WO1992020481A1

WO1992020481A1 - Alloy with high density and high ductility

Info

Publication number: WO1992020481A1
Application number: PCT/SE1992/000251
Authority: WO
Inventors: Allan Hede; Hans Gunnar Larsson
Original assignee: Powder Tech Sweden Ab
Priority date: 1991-05-17
Filing date: 1992-04-16
Publication date: 1992-11-26
Also published as: SE9101500D0; SE9101500L; SE470204B

Abstract

The invention relates to a method of manufacturing an Ni-base alloy with high density and high ductility and objects made of said alloy. The method is characterized in that an alloy containing 15-70 % (per cent by weight) W and/or Ta, 0-25 % Fe, 0-15 % Si and 0-2 % Mn, is manufactured by means of a powder metallurgical process, suitably in equipment producing fine particle sizes in the powder.

Description

Allov with high density and high ductility

Technical Field

The invention relates to a method of manufacturing an Ni-base alloy with high density and high ductility and objects made of said alloy.

Background Art

High-density material is of interest for many applications, both civilian and military. For civilian applications these materials are useful for counterweights, gyros and certain blasting purposes, while for military applications they are useful for high-efficiency active parts against fighter aircraft, armoured vehicles, missiles, ships and other armoured targets.

The high-density material may be included in the form of pre-fragmented shell, such as in explosive shells in the form of pellets, such as pellet explosive shells, and pellet-based active parts in the form of arrow-shaped rods such as in modern arrow ammunition. In recent years high-density material has also become of interest for active parts based on the directed explosive action principle (DEA), and has been developed in order to combat armoured targets as well as for various civilian purposes. The explosive action is achieved by the metal-liner (usually in the form of a cone or cap) included in the DEA charge forming a jet or projectile with extremely high initial velocity (> 5 km/s) and thus high penetration capacity into armoured targets. Hitherto extremely pure copper with fine particle size and minimum texture has been used for these liners for jet-producing DEA.

Efforts have been made to improve the penetration capacity for DEA charges by gradually improving and developing all the parts and a material has been aimed at for the liner material that would have greater density than copper while retaining the same properties in other respects, i.e. soft and with great ductility at fast deformation, and also a melting point not deviating too far from that of copper. Two other important requirements are that the material should be fine-particled and texture-free.

In order to achieve these properties the use has been proposed of either a heavy-metal composite with 40-90% W, or an alloy with approximately the same composition as the tough binder phase in Ni-Fe heavy metal, i.e. approximately 55% Ni, 25% Fe and 20% W.

However, the heavy-metal composite proved to be not very suitable as DEA material since it was not sufficiently tough at rapid deformation processes. Interest has therefore been focussed recently on the tough binder-phase alloy. This alloy cannot be manufactured using melt metallurgical methods, due to its high segregation tendency and consequent brittleness. The use of powder metallurgical methods has therefore been proposed, primarily sintering or hot isostatic pressing of a fine-particled mixture of the pure metal powders. Gas atomized powder has also been indicated as possible starting powder. In all experiments performed alloy compositions were aimed at having W contents of between 15 and 30% and Ni and Fe contents in a proportion of 7:3 since this Ni/Fe ratio has proved best for heavy metal from the tenacity aspect. In some cases Co were included, while elements such as Si, Mn and others were deemed "poisons". However, no particularly good DEA results were reported when using these alloys, probably because the alloys were not a hundred per cent single phase, sufficiently pure, with sufficiently low oxygen content (= low surface oxygen content in the powder), etc. These alloys were produced by sintering processes.

Summary of the Invention

The invention aims at a solution of the problems described above and problems associated therewith. The invention relates to a method of manufacturing an alloy- containing 15-70 per cent by weight W and/or Ta, 0-25 per cent by weight Fe, 0-1 per cent by weight Si and 0-2 per cent by weight Mn, by means of a powder metallurgical process. This should preferably be carried out in installations that produce fine powder particle sizes. In order to achieve the desired properties for jet-producing DEA (= high density, high ductility) the alloy used shall suitably be a single phase alloy. The alloy powder should suitably be produced by a method giving low oxygen content, such as gas atomization. An alloy consisting of 25-40 per cent by weight W, max. 10 per cent by weight Fe, approximately 0.1 per cent by weight Si (or similar deoxidant) and the rest Ni may be used, and a starting powder with high purity and low surface oxygen content. Multi-phase alloys, i.e. alloys containing 40-70 per cent by weight W, may also be considered for projectile-forming DEA. In the alloys used W and/or Ta are not used as composite material, and these alloys are initially just melt compositions. The alloy shall suitably contain 50-70 per cent by weight Ni, preferably 55-65%. Detailed information and examples .

The alloy used for the method according to the invention shall thus contain 15-70% W, 0-25% Fe, 0-1% Si and 0-2% Mn + the normal impurities. The alloy shall preferably contain 25-40% W, max. 0-25% Fe, and the rest Ni (per cent by weight).

