CERAMIC ARMOR WITH CONTROLLED PORE SIZE DISPERSION

Abstract

Anti-ballistic armor element, comprising a ceramic body comprising a sintered material consisting of ceramic grains with a Vickers hardness of more than 5 GPa, the total pore volume of said material being between 0.5 and 10%, said ceramic body being characterized in that the cumulative volume of pores with a diameter of between 30 and 100 micrometers represents between 0.2 and 2.5% of the volume of said material, the cumulative volume of pores with a diameter of more than 100 micrometers is less than 0.2% of the volume of said material , the remainder of said total pore volume consisting of pores whose diameter is less than 30 micrometers.

Claims

1. An anti-ballistic armor element, comprising a ceramic body comprising a sintered material consisting of ceramic grains with a Vickers hardness of more than 5 GPa, the total volume of the pores of said material being between 0.5 and 10%, said ceramic body being characterized in that: the cumulative volume of pores with a diameter of between 30 and 100 micrometers represents between 0.2 and 2.5% of the volume of said material, the cumulative volume of pores with a diameter greater than 100 micrometers is less than 0.2% of the volume of said material, the rest of said total pore volume consists of pores with a diameter of less than 30 micrometers; and wherein the distribution by volume of the diameter of the pores of said matereial is multimodaland comprises at least a first peak with a maximum within a range of pore diameters comprised between 0.1 and 15 micrometers and a second peak with a maximum within a pore diameter interval of between 40 and 80 micrometers.

2. An armor element according to claim 1, wherein at least 95% of said ceramic grains have a diameter comprised between 1 and 50 micrometers.

3. An armor element according to claim 1, in which the cumulative volume of the pores of said material of diameter comprised between 30 and 100 micrometers is greater than 0.3% and/or less than 2.3% of the volume of said material.

4. An armor element according to claim 1, in which the cumulative volume of the pores of said material of diameter greater than 80 micrometers is less than 0.8% of the volume of said material.

5. An armor element according to claim 1, in which the cumulative volume of the pores of said material of diameter comprised between 40 and 80 micrometers is greater than 0.5% and/or less than 1.5% of the volume of the said material.

6. An armor element according to claim 1, in which the cumulative volume of the pores of said material of diameter less than 40 micrometers is less than 1.5% of the volume of said material.

7. An armor element according to claim 1, in which the distribution by volume of the diameter of the pores of said material is.

8. An armor element according to claim 1, in which at least 70% by volume of the pores of said material with a diameter of more than 30 micrometers have a sphericity of more than 0.8.

9. An armor element according to claim 1, in which said ceramic body is monolithic and has an impact surface of more than 2 cm2 and a thickness of more than 3 mm.

10. An armor element according to claim 1, in which the grains of said sintered material are grains of alumina, silicon carbide, boron carbide, or comprise a boride.

11. An armor element according to claim 10, in which the grains are made of silicon carbide, of which at least 95% have a diameter of more than 2 micrometers and/or less than 30 micrometers and have preferably an alpha crystal structure ?.

12. An armor element according to claim 1, in which the ceramic body is chosen from among a plate, a breastplate, a helmet, a vehicle bodywork element, a tube.

13. An armor element according to claim 1, comprising a ceramic body comprising a material, provided on its inner face or opposite the impact face with a rear energy dissipation coating, consisting of a material of hardness lower than that of the material constituting the ceramic body, in which the material that constitutes the rear coating is chosen from polyethylenes (PE), in particular ultra-high density polyethylenes (UHMPE), glass or carbon fibers, aramids, metals such as aluminum, titanium or their alloys or steel.

14. An armor element according to claim 13, in which the ceramic body-rear coating assembly is surrounded by an envelope of a confinement material, said material constituting the envelope being chosen from polyethylenes (PE), in particular ultra-high density polyethylenes (UHMPE), glass or carbon fibers, aramids, metals such as aluminum or steel.

15. Method for manufacturing the sintered material of the ceramic body of the armor element according to claim 1, comprising the following steps: a) preparation of a starting filler comprising: a ceramic particle powder, the median particle diameter of which is between 0.1 and 30 micrometers, preferably at least one sintering additive powder, a porogen powder chosen from polyethylene; polystyrene; polymethacrylates, polyvinyl chlorides (PVC); cellulose acetate, epoxy or polyimide resins; or derivatives or a mixture thereof, the median particle diameter of which is between 60 and 80 micrometers, b) shaping of the starting filler in the form of a preform, c) solid phase sintering of said preform comprising a debinding step in order to vaporize any part of the porogen so as to obtain a product according to the invention.

