US3476614A - Ductility of dispersed phase alloys,particularly al-al2o3 - Google Patents

Description

United States Patent US. Cl. 148-11.5 12 Claims ABSTRACT OF THE DISCLOSURE The ductility of dispersed phase alloys, more particularly Al-Al O is improved by a process wherein an ingot is produced by spraying the dispersed phase alloy powder or wire onto a base (basis) body at a temperature of at least 800 C. and wherein the thus obtained billet is submitted to degassing and oxide stabilization at a temperature of about 550-625 C. in a vacuum furnace (10 to 10 mm. Hg) for from to 30 hours. The billet is then ready for fabrication into finished products. Normally the billet is removed from the base body before it is submitted to mechanical working, but in some cases the mechanical working is effected without removing the billet from the base body.

This invention relates to a process for improving ductility of metal-oxide composite materials or dispersed phase alloys and specially concerns aluminum-alumina composite material.

As it is known, the aluminum-alumina composite material generally used is sintered Al-Al O a metallurgical composite of the dispersed phase alloy type, Which offers multiple advantages for various purposes, such as for example, canning material for fuel elements of certain types of nuclear reactors.

This material is prepared principally in the following way: a powder of aluminum is partially oxidized to A1 0 The part of weight of A1 0 in the oxidized powder can vary from 2% to 20%. The oxidized powder is first cold compacted and then sintered to form an ingot or billet.

Preferably, before sintering, the compacted powder is degassed; the sintered ingot or billet is then metallurgically processed, by way of at least one extruding process, in order to achieve the needed properties of a semi-finished or finished product.

Within the scope of manufacturing nuclear fuel elements cladding using this Al'Al O material, it is now well known that this material possesses good mechanical characteristics of thermal resistance, which were also proved by means of long term tests.

However its use is actually limited to the manufacture of fuel elements cladding in the form of a self-resistant rigid can because of the lack of creep ductility which this material shows.

By way of example, tensile and creep tests carried out at 450 C. with specimens of sintered Al-Al O yield the following mean values.

Example 1.-Extruded bars of sintered Al--Al O;, containing 4% alumina Tensile tests (fast traction) Ultimate tensile strength: R=6 kg./mm.

Patented Nov. 4, 1969 ICC 0.2% yield limit (strength): S =5.5 kg./mm. Total elongation percent (5 diameters): A =6% Creep tests at 1000 h.

Rupture stress a 4 kgJmm.

Total elongation percent (5 diameters) A, 0.5%

Example 2.--Extruded bars of sintered Al-AI O containing 7% alumina Tensile tests (fast traction) Ultimate tensile strength: -R=8 kg./mm. 0.2% yield limit (strength): 8 :7 kg./mm. Total elongation percent (5 diameters): A =4% Creep tests at 1000 h.

Rupture stress :7 5 kgJmm.

Total elongation percent (5 diameters) A5 0.7%

The elongation before rupture is about 0.5%.

Example 3.-Extruded helical finned tubes of sintered Al-Al O containing 7% alumina Tensile tests (fast traction) Ultimate tensile strength: R=8.5 kg./mm. Total elongation percent (5 diameters): A =4% Burst test Bursting stress: a-=7 kg./mm.

The value of elongation at rupture A which generally is less than 1% for Al-AlgOg materials of different oxide content too, is very representative of the very low creep ductility of the material.

Hence the interest of improving this creep ductility accompanied nevertheless by the aforesaid good mechanical properties, as far as the use of this material for nuclear purpose is concerned, in order to make from this material fuel element claddings, the claddings having the form and properties of resistant and ductile sheaths.

We have found that composite material Al-Al O containing from 2% to 20% of weight of alumina, of improved ductility, principally creep ductility, is obtained by a process which, according to the present invention, is characterized in that an ingot or billet. is produced from Al-Al O -powder or -wire by metal-projection or spraying of the same onto a basis body, and that the billet is then submitted to metallurgical transformation, by mechanical working in order to achieve the final mechanical properties for semi-finished or finished products. Use can be made of oxidized powders A1-Al O or alternatively of semi-finished sintered hot compacted composite material Al-Al O the latter being previously reduced from the original diameter of a bar or an ingot or a billet to fires of a small diameter by way of wire-extrusion and following wire-drawin operations.

The diameter size of the wires obtained from ingots, the diameter of which is normally comprised between 70 and 20 mm., to be used for the metal projection is comprised between 1 and 10 mm.

