U.S. patent application number 11/867988 was filed with the patent office on 2012-07-12 for methods of making and using reactive shaped charge shock initiation devices including reactive multilayer structures.
Invention is credited to Timothy Langan, Michael A. Riley.
Application Number | 20120174740 11/867988 |
Document ID | / |
Family ID | 38562025 |
Filed Date | 2012-07-12 |
United States Patent
Application |
20120174740 |
Kind Code |
A1 |
Langan; Timothy ; et
al. |
July 12, 2012 |
Methods of Making and Using Reactive Shaped Charge Shock Initiation
Devices Including Reactive Multilayer Structures
Abstract
The invention provides shock initiation devices comprising
multilayer structures with constituent layers that undergo an
exothermic self-propagating reaction once initiated by shock. The
multilayer structures may be used as components in shaped charges,
EFP devices, warheads, munition casings, interceptors, missiles,
bombs, and other systems. The reactive layer materials may be
selected based on required structural properties, density and
reaction temperature.
Inventors: |
Langan; Timothy;
(Catonsville, MD) ; Riley; Michael A.; (Towson,
MD) |
Family ID: |
38562025 |
Appl. No.: |
11/867988 |
Filed: |
October 5, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10855298 |
May 27, 2004 |
7278354 |
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11867988 |
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10839638 |
May 5, 2004 |
7278353 |
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10855298 |
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60473509 |
May 27, 2003 |
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Current U.S.
Class: |
86/20.1 |
Current CPC
Class: |
F42B 12/76 20130101;
F42B 12/06 20130101; C06B 45/14 20130101; F42B 39/00 20130101; F42B
1/032 20130101 |
Class at
Publication: |
86/20.1 |
International
Class: |
F42B 1/036 20060101
F42B001/036 |
Goverment Interests
GOVERNMENT CONTRACT
[0002] The United States Government has certain rights to this
invention pursuant to Contract No. DASG-60-02-0171 awarded by the
U.S. Army Space Missile Defense Command, Contract No.
N68936-03-C-0019 awarded by the U.S. Navy, and Contract No.
F08630-02-SC-0048 awarded by the U.S. Air Force.
Claims
1: A method of making a shaped charge shock initiation device
comprising: depositing layers of reactive materials onto a
substrate to form a reactive multilayer structure comprising layers
which are capable of subsequently reacting with each other; and
incorporating the reactive multilayer structure in a reactive
shaped charge shock initiation device.
2: The method of claim 1, wherein the deposition process comprises
magnetron physical vapor deposition, electron-beam physical vapor
deposition or chemical vapor deposition.
3: The method of claim 1, further comprising removing the reactive
multilayer structure from the substrate.
4: The method of claim 1, wherein the substrate comprises a
mandrel.
5: The method of claim 1, wherein the reactive materials are
deposited on the substrate at a rate of at least 0.01 mm per
hour.
6: The method of claim 1, wherein each of the layers has a
thickness of from about 1 micron to about 5 mm.
7: The method of claim 1, wherein the layers of reactive materials
are directly adjacent each other.
8: The method of claim 1, further comprising forming an
interdiffusion zone between adjacent reactive material layers.
9: The method of claim 8, wherein the interdiffusion zone inhibits
reaction between the reactive material layers when the multilayer
structure is subjected to a localized heat source.
10: The method of claim 8, wherein the interdiffusion zone has a
thickness sufficient to prevent reaction between the reactive
material layers when the multilayer structure is subjected to a
localized heat source.
11: The method of claim 1, wherein the reactive material layers are
separated from each other.
12: The method of claim 11, wherein the reactive material layers
are separated by at least one layer of inert material.
13: A method of reacting a multilayer shaped charge structure
comprising: forming a reactive multilayer shaped charge structure
comprising repeating layers of reactive components which are
capable of subsequently reacting with each other; and initiating
reaction of the reactive components by subjecting the components to
shock.
14: The method of claim 13, wherein the shock is provided by an
explosive.
