GB2235145A

GB2235145A - Metal matrix composite materials

Info

Publication number: GB2235145A
Application number: GB8830129A
Authority: GB
Inventors: Peter Raymond Lee; Geoffrey Robert Loosemore
Original assignee: Royal Ordnance PLC
Current assignee: BAE Systems Global Combat Systems Munitions Ltd
Priority date: 1988-12-23
Filing date: 1988-12-23
Publication date: 1991-02-27
Anticipated expiration: 2008-12-23
Also published as: GB2235145B; GB8830129D0

Abstract

A metal matrix composite material comprises a continuous matrix phase formed of a DU-rich or tungsten-rich metallic material in which a multiplicity of fibres, wires, particles or whiskers of a reinforcing phase are disposed substantially uniformly or heterogeneously and selectively throughout the matrix phase.

Description

METAL MATRIX COMPOSITE MATERIALS The present invention relates to metal matrix composite materials and components produced therefrom.

Components made from the heavy metals tungsten and depleted uranium (DU) and alloys thereof are well known in the munitions industry.

Such high density components are particularly suitable for use in applications such as armour piercing penetrator rods and warhead liner materials, where high kinetic energy is required.

Alloys conventionally used for penetrator rods, especially tungsten based alloys, have the major shortcomings of a low percentage strain making them relatively brittle and a low ultimate tensile strength (UTS) compared with depleted uranium, DU alloys. Consequently, such rods tend to fracture when subjected to lateral forces when passing through certain modern armours. Consequently, DU although much more expensive than tungsten and hazardous, is preferred for use in many modern applications.

Tungsten penetrator rods having reinforced fibres provided substantially continuously along the length of rod have been proposed in the prior art in United States Statutory Invention Registration No. H343. Although these rods would have an improved strength along the axis of the rod, their brittleness and ability to fracture at the fibre/matrix interface would be increased.

It is the purpose of the present invention to provide tungsten and DU containing metallic materials having improved mechanical properties desirable in munitions applications, such as a combination of improved UTS and percentage strain to failure.

According to the present invention, there is provided a metal matrix composite material comprising a continuous matrix phase formed of a tungsten-rich or DU-rich metallic material in which non-continuous particles, fibres, wires or whiskers of a reinforcing phase are dispersed, substantially uniformly or heterogeneously and selectively throughout the matrix phase, such that the combination of strength and toughness of the matrix material is improved by the addition of the reinforcing phase.

The composite material may be used in the manufacture of heavy metal sub-projectiles, eg. penetrator rods for gun ammunition for use in armour piercing applications.

The metallic material of the matrix phase may be tungsten or a tungsten alloy, e.g one of the alloys conventionally used in munitions having metal applications such as tungsten/nickel/iron; or tungsten/nickel/copper; or DU or DU alloy commonly used for munitions.

In the case of the tungsten alloys, preferably the matrix phase contains at least 80%, desirably at least 90% by weight of tungsten to provide a high material density and hence a high component mass when projected at high velocity as a projectile or fragment.

The reinforcing phase may be one or more ceramic materials known for use as the reinforcing phase in metal matrix compositions. For example, the reinforcing phase may be selected from one or more of A1203, SiC, BN, and WC and carbon in one of the forms in which these phases are known as reinforcing phases in metal matrix composites.

Where the reinforcing phase is in the form of particles or short whiskers or fibres, the particles whiskers or fibres of the reinforcing phase may, for example, have a length or maximum dimension of less than lmm, eg. less than 100 mircrometers. The mean diameter of the particles, whiskers or fibres of the reinforcing phase may for example be 15 micrometers or less.

Preferably, the reinforcing phase loading content is from 2 to 60 per cent by volume. At the higher end of this range a greater improvement in mechanical properties may be achieved but with a greater reduction in density (compared for example with elemental tungsten), whereas at the lower end of this range the improvement in mechanical properties is lower but with a smaller reduction in density. The extent of loading is therefore selected according to the combination of properties required.

The reinforcing phase may alternatively or in addition comprise whiskers of a metallic material, especially a ductile metal selected from one or more of copper, silver, nickel, iron or a refractory metal In this case, the reinforcing material may advantageously be coated with a chemical barrier layer, eg. by oxidation in strong acids, to prevent migration of ions of the reinforcing phase into the matrix material to cause a solid state chemical reaction.

Metal matrix composite materials embodying the present invention may be manufactured by methods which are generally known per se for the production of metal matrix composite materials. For example they may be manufactured by uniformly mixing the reinforcing particles or whiskers with a powder of the metallic matrix and then isostatically pressing followed by annealing of the resulting composite in a known way. Alternatively, they may be made by the technique of liquid forming, by plasma deposition or by diffusion bonding An example of a prior art reference to a method of manufacture of metal matrix composites is for instance UK Patent No. 1,334,358.

Composite material embodying the present invention may be provided with a combination of improved UTS, stiffness and strain to failure, compared with the basic matrix material thus providing increased strength and stiffness with acceptable levels of toughness, improving its attractiveness for use in modern munition applications.

Claims

1. A metal matrix composite material comprising a continuous matrix phase formed of a DU-rich or tungsten-rich metallic material in which a multiplicity of fibres, wires, particles or whiskers of a reinforcing phase are disposed substantially uniformly or heterogeneously and selectively throughout the matrix phase.

2. A composite material as claimed in claim 1 and wherein the tungsten-rich metallic material is selected from tungsten, an alloy of either tungsten, nickel and iron or tungsten, nickel and copper containing at least 90 per cent by weight of tungsten; and a DU rich metallic material.

3. A composite material as claimed in claim l, claim 2 or claim 3 and wherein the reinforcing phase comprises particles fibres or whiskers selected from A12O3, SiC, BN and WC.

4. A composite material as claimed in claim 1, claim 2 or claim 3 and 4 wherein the reinforcing phase comprises particles, fibres or whiskers having a length or maximum dimension of less than lmm.

5. A composite material as claimed in claim 4 and wherein the particles, fibres or whiskers have a mean diameter of 15 micrometers or less.

6. A composite material as claimed in claim 1 or claim 2 and wherein the reinforcing phase comprises particles, fibres or whiskers of a ductile metal.

7. A heavy metal sub-projectile for a munition which sub-munition comprises a composite material as claimed in any one of the preceding claims.

7. A composite material as claimed in claim 6 and wherein the ductile metal is selected from one or more of copper, tungsten, molybdenum, tantalum, silver, nickel and iron or an alloy thereof.

8. A composite material as claimed in claim 6 or claim 7 and wherein the ductile metal particles, fibres or whiskers have a coating comprising a chemical barrier layer.