US3408710A - Process for the manufacture of beryllium products - Google Patents

Description

3,408,710 aw liar-s 1 9 Un St tes, a en f 51,89 3 Claims. (Cl. 29-423) ABSTRACT F DlSCLOS URE A cast beryllium ingot is covered with a thin soft steel coating; compressed at 800 Q; extruded at about 900 (2.; covered with a thick soft steel envelope; and forged.

After heating to 1000" C. the'ingot is compressed and the steel cover removed. The billet maybe coated'with silver and then extruded at 900 C.

The present invention relates to improvements in processes for the manufacture of beryllium products as used particularly in the fields of aviation, astronautics and atomic energy.

The invention is concerned more particularly with processes for the manufacture of beryllium tubes, and more particularly tubes suitable for casing the fuel elements of nuclear reactors.

Since the beginning of the use of beryllium in aircraft, and then for spacecraft, and finally as a nuclear material, for which fields it is particularly suitable by virtue of its remarkable properties, the desired beryllium products have been produced from billets or blooms of sintered beryllium. Only some parts of simple shape, such as sheets, have been obtainable from cast metal, and in addition it has been necessary to proceed with a grain refinement in order that this material may have acceptable mechanical characteristics.

In the past attempts have been made to improve the ductility of beryllium tubes and for this reason recourse has been had to powder metallurgy for the manufacture of such tubes, the sintered metal having a much finer grain than the cast metal, and also much higher longitudinal ductility, at ambient temperature.

The present invention relates to a process for the preparation of beryllium products and particularly tubes, which more fully satisfies than hitherto the various practical requirements, notably by virtue of the fact that it makes it possible to obtain a less fragile product of more favourable texture in the sense that it conforms to the following two characteristics:

(1) The base planes of the elemental crystallites are for the greater part disposed in parallel relationship to the extruding direction,

(2) The maximum angular distribution of these planes is located in the tangential direction.

For this purpose, the process according to the invention consists mainly-while using a cast beryllium ingot as starting material, optically subjected to compressionin subjecting it, in the course of its shaping, to at least one hot working operation followed by a forging, notably in a press, optionally .under a thick steel casing, and by at least one further extrusion performed after removal of the casing, when necessary.

Apart from this main feature, the invention further comprises other features which are preferably used at the same time, considered separately or in all the technical possible combinations:

(a) The said hot working operation consists in an extrusion in a casing, which casing may consist of soft steel, and

(one s anqeam ion as use! trusionftlie metal being, coated with l a t r. 'of silver. In any case, it will be more'readilypn erstood'frorn the following further descriptionandfrorn eflfollowiiig examples, whichfurther descriptioii' andsex rrjples are 1 of course, given only by way of example-I and ha ing character, z r

The use of cast'metal as starting 'ni terial, ins iadof sintered ,metafas isusliah'isla feat i .th'e ,pr e vention, because if is found th hot wdrked cast met al issubstantially' free. from .hot "fragi 'ty, that its. texture .is more favourablelthan that of h0tfW l diutered m ta), that the maintenance at ademperatureof 600 fror'long periods is", beneficial to? hot .wor p hue "being harmful to hotjwofk d .sintei edf met radiographs of inclusions liaye 're vealedIhighrff cl ness of the hot worked metaliajnd finally'that its presentation'and its surface appearance do not appear to' be so good, it is ets subject to defects Silents intergranular microcra'cks, which are, harmful to transverse ductility in the case of tubes. I I The following table shows a comparison of the longitudinal and transverse ductilities in the 'case of ingots of sintered and cast beryllium.

Minimum temperature for an elongation oi 10% 4 Longitudinal Transverse Since the transverse ductility is much greater than the longitudinal ductility in the case of tubes, notabl for casings, the superiority of cast beryllium will be seen from this table.

After the choice of the cast metal, the choice of the hot working operation acts as a second factor. Methods as different as impact extrusion and the conventional cased extrusion technique may be employed, 'this second method, however, giving tubes of greater length and greater homogeneity.

It is found that a further means of improing the transverse ductility D is to vary the angular distribution of the base planes. If these are radially disposed (as in the case of a tube), longitudinal fissures will tend to appear and cleavage will be facilitated.

Attempts have been made to produce tubes having a texture characterised by the following points:

(1) The base planes of the elemental crystallites disposed for the greater part in parallel relationship to the extruding direction, and

(2) Maximum angular distribution of these planes in the tangential direction.

There will therefore be given in the following an example of the production of beryllium tubes by the process according to the present invention.

Example A cast metal cylinder is coated with a thin layer of soft steel 2 mm. thick. The whole is compressed at 800 C., and then extruded at about 900 C. with a cold working degree of 6. A bar 40 mm. in diameter is obtained, from which a billet is sliced.

This billet is disposed in a soft-steel envelope 10 mm. thick and will be subjected to the forging operation. After heating to about 1000 C., the billet together with its envelope is compressed in the press along its axis so as to bring its height from the value H to the value h.

The extent of deformation thus obtained is:

f i .3? :2 Ema-e55 i l q "fhe billet time thus deformed is thereafter freed from a thin layer cg soft steel then subjectingsaid eqategl ingot it's steelerivlofiefniachinegl, 'di'illed 'ah dfoated witl'fa thin silver layer. e fisst d, atabwt 9 to l'j Theubes hu obtainedfhave fi t r, c. a (A mar 'th e'ii ioq sfinino,w x f,v @"SaeHrjagspH a'uQn ig' hich lIas ju's t been referredtoif nor the embodiment described by way of examplef, but

covers alhyaiiarits thereof, and notably the production of beryllium products from cast'frnetal, not'o'n'ly fqr nuclear uses but also for the requirements of aviation and ast'ronautics.

What we claim is: 1.- In a process for the manufacture of beryllium prod- 'ucts, the steps'of coating an ingot of cast beryllium with to'co rn ir'es sion at about 80Q C, then subjecting s'aid' iiig'ot in the course of shaping toj'at least one hot working operation at about 900 C., then applying a. thick steel casing to said ingot, then rforging, said ingot at about 1000 C. in 'a press, thengr'moying said thick easingwnu then d g tto' at least onefurthe SS W 1i UN ???r TTl fP "I 5 41:2211 wsoa var 1 1/1963 Reichl twists-twir OTHER REFERENCES Space Age Materials Extruded byNew Techniques, by

laul ,Loyyenstein, in The Tool and Manufacturing Ens a srin avl 945 91 fiaM 6 PP