US3685988A

US3685988A - Beryllium alloy

Info

Publication number: US3685988A
Application number: US863327A
Authority: US
Inventors: Jean-Mathieu Frenkel; Jean-Marie Logerot; Pierre Petrequin; Robert Syre; Michel Weisz
Original assignee: Trefimetaux GP
Current assignee: Trefimetaux GP
Priority date: 1968-10-09
Filing date: 1969-10-02
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22
Also published as: DE1950973B2; LU59590A1; NL6914827A; DE1950973A1; FR1585351A; AT291609B; BE740005A

Abstract

THE ALLOY IS PREPARED BY ADDING TO THE BERYLLIUM 0.05% TO 3% BY WEIGHT OF CALCIUM AND 0.15 TO 3% BY WEIGHT OF AT LEAST ONE ADDITION METAL SELECTED FROM THE GROUP COMPRISING IRON, PALLADIUM, GOLD, PLATINUM, IRIDIUM, RHODIUM, THE REMAINDER BEING ESSENTIALLY CONSTITUTED BY BERLLIUM, THE PRODUCT OBTAINED BEING SUBJECTED TO A HEAT TREATMENT OF 1 TO 10 HOURS AT 750-1000*C. FOLLOWED BY TEMPERING FOR A PERIOD OF 10 TO 200 HOURS AT 500-700*C.

Description

United Smtes Patent 3,685,988 Patented Aug. 22, 1972 3,685,988 BERYLLIUM ALLOY Jean-Mathieu Frenkel, Paris, Jean-Marie Logerot, Neuilly, Pierre Petrequin, Villebon-sur-Yvette, Robert Syre, Louveclennes, and Michel Weisz, Orsay, France, assignors t Societe Trefimetaux G.P., Paris, France No Drawing. Filed Oct. 2, 1969, Ser. No. 863,327 Claims prority, appliittgioslgfrance, Oct. 9, 1968,

Int. (:1. 6m 25/00 US. Cl. 75-150 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a novel beryllium alloy which is intended for use at high temperature in an oxidizing atmosphere. This novel alloy is particularly suited for use in the hot zones of nuclear reactors in which the removal of heat is carried out by circulation of carbon dioxide gas. The structural elements of a reactor of this type are subjected to the eflects of elevated temperature, of mechanical stresses, of corrosion by carbon dioxide gas and of neutron bombardment.

The alloys which have been proposed up to the present time do not prove wholly satisfactory. For example, the binary alloy which contains 0.05% to 3% calcium as described in French Pat. No. 1,307,236 granted to Associated Electrical Industries on Dec. 1, 1961, exhibits satisfactory behavior in carbon dioxide gas up to 700 C. but reveals in the first place that an improvement in the mechanical properties and creep strength at high temperatures would be desirable and in the second place that it is rapidly embrittled under the action of neutrons.

As a result of the researches carried out by the present applicant, the mechanical properties both at ordinary temperature and at high temperature as well as the creep characteristics of a beryllium-calcium alloy can be appreciably improved by the addition of a predetermined quantity of iron, palladium and also of gold, platinum, iridium and rhodium. Resistance to the corrosive action of carbon dioxide gases on these novel alloys is not affected by the presence of the addition element, whereas this is not the case of the alloys of the prior art, even when other addition elements are present as in the case of alloys which contain both calcium and zirconium, e.g. those described in French Pat. No. 1,326,909 granted to Associated Electrical Industries on June 27, 1962.

A micrography of a beryllium alloy containing either one or a number of the addition elements mentioned above shows a large number of intermetallic precipitates whose presence within the matrix explains the hardening effect which is obtained.

Embrittlement of beryllium and beryllium alloys under exposure to radiation is caused by gases (mainly helium) which are generated in the metal under the action of neutrons according to the following reactions:

The gas atoms which initially occupy positions adjacent to those of the beryllium atoms from which they are derived migrate and finally collect in the form of bubbles in the grain boundaries and also in the matrix. Under the action of the mechanical or thermal stresses to which the part is subjected in service and if the temperature is of a high order, the bubbles of the grain boundaries will increase in size as a result of creation of lattice vacancies and will result in total decohesion of the boundaries.

