and annealing in accord-ance with the present invention would produce a final product having a substantially random precipitate distri-bution and a fine precipitate size in its inner layer.
In applying the present process to Zirconium-niobium alloys it is preferred that the material be aged at 400-600C after cold working. This aging will occur during intermediate and final anneals performed on the material after the laser surface treatment.
The above examples of this invention are only illustrative of the many possible products and processes coming within the scope of the attached claims.

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18 48,331 TABLE II
ZIRCALOY-4 LASER HEAT TREATME~TS

Rotation RateTranslation Optical Microhardness (rpm) Rate (in/min) Microstructural Observations (kg/mm ) 485 145.5~o Observable Effect 219 473 142 " 228 4S5 136.5 " 215 430 129 " 228 407 122 " 222 376 113 " 224 332 100 " 223 285 85.5 " 207 241 72Fine Recrystallized Structure 222 196 59~Tidmanstatten Structure 196 147 44l~idmanstatten Structure 196 TABLE III
454C (850F) CORROSIO~ DATA OBTAINED ON

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21 48,331 TABLE V
INGOT CHEMISTRY OF ZIRCALOY TUBES
PROCESSED IN ACCORDANCE WITH THE INVEN~ION

Zircaloy-4 Heat A Zircaloy-4 Heat B ~ircaloy-2 Run Nos. 23-43 ~un Nos. 44-48Run Nos. 49-63 Sn1.46-1.47 w/o 1.42-1.52 w/o 1.44-1.63 w/o Fe.22-.23 w/o .19-.23 w/o .14-.16 w/o Cr.11-.12 w/o .lO-.12 w/o .11-.12 w/o Ni ~50 ppm C35 ppm .05-.06 w/o Al42-46 ppm 39-58 ppm ~35 ppm B <0.5 ppm < 0.25 ppm < 0.2 ppm Ca NR <15 ppm NR
Cd<0.5 ppm <0.25 ppm ~0.2 ppm C115-127 ppm 125-165 ppm 10-40 ppm Cl <10 ppm 7-11 ppm <~0 ppm Co<~0-13 ppm <~0 ppm ~10 ppm Cu <10 ppm <25-44 ppm <25 ppm Hf52-53 ppm <80-84 ppm 51-57 ppm Mn <~0 ppm <25 ppm <25 ppm 20 Mg <~O ppm <~O ppm <10 ppm Mo <20 ppm ~2; ppm ~25 ppm Pb NR <25 ppm NR
Si 52-54 ppm 60-85 ppm 99-119 ppm Nb <50 ppm <50 ppm NR
Ta100 ppm <100 ppm NR
Ti18-48 ppm <25 ppm ~25 ppm U<0.5 ppm <1.8 ppm ~1.8 ppm U235 .002-.004 ppm .010 ppm NR
V<20 ppm <25 ppm NR
W<50 ppm <50 ppm <50 ppm Zn~50 ppm NR NR
H2-18 (12-17) ppm 5-7 ppm (<~2) ppm N35-40 (35-43) ppm 40 ppm (21-23) ppm 01100-1140 (1100-1200) ppm1200-1400 ppm (1350-1440) ppm Values reported typically represent the range of analyses determined from various positions on the ingot.
Values in parentheses represent the range of analyses as determined on TREX.
NR = not reported ~S5'~
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Claims (51)

24 48,331 CLAIMS:

1. A process for improving the high temperature steam corrosion resistance of an alpha zironium alloy body having a random precipitate distribution comprising the steps of:
beta treating a first layer of said body, wherein said first layer is beneath and adjacent to a first surface of said body, and wherein said beta treating produces two dimensional linear arrays of precipitates in said first layer;
while forming a second layer of alpha recrystallized grains beneath said first layer while maintaining said random precipitate distribution in said second layer;
then cold working said body;
then final annealing said body;
and wherein after said final anneal both said first layer and said second layer have said improved high temperature steam corrosion resistance as evidenced by an adherent sub-stantially black continuous oxide film formed on both said first layer and said second layer upon 24 hours exposure of said first layer and said second layer to a 500C, 1500 psi steam test.

