Alloys or metallic compositions – Niobium base
Patent
1990-01-08
1991-09-17
Roy, Upendra
Alloys or metallic compositions
Niobium base
148 115P, 148 127B, 148133, 148421, 419 19, 419 46, 419 47, 420427, B22F 312, B22F 500
Patent
active
050493558
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a process for manufacturing a ductile, high strength, oxide dispersion hardened sintered alloy based on a metal with a high melting point, if necessary with small additions of substitution mixed-crystal phase which, however, do not have a serious effect on alloy properties, in which a metal oxide powder in dispersoid form is mixed with the basic metal powder, using oxides of those metals whose binding energy at temperatures <0.5 T.sub.M is higher than that of the oxides of the basic metal.
2. Description of Related Art
Classical processes for altering the strength properties of metals include the forming of alloys via mixed-crystal phases and mechanical reshaping. In addition, it is known that the strength of materials produced by fusion metallurgy or powder metallurgy can be increased by introducing or removing dispersoids. According to the definition, dispersoids are particles, usually included in the metallic base matrix in a continuous fashion, which even at higher temperatures do not react with the basic metal or dissolve, and are not built into the base lattice as substitution metals. Particularly oxides, carbides and nitrides are used as dispersoids.
According to established doctrine, the disadvantage of dispersion hardening versus alloy hardening by continuous or discontinuous precipitation of a second phase within the basic phase from a common solution (precipitation hardening consists in the fact that "it is hardly possible to achieve the same degree of dispersion and strength increase as can be realized with precipitation processes in many cases" (H. Bohm, Introduction to Metallurgy, Hochschultaschenbucher Verlag, Mannheim, Zurich).
For producing dispersion-hardened alloys by processes of powder metallurgy, the dispersoids are usually introduced by soaking the powder with a dispersoid suspension, or by blending dispersoids in powder form with the basic metal powder.
Dispersoids introduced in this manner can be further homogenized by "mechanical alloying". The objective of mechanical alloying is to distribute the dispersoids as homogeneously as possible, even within the individual metal powder grains. These processes are very time-consuming and require grinding equipment of high quality. They are therefore very expensive, and their applicability depends on the state of the components. Moreover, practical application demands a compromise between the degree of homogenization and the cost of grinding, i.e. the grinding operation is limited in time.
The application DE-A1 35 4 255 contains a proposal for producing an ODS alloy by mixing the basic metal in the form of a salt solution with the dispersion particles in colloidal suspension and to finally reduce it to metal. As a special advantage, the finely distributed, homogeneous introduction of the dispersoid into the metal matrix is cited. However, even with this process, distribution is limited by the particle size of the components.
The production of dispersion hardened alloys consists in introducing particles as dispersoids which by definition do not react or alloy with the basic matrix. In connection with this fact, the sintered-metallurgy processes for producing dispersion alloys up until the present have used dispersoids with melting points that are usually considerably higher than the alloy sintering temperature. The dispersoids exist in the solid phase during the entire manufacturing process.
Due to the doctrine mentioned above, that dispersion hardening achieves only relatively small increases in strength, the additional means of mixed-crystal alloy hardening or precipitation hardening was applied in cases where greater mechanical strength was required. To achieve this, greater doses of additive metals were blended with the basic metals, next to dispersoids.
Next to powder metallurgy processes, it is known that oxide dispersion alloys of high-melting metals can be produced by fusion metallurgy, particularly by arc melting.
For instance, a process is known from D
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Gennari Udo
Glatzle Wolfgang
Roy Upendra
Schwarzkopf Development Corporation
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