The metal projection is carried out at a distance varying from 50 mm. to 250 mm. from the basis body.

The projection direction can vary from perpendicular to parallel with respect to the bodys axis, the parallel direction being preferred.

The projection should be executed at a temperature of about at least 800 C. and within strictly limited projection periods of some seconds, or preferably less than one second.

The prepared billet is to be submitted to thermal degassing and oxide stabilization in a vacuum furnace.

These operations should be eflected at temperatures varying from 550 C. to 625 C., at a residual pressure comprised between 10 and 10 mm. Hg, for periods of 10 to 30 hours, preferably of 20 to 24 hours.

The semi-finished or finished products, as bars, smooth or finned clads (with right or straight or helicoidal fins) are particularly obtained by metallurgical operations as known for usual production, comprising for instance extrusion and eventually drawing with intermediate annealing.

In order that the invention may be more readily understood, four specific embodiments of the same will now be described by way of example.

Embodiments 1 and 2.-4% Al-Al O 7% Al-Al O A first ingot or billet of sintered AlAl O material with 4% r 7% of alumina, obtained by normal fabrication, having a diameter of 70 mm. was wire-extruded at a temperature of about 570 C. through a die to obtain mm. diameter bars and then these bars were wire-drawn at room-temperature to provide in 3 or 4 runs 3 mm. diameter Wires.

These wires were projected by means of a metallising gun (Mark Metco) to create a new billet.

The metal projection was effected at the following operating conditions:

Oxygen (O flow rate 50 liters/minute.

Acetylene flow rate 50 liters/minute. Compressed air pressure 4.5 kg./cm.

Projection distance About 100 mm.

Projection direction At a right angle to the axis of the billet in preparation.

The projection operation was stopped when a billet had been obtained with a thickness of about 2 cm. sufiicent to permit its working by means of a lathe in order to obtain an entirely cylindrical surface.

After this cylindrical turning or grinding the projection operation was pursued until a billet of about 70 mm. diameter was obtained. This billet was turned on a lathe to a diameter of 68.4 mm. and then degassed in a furnace under high vacuum, namely of 10- mm. Hg, by heating at a temperature of 600 C. during 20 hours.

The degassed billet was then extruded through a die at 520 C. to provide 20 mm. diameter bars.

The extrusion data were:

Container diameter: 70 mm. Container temperature: 500 C. Die temperature: 480 C. Extrusion ratio: 12.3

Extrusion speed: 7.38 m./min.

In the case of 4% Al-Al O the tensile and creep tests were carried out at 450 C. to yield the following average values:

Tensile test (fast traction) Ultimate tensile strength: R=6 kg./mm. 0.2% yield limit (Strength); S =5.5 kg./mm.

Total elongation percent (5 diameters): A =15% Creep test at 1000 h.

Rupture stress e 4 IrgJJzmn.

Total elongation percent (5 diameters) A5 15% It can be seen from these results that thermal resistance characteristics are maintained at aforesaid values While the creep and tensile ductilities become much higher, especially the creep ductility value A is increased from less than 1% to about 15%.

In the case of 7% Al-Al 0 the creep tests were carried out at 450 C. to yield the following average values:

Creep test at 1000 h.

Rupture stress a 6.2 kg.lmm.a

Total elongation percent (4 diameters) A6 z 4.5%

It can be seen from these results that thermal resistance characteristics are maintained at the aforesaid values, while the creep ductility increases considerably, namely from less than 1% to about 4.5%.

Embodiment 3.(7% Al-AI O projected on Al-tube) The transformation of the basis material into wire, and the operating conditions during metal projection are the same as described'above for the first and second embodiment of the invention. But instead of projecting on a massive billet core (a bar rotating at 10/ .70 rev/min.) projection was carried out on a rotating Al-tube (10/ .70 rev./min.) until a billet of about 70 mm. outer diameter was obtained. This billet was turned then on a lathe to provide a 68.4 mm. outer diameter by a 25.75 mm. inner diameter. Further, this billet was degassed in a vacuum furnace (10* mm. Hg) at a temperature of 600 C. during 20 hours.

The degassed billet tube was then extruded through a die at 575 C. to deliver a helical finned tube.

The extrusion data were:

Container diameter: 70 mm. Container temperature: 550 C. Die temperature: 540 C. Extrusion ratio: 25

Extrusion speed: 25 m./min.

The mechanical tests were carried out at 450 C. to yield the following average values:

Tensile test (fast traction) Ultimate tensile strength: R=9 kg./mm.