It is clearly not possible to prevent the formation of these gases; on the other hand, it is possible to modify the speed at which said gases migrate and to delay the moment at which the quantity of gases which collect at the grain boundaries becomes hazardous.

One of the objects of this invention is to provide a means for obtaining this result. The present applicant has in fact found that the intermetallic precipitates set up an obstacle to the motion of gas bubbles within the irradiated beryllium matrix. Moreover, said precipitates are correspondingly more eifective as they have a smaller grain size, are more numerous and more uniformly distributed.

The alloys in accordance with the invention can be fabricated by means of known powder metallurgy techniques, the powder being obtained by comminution of flakes obtained by lathe turning of cast ingots. Said ingots can be fabricated from a metal which may or may not have been electrolytically produced. However, a preferred method of fabrication consists of vacuum melting followed by direct conversion of the ingot by extrusion, forging or rolling.

The tables given 'below show by way of example the properties of some of the alloys which are prepared in accordance with the invention in comparison with those of alloys which are already known. All these alloys have been prepared from electrolytic beryllium. The alloys A, B, C are not in accordance with the invention; metal A has been obtained by powder metallurgy and is sintered beryllium. Metal B is an alloy containing 0.4% Ca in accordance with French Pat. No. 1,307,236; C is an alloy containing 0.4% Ca and 0.2% Zr in accordance with French Pat. No. 1,326,909.

Alloys D and E are in accordance with the present invention: the alloy D contains 0.4% Ca and 0.5% Pd; the alloy E contains 0.4% Ca and 0.2% Fe.

All these alloys except A have been fabricated by vacuum melting in an induction furnace of a mixture of electrolytically produced beryllium flakes and of previously prepared master alloys Be-Ca, Be-Fe, Be-Pd. The cast billets thus obtained were then converted to round rods by press extrusion.

Iron is an inevitable impurity of beryllium and particularly of sintered products since the attrition mills are mostly constructed of steel. However, the iron content does not usually exceed 300 p.p.m. in the case of electrolytically produced flakes, 800 p.p.m. in the case of the powder obtained from these flakes and 1500 p.p.m. in the case of a powder obtained from a metal prepared by the magnesiothermic reduction process.

The proportions of iron contained in alloys E and F are distinctly higher than these values as a result of an intentional addition.

Table I gives the ultimate strengths and the elongations at fracture of alloys D and E in the extruded state and annealed (one hour at 800 C.) in respect of different temperatures. Very closely related values have been obtained in the as-extruded state, in the stabilized state (500 hrs. at 575 C.), in the hardened and tempered state. The additions of Pd and Fe increase the ultimate strengths of the 0.4% Ca alloy to a greater extent than is achieved by the addition of Zr and the same applies 4 to An, Pt, Ir, Rh. It is possible to obtain even higher of mechanical testing is adopted for the purpose of detertensile strength properties by increasing the quantity of mining the degree of embrittlement as a result of neutron Fe, Pd, and so forth which is introduced; however, beirradiation: yond a total quantity of 3% of these elements, the high- Metal irradiated at a dose of 5X10 n.v.t. (total time temperature conversion of the alloy becomes very difr integrated flux) at 650 C. ficult. J Maintaining an imposed deformation which produces TABLE I an initial stress equal to the elastic limit of the metal; Ultimate the test temperature is higher than 600 C. Alloy extruded and strength in Elongation at fracture in Aflter the stress has been reheved, a further deforma a a d State J 20 mm- (p w tron 1s applied in order that the elastic limit may again Various b6 attained. pe percent The load cycles referred-to above are continued until 0.4 24/40 18/655 125/55 94/100 /130 failure of the test sample occurs. The number of cycles 8:: 8:; 2%? 1- up to fallure indicates the degree of embrittlement of the 0.4 0.2 Fe 28. 5 21 25/32 21/20 1/0205 9.6/34 15 ll'rfldlatefl Beryllium alloyed with 0.4% Ca and contalmng a small Table II shows the superiority of the alloys in accordproportion of precipitable elements is capable of withance with the invention over non-alloyed sintered berylstanding only one cycle. lium and a binary beryllium-calcium alloy in regard to Beryllium alloyed with 0.4% Ca containing 1600 ppm. creep h t i ti of iron is capable of withstanding 5 cycles prior to failure.