The following may be mentioned as examples of alloys used in the method according to the invention:

Alloy 1: 0.01% C, 0.05% Si, 0.05% Mn, 57% Ni, 22% Fe and 21% W;

Alloy 2: 0.03% C, 0.14% Si, 0.23% Mn, 62% Ni, 9% Fe and 29% W;

Alloy 3: 0.02% C, 0.12% Si, 0.16% Mn, 65% Ni and 35% W;

The properties of these alloys may be classified as follows:

Alloy 1 Alloy 2 Alloy 3

Fine-particled powder of the alloy according to the invention was produced by means of gas atomizing, suitably in installations giving fine powder particle size and low surface oxygen content. The powder is suitably filled into metal capsules and subjected to hot isostatic pressing (HIP). Test rods were manufactured by hot isostatic pressing of such cylindrical metal capsules filled with powder. Prior to manufacture of the test rods the compacted blanks were quench annealed at temperatures from 1200°C and 1250°C.

The invention thus covers methods of manufacture that produce objects with better properties than objects, copper-based and others, already known.

The method can be exemplified as follows:

Powder metallurgical manufacture from a starting material consisting of extremely pure, gas atomized powder with low surface oxygen content and small powder particle size.

Gas atomizing in powder plants, which produces powder of the type described above.

Compacting the powder by means of cold compacting, sintering or pressure sintering (HIP, sinter-HIP, etc.) to semi-manufactured products for further cold or hot working to almost finished form with certain subsequent machining, or to finished form without subsequent machining. The method according to the invention (see above) entails great advantages with regard to performance and cost in comparison with conventional processes.

Experiments with alloys and methods according to the invention have shown the following:

The highest possible density in single-phase Ni-Fe-W-alloys (i.e. without the occurrence of free W in the structure), is achieved in Fe-free or almost Fe-free Ni-base alloys. After quench annealing from 1200°C an Fe-free alloy may contain approximately 40% W in stable solution. The density of such an alloy will be about 13 g/cm.

The highest possible W-content achievable in a melt that can be atomized is approximately 65%. An Ni-65% W alloy is two-phase and gives a density of approximately 15.5 g/cm.

High ductility (> 30%) can be achieved with single-phase Ni-Fe-W-alloys having a W content of 15-40% and Ni/Fe ratio » 7:3 if they are manufactured using powder metallurgical methods as described below and quench annealed from a temperature of at least about 1000-1100°C after compacting, or quick-cooled in conjunction with compacting.

To enable high ductility to be achieved, a starting powder must be used that has low surface oxygen content and fine powder particle size. The method of manufacture according to the invention gives such a powder.

The invention also relates to a method of manufacturing active parts for DEA ammunition. Alloys according to the invention have been tested and the following been found:

These alloys are extremely suitable for such purposes and produce a marked increase in the efficiency of such ammunition when used against armoured targets with directed explosive action. These parts are suitably manufactured by encapsulating the powder in metal, followed by hot isostatic pressing, or by means of cold compacting or dynamic compacting (explosion compacting or punch compacting). The aim is to achieve full density. The alloy may be included as binder between pellets of W or other heavy metal, for instance in cylindrical, sleeve-shaped ammunition, or in conical parts, the latter manufactured by means of punch compacting or pressure turning. The compacting may possibly be followed by sintering.

The invention can be varied in many ways within the scope of the following claims.

Claims

1. A method of manufacturing an Ni-base alloy with high density and high ductility and objects made of said alloy, characterized in that an alloy containing 15-70 per cent by weight W and/or Ta, 0-25 per cent by weight Fe, 0-1 per cent by weight Si and 0-2 per cent by weight Mn, is manufactured by means of a powder metallurgical process.

2. A method as claimed in claim 1, characterized in that- the alloy powder is manufactured by means of a method giving low oxygen content, such as gas atomizing.

3. A method as claimed in claim 1 or 2, characterized in that the alloy produced in powder form is consolidated to active parts in high-efficiency ammunition, such as for directed explosive action.

4. A method as claimed in any of the preceding claims, characterized in that the objects produced, e.g. active parts, are manufactured by means of metal encapsulation and hot isostatic pressing (HIP).

5. A method as claimed in any of claims 1-3, characterized in that the objects produced, e.g. active parts, are manufactured by means of cold compacting, possibly followed by HIP, in order to achieve full density.

6. A method as claimed in claim 4 or 5, characterized in that the active parts are produced as blanks by means of hot or cold compacting powder, and that these blanks are thereafter shaped to their final form by means of cold-merge compression, pressure turning and similar methods.

7. A method as claimed in any of claims 4-6, characterized in that the active parts are produced using the alloys as binder between pellets and fragments which in turn contain W or some other heavy metal, in cylindrical, tubular ammunition, for instance, or in conical ammunition parts.

8. A method as claimed in any of the preceding claims, charac¬ terized in that the objects, e.g. the active parts are manufactured by means of hot or cold compacting or by means of dynamic compacting (explosion or punch compacting) to full density, possibly followed by sintering. /WENDED CLAIMS

[receⁱved by the International Bureau on 22 September 1992 (22.09.92) • original claims 1-8 replaced by amended claims 1-8 (1 page)]

1. A method of manufacturing an Ni-base alloy with high density and high ductility, characterized in that an alloy containing 15-70 per cent by weight W and/or Ta, 0-25 per cent by weight Fe, 0-1 per cent by weight Si and 0-2 per cent by weight Mn, is manufactured as a gas atomized powder of pure melt compositions of the alloy.

2. A method as claimed in claim 1, character i zed in that the alloy powder is manufactured by means of a method giving low oxygen content, such as gas atomizing.

8. A method as claimed in any of the preceding claims, charac¬ terized in that the objects, e.g. the active parts are manufactured by means of hot or cold compacting or by means of dynamic compacting (explosion or punch compacting) to full density, possibly followed by sintering.