DE4031550A1 - Ballistic armour material for helmet - comprises plate or shell of ceramic layer soldered to layer of shape memory alloy for walls and vehicles - Google Patents

Abstract

Material is cpd. material with ceramic layer(s) (3) and plate layer(s) (5), secured to the ceramic layer (3) by hard solder, made from a shape memory alloy. Pref. ceramic layer (3) is of an oxide ceramic, pref. aluminium- or silicon-oxide ceramic. If the material comprises solely ceramic- (3) and plate-layers (5), plate layer(s) is of a conventional ductile metal, esp. high tensile tough steel, integrated into the sandwich by solder bonding to the SMA plate layer (5) which is soldered to the ceramic layer (3). The soldering is through an active solder layer. The SMA plate layer (5) has a plated blocking layer, on the side(s) towards the solder, of niobium, silver or other noble metal with a plated layer thickness of at least 5-10 micron. The ceramic layer(s) and the layer(s) (5) of SMA plate are initially soldered together at solder melting temp. of more than 800 deg.C. The steel plate layer (4) is soldered to the SMA layer (5) at less than 500 deg.C. USE/ADVANTAGE - Improved impact resistance esp. against ballistic projectiles.

Description

The invention relates to a ballistic protective armor the preamble of claim 1, such as from the DE-OS 34 25 634 emerges as known.

This document describes a bulletproof armor plate several layers of resin-impregnated fabric, the Harzan parts selected to different degrees within the fabric layers are and on the one hand a great hardness, on the other hand also one get some flexibility after one shot.

The US-PS 30 42 555 describes the manufacture and use an aluminum plate for ballistic protective armor, through targeted heat treatment with different Depth effect a graded in the thickness of the aluminum plate Hardness is brought about.

It would be desirable to have a particularly hard ceramic plate or hard metal plate with a flexible and ductile metal plate alternately to create a ballistic To create protective armor. A mere glue between Ceramic plate and metal base gives the material ver However, the bond is not sufficiently high because one Shot in the very brittle ceramic plate in very small parts decays, which is not sufficiently high due to the adhesive Strength could be held together. The ceramic plate was in such a case without great breakdown resistance  flaking off the metal surface over a large area, so that practically only the dielectric strength of the metal Underground would be available.

DE-PS 33 45 219 shows a multilayer solder lie for soldering ceramic parts to metal parts, whereby the solder foil a metallic intermediate layer of about 50 to 30 microns made of copper, iron, nickel or a copper beryllium Alloy or of a nickel-iron alloy that contains does not directly participate in the solder connection, but the only residual stresses between the components to be soldered to dismantle. However, this is only a limited amount of chip removal degradable and therefore only small-area solder connections possible.

The object of the invention is the generic ge put ballistic armor in view of a higher Further develop dielectric strength.

This object is achieved by the characterizing Features of claim 1 solved. Thanks to the use of a ke ramic layer becomes very hard on the impact side of the Protective armor created. Thanks to the brazing with a metal mical base from a shape memory alloy becomes a high-strength connection of the ceramic layer with the metal on the other hand, thanks to the Use a base or an intermediate layer Shape memory alloy is even a large-scale hard enables ceramic to be soldered to metal. Because of the strong different temperature expansion of the two materials Ke Ceramic and metal on the one hand and due to the very low The ductility of ceramics usually build up in Very high solder connections with such a material pairing Internal stresses that lead to the destruction of the ceramic part  and / or lead the solder joint. When using Shape memory alloys, however, do not experience this phenomenon on because these very strong ductile metal alloys the residual stresses within the large-area solder joint reduce to easily tolerable values.

Advantageous embodiments of the invention can the Unteran sayings are taken. Otherwise, the invention is based an embodiment shown in the drawings explained below; show:

Fig. 1 shows a cross section through the part of a ballistic armor according to the invention and

FIG. 2 shows an enlarged individual representation of detail II from FIG. 1.

. The plate shown in Figure 1 1 for a ballistic protective armor is triple-layered with an externally - outside 7 - lying ceramic layer 3, an inside of parent steel sheet layer 4 and an interposed soldered sheet metal layer 5 made of shape memory alloy. As can be seen in FIG. 2, the three layers 3 , 4 and 5 are each soldered to one another, with a solder layer 6 being formed between two layers. The solderings are active solder layers that can be easily manufactured.