2. The process according to claim 1 wherein said cold working step comprises two or more cold working steps separated by an intermediate annealing step.

3. The process according to claim 1 wherein said cold working step comprises cold working said body to a degree sufficient to redistribute said two dimensional arrays of precipitates in a substantially random manner.

48,331

4. The process according to claim 1 wherein said beta treating step is performed by directing a high energy beam on to said first surface.

5. The process according to claim 4 wherein said high energy beam is a laser beam.

6. The process according to claim 1 wherein during said beta treating step the temperature of said first layer of said body is above the alpha + beta transus temper-ature for only a fraction of a second.

7. The process according to claim 2 wherein said cold working, and said annealing are performed at a temper-ature below approximately 600°C.

8. The process according to claim 1 wherein said alpha zirconium alloy is selected from the group con-sisting of Zircaloy-2, Zircaloy-4 and zirconium-niobium alloys.

9. The process according to claim 3 wherein said alpha zirconium alloy is selected from the group con-sisting of Zircaloy-2 and Zircaloy-4.

10. An alpha zirconium alloy final size component produced in accordance with claim 1 and comprised of Zircaloy.

11. An alpha zirconium alloy final size component in accordance with claim 10 wherein said component is a thin walled tubular fuel cladding.

12. A method of improving corrosion resistance of an alpha zirconium alloy body having a first major surface separated from an oppositely facing second major surface by a predetermined distance, said method comprising the steps of:
scanning said first major surface at a predetermined speed with a means for rapidly introducing energy to said body through localized area of said first major surface;
controlling said speed and the rate of introducing energy through said localized area to produce a first layer of microstructure extending from said first major surface toward said second major surface, and a second layer of microstructure beneath said first layer of microstructure and adjacent to said second major surface;

26 48,331 wherein said first layer of microstructure is characterized by a Widmanstatten microstructure and said second layer of microstructure is characterized by equiaxed recrystallized alpha grains; after said scanning step, cold working said body and then annealing said body; and wherein both said first layer and said second layer are characterized by an adherent substantially black continuous oxide film after 24 hours exposure to a 500°C, 1500 psi steam test.

13. Channel plate produced by the method according to claim 12.

14. Fuel element cladding produced by the method according to claim 12.

15. A Zircaloy alloy body comprising:
a first cold worked and alpha annealed microstructural layer;
a second cold worked and alpha annealed microstruc-tural layer;
wherein said first microstructural layer contains precipitates and a substantial portion of said precipitates are distributed in two dimensional linear arrays;
wherein said second microstructural layer also con-tains said precipitates, but said precipitates are distributed substantially randomly;
wherein both said first and said second microstruc-tural layers exhibit anisotropic crystallographic textures resulting from cold working and alpha annealing;
and wherein in a 500°C, 1500 psi, 24 hours, steam corrosion test said first and said second microstructural layers are resistant to nodular corrosion as indicated by the formation of continuous and adherent substantially black oxide films on both said first and second microstructural layers.

16. The Zircaloy alloy body according to claim 15 wherein said body is a final size tubular fuel element clad-ding having an outside diameter surface, an inside diameter surface and a wall thickness separating said outside diameter surface from said inside diameter surface;

27 48,331 wherein said first microstructural layer extends inwardly from said outside diameter surface to a depth of about 10 to about 35 percent of said wall thickness;
and wherein said second microstructural layer is adjacent to said inside diameter surface.

17. The Zircaloy alloy body according to claim 16 wherein said cladding is in a cold worked and stress relief annealed condition.

