GB2329395A

GB2329395A - Composite material containing a martensitic phase

Info

Publication number: GB2329395A
Application number: GB9819651A
Authority: GB
Inventors: Ulrike Huber; Rainer Rauh; Eduard Artz
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1997-09-18
Filing date: 1998-09-09
Publication date: 1999-03-24
Anticipated expiration: 2018-09-09
Also published as: CA2247654A1; FR2768436B1; FR2768436A1; DE19741019C2; GB2329395B; DE19741019A1; ITMI981992A0; IT1303678B1; GB9819651D0; JPH11158570A; ITMI981992A1

Abstract

A method of making a composite material by combining a powdered matrix material with a second material, to form a composite comprising an at least partially martensitic phase in a matrix. The at least partially martensitic phase may be in the form of particles or wires or layers and it may contain elements such as Zr, Hf, Cu, Nb, Mn, Pd, Pt and/or Fe to stabilise the martensite. Furthermore, the composite may be manufactured by hot isostatic pressing, sintering, extrusion, forging or adding the second material in liquid form. In a specific example, the composite comprises 5-60 vol % martensitic nickel-titanium particles (of composition 48-52 atomic % of each of Ni and Ti) in a 6061 aluminium alloy matrix and is formed by mixing powdered aluminium with Ni-Ti powder, consolidating and then hot isostatic pressing.

Description

Material and process for its production The invention relates to a material having high material absorption and tensile strength, made of a substantially metallic base material and a secondary phase, and a process for the production of such a material.

The high acceleration of mechanically moving parts causes undesirable oscillations over a wide frequency spectrum. The high vibration stresses in the oscillating systems lead to long idle times which are caused by long oscillation procedures, and limit the service life of the stressed components. A further problem is the noise stress caused by the oscillations.

Because of their high strength, low weight and good corrosion properties, metals and alloys have a wide field of application. However, generally they have only slight absorption and so pure absorption materials are additionally used. These are mostly plastics and, at temperatures above their melting point and with a limitation of the space provided, this leads to limitations in their range of usage. Grey cast iron or pure magnesium certainly have greater absorption but on the other hand they have a limited strength.

US Patent 4 946 647 discloses metallic materials of a base material and a secondary phase of graphite.

However, the tensile strength of the given materials at a maximum of 190 MPa is far below that of the base material, and the breaking elongation is at the most 4% even when pure aluminium is used as the base material.

These mechanical characteristics show that in the case of these materials, material absorption is accompanied by a drastic loss in strength and they are therefore not suitable for use as a structural material.

The aim of the present invention is to provide a material of a substantially metallic base material and a secondary phase, which already has good material absorption at low oscillation amplitudes, but nevertheless shows such a high tensile strength and breaking elongation that it can be used as a structural material. These materials are particularly suitable for automotive, aeronautical and applications relating to space flight.

To achieve this aim, a material of the above described type is characterised according to the invention in that the secondary phase introduced into the base material is metallic and has at least partially a martensitic structure.

According to one aspect of the present invention, there is provided material having high material absorption and tensile strength, made from a substantially metallic base material and a secondary phase, characterised in that the secondary phase is metallic and has at least partially a martensitic structure.

According to another aspect of the present invention, there is provided a process for the production of a material according to one or more of the preceding claims, characterised in that a mixture of base material, present in powder form, and a secondary phase is consolidated by heat treatment in a temperature range of from 400-7000C and at a pressure of 1000-3000 bar.

At low oscillation amplitudes the material of the invention already has highly-absorbent properties. A further advantage is that the partially martensitic secondary phase present does not have a negative effect on the mechanical characteristics of the base material (such as the tensile strength of the base material) , so that the material can also be used as a structural material. It can also be seen that the material of the invention has no limitation as regards the selection of the outer shape of the secondary phase, and hence the material can be easily adapted to different requirements.

The secondary phase preferably includes an alloy.

The use of an alloy of nickel and titanium has an advantageous effect on the material absorption when these alloy components are mixed in a range of 48 to 52 atomic %, especially when the alloy contains 49.9 atomic k nickel and 50.1 atomic k titanium. These components of the alloy are only to be regarded as preferred values but not as a limitation of the invention.

