DE1150561B - Process for making sintered, porous workpieces from refractory metals and their alloys machinable - Google Patents

Description

It is known that workpieces made of refractory metals such. B. tungsten or molybdenum, or from alloys of such metals, in the sintered, porous state only with difficulty with narrow Have tolerances machined by turning, milling, drilling and grinding. Also close the pores on the machined surface of the workpieces. They have already tried that To achieve machining to exact dimensions by the fact that the workpieces with copper, Silver or other relatively low-melting metals soaked and then worked, thereby creating a slightly better post-processing of the workpieces was achieved, but at least the complicated one thermal aftertreatment for the purpose of evaporation of the impregnation metal from the porous workpiece had to be accepted. To the high necessary for the evaporation of the impregnation metal To avoid temperature, it has also already been suggested that the workpiece be coated with alkali halides soak, which then after machining the workpiece by evaporation or dissolving again removed. This procedure also turned out to be cumbersome and in no way showed what was expected Results.

The invention provides a way of making sintered, porous workpieces made of refractory metals, for example tungsten, machinable. Molybdenum or the like, or their alloys, preferably by turning, milling, drilling, grinding, wherein the workpieces are impregnated with a metal or an alloy of low melting point and the impregnating agent is removed or evaporated from the workpieces after processing will. According to the invention, an alkali metal or an alloy is used as the impregnating agent Alkali metals, preferably with a melting point between 50 and 400 ° C, are used. Through the Invention not only avoid the difficulties encountered so far, but also according to the invention treated bodies are particularly easy to process.

To carry out the method according to the invention, for. B. lithium or sodium pieces from the tin cans in which these metals are under petroleum or argon, the tarnished surface layers' are cut away and then put these metal pieces dry on the porous work pieces to be impregnated, these are in a form made of iron. There is a slight heating, and at the same time the furnace in which this is carried out, something

sintered, porous workpieces

made of refractory metals

and their alloys

Applicant:

Metallwerk Plansee Aktiengesellschaft,
Reutte, Tyrol (Austria)

Representative: Dr.-Ing. Hj. V. Black, patent attorney.
Krefeld, Westparkstr. 14th

Claimed priority:
Austria from March 25, 1959 (No. A 2361-59)

Dr. techn. Ing.Karl Sedlatschek,

Reutte, Tyrol (Austria),
has been named as the inventor

can be evacuated to facilitate the penetration of the impregnation metal.

According to another method, the workpiece to be soaked is placed in a steel die with liquid Lithium overlaid. Under a pressure of about

2 t / cm ² , the impregnating metal easily penetrates the porous workpiece.

In the subsequent mechanical processing, it in no way interferes with the fact that the surface of the soaked workpieces starts up.

The alkali metal introduced by soaking leaves

can be removed easily, using much lower temperatures than for the use of copper or the like as impregnation metal.

Lithium in particular has proven itself in practice

and lithium-sodium alloys. But potassium can also be used, and it is furthermore also possible to use rubidium and cesium.

example 1

Porous tungsten in rod form. Porosity 2O ¹ Vo, pore size 3 to 10 μ, is impregnated with molten lithium at 220 ° C. After cooling, hollow cylinders are machined from the saturated tungsten by drilling and turning. By

3 hours of storage under water

309 617/123

At room temperature, the lithium is completely dissolved out of the pores of the porous tungsten workpieces.

Example 2

A mixture of 80 percent by weight tungsten powder and 20 percent by weight tantalum powder is used sintered to achieve mixed crystal formations, pulverized, pressed into porous workpieces and sintered to achieve sintered bodies with a porosity of 25%. The porous sintered bodies are at 250 ° C with an alloy consisting of 80% sodium and 20% lithium, soaked and after Cooling processed to the final dimensions. The finished-turned workpieces are stored freed from sodium and lithium in water.

Example 3

Porous tungsten obtained by sintering of pressed bodies of tungsten powder, grain size 40 to 60 μ, pressure was 5 t / cm ^2, sintering temperature 2100 ° C, 4 hours in hydrogen, performed at temperatures of 100 ⁰ C with an alloy of potassium and sodium (90 % Potassium, 10% sodium) soaked in a protective gas atmosphere (argon) and, after cooling, turned into workpieces (hollow cylinders) with precise dimensions. Potassium and sodium are evaporated off at 360 ° C. by heating in vacuo (10 to 2 mm Hg).

Although alkali metals and their alloys have a particularly high reactivity, requires their use as impregnating agents according to the invention no further precautionary measures than the usual ones when dealing with these metals and alloys.

Claims (2)

PATENT CLAIMS: 1. A method for making divided, porous workpieces made of refractory metals and their alloys machinable, preferably by turning, milling, drilling, grinding, the workpieces being impregnated with a metal or an alloy with a low melting point and the impregnating agent being removed from the workpieces after machining or is evaporated, characterized in that an alkali metal or an alloy of the alkali metals, preferably with a melting point between 50 and 400 ° C, is used as the impregnating agent. 2. The method according to claim 1, characterized in that the impregnating agent or lithium Lithium alloys are used. Considered publications:
British Patent No. 707 512;
Hollemann-Wiberg, Inorganische Chemie, 40th to 46th edition, 1958, p. 419 ff.