15: The method of claim 13, wherein the shock is provided by impact
of the device with an object.
16: The method of claim 13, further comprising dispersing the
components.
17: The method of claim 16, wherein the components are dispersed
after they are subjected to the shock.
18: The method of claim 16, wherein the components are dispersed in
a pattern.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/855,298 filed May 27, 2004, which claims the benefit of
U.S. Provisional Patent Application Ser. No. 60/473,509 filed May
27, 2003. Application Ser. No. 10/855,298 is also is a
continuation-in-part of U.S. application Ser. No. 10/839,638 filed
May 5, 2004. Each of these applications is incorporated herein by
reference.
FIELD OF THE INVENTION
[0003] The present invention relates to reactive devices, and more
particularly relates to shock initiation devices such as reactive
shaped charges, munitions casings, kinetic interceptors and the
like, which include reactive multilayer structures.
BACKGROUND INFORMATION
[0004] Exothermic warhead technology has been shown to produce
benefits by combining kinetic and thermal energies in the attack
process (Bailey and Nooker, "Coruscative Liner Materials", Applied
Physics Lab, 1963). Later studies by Zaviatsanos and Riley (1990)
further confirmed the benefits of reactive intermetallic systems as
fragmenting warhead systems. Exothermic or pyrophoric materials
have also been investigated for compound target effects, such as
the initiation of fuels and other combustibles. However, the radial
dispersion of thermal energy of conventional reactive intermetallic
materials is low, and the materials are subject to shielding. For
conventional penetrators to perform optimally, key characteristics
include material density, fracture toughness and grain
size/orientation. In some existing systems, grain size can be on
the order of millimeters. This large grain structure produces
orientation anomalies, e.g., from the pancake forging process, and
is in part responsible for a high rejection rate of forged liner
products.
[0005] Problems with conventional reactive intermetallic systems
include their low density, their inability to fully react, and
their lack of physical strength necessary to survive the
high-vibration environments of military hardware. This is due to
the fact that approaches to date have utilized pressed powders.
Many of these systems have failed either in production, or through
vibration testing, both of which can result in frictional
initiation. As reactive powders are pressed, each powder element
has trapped gas on it, typically oxides. When reacted in a highly
constrained manner, the gases create very high, localized
pressures, which tend to tear the pressed body apart, reducing the
amount of large mass available to impart thermal damage.
Furthermore, long time exposure of powder metallurgy materials in
storage makes them susceptible to moisture and vibration, and their
lack of inherent mechanical strength has a direct impact on the
fragment size available for target interaction. In addition,
pyrophoric solid metals that rapidly oxidize when explosively
deformed do not meet their anticipated benefits, since burning is
typically a surface phenomenon, and the bulk of these incendiary
fragments are only slightly elevated in temperature.
[0006] The present invention overcomes these problems by
incorporating reactive materials in multilayer structures, which
have densities that approach theoretical values, and which have
good structural integrity and good mechanical properties.
SUMMARY OF THE INVENTION
[0007] The invention provides devices comprising reactive
multilayers which undergo an exothermic reaction upon shock
initiation. The shock initiation devices may be shaped charges, EFP
devices, warheads, munitions casings, interceptors, missiles,
bombs, rocket propelled grenades and other systems. The reactive
multilayer structures of the devices may be selected based on
required structural properties, density and reaction
temperature.
[0008] An aspect of the present invention is to provide a method of
making a shaped charge shock initiation device comprising:
depositing layers of reactive materials onto a substrate to form a
reactive multilayer structure comprising layers which are capable
of subsequently reacting with each other; and incorporating the
reactive multilayer structure in a reactive shaped charge shock
initiation device.
[0009] Another aspect of the present invention is to provide a
method of reacting a multilayer shaped charge structure comprising:
forming a reactive multilayer shaped charge structure comprising
repeating layers of reactive components which are capable of
subsequently reacting with each other; and initiating reaction of
the reactive components by subjecting the components to shock.