The shape memory alloys mentioned here for the sheet metal layer 5 are also known under the designation Shape Memory Alloy (SMA). These are special, particularly pure alloys with precisely coordinated alloy components that reveal the special properties of these alloys. Technically used are nickel-titanium alloys, copper-zinc-aluminum alloys and copper-aluminum-nickel alloys; Iron base alloys of this type are also known which are of increasing interest for reasons of price. Shape memory alloys change their crystal structure depending on temperature and stress. The material is in the martensitic state below a critical temperature and in the austenitic state above another critical temperature. The transformation takes place in a narrow temperature range, the location and width of which are alloy-specific. One of the properties of the superelasticity of these alloy types that is of interest here is a phenomenon that occurs only in the austenitic range, that is to say above the transition temperature. This property represents an elastic, rubber-like extensibility of several percent, whereby the stresses that occur are moderately high but dependent on strain. Another property of shape memory alloys that is also of interest here is the pseudoplasticity that can be observed in the martensitic state, in which the material can be permanently deformed to a high degree under the effect of low stresses, the stresses required for deformation being almost independent of strain.

When cooling the solder joint from the very high soldering temperature The shape memory alloy initially lies in egg state in which it is neither super elastic nor is pseudoplastic, but similar to a conventional one Steel behaves at high temperatures. Only when the Solder connection far below the solidification temperature of the Lo The shape memory alloy then shows the first super elastic property. Until then in the joint Thermal residual stresses built up due to cooling can who are now broken down due to the super-elastic behavior the, but with increasing, cooling-related  thermal relative expansion of the components at the joint Tension - albeit at a low level - increases. Sometime the temperature range of the microstructure becomes with further cooling passed through and the material changes more and more into the martensitic state, so that more and more the pseudoplastic property comes into play. The Material can stay at relatively low and constant deform permanent stresses and the residual stresses mine this low level.

The nickel-titanium alloys allow a super elasticity of 8% elongation, which is a lot for metals; however, this type of alloy is very expensive. The two other alloy types mentioned above are cheaper, but only allow super elasticity of 2%, which is also a lot. If sheet metal layer 5 is used sparingly, the expensive type of alloy may well be justifiable in terms of cost, especially since the layer thickness for nickel-titanium alloys only needs to be about a quarter of the layers made of the other super-elastic alloys with otherwise comparable boundary conditions.

It should be emphasized that the soldering can be carried out as simple active soldering without special pretreatment in a single operation. The solder is also introduced in foil form in the joint and the parts in the order of steel sheet layer 4 , foil for the steel-side soldering 6 ', sheet layer 5 made of shape memory alloy, further soldering foil for the ceramic-side soldering 6 and ceramic layer 3 are layered on top of each other and countered in the evacuable soldering furnace ben. It should be mentioned in this connection that the soldering of the sheet metal layer 5 without pretreatment in a certain edge zone due to the diffusion of solder into the material of the intermediate layer changes slightly in alloy and the shape memory properties can already be disturbed thereby. Such an edge zone would therefore be lost for the usable superelasticity or pseudoplasticity, which would be inappropriate. This loss would have to be taken into account by choosing a correspondingly thicker wall thickness of the starting material. It would be more appropriate to prevent such a diffusion of solder into the shape memory alloy by electroplating a metallic barrier layer. For example, silver in a layer thickness of about 5 to 10 μm would be suitable for this; niop, gold or platinum could also be used in principle. It should also be mentioned that - what is possible today - such an alloy type of shape memory alloy must be selected that survives the soldering temperatures overall without losing the shape memory property of the material. At least with short-term exposure to 900 ° C in the range of about 2 minutes, the shape memory property of the sheet layer 5 is still preserved th. This should be heated up very quickly at least in the range above 600 ° and very quickly after the solder has reacted with the ceramic be cooled down again. For example, when soldering a layer of nickel-titanium shape memory alloy to ceramic, it took about 90 minutes to heat up to 600 ° C from room temperature, whereas the final heating to 850 ° C with an over three times faster heating rate (20 degrees per minute) Took 12 minutes. After a short holding time of about 10 seconds, cooling took place in a room temperature atmosphere, with an average cooling rate in the temperature range between 850 and 400 ° C. of over 60 degrees per minute; even below that, the rate of cooling slowed slowly. When the workpiece is heated to soldering temperature in a vacuum furnace with heat transfer only by radiation, the above-mentioned heating speeds are difficult to achieve. For this reason, it is expedient to accomplish the heating inductively by means of a form inductor, the required heating speeds not causing any difficulties. After the soldered-on ceramic material does not heat up during inductive heating and thus remains essentially at room temperature, this temperature gradient can be used after cooling of the solder with the ceramic for cooling by heat conduction. With inductive heating, the ceramic is only heated close to the surface, whereas the lower ceramic layers are still cool. The cooling can also by blowing with a cold protective gas, e.g. B. Accelerated forming gas; in an advanced cooling phase, water can also be used.

