Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2000-06-15
2002-02-12
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S249000, C419S030000, C419S035000, C419S049000
Reexamination Certificate
active
06346132
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 197 41 019.7, filed on Sep. 18, 1997, of which the entire disclosure is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a structural material, and particularly a metal based composite material, having a high damping capacity and a high tensile strength, comprising an essentially metallic base material or matrix and a second phase in the matrix. The invention further relates to a method of making such a material and to rigid structural parts made of such a material.
BACKGROUND INFORMATION
In various fields of industry, the presently typical high accelerations of mechanically moving parts cause undesirable vibrations in those parts over a wide frequency spectrum. The high vibration loading in the vibrating systems leads to long dead or idle times, for example due to long run-up transient processes, and also limits the operating lifetime of the vibrationally loaded parts. Another significant problem is the noise generated by the vibrations.
In order to overcome or avoid these problems of vibrations, it is generally known to use materials having a high damping capacity to damp out the vibrations as much and as quickly as possible. However, present structural materials do not possess a sufficient damping capacity in and of themselves, and present damping materials do not possess a sufficient strength to perform as structural materials themselves.
Metals and metal alloys are predominantly used as structural materials in a broad field of applications, due to their high strength, low weight or density, and good corrosion resistance. However, such metals and metal alloys typically have a rather low damping capacity, so that it becomes necessary to use additional damping materials purely for the purpose of achieving the desired damping in structures comprising metal and metal alloy structural parts. Such damping materials are generally synthetic polymers or plastics, but such materials suffer limitations in their applicability for example in applications at temperatures above the respective melting points of the materials or in situations of limited space. Gray cast iron and pure magnesium are characterized by a higher damping capacity, but on the other hand these materials possess a rather limited strength.
U.S. Pat. No. 4,946,647 (Rohatgi et al.) discloses metallic composite materials of an aluminum matrix with graphite particles dispersed therein as a second phase, as well as a method for making the same. While the known composite materials are said to have an improved damping capacity relative to aluminum or aluminum alloys per se, the disclosed composites have a significantly reduced strength compared to aluminum or aluminum alloys per se. Particularly, the disclosed materials have a tensile strength of at most 190 MPa, which is far below that of the matrix, and an elongation of at most 4%, even when pure aluminum is used as the matrix material. These mechanical properties demonstrate that the disclosed composite materials achieve the desired damping characteristics only at the expense of a drastic reduction in strength, and the materials are thus not suitable for use as structural materials. The reference even admits this deficiency in the strength, and suggests that the graphite content must be controlled or limited to achieve the required strength values. Of course, such limitations on the graphite content will in turn reduce the desired damping characteristics.
U.S. Pat. No. 4,236,925 (Onuki et al.) discloses a method of producing a sintered material having an increased damping capacity and comprising a second phase of graphite, lead or magnesium. The disclosed method includes steps of mixing the second phase material in powder form with the remainder of a powdery iron, copper, or aluminum metal, compression-molding the mixture, sealing or canning the compression-molded mixture in a deformable vessel, subjecting the vessel and the mixture therein to a plastic deformation treatment, and then sintering the plastically deformed vessel and mixture therein. The heating temperature in the sintering step must be above the recrystallization temperature of the matrix metal, so that the matrix metal becomes recrystallized, and the second phase material is aggregated in the form of spindles on the crystal surface or in the crystals of the matrix metal. These steps are complicated and costly, and the method necessarily limits the second phase material to have a spindle shape.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a material that comprises an essentially metallic base material or matrix and a second phase in the matrix, which has both an increased damping capacity already at low vibration amplitudes, as well as a sufficiently high tensile strength and elongation so that it may be used as a structural material particularly for rigid, form-stable structural parts. A further object of the invention is to provide a method for producing a material having a high damping capacity and a high strength, without requiring additional complicated method steps such as high temperature sintering or the like, and without limitation of the form of the second phase material. The invention further aims to avoid or overcome the additional disadvantages of the prior art, and to achieve additional advantages, as apparent from the present description.
The above objects have been achieved in a metallic material according to the invention, having a high damping capacity and a high tensile strength, comprising a metallic base material or matrix and a second phase in the matrix, wherein the second phase is metallic and at least partially comprises a martensitic grain structure. It has been discovered that the inventive combination of a metallic second phase at least partially comprising a martensitic grain structure in a metallic matrix achieves high damping characteristics, even at low vibration amplitudes. A further advantage is that the partially martensitic second phase does not negatively influence the mechanical properties of the matrix, so that the overall material maintains its strength characteristics and therefore can be used as a structural material in the same manner and the same applications as the matrix material could be used by itself.
It is further significant that the inventive material does not place any particular limitations on the selection of the outer shape, form or configuration of the second phase. Namely, the second phase can be in the form of granular or globular particles fibers, strands, whiskers, wires, or the like. By appropriately selecting the form of the second phase, it is possible in a simple manner to adapt the respective characteristics of the overall material to the requirements at hand in any particular application. It should be noted that the second phase is preferably dispersed throughout the matrix in an unmixed and un-alloyed condition relative to the matrix, such that distinct particles of the second phase remain embedded in the matrix, thus providing an overall composite structure for the inventive material. In other words, the overall material according to the invention is especially not a homogenous alloy, but rather a composite of un-mixed materials.
Preferably, the second phase itself is an alloy. An advantageous material damping capacity can be achieved if an alloy of nickel and titanium is used as the second phase, and particularly when each of these alloying components is present and intermixed in the range of 48 to 52 atom %. The most preferred alloy composition of nickel and titanium for the second phase is 49.9 atomic % nickel, and 50.1 atomic % titanium. These components and compositions of the alloy are only preferred values, and are not necessary limitations on the broadest scope of the invention.
The material damping capacity can be even further increased if the second phase includes additives in a positive amount up to 25 atomic %, for stabilizin
Arzt Eduard
Huber Ulrike
Rauh Rainer
Daimler-Chrysler AG
Fasse W. F.
Fasse W. G.
Mai Ngoclan
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