Total elongation percent (5 diameters): A =4% Rapid (fast) burst test at 450 C.: Bursting stress o'=8 kg./mm.

Embodiment 4.(7% Al'Algoa projected in parallel to the billets axis) Also in this case, the wire-extrusion and the operating conditions during projecting correspond to the above quoted data. But whereas in the case of the first three embodiments of the invention, projection was carried out perpendicularly to the billets axis, this time, projection was carried out more or less in parallel to said axis onto a disc rotating at 30 rev./min. In that way, a massive billet was prepared of 70 mm. diameter and 120 mm. of length. The billet was turned down on a lathe to 68.4 mm. diameter and mm. of length. Then the billet Was degassed in the same way as described for the other cases.

Likewise, the transformation of the billet into a bar of 20 mm. diameter was carried out according to the data listed above for the embodiments 1 and 2.

Creep tests were carried out then at 450 C., which yielded the following average values:

Creep test (at 300 h.)

Rupture stress =53 lrgJmm.

Total elongation percent diameters) A :4%

The elongation before rupture was about 2.5%.

It can be seen from these results, that also in the case of the third and fourth embodiments of the invention, the thermal resistance characteristics of the material are preserved, while the creep ductility becomes much higher.

What we claim is:

1. A method for producing dispersed phase alloys of improved ductility composed of a metal and an oxide of that metal, said process comprising pulverizing the metal, partially oxidizing the resultant powder, metal-spraying the partially oxidized product on a basis body, said spraying being carried out at a distance varying from 50 mm. to 250 mm. from the basis body at a temperature of at least 800 C. with time of flight periods of not more than a few seconds thereby providing a billet, removing said billet from the body, and then submitting said billet to mechanical working in order to obtain the final mechanical properties of the semi-finished or finished product.

2. The method of claim 1, wherein the basis body is rotated during the metal projection operation and the projection direction is perpendicular or oblique to the rotating surface of the body.

3. The method of claim 2, wherein the billet is submitted to thermal degassing and oxide stabilization in a vacuum furnace.

4. The method of claim 3, Wherein degassing and oxide stabilization is effected between 550 and 625 C. at a pressure between and 10- mm. Hg for periods of 10-30 hours.

5. A method for producing dispersed phase alloys of improved ductility and composed of a metal and oxide of that metal comprising pulverizing the metal, partially oxidizing the resultant powder, cold pressing the oxidized powder, subjecting the compressed powder to a sintering and a vacuum heat treatment, hot pressing the material to form a billet, reducing said billet to wire by wire-extrusion and a wire-drawing, metal-spraying said wires on a basis body, said spraying being carried out at a distance varying from 50 mm. to 250 mm. from the basis body at a temperature of at least 800 C. with time of flight periods of not more than a few seconds thereby providing a billet, removing said billet from the body, and then submitting said billet to mechanical working in order to obtain the final mechanical properties of the semi-finished or finished product.

6. The method of claim 5, wherein the basis body is rotated during the metal projection operation and the projection direction is perpendicular or oblique to the rotating surface of the body.

7. The method of claim 5, wherein the billet is submitted to thermal degassing and oxide stabilization in a vacuum furnace.

8. The method of claim 7, wherein degassing and oxide stabilization is efiected between 550 and 6-25 C. at a pressure between 10* and 10* mm. Hg for periods of 10'.30 hours.

9. A process for producing dispersed phase alloys of improved-ductility which comprises mixing A1 powder and A1 0 powder, metal spraying the Al-Al O mixture upon a basis body, said spraying being carried out at a distance of from 50 mm. to 250 mm. from the basis body, at a temperature of a least 800 C., with time of flight periods of not more than a few seconds, thereby producing an alloy billet, stripping said billet from said body, heating said billet to a temperature of 550 C. to 625 C. at a pressure between 10'- and 10- mm. Hg for from 10 to 30 hours to degassify and stabilize the alloy thereof, and then mechanically working said billet to develop the mechanical properties of a semi-finished or finished product.

10. A method according to claim 9, wherein the metal oxide content of the mixture is from 2 to 20% by weight.

11. A method according to claim 1, wherein the alloy is Al-Al O and the A1 0 content is from 2 to 20% by weight.

12. A method according to claim 5, wherein the alloy is Al-Al O and the A1 0 content is from 2 to 20% by weight.

References Cited UNITED STATES PATENTS 3/1961 White et al. 117105.2 6/1961 Kubera et al. 29528 US. Cl. X.R.