As preferably used as the material for the steel sheet layer 4, a quenched and tempered steel, alloy steel is used, the temperature should be Löttem in the soldering of this steel is not higher than 500 ° C, so that steel does not lose its hardness. On the other hand, a temperature of over 800 ° C must be maintained at least briefly when soldering the ceramic layer so that the reaction required for soldering with the ceramic material occurs. Therefore, the ceramic layer 3 is advantageously carried out with the sheet metal layer 5 made of shape memory alloy with a hard solder 6 , for example with a silver-titanium solder, which melts at 850 ° C., whereas the steel sheet layer 4 is soldered to the shape memory alloy by means of a high-melting soft solder 6 ' becomes. Suitable solders here for z. B .:

• - Tin / antimony solder (95: 5) with a melting temperature of 240 ° C,
• - Tin / silver solder (90:10) with a melting range of 220 up to 300 ° C,
• - Lead / silver solder (97: 3) with a melting temperature of 305 ° C or  
• - Lead / indium solder (96: 4) with a melting temperature of 325 ° C.

If it succeeds to add new, even higher melting soft solders develop, these would also be applicable; would be similar it is also conceivable to use extremely low-melting brazing alloys to be used if such should become known, whereby the processing temperature of these solders is below 500 ° C To be able to solder steel. Unrefined steel can self-ver are soldered constantly at higher temperatures, al However, its strength is less than that of tempered Stole.

In the ceramic layer, an impact-resistant ceramic is preferably used, preferably a silicon nitride ceramic, which has proven to be particularly impact-resistant and tough, but which has a particularly low coefficient of thermal expansion of only 3 × 10 ^-6 per degree and accordingly changes in temperature only about 27% of the thermal expansion of steel with a thermal expansion coefficient of 11 · 10 ^-6 per burr.

To demonstrate the stability of the solder joint according to the invention was a square plate with a side length of 20 mm and the following layer structure:

• - 4 mm thick ceramic plate made of silicon nitride,
• - Active solder foil (silver-titanium), 0.2 mm thick,
• - Nickel / titanium shape memory alloy (50/50 atomic percent), 0.3 mm thick,
• - Active solder foil (silver-titanium), 0.2 mm thick and
• - Sheet steel layer, 2 mm thick, low carbon construction steel.

This soldered composite die was made from room temperature quenched in liquid nitrogen and then through Leave to warm up again at room temperature. It has this Shape memory alloy survived without damage. A like one Comparative sample, but without the intermediate layer from the shape memory alloy was completely damaged after the quenching attempt sigt; the ceramic layer was completely chipped. They are par shell-like allel to the solder joint Observe flaking of material from the ceramic plate been.

Thanks to the intermediate soldered sheet metal layer 5 , the ceramic layer 3 can be soldered indirectly to a steel sheet layer 4 , a low-stress and permanent, high-strength connection being achieved. The parts of the ceramic layer that break apart due to the impact of a projectile 2 on the ceramic layer are held together securely thanks to the soldering, so that the ceramic layer 3 is able to effectively brake the projectile 2 despite numerous cracks and near-surface material flaking. Due to its ductility, the sheet steel layer 4 underneath takes up deformation work and thereby contributes to retarding the projectile 2 . After a first shot, the protective armor is readily able to effectively catch a closely adjacent second shot.