[0010] These and other aspects of the present invention will be
more apparent from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 schematically illustrates a reactive multilayer
structure comprising alternating layers of reactive components
which may be used in a shock initiation device in accordance with
an embodiment of the present invention.
[0012] FIG. 2 schematically illustrates a reactive multilayer
structure comprising layers of reactive components separated by
layers of inert material which may be used in a shock initiation
device in accordance with another embodiment of the present
invention.
[0013] FIG. 3 schematically illustrates a reactive multilayer
structure comprising pairs of reactive component layers separated
by layers of inert material which may be used in a shock initiation
device in accordance with a further embodiment of the present
invention.
[0014] FIG. 4 is a partially schematic cross-sectional view of a
reactive shaped charge including a reactive multilayer structure in
accordance with an embodiment of the present invention.
[0015] FIGS. 5-10 are differential scanning calorimetry (DSC) scans
of various reactive multilayer structures during reaction
thereof.
DETAILED DESCRIPTION
[0016] The present invention provides reactive devices including
reactive multilayer structures which may be ignited by shock
initiation. As used herein, the term "shock initiation device"
means a device or component thereof which undergoes a substantially
simultaneous or bulk exothermic reaction when subjected to
sufficient shock. Reactive components of the device undergo a
substantially simultaneous exothermic reaction upon shock
initiation. The shock may be generated by means such as explosives,
impact with another object or target, or the like. The device may
be arranged such that shock initiation results in an exothermic
wave front which propagates in a direction substantially
perpendicular to the reactive layers, thereby facilitating bulk or
substantially simultaneous initiation of the multilayer structure.
Typical shock initiation devices may disperse the reacted or
reacting material in a desired manner, such as a unidirectional or
omnidirectional pattern.
[0017] The shock initiation devices include reactive multilayer
structures comprising at least two layers of reactive components.
As used herein, the term "reactive components" means materials that
exothermically react with each other upon shock initiation and
which produce a sufficiently high heat of reaction. Elevated
temperatures of at least 1,000.degree. C. are typically achieved,
for example, at least 2,000.degree. C. In one embodiment, the
reactive components may comprise elements that exothermically react
to form intermetallics or ceramics. In this case, the first
reactive component may comprise, for example, Ti, Ni, Ta, Nb, Mo,
Hf, W, V, U and/or Si, while the second reactive component may
comprise Al, Mg, Ni, C and/or B. Typical materials formed by the
reaction of such reactive components include TiAl.sub.x (e.g.,
TiAl, TiAl.sub.3, Ti.sub.3Al), NiAl, TaAl.sub.3, NbAl.sub.x, SiAl,
TiC, TiB.sub.2, VC, WC and VAl. Thermite powders may also be
suitable. In this case, one of the reactive components may comprise
at least one metal oxide selected from Fe.sub.xO.sub.y,
Ni.sub.xO.sub.y, Ta.sub.xO.sub.y, TiO.sub.2, CuO.sub.x and
Al.sub.2O.sub.3, and another one of the reactive components may
comprise at least one material selected from Al, Mg, Ni and
B.sub.4C. In one embodiment, one of the reactive components may
comprise TiO.sub.2, Al.sub.2O.sub.3, Fe.sub.3O.sub.4, SiO.sub.2
and/or NiO.sub.2, and another of the reactive components may
comprise Al, Fe, Ni, B.sub.2O.sub.3 and/or TiO.sub.2. More than two
reactive components may be used, e.g., Al/Ni/NiO, Ni/Al/Ta,
etc.
[0018] By proper selection of components, it is possible to form an
unreacted layered structure with a bulk composition that will
chemically equal an intermetallic or ceramic compound. The
unreacted body is a substantially fully dense solid multilayer
structure complete with mechanical properties that permit its use
as a load bearing material. Under proper shock conditions
(explosive or other), the materials undergo an exothermic reaction.