The secondary phase preferably contains additives in a range of up to 25 atomic % for stabilising the martensitic phase and for adapting to the operating conditions, and a further increase in material absorption is achieved. These preferred range limits are also not to be seen as a limitation, any more than the selection of additives is, these preferably being zirconium, hafnium, copper, niobium, manganese, palladium, platinum and iron. The stabilisation of the martensitic phase can also be increased by a preliminary treatment of the secondary phase, with deformation of the secondary phase or homogenisation of the alloy components being carried out, for instance.

The secondary phase can have the form of particles, wires or short fibres and be present as a layer in the base material, so that the material can preferably thus be adapted to optimise the externally predetermined requirements. This can also be achieved by varying the proportion of total material in the secondary phase, preferably between 5 and 60 volume , in accordance with the desired properties. Here also there is no limitation of the invention. It is also possible for the secondary phase to be present as several layers inside the base material.

In order to be able to better ensure the necessary transfer of stress from the base material to the secondary phase during absorption, it is advantageous if the secondary phase forms a compound with the base material on the boundary surface with the base material.

The metallic secondary phase having at least a partial martensitic structure within the base material means that the requirements made of the material for absorption of material are only to be fulfilled by the secondary phase, whilst the tensile strength and breaking elongation are determined above all by the base material. For this reason, the base material can be selected as the structural material for any requirement. However, because of the mechanical properties the base material is preferably a soft metal or a soft metal alloy, the Al alloy EN AW-6061, according to DIN EN 573, being particularly preferred here. However, there may also be circumstances which make greater strengths necessary, and hence base materials which have a different structure or which have at least a further third phase as a compound material are used for reinforcement purposes. A thermo-mechanical treatment matched to the base material also leads to a desirable increase in the strength of the base material.

The following part of the description relates to the industrial engineering aspect of producing a material of the invention.

Materials with a secondary phase of graphite, lead or magnesium are produced by processes in accordance with US 4 236 925 and have good material absorption.

However, the production process has to be carried out in such a way that the secondary phase is present in spindle form after an additional process step in which the material is subjected to plastic deformation, and the material is heated in a further step above the recrystallisation temperature of the base material.

The aim of the present invention is further to provide a process for producing a material with high material absorption and strength which manages without additional complex process steps.

The aim is achieved in accordance with the invention in that a mixture of base material, present in powder form, and a secondary phase is consolidated by heat treatment in a temperature range of 400or to 700 C and at a pressure of 1000 bar to 3000 bar.

The aggregation period can be between 1 hour and 6 hours. However, carrying out consolidation at 5400C, 2000 bar and 2 hours aggregation time achieves the best results. This is true also for the selection of the composition of the starting stages for the base material and the secondary phase, when the base material is introduced as material evaporated in inert gas. If the choice of the outer shape of the secondary phase allows it, the secondary phase is also present in this processing form. A preferred process step is the degasification of the mixture of base material and secondary phase, before it is consolidated. This consolidation can be effected by hot isostatic pressing, sintering, extrusion or forging.

According to a further solution, it is also possible to produce the material of the invention by conveying the secondary phase to the base material present in liquid form.

When introducing the secondary phase into the liquid base material it is advantageous, for protection of the secondary phase, to provide it also with a coating so as to prevent too strong a reaction with the base material.

In both methods of production of the invention the secondary phase can be introduced in different forms.

However, it is preferably present in both processes as a particle, wire, short fibre or layer. In a preferred step the secondary phase is pre-treated before consolidation in order to stabilise the martensitic phase. This may be deformation of the secondary phase or homogenisation of the components of the secondary phase in it.

The processes for producing the material do not necessitate any critical process steps in which the secondary phase has to be brought to a specific outer shape. Furthermore, in order to have high material absorption the material does not need to be heated in an additional step above the recrystallisation temperature of the base material.

The invention will be described in detail below by means of an exemplary embodiment, from which further details, features and preferences can be seen.