Instead of a three-layer structure, it is also conceivable to provide an even larger number of layers. A ceramic layer can expediently alternate with a metallic layer, these different layers being brazed to one another. However, even with such an increased number of layers, care should be taken to ensure that a ceramic layer is only ever indirectly soldered to a steel layer, or - which would also be easily conceivable - to a layer of high-strength aluminum; it must always be between a ceramic layer and a steel or aluminum layer, a sheet metal layer 5 made of memory alloy to reduce the thermally induced inherent stresses, so that the soldering is permanent on the larger areas.

It is also conceivable that the sheet metal layer 5 from shape memory alloy not only takes on the function of residual stress reduction in the area of brazing, but also takes on the function of the supporting metallic layer within the protective armor, where, however, the sheet metal layer made of shape memory alloy should be dimensioned accordingly . In view of the high costs of this alloy, however, efforts will be made to use this material as sparingly as possible and to have load-bearing functions taken over by other less expensive materials wherever possible. However, it should be emphasized that the shape memory alloys are particularly well suited to absorb high deformations and accordingly high deformation work due to their extremely high extensibility, which is particularly important for retarding the impacting projectile. Accordingly, it would be quite conceivable to build up a two-layer ballistic protective armor from a ceramic layer and from a relatively strong sheet metal layer made of shape memory alloy.

As further alternative forms for protective armor of the type in question, it would be conceivable to provide a plurality of ceramic layers within the protective armor, each of which is brazed to one another with the interposition of a relatively strong sheet metal layer made of shape memory. It would be an advantage to have the thickness of the individual ceramic layers decrease from the outside to the inside and to have the SMA metal layers increase from the outside to the inside. Towards the outside 7 , the hardness of the ballistic protective armor should predominate, which is primarily caused by the ceramic plates and their hardness, whereas towards the opposite inside, the deformability and the ability to work of the protective armor, which is caused by the soldered metal layers, should increase becomes.

The ballistic protective armor can be designed in the form of a shell det be so that z. B. hard hats or armor for Building doors or vehicle walls and vehicle doors made from them can be produced. If there are several small plates from palm-sized to a movable covering put together, such a coating can be in a shot vest sewn in, which can be worn on the body.

Claims (7)

1. Ballistic protection armor in the form of at least one panel or shell made of a layer-like-structured composite material to high mechanical breakdown resistance, characterized in that the composite material of at least one layer (3) made of ceramic and at least one with the ceramic layer (3) hard-soldered sheet metal layer (5) contains a shape memory alloy. 2. Protective armor according to claim 1, characterized in that the ceramic layer ( 3 ) made of oxide ceramic, preferably made of aluminum oxide ceramic or silicon nitride ceramic. 3. Protective armor according to claim 1 or 2, characterized in that in the event that only one ceramic layer ( 3 ) and only one sheet metal layer ( 5 ) is provided, the ceramic layer ( 3 ) on the outside ( 7 ) is arranged. 4. Protective armor according to one of claims 1 to 3, characterized in that in the layered composite material we at least one sheet metal layer ( 4 ) made of conventional, ductile metal, in particular made of high-strength, tough steel, this sheet metal layer ( 4 ) only is indirectly soldered to a ceramic layer ( 3 ) with the interposition of a soldered sheet metal layer ( 5 ) made of shape memory alloy. 5. Protective armor according to one of claims 1 to 4, characterized in that the solderings ( 6 ) are designed in the form of an active solder layer. 6. Protective armor according to one of claims 1 to 5, characterized in that the sheet metal layer ( 5 ) made of shape memory alloy to solder ( 6 ) with a preferably electroplated metallic barrier layer made of niobium, silver or other precious metals in a layer thickness of at least 5 to 10 µm is provided. 7. protective armor according to claim 4, 5 or 6, characterized in that the ceramic layer (s) ( 3 ) with the (the) sheet metal layer (s) ( 5 ) made of shape memory alloy (each) with a first solder ( 6 ) is soldered together (Are) whose melting temperature is higher than 800 ° C and that the steel sheet layer (s) ( 4 ) with the (the) sheet layer (s) ( 5 ) made of shape memory alloy (each) is soldered together with a second solder ( 6 ') (are) whose melting temperature is lower than 500 ° C.