16. Use of the armor element according to claim 1, as ballistic protection of a person or a land, sea or air vehicle, or of a fixed installation such as a building, an enclosure wall, or a guardhouse, in particular in the form of a plate, a tile, a mosaic, for example in the form of hexagons or nodules, of a breastplate, of a shield, of a helmet, of a bodywork element of a vehicle such as a door, a seat, a tube.

17. The method of claim 15, wherein sintering comprises sintering at a temperature above 1700? C.

18. The method of claim 15, wherein sintering comprises sintering at a temperature below 2300? C.

19. The method of claim 15, wherein sintering hot pressing, hot isostatic pressing, or spark plasma sintering.

20. The method of claim 15, wherein sintering comprises applying a pressure above 10 MPa.

Description

FIGURES

[0076] FIG. 1 is an image taken under a scanning microscope of a polished section of the sintered material of the ceramic body of example 2 according to the invention.

[0077] FIGS. 2 and 3 show the fracturing diagram of armor elements, respectively, of Example 4 (comparative) and Example 2 (according to the invention) following successive firings of 7.62?51 mm P80 ammunition as described in the examples.

[0078] FIGS. 4 and 5 show the volume distribution of the sphericity of the pores as a function of their median diameter in micrometers, measured by tomography according to the technique explained above, for example 2 (according to the invention) and for example 3 (comparative), respectively.

[0079] The examples which follow are given purely by way of illustration and do not limit the scope of the present invention under any of the aspects described.

EXAMPLES

[0080] In all the following examples, ceramic bodies in the form of plates, of 100 mm?100 mm format and 7 to 10 mm thickness, were initially produced by pressing a mixture of atomized powders. The shaping mixture of example 1 (comparative) was made in the same way as described in example 1 of US 5589428. That of example 2 (according to the invention) differs in that the PMMA powder used has a substantially narrower diameter distribution. Example 3 (comparative) differs from example 1 in that its median porogen diameter is larger. Example 4 (comparative), unlike the previous examples, does not contain added porogen in the form of PMMA beads.

[0081] The formulations of the various examples have been reported in Table 1 below.

TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 % by weight (comparative) (invention) (comparative) (comparative) Green SiC powder ?325 mesh 94.78 94.78 94.78 94.78 Norton SIKA ground to 0.45 ?m B4C powder 0.66 0.66 0.66 0.66 Norbide Boron Carbide? D.sub.50 = 3.6 ?m Occidental Chemical Company's 4.56 4.56 4.56 4.56 Plyophen 43290 phenolic resin comprising 42.5% coke by weight total mineral filler % 100 100 100 100 Addition of porogen % +2.84% +0.75% +1.70% No PMMA beads PMMA beads PMMA beads PMMA beads D.sub.10 (?m) 53 63 62 D.sub.50 (?m) 70 70 85 D.sub.90 (?m) 110 75 118 (D90 ? D10)/D50 0.81 0.17 0.65 additions % relative to the weight of +9.00% +9.00% +9.00% +9.00% mineral filler Binder + dispersant added
The ceramic bodies were shaped by casting.
The parts were removed from the mold and then dried for 24 hours at 110? C. before firing under argon at 2150? C. for 1.5 hours. The characteristics of the ceramic body and the composition of the various materials constituting it are shown for each embodiment in Table 2.
The pore diameter and volume were determined by X-ray tomography using the INSA Lyon CT scanner on the basis of 3 mm*3 mm*4 mm samples. The resolution was adapted to the diameter of pores observed, typically 3 ?m/voxel for pores with a diameter of more than 30 micrometers and 0.3 um/voxel for pores with a diameter of less than 30 micrometers in order to constitute a volume distribution diagram of pores and calculate the cumulative pore volumes. The volume percentage of pores with a diameter of more than 30 ?m whose sphericity is greater than 0.8 was calculated from the curves shown in FIGS. 4 and 5.
The (equivalent) diameters of the grains could be determined from scanning electron microscope images of a polished section of said sintered material treated with Murakami reagent on an image of 100?150 micrometers, from which 700 grains were counted.

[0082] The free or residual carbon and boron contents were measured respectively by LECO and ICP. The crystallographic form aof SiC present was determined by X-ray diffraction analysis.