The composition and thickness of each layer is selected such that
bulk or substantially simultaneous initiation of the entire
structure occurs upon shock initiation. In many types of shock
initiation devices incorporating reactive multilayers, the reacted
or reacting material is dispersed in a desired manner, such as a
unidirectional or omnidirectional dispersion pattern.
[0019] The present reactive multilayer structures can differ from
compressed powder materials because there is substantially no
impurity outgassing. In addition, pressed powder compositions tend
to rapidly disperse into powders after shock initiation. The
reactive multilayer structures also differ from pyrophoric metals
like zirconium because the entire body reaches its peak exotherm,
not just the exposed edges. This permits the fragmented sections of
the body to maintain thermal output levels much longer than either
powder reactants or individual pyrophoric metals. Given the ability
to control reactions via the forming process, a great degree of
tailorability may be achieved with the present reactive
multilayers.
[0020] A partial list of candidate reactive layer materials is
shown in Table 1.
TABLE-US-00001 TABLE 1 Alloy Heat of Peak Reaction Components
Reaction Fluence Temperature 2Si + V 700 cal/g 2400 cal/cm.sup.3
3341 K 3Si + 5Ti 428 cal/g 1590 cal/cm.sup.3 2548 K 5Nb + 3Si 222
cal/g 1390 cal/cm.sup.3 2518 K Al + Ni 330 cal/g 1710 cal/cm.sup.3
2362 K Al + Co 307 cal/g 1590 cal/cm.sup.3 2195 K 2Si + Zr 258
cal/g 1040 cal/cm.sup.3 1988 K 2Al + Zr 267 cal/g 1130 cal/cm.sup.3
1923 K 2Si + Ti 308 cal/g 967 cal/cm.sup.3 1913 K Mo + 2Si 187
cal/g 855 cal/cm.sup.3 1854 K Ni + Si 235 cal/g 1140 cal/cm.sup.3
1838 K 2Si + Ta 120 cal/g 851 cal/cm.sup.3 1781 K 5Al + 2Co 277
cal/g 1110 cal/cm.sup.3 1755 K Co + Si 299 cal/g 1450 cal/cm.sup.3
1733 K 5Cr + 3Si 226 cal/g 847 cal/cm.sup.3 1671 K 2Al + Ti 314
cal/g 1100 cal/cm.sup.3 1643 K Al + Ti 240 cal/g 872 cal/cm.sup.3
1597 K 3Al + Fe 278 cal/g 1020 cal/cm.sup.3 1407 K
[0021] FIG. 1 schematically illustrates a reactive multilayer
structure 10 comprising alternating layers of a first reactive
component material 12 and a second reactive component material 14
which may be used in shock initiation devices of the present
invention. The layers 12 and 14 typically have thicknesses of from
about 10 nanometers to about 0.5 mm, preferably from about 10
nanometers to about 1 micron. The layer thicknesses are selected
such that the multilayer structure 10 is capable of substantially
simultaneous or bulk initiation when subjected to selected shock
conditions. The total thickness of the multilayer structure 10 is
typically from about 100 nanometers to about 25 mm, preferably from
about 1 micron to about 1 mm.
[0022] FIG. 2 illustrates a reactive multilayer structure 20
comprising layers of first and second reactive components 22 and
24, separated by layers of inert material 26 which may be used in
shock initiation devices of the present invention. The reactive
component layers 22 and 24 may have thicknesses as described above.
The inert material layers 26 may comprise any suitable material
such as glasses and ceramics, and may be thermally sprayed, or may
be deposited by any other suitable technique. The layers 26 may
also comprise an interdiffusion zone (IDZ) between the reactive
component layers 22 and 24. The thickness of each inert layer 26 is
typically from about 10 nanometers to about 1 mm, preferably from
about 10 nanometers to about 10 microns.
[0023] FIG. 3 illustrates a reactive multilayer structure 30
comprising pairs of reactive component layers 32 and 34 having
thicknesses as described above, separated by layers of inert
material 36 having thicknesses as described above which may be used
in shock initiation devices of the present invention.