18. A final size nuclear reactor component, having a predetermined final cross sectional thickness, said com-ponent comprising:
a Zircaloy alloy comprising said component;
a major surface on said component normal to the direction defined by said cross sectional thickness;
a first layer of Zircaloy alloy microstructure be-neath, parallel and adjacent to said major surface and extending away from said major surface for a fraction of said predeter-mined final cross sectional thickness;
a second layer of Zircaloy alloy microstructure beneath and parallel to said first layer of Zircaloy alloy microstructure;
said first layer of Zircaloy alloy microstructure is characterized by two dimensional arrays of precipitates in a cold worked grain structure;
said second layer of Zircaloy alloy microstructure is characterized by a cold worked grain structure and a random distribution of precipitates having an average size of approxi-mately 0.3 microns;
and wherein both said first layer of Zircaloy alloy microstructure and said second layer of Zircaloy alloy micro-structure have high temperature aqueous corrosion resistance characterized by an adherent substantially black oxide film and an average weight gain of less than about 71 mg/dm2 after exposure to a 500C, 1500 psi, 24 hour steam test.

19. The nuclear reactor component according to claim 18 wherein said component is a fuel element cladding, having a tubular cross section.

28 48,331

20. The nuclear reactor component according to claim 18 wherein said component has a cylindrical cross section.

21. The nuclear reactor component according to claim 18 wherein said predetermined final cross sectional thickness is between about 0.023 and about 0.033 inches.

22. The nuclear reactor component according to claim 19 wherein said fraction of said predetermined cross sectional thickness is about 10 to about 35 percent.

23. The nuclear reactor component according to claim 18 wherein said fraction of said predetermined cross sectional thickness is about 10 to about 35 percent.

24. The nuclear reactor component according to claim 18 wherein the high temperature aqueous corrosion resistance of said first layer of Zircaloy alloy microstructure and said second Layer of Zircaloy alloy microstructure are further characterized by having oxide film thicknesses after an exposure to an 850°F, 1500 psi, 20-day steam test which are about equal.

25. The nuclear reactor component according to claim 18 further comprising a second surface on said component;
and wherein said second layer of Zircaloy alloy microstructure is adjacent to said second surface.

26. A final size, rectangular cross section, nuclear reactor component, having a predetermined final cross sectional thickness, said component comprising:
a Zircaloy alloy comprising said component;
a major surface on said component normal to the direction defined by said cross sectional thickness;
a first layer of Zircaloy alloy microstructure be-neath, parallel and adjacent to said major surface and extending away from said major surface for a fraction of said predeter-mined final cross sectional thickness;
a second layer of Zircaloy alloy microstructure beneath and parallel to said first layer of Zircaloy alloy microstructure;

29 48,331 said first layer of Zircaloy alloy microstructure is characterized by two dimensional arrays of precipitates in an alpha worked and annealed grain structure;
said second layer of Zircaloy alloy microstructure is characterized by an alpha worked and annealed grain structure characterized by a random distribution of precipitates having an average size of approximately 0.3 microns;
and wherein both said first layer of Zircaloy alloy microstructure and said second layer of Zircaloy alloy micro-structure have high temperature aqueous corrosion resistance characterized by an absence of spalling nodular corrosion product after exposure to a 500C, 1500 psi, 24 hour steam test.

27. The nuclear reactor component according to claim 26 wherein said component is a channel plate.

28. A process for increasing the corrosion resis-tance of a surface of an alpha zirconium alloy body having a substantially random precipitate distribution throughout said body, comprising the steps of:
rapidly scanning said surface of said body with a means for rapidly heating said body;
controlling said scanning and said means for rapidly heating said body to heat said surface to a temperature high enough to produce partial dissolution of precipitates in a microstructural region adjacent to said surface, but low enough to retain said substantially random precipitate dis-tribution in said microstructural region; wherein the cor-rosion resistance of said surface is increased to a level wherein said surface is characterized by a black oxide film after 5 days exposure to 454°C, 1500 psi steam.

29. The process according to claim 28 wherein said alpha zirconium alloy is selected from the group consisting of Zircaloy-2 and Zircaloy-4.

30. A process for increasing the corrosion resis-tance of a surface of an alpha zirconium alloy body in a cold worked condition and having a substantially random precipitate distribution throughout said body, comprising the steps of:

48,331 rapidly scanning said surface of said body with a means for rapidly heating said body;
controlling said scanning and said means for rapidly heating said body to produce an absorbed specific surface energy on said surface high enough to produce a partially re-crystallized microstructural region adjacent said surface, but low enough to retain said substantially random precipitate distribution in said partially recrystallized microstructural region; wherein the corrosion resistance of said surface is increased to a level wherein said surface is characterized by a black oxide film after 5 days exposure to 454°C, 1500 psi steam.

