US3218162A - Process for making zirconium alloys - Google Patents

Description

nited States The present application is a continuation-in-part of patent application Serial No. 33,907, filed June 6, 1960, by the same applicants, and now abandoned.

This invention relates to alloys suitable, inter alia, f r use at high temperatures in an atmosphere of carbon dioxide.

Consideration has been given to the use of alloys of zirconium as structural materials within the cores of graphite-moderated carbon dioxide-cooled nuclear reactors.

Alloys of zirconium with copper and/ or chromium and molybdenum having adequate resistance to creep and with good corrosion resistance up to temperatures of the order of 525 C. have been developed as described in US. Patent No. 2,924,518, filed by us on July 17, 1958, and assigned to Metropolitan-Vickers Electrical Co. Ltd.

It has now been discovered that if tungsten is added to a zirconium-copper alloy, the corrosion resistance properties are further enhanced.

An alloy according to the invention consists of from 0.5% to 1.5%, by weight, of copper, from 0.25% to 1.5% by weight of tungsten with the remainder zirconium, except for impurities as may be unavoidably present. Such impurities may arise from their inclusion in sponge zirconium from which the zirconium content of the alloy is derived.

Examples of preferred alloys within the range of constituents covered by the invention are as follows:

(a) Copper 0.5%, tungsten 0.5 remainder zirconium. (b) Copper 1.5%, tungsten 1.0%, remainder zirconium.

The resistance to corrosion by carbon dioxide of alloys given by the above examples may be judged by the gain in weight of the alloy when in contact with carbon dioxide for an extended period at an elevated temperature. Weight gain of the alloys exemplified, compared with the weight gains under the same conditions of zirconium, the alloy known as Zircaloy-Z and consisting of 13-16% tin, 0.07- 0.2% iron, 0.050.l% chromium and 0.030.08% nickel; an alloy of zirconium with 0.5% copper and 0.5% molybdenum, and an alloy of Zirconium with 1.0% copper and 1.5% molybdenum are given in the following table:

Exposure to C 0 at atmospheric pressure and 700 C.

If this exposure is increased to 1200 hours, the gain in weight of alloy (a) increases to 11.5 mg./cm. while the gain in Weight for the alloy containing 0.5 copper and 0.5 molybdenum increases to 25 mg./cm. In the same conditions, the gain in weight for alloy (b) is only 7.6 mg./cm.

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The alloys (a) and (b) have thus appreciably higher corrosion resistance in CO than the zirconium-coppermolybdenum alloys, and alloy (b) has even superior resistance to alloy (a). Both alloys (a) and (b) have a much greater resistance to corrosion than Zircaloy-2.

For the zirconium-copper-tungsten alloys of the invention to exhibit the enhanced corrosion resistance desired, it is essential for the alloys to be homogenous and threephase. In the event that the tungsten is permitted, during production, to segregate in the zirconium, and this may happen as a result of the widely difiering melting temperature of zirconium ('1600 C.) and tungsten (300O C.), corrosion may well occur at those parts of the alloy where the segregated tungsten is exposed to the action of heated carbon dioxide with the resulting formation of olive-greencoloured oxide blisters.

In order to obtain the required ternary alloy of the invention, it is essential to proceed in the following manner. An alloy of tungsten and copper containing approximately equal proportions, by weight, is first prepared by compacting an intimate mixture of powdered copper and powdered tungsten, and then sintering the mixture. The proportions of the mixture may be varied when it is desired that the final alloy contains other than equal proportions of the alloying ingredients. The sintered alloy is then melted in a non-consumable electrode argon arc furnace by heating to a temperature between 1200 C. and 1600 C. with zirconium to give a master alloy containing approximately 18% copper, and 18% tungsten, by weight. This master alloy is again melted and then diluted by the addition of further amounts of zirconium to make the alloys in the required range. The resultant alloys are homogeneous and three-phase.

By the multiple melting process above described, the coppertungsten master alloy initially produced is progressively diluted with the zirconium, and the segregation of the tungsten thereby avoided.

What we claim is:

The process of manufacturing a ternary alloy of zirconium with from 0.5 to 1.5%, by Weight, of copper, and from 0.25% to 1.5%, by weight, of tungsten, which comprises intimately mixing substantially equal proportions, by Weight, of powdered copper and powdered tungsten, sintering said mixture, melting said sintered mixture and adding zirconium to form a master alloy of copper, tungsten and zirconium, and melting a required proportion of said master alloy with additional zirconium in order to obtain a homogeneous ternary alloy.

References Cited by the Examiner UNITED STATES PATENTS 2,030,229 2/1936 Schwarzkoff 177 X 2,813,073 11/1957 Saller et a1 75177 X 2,924,518 2/1960 Raine et al. 75-177 2,932,887 4/1960 McCuaig et al. 75l77 X FOREIGN PATENTS 488,322 7/ 1938 Great Britain.

OTHER REFERENCES AECU 3561, Scaling of Zirconium and Zirconium Alloys, US. Atomic Energy Comm, August 1957 (page 12 relied upon).

DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.