[0024] FIG. 4 is a sectional view of a shock initiation device in
the form of a shaped charge 40 including a reactive multilayer
shaped charge liner 42 in accordance with an embodiment of the
present invention. The shaped charge 40 includes a casing 44 made
of any suitable material such as aluminum, steel or fiber-wrap
composite filled with an explosive material 46 made of any suitable
material such as PETN, Octol or C-4. In the embodiment shown in
FIG. 4, the reactive shaped charge liner 42 is substantially
cone-shaped. The height of such a cone-shaped liner typically
ranges from about 1 to about 100 cm. The diameter of the
cone-shaped liner, measured at its base, typically ranges from
about 1 to about 100 cm. Although a cone-shaped liner is shown in
FIG. 4, other shapes may be used, such as spheres, hemispheres,
cylinders, tubes, lines, I-beams and the like. In addition, the
present reactive multilayer structures may be used in other shock
initiation devices including munitions casings, kinetic
interceptors, rocket propelled grenades and the like. In accordance
with embodiments of the present invention, the reactive multilayers
comprise structural or load-bearing components of such devices.
[0025] The multilayer structures may be formed by techniques such
as vapor deposition, rolling of foils or forging. Alternatively,
the multilayer structures may be formed by thermal spraying
techniques such as those disclosed in U.S. patent application Ser.
No. 10/839,638 filed May 5, 2004, which is incorporated herein by
reference. Various vapor deposition techniques such as magnetron
sputtering, chemical vapor deposition, electron-beam physical vapor
deposition (PVD) and laser assisted PVD can be used to form the
structural multilayers. Deposition parameters are selected to
control the thickness of the layers and the interdiffusion zone
(IDZ) between the layers. The present multilayer structures can be
fabricated such that the initiation wave front propagates
substantially perpendicular to the reactive layers. Thus, the
entire structure can be initiated substantially simultaneously.
[0026] The energy required to initiate the exothermic reaction and
the rate of the reaction are directly related to the physical
properties, e.g., thickness, and the composition of the IDZ. The
sensitivity for shock initiation of the exothermic reaction is
defined based on the characteristics of the IDZ. The IDZ may be
modified by varying the deposition parameters, changing the
characteristics of the deposition substrate, the use of inert
layers, or through post deposition thermal processing of the
multilayer material. For example, the thickness of the IDZ can be
increased to a point at which local or point ignition of the
multilayer structure does not occur, but bulk ignition by shock
initiation is possible. Exothermic multilayer structures can thus
be fabricated that can be bulk initiated by shock or impact loading
but not by localized thermal or spark initiation.
[0027] The following examples are intended to illustrate various
aspects of the present invention, and are not intended to limit the
scope of the invention.
Example 1
[0028] Samples comprising Ni/Al multilayers on copper cones were
made. The multilayers were applied using a Magnetron sputtering
process. This process is done in a vacuum chamber (<10-5 Torr)
using sputter guns, plasma formation and large electrical
potentials to dislodge atoms from a target material and deposit
them on the substrate. The process occurs on the atomic level and
deposition rates are influenced by factors such as applied voltage,
distance from sputter target, substrate orientation, vacuum, etc.
For this series of tests, alloys AA-1100 (99% Al) and Inconel 625
(61 Ni-22 Cr-2.5 Fe-9 Mo) were used as target materials.
[0029] Al/Ni coatings were formed on conical copper liners, and
monolithic Al/Ni cones were formed on a mandrel and removed.
However, as the coating trials progressed, it became evident that
slow sputtering rates were associated with the latter. The time
required to the requisite 0.048-inch thickness would have been
long. Therefore, the efforts focused on coating copper backing
liners. These liners were fabricated using wall thicknesses of
approximately 0.024-inch. The half-thickness liners were mounted on
a rotational device driven by a toothed ring at the base of the
vacuum chamber. The liner was placed on a solid, copper mandrel,
designed to closely conform to the inside dimensions of the cone.
