EP0290820B1 - Process for preparing dispersion-hardened metal alloys - Google Patents

Description

The invention relates to a method for producing dispersion-hardened metal alloys, in particular for components of complex shape which are resistant to high temperatures, particles of a second phase being incorporated into a metallic matrix (first phase) with the aid of a colloidal suspension, the metallic components of the first phase initially being in the form of a salt solution, the solution is mixed with the particles of the second phase, which do not react with the metallic constituents of the first phase and their salt solution, a deglomerating agent is added, the solution is atomized and, after removal of the solvent, a reduction to metal takes place.

Metal alloys, in particular superalloys for high-temperature-resistant components in a complicated form, such as turbine blades or similarly complicated moldings, often contain highly reactive elements, such as titanium, chromium, aluminum and the like. In the conversion of such metal alloys into metal powder, mixed oxides can be formed already when removing the solvent or the water of crystallization due to the reactive elements, which can not or only very difficultly be reduced to metal.

The object of the invention is the method according to EP-A-0 223 196 to improve so that the target alloys can be produced almost as metal powder, although they contain highly reactive elements.

The solution of the invention is contained in claim 1. In particular, the invention relates to a method for producing dispersion-hardened metal alloys for high-temperature-resistant components of complicated shape, particles of a second phase being incorporated into a metallic matrix with the aid of a colloidal suspension.

The invention improves the method according to EP-A-0 223 196 and extends its field of application very significantly.

Further advantages of the invention can be found in the subclaims and the description of exemplary embodiments.

Furthermore, according to the invention, in addition to the metallic particles, non-reactive, in particular oxidic, dispersions can be introduced into the suspension as a second phase in the form of particles.

The effect of an optionally provided dispersion hardening according to the prior art known from EP-A-0 223 196 and GB-A-917 005 can hereby be increased considerably. This is particularly advantageous if you want to prevent grain growth, in particular during sintering, and if you want to maintain the formation of narrow sub-grain boundaries in the molded body under high loads, in particular with thermal expansion (creep).

The heat treatment in the temperature time program before or after the powder is compacted allows the metal of the particles to be evenly diffused into the matrix, even if they are oxidized on the surface. The examples given in EP-A-0 223 196 also apply here.

Alloys can thus be processed to metal powder, which also contain the reactive elements mentioned. Metal salts or mixtures of salts of metals which can be reduced from their salts are used as starting materials for the solution to form a suspension. A suspension of fine powder particles of the highly reactive elements or suitable master alloys from these elements is thus produced by slurrying, optionally with deglomerating agent. When this mixture is atomized, dried and reduced, at most a thin surface layer of this metal powder is oxidized. The remaining metallic residue can be uniformly distributed in the metallic matrix to the desired extent by diffusion treatment before or after compacting the powder. If a mixture of salt solutions of reactive metals is used, powders and sintered shaped bodies can be produced from them, which additionally contain a uniform distribution of the finest oxidic particles. The particle size and distribution then depend on the sintering conditions of the shaped body. This gives optimally composed superalloys with different disperse populations to reinforce the matrix. Instead of the colloidal suspension, for example, a non-colloidal particle distribution in the solution can also be used as a suspension.

Claims (5)

1. Method of preparing dispersion-hardened metal alloys, in particular for high-temperature-resistant components of complex shape, particles of a second phase being incorporated in a metallic matrix (first phase) by means of a colloidal suspension, the metal components of the first phase initially being present as a salt solution, the particles of the second phase, which does not react with the metal components of the first phase and its salt solution, being added to the solution, a deagglomeration agent being added, the solution being atomised and reduced to metal after removal of the solvent, characterised in that metal salts, which can be reduced to metal, or mixtures of salts are used as the initial substance of the solution for forming a suspension, and metal powder particles are mixed as the second phase with the solution, the metal powder particles consisting of metals or their alloys of which the salts cannot readily be subjected to a reduction process.
2. Method according to Claim 1, characterised in that non-reactive, in particular oxidic, dispersing agents are introduced into the solution in addition to the powder particles.
3. Method according to Claim 1 or Claim 2, characterised in that salts of reactive metals, which, when dried and treated reductively form metal oxides, are also added to the solution.
4. Method according to Claim 3, characterised in that salts of metals such as titanium, chromium, aluminium and similar reactive elements are added to the solution.
5. Method according to any one of the preceding claims, characterised in that the metal powder, including for example superficially oxidised metal powder particles, is distributed uniformly in the metal matrix by means of a diffusion heat treatment before or after the powder has been compacted.