In one embodiment of the process according to the invention for producing the material, powder evaporated in argon from the Al alloy EN AW-6061, in accordance with DIN EN 573, with a particle size less than 45jim, and NiTi powder produced in the same way with a particle size smaller than 180 Hm and a composition of 49.9 atomic % nickel and 50.1 atomic % titanium, is used. The powder mixture filled into capsules contains 10 volume % of the NiTi powder with the remaining 90% being powder of the Al alloy EN AW-6061. The mixture is degasified at room temperature to avoid gascontaining pores, and the capsule is sealed in a gastight manner. The consolidation of the material is effected by hot isostatic pressing for two hours at a pressure of 2000 bar and a temperature of 5400C.

In a material produced in accordance with this process, the NiTi particles are homogenously distributed in the Al alloy EN AW-6061. The tensile strength of this material (223 MPa) corresponds to that of a material produced by hot isostatic pressing and consisting only of the Al alloy EN AW-6061. However, the damping capacity of 5x10-3 for this material is ten times greater than that for aluminium. Moreover, the material has a breaking elongation greater than 10%, thus making it possible to use it as a structural material.

In summary, the tensile strengths of the base materials of the present invention are hardly affected by the presence of the secondary phase so these materials are able to bear heavy loads. However, the damping capacity (which is determined by measuring the decrease in amplitude of free oscillations in the material) is significantly improved.

Claims

1. Material having high material absorption and tensile strength, made from a substantially metallic base material and a secondary phase, characterised in that the secondary phase is metallic and has at least partially a martensitic structure.

2. Material according to claim 1, characterised in that the secondary phase includes an alloy.

3. Material according to claim 2, characterised in that the alloy contains nickel and titanium in a range of from 48-52 atomic %, preferably 49.9 atomic % nickel and 50.1 atomic % titanium.

4. Material according to one or more of the preceding claims, characterised in that the secondary phase contains additives of up to 25 atomic %.

5. Material according to claim 4, characterised in that the additives are zirconium and/or hafnium and/or copper and/or niobium and/or manganese and/or palladium and/or platinum and/or iron.

6. Material according to one or more of the preceding claims, characterised in that the secondary phase is present in the form of particles and/or wires and/or short fibres and/or in layers.

7. Material according to one or more of the preceding claims, characterised in that the amount of secondary phase in the total material is 5-60 volume %.

8. Material according to one or more of the preceding claims, characterised in that the base material is a soft metal or a soft metal alloy.

9. Material according to one or more of the preceding claims, characterised in that the base material is the Al alloy EN AW-6061, in accordance with DIN EN 573.

10. Material according to one or more of the preceding claims, characterised in that the base material has a different structure.

11. Material according to one or more of the preceding claims, characterised in that the base material is a compound material having at least a third phase.

12. Material according to one or more of the preceding claims, characterised in that the secondary phase forms a compound on the boundary surface with the base material.

13. Material according to any preceding claim substantially as hereinbefore described.

14. Process for the production of a material according to one or more of the preceding claims, characterised in that a mixture of base material, present in powder form, and a secondary phase is consolidated by heat treatment in a temperature range of from 400-7000C and at a pressure of 1000-3000 bar.

15. Process according to claim 14, characterised in that the base material, and the secondary phase if its outer shape permits it, are present as a material evaporated in inert gas.

16. Process according to claim 14 or 15, characterised in that the mixture of base material and secondary phase is degasified cold and/or hot before consolidation.

17. Process according to claim 14, 15 or 16, characterised in that the heat treatment involves hotisostatic pressing, so-called HIPpen, and/or sintering and/or extrusion and/or forging.

18. Process for the production of a material according to one or more of the preceding claims 1 to 12, characterised in that the secondary phase is conveyed to the base material present in liquid form.

19. Process according to one or more of the preceding claims 14 to 18, characterised in that the secondary phase is provided with a coating.

20. Process according to one or more of the preceding claims 14 to 19, characterised in that the secondary phase is introduced as particles and/or wires and/or short fibres and/or as layers.

21. Process according to one or more of the preceding claims 14 to 20, characterised in that the secondary phase is pre-treated before the processing.

22. Process according to claim 21, characterised in that the pre-treatment is deformation and/or homogenisation.

23. Process according to any of claims 14 to 22 substantially as hereinbefore described.