During rotation, the mandrel was in constant contact with a
water-cooled, copper base plate. This configuration allowed cooling
of the liner during the coating operations. In order to prevent
diffusion and formation of unwanted nickel aluminides during
sputtering, a stainless steel shield was installed to mask each
side of the cone.
[0030] A low sputter gun power (40-50 W) was used in order to
prevent heat build up. This resulted in relatively low deposition
rates. Other coating efforts, with larger substrates, show that
power levels of 250 W and continuous run times of 8 hours are
achievable. The rotating device was dismantled and ultrasonically
cleaned a number of times to remove any traces of oil, grease or
other contamination from crevices, holes and fasteners. In
addition, stainless steel sheet was formed and placed over the
frame to thermally insulate it and a conductive epoxy was used
between the copper liner and mandrel for more efficient heat
transfer. Sample TSS-3 was run for a total of 16 hours at 150 W on
both sputter guns. At the end of this period, total coating
thickness was 0.006-0.011 inch. The thickness varied slightly
depending on location and this is believed to result from the
slight gun-substrate standoff distance between the top and bottom
of the cone.
[0031] After fabrication, steel containers were filled with a
quantity of A-5 high explosive and the conical liners were pressed
into the explosive. A critical factor in shaped charge fabrication
is maintaining the axial alignment of the container, liner,
detonator and explosive charge. Symmetry around the centerline is
required to form a penetration jet of the proper shape and density.
Pressing parameters (density, pressure, alignment tolerance, etc.)
for these tests conformed to standard industry practice for copper
liners.
[0032] Each shaped charge was tested to determine its ability to
penetrate mild steel plate. Before each test, the underlying ground
was leveled and a 12.times.12.times.1-inch thick base plate was
situated. Several steel target plates, 8.times.8.times.1-inch
thick, were stacked on the base and checked for level. The
detonation assembly was mounted, leveled and taped in place. The
results of testing are shown in Table 2.
TABLE-US-00002 TABLE 2 Explosive Entrance Sample Weight Penetration
Hole ID Sample Type (g) Depth (in) Diameter (in) Comments TSS-1
Sputtered Ni/Al 50.79 4.25 0.50 Bright flash, ragged coating on
entrance hole with copper liner evidence of burning TSS-2 Sputtered
Ni/Al 50.69 3 0.50 Bright flash, "figure- coating on 8" entrance
hole with copper liner evidence of burning TSS-3 Sputtered Ni/Al
50.15 5+ 0.50 Similar to TSS-1, coating on solid portion of jet
copper liner found in plate #6
Example 2
[0033] Two alloy systems were selected: nickel-aluminum and
tantalum-aluminum. Two-inch cathodes (one of Ni and one of Al) are
positioned in opposite directions, at a 2 inch distance from the
substrate holder (drum), which rotates at an adjustable speed. The
substrates to be deposited on are positioned on the rotating drum,
and moved past each target sequentially. This allows deposition of
the desired number of bi-layers, and desired total foil thickness,
as determined by rotation speed, selected deposition rate, and
total run time.
[0034] To establish predictable deposition rates for the materials,
deposition onto precision gage blocks was made. This was done with
one segment covered, that when removed after deposition left a
sharp "step" from the gage block surface to the top of the
deposited material. This was measured using a high sensitivity
lever gage indicator with submicron resolution. Gage blocks were
held on the substrate holder at a distance of 3 inches from source
to substrate (target).
[0035] This was accomplished by starting with Al sputtered at a 12
W/in.sup.2 DC power density for 30 minutes duration and rotation
speed of the drum of 2 PRM. Multiple runs of the same parameters
resulted in consistent measurements of thickness that could then be
related to an estimate of predictable layer thickness per pass (of
the drum past the ingot source) for each alloy. This rate was 0.75
for Al settings which related to a build-up of approximately 12 nm
per pass of the substrate. The same process was repeated with
Inconel for the nickel component, and a set of rates was
established for this alloy. Nickel parameters included a higher
power density setting