Bulk Metallic Glass/Graphite Composites

Abstract

A composite material based on a bulk metallic glass is disclosed. In an amorphous alloy phase forming a substantially continuous matrix, a second phase comprising graphite particles is embedded. The alloy is preferably zirconium based. The particles may have a carbide surface layer, which may be formed phase comprising carbide particles may also be present. The composite material has high plasticity, high yield strength, good elasticity and low coefficient of friction, which renders it a good candidate for applications like joints, frictional bearings or Springs.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]The present application is a national phase entry under U.S.C. §371 of International Application No. PCT / CH2006 / 000466, filed Aug. 29, 2006, published in English, which claims benefit of U.S. Provisional Patent Application No. 60 / 722,409, filed Oct. 3, 2005. The disclosures of all of said applications are incorporated by reference herein.FIELD OF THE INVENTION[0002]The present invention relates to a composite material having a first, amorphous alloy phase forming a substantially continuous matrix and having a second, reinforcing phase embedded in the matrix.BACKGROUND OF THE INVENTION[0003]Many amorphous metallic alloys with good glass-forming ability have been developed over the last few years. These bulk metallic glasses (BMGs) possess very interesting mechanical, magnetic, thermophysical and structural properties. They display, for example, up to double the fracture strength and four times the elasticity of their crystalline counterpart...

AI Technical Summary

Benefits of technology

The present invention provides a composite material with improved plasticity and yield strength, as well as better thermal stability and resistance to abrasion. This is achieved by embedding graphite particles in a matrix of amorphous alloy, which has a high volume fraction of the second phase. The composite material has a high degree of plasticity while still maintaining its yield strength. The embedded graphite particles also improve the material's resistance to friction and abrasion. The composite material is suitable for use in dry sliding applications, such as frictional bearings. The size of the graphite particles can vary, but particles with sizes between about 10 and about 75 micrometers are preferred. The volume fraction of the second phase should ideally be at least 1% of the total volume of the composite material. The composite material should also have a uniform distribution of the second phase throughout the material, with shear bands formed close to the graphite particles. The matrix alloy should have good mixing and close contact with the graphite particles, and the second phase should ideally be uniformly distributed in the matrix.

Problems solved by technology

Unfortunately, these properties cannot be fully exploited due to the alloys' brittle fracture behavior.

With no crystalline structure, deformation via dislocation movement is impossible, but takes place in one or a few highly-localized shear bands.

Even though BMGs may show-some type of “ductile” fracture mechanism on a microscopic scale, metallic glasses are generally brittle because the fracture energy is concentrated in a very small volume of the sample.

However, it is believed that the properties, in particular, plasticity in relation to yield strength, of such previously disclosed foreign-particle-reinforced BMGs are not yet at their optimum.

They have been shown to be even more brittle than the corresponding monolithic BMG.

In addition, carbon nanotubes are relatively expensive to produce.

Images