The present applicant has also found that, after a heat This test clearly demonstrates the advantage of additreatment which consists in dissolving at a relatively low tion elements which give rise to finegrained intermetallic temperature (750 C. to 950 C.) for a period of a few precipitates inasmuch as these latter inhibit the coalescence hours followed by tempering for a few tens of hours at of helium in the form of bubbles which are liable to 500-700 C., the alloy exhibits a relatively fine grain result in fracture.

structure and the distribution of the intermetallic pre- What we claim is: cipitates is remarkably fine and homogeneous. 1. A beryllium alloy containing 0.05% to 3% by TABLE II Alloy Extruded and annealed state Ca Various Stationary creep rate percent percent (10 percent/hr.) Total elongation in 100 hrs.

A 20/- 20/ 6.3/ 12. 5/ 17.2/ 9.4/- B 0.4 22/ 50/ 6. M Very rapid D 0. 4 0.5 Pd 19. 5/0. 26 6. 5/0. 07 3. 2/0. 03 78/0. 8 3. 9/0 0 /0. 7 39 0. b E 0. 4 0.2 Fe 14. 3/0. 16 3. 9/0. 05 1. 9/0. 02 0. 4/0. 13 2. 6/0 02 3. 0/0. 00 1. 0/0. 01

Test stress in kgx/mrn. 15 12 10 5 2. 5 2 1. 5

Test temperature in C 400 500 600 Table III gives a few of the values which have been weight of calcium and 0.15 3% by weight of at least foulldlll respect f grain SiZe, number and SlZe P grams 0f one addition metal selected from the group comprising precipitate per unit of volume as compared with the best 4 iron, n di m, gold, platinum iridium rhodium the a 1 o 3 J 3 values obtamed the case of the bmary Be ca alloy remainder being essentially constituted by beryllium.

under identical conditions of extrusion.

Further experiments have served to demonstrate that An alloy accordance Wlth clalm rem the this heat treatment did not aiiect either the mechanical Proportion of calcium is Within the a g Of 0.3 to 0.8%

properties described earlier or the behavior of the alloy in y g tcarbon di id gas, 3. An alloy in accordance with claim 1 wherein the TABLE III Alloys Precipitates Grain Ca Various size Number! Size percent percent Heat treatment mm.

, 120 Small 10-30 0.4 1 hr. 800 C -80 Small 10-30 0.4 0.2 Fe 1 hr. 800 0., oil h del Hg plus 24 hrs 00 0. 1 90 10 w 0.1-0.2 0.4 0.2 Fe 1 hr. 800 0., oil hardening plus 200 hrs. 600 C 00 10 D 0.10.2 0.4 0.2 Fe 1 hr. 800 C. plus 5 hrs. 700 C 00 10 6 o. a

1 Numerous sub-grains.

Several thousand hours of continuous service at opproportion of said addition metal is within the range crating temperatures of heavy-water moderated gas-cooled of 0.15 to 1% by weight. reactors, namely 550650 0, having not substantially 4. An alloy in accordance with claim 1 comprising modified either the density or the dimensions of these inter- 0.15 to 0.5% by weight of iron. metallic precipitates. 5. An alloy in accordance with claim 1 comprising The irradiation behavior of the alloys in accordance 70 0.2 to 1% by weight of palladium. with the invention has been studied. 6. An alloy in accordance with claim 2 wherein the 'Embrittlement of irradiated beryllium at high temperproportion of said additional metal is Within the range ature is mainly exhibited at the time of application of of 0.15 to 1% by weight. a stress which causes an increase in size of the helium 7. An alloy in accordance with claim 2 comprising bubbles within the grain boundaries. The following method 0.15 to 0.5% by weight of iron.

6 8. An alloy in accordance with claim 2 comprising 0.2 FOREIGN PATENTS to 1% by welght of Palladlum- 1,146,452 3/1969 Great Britain 75-150 References Cited L. DEWAYNE RUTLEDGE, Primary Examiner UNITED STATES PATENTS 5 E. L. WEISE, Assistant Examiner 3,145,098 8/1964 Raine et a1. -1 75-150 US. (:1. X.R.

3,169,059 2/1965 Raine et a]. 75-150 17691