31. A process for increasing the corrosion resis-tance of a surface of an alpha zirconium alloy body in a cold worked condition and having a substantially random pre-cipitate distribution throughout said body, comprising the steps of:
rapidly scanning said surface of said body with a means for rapidly heating said body;
controlling said scanning and said means for rapidly heating said body to heat said surface to a temperature high enough to produce a fully recrystallized equiaxed alpha micro-structural region adjacent to said surface, but low enough to retain said substantially random precipitate distribution in said fully recrystallized microstructural region; wherein the corrosion resistance of said surface is increased to a level wherein said surface is characterized by a black oxide film after 5 days exposure to 454°C, 1500 psi steam.

32. The process according to claim 30 wherein said alpha zirconium alloy is selected from the group con-sisting of Zircaloy-2 and Zircaloy-4.

33. The process according to claim 31 wherein said alpha zirconium alloy is selected from the group con-sisting of Zircaloy-2 and Zircaloy-4.

34. The process according to claim 28 followed by the additional steps comprising cold working and annealing said body while retaining the corrosion resistance imparted 31 48,331 to said body by said rapid scanning.

35. The process according to claim 30 followed by the additional steps comprising cold working and annealing said body while retaining the corrosion resistance imparted to said body by said rapid scanning.

36. The process according to claim 31 followed by the additional steps comprising cold working and annealing said body while retaining the corrosion resistance imparted to said body by said rapid scanning.

37. The process according to claim 34 wherein said alpha zirconium alloy is selected from the group consisting of Zircaloy-2 and Zircaloy-4.

38. The process according to claim 35 wherein said alpha zirconium alloy is selected from the group consisting of Zircaloy-2 and Zircaloy-4.

39. The process according to claim 36 wherein said alpha zirconium alloy is selected from the group consisting of Zircaloy-2 and Zircaloy-4.

40. A process for alpha annealing cold worked Zircaloy tubing comprising the steps of:
scanning a cold worked Zircaloy tube with a rapid heating means for raising said Zircaloy to an elevated temperature;
upon attaining said elevated temperature immediately beginning cooling of said Zircaloy;
said process producing an alpha annealed microstructure.

41. The process according to claim 40 wherein said rapid heating means raises the Zircaloy to the elevated tempera-ture within about on-third of a second.

42. The process according to claim 40 wherein said alpha annealed microstructure is a partially recrystallized microstructure.

43. The process according to claim 40 wherein said alpha annealed microstructure is a fully recrystallized microstructure.

44. The process according to claim 41 wherein said alpha annealed microstructure is a partially recrystallized microstructure.

32 48,331

45. The process according to claim 41 wherein said alpha annealed microstructure is a fully recrystallized microstructure.

46. The process according to claim 40 further comprising the steps of:
further cold working the alpha annealed tube;
and then alpha annealing the further cold worked tube.

47. The process according to claim 41 further comprising the steps of:
further cold working the alpha annealed tube;
and then alpha annealing the further cold worked tube.

48. The process according to claim 43 further comprising the steps of:
further cold working the alpha annealed tube;
and then alpha annealing the further cold worked tube.

49. The process according to claim 45 further comprising the steps of:
further cold working the alpha annealed tube;
and then alpha annealing the further cold worked tube.

50. A Zircaloy alloy body comprising:
a major surface of said body;
a region of microstructure within said body and adjacent said major surface having a precipitate size and a precipitate distribution typical of conventionally alpha worked Zircaloy;
wherein said region of microstructure has an alpha worked anisotropic crystallographic texture;
and wherein said major surface is resistant to nodular type corrosion and is characterized by an adherent substantially black continuous oxide film upon 24 hours exposure to 500°C, 1500 psi steam.

51. The Zircaloy alloy body according to claim 50 wherein said region of microstructure is characteristic of the microstructure throughout said body.