TABLE-US-00002 TABLE 2 Example 1 Example 2 Example 3 Example 4 (comparative) (invention) (comparative) (comparative) Characteristics body/ceramic material after firing Microstructural characteristics Vickers hardness of the grains of sintered material (GPa) >10 Measured according to ASTM C1327:03 apparent density g/cm.sup.3 according to ISO 18754 3.00 3.12 3.04 3.15 Measurements made by X-ray tomography and interpreted by 3D image analysis % by number of grains of diameter >95% between 1 and 50 ?m Median grain diameter in number of the material (?m) N/M 3.9 4.1 4.0 D10 of grains in number of the material (?m) N/M 2.2 2.3 2.1 D90 of grains in number of the material (?m) N/M 6.6 6.5 6.4 Porosity or total pore volume % 7.5 2.3 4.5 1.2 cumulative pore volume <30 ?m (vol %) N/M 0.95 1.3 1.2 cumulative volume of pores between 30 and 100 ?m (vol %) N/M 1.3 2.9 <0.1 cumulative volume of pores >100 ?m (vol %) N/M <0.05 0.3 <0.1 cumulative pore volume <40 ?m (vol %) N/M 0.95 1.3 1.2 cumulative volume of pores between 40 and 80 ?m (vol %) N/M 1.2 2.0 <0.1 cumulative volume of pores >80 ?m (vol %) N/M 0.05 1.1 <0.1 Median pore diameter (D.sub.50) (?m) 70 48 62 <5 Maximum of 1st pore peak (?m) N/M <5 <5 <5 Maximum of 2nd pore peak (?m) N/M 55 60 None Average sphericity N/M 0.94 0.88 N/M Volume percentage of pores with a diameter of more than 30 N/M 84% 66% N/A micrometers whose sphericity is greater than 0.8 chemical composition (% by weight) Silicon carbide SiC (LECO) >98 >98 >98 >98 B (ICP) <1 <1 <1 <1 Free carbon (LECO) <1 <1 <1 <1 N/M = not measured; N/A = not applicable

[0083] For each example, eight ceramic plates obtained according to the process described above with a surface density of 21.2 Kg/m.sup.2 (?0.5 Kg/m.sup.2) were bonded to 200 mm?200 mm?5 mm metal plates of aluminum 7020 T6.

Areal density ?.sub.a is calculated according to the following formula

?.sub.a=t??.sub.v

where:
?.sub.a is the surface density expressed in Kg/m.sup.2 [0084] t is the thickness of the plate, expressed in mm
?.sub.v is the apparent density expressed in Kg/dm.sup.3 typically measured according to standard ISO 18754.

[0085] Each ceramic-metal assembly was exposed to a shot from a distance of 15 meters with a 7.62?51 mm P80 ammunition (armor-piercing ammunition with steel core) at different impact speeds. A graph representing the status of the perforation (protection or complete perforation) as a function of the impact speed was established for each example. From this graph, the median velocity V50 from which the probability of perforation is 50% is determined for each example. A velocity of more than 700 m/s taking into account this type of ammunition is considered satisfactory. A high velocity corresponds to a ballistic performance that is higher the lower the surface density. The ballistic properties of the final armor plate are gathered in the following Table 3:

TABLE-US-00003 TABLE 3 Example 1 Example 2 Example 3 Example 4 (comparative) (invention) (comparative) (comparative) Ballistic tests Median velocity V.sub.50 (m/s) 721 789 765 752 for a surface density of 21.2 kg/dm.sup.2
The results grouped together in Table 3 indicate that the choice of material used to manufacture an armor element leads to a better V.sub.50 velocity than the comparative examples. A plate of Example 2 according to the invention was glued using an epoxy adhesive onto a layer of fiberglass connecting it with a polyethylene (UHMWPE) plate. The assembly is wrapped in a layer of Kevlar fabric also bonded with an epoxy resin to form an armor element. A second armor element was also made in the same way but with a plate according to Example 4 (comparative). The multi-impact ballistic performance was evaluated following successive firings of 7.62?51 mm P80 ammunition. Three shots were made on each piece of armor. The results are reported in Table 4.

TABLE-US-00004 TABLE 4 example 2 comparative invention example 4 thickness (mm) 8.5 Plate shape flat surface (cm.sup.2) 670 Characteristics of backing Fiberglass + high density PE Thickness: 17 mm Characteristics of containment Aramid fibers (Kevlar?) envelope weight/surface ratio (Kg/m.sup.2) 42 +/? 0.5 Visual observation after firing no perforation no perforation Observation No crack Presence of cracks connecting impact connecting impact holes holes Sign of weakening after several impacts
The results of these tests are also illustrated by FIGS. 2 and 3, corresponding respectively to the armor element with a sintered material according to example 4 and according to example 2 according to the invention.
These latter results show that the armor element according to the invention, the ceramic body of sintered material of which has a controlled pore diameter distribution, has improved multi-impact resistance. This is related to the ceramic's ability to localize damage after an impact, leaving a larger healthy (crack-free) area to stop subsequent impacts.
In addition, the comparison of FIGS. 4 and 5 (comparative example) also shows that the example according to the invention (FIG. 4) has a lower proportion of elongated pores among the larger pores, which indicates lower pore agglomeration and consequently a better pore distribution in the material according to the invention.