Method of Joining Graphite and Metallic Material With a Material Comprising Titanium, Nickel and Copper

The present invention relates to a material for joining graphite and metallic material, and to a method of joining them.

More particularly, the present invention relates to a joining material of general graphite material (neuclear reactor class, for electrode, specific graphite material) and general metallic material (particularly, refractory material, reactor material, good thermal conductive material), which can be used as a structual material and a portion thereof in a field of ordinary temperature and specific high temperature, and to a joining method using the same.

As a prior art of joining of graphite and metal, a technique using graphite/copper (Lloyd O. Lindquist and Richard MAH.: LA-6928-MS, (1977) ), graphite/molybdenum (M. Fukutomi, et al: J. of Nuclear Materials, 128 and 129, 908 (1984) ) and others has been known, but there has been no such instance as joining of graphite and various alloys as SUS, Hastelloy, Incolloy and Inconel systems. Further, even in the above described joining cases, the joining of graphite to a large scale of base material has been often impossible because the melting temperature of joining material is so high that the material is degenerated at the joining time and a crack is produced due to the great difference between graphite and metal in thermal expansion and also because the joining condition is special. Numerous problems they are present to overcome for practical use of the joining method.

An object of the present invention is to provide a joining material used in a technique for protecting a structural rerfractory metallic material from a special high temperature atmosphere, in particular in a technique of joining the first wall of nuclear fusion reactor and its surrounding apparatuses with graphite to decrease damages sufferred from plasma and to improve their coexistence with plasma, and to a joining method using the same.

FIG. 1 is a diagram showing a three-layer construction of joining of graphite and a metallic material having a close coefficient of thermal expansion, for example molybdenum.

In the figure,

.circle.1 is a graphite layer;

.circle.2 is a jointing material layer; and

.circle.3 is a molybdenum plate.

FIG. 2 is a diagram showing a seven-layer construction of joining of graphite and a metallic material greatly different therefrom in the coefficient of thermal expansion, for example SUS 316.

In the figure,

.circle.1 is a graphite layer;

.circle.2 is a joining material layer;

.circle.3 is a molybdenum plate;

.circle.4 is a joining material layer;

.circle.5 is a nickel plate;

.circle.6 is a joining material layer; and

.circle.7 is a SUS 316.

The joining material of the present invention must have a melting temperature near 1000.degree. C. so that the joining metallic material (copper, SUS system, Hastelloy, Incolloy, molybdenum and others) is not degenerated at the time of joining heat treatment, and simultaneously must have excellent wettability with graphite and the metallic material.

As the result of numerous experiments, the present inventor has obtained, as one satisfying these requirements, a joining material comprising titanium, nickel and copper in a composition ratio of, by weight,

Ti 69-57

Ni 24-20

Cu 7-23.

The joining material of the present invention is called "titanic wax material" and can be used in powder or other forms according to its use.

In joining graphite and metal using the joining material of the present invention, a heating oven is employed which is maintained at a high vacuum above 10.sup.-5 torr in degree of vacuum and at an elevated temperature above 1100.degree. C. and the joining is carried out in an argon atmosphere. At the time of heating the heating rate is not specified in particular. The maximum temperature at the time of joining is approximate 980.degree.-1200.degree. C. and the temperature is necessary to be maintained for about 1-50 minutes. At the time of cooling the cooling rate must be below 20.degree. C. per minute. And also the jointing zone at the time of jointing must be held in a state uniformly heated.

In case of joining graphite and a metallic material having a close coefficient of thermal expansion, such as molybdenum and others, the joining can be carried out as graphite--joining material--molybdenum, as shown in FIG. 1, while, in case of joining graphite and a metallic material greatly different therefrom in the coefficient of thermal expansion, for example SUS 316, the joining is carried out in a seven-layer construction as graphite--joining material--molybdenum plate--joining material--nickel plate--joining material--SUS 316, as shown in FIG. 2. In this case, as the result of a joining test, the thickness of the metal sheet, molybdenum plate and nickel plate, which is an intermediate layer, is necessary to be above 1 mm, as shown in Table 1.

The combination of graphite and metallic material in which a joining test has been successfully performed using the joining material of the present invention was as follows:

In the nuclear fusion reactor FER (Fusion Experimental Reactor) the heat-removing efficiency is expected to be improved by joining SUS 316 of a first wall to graphite, and thereby the dimension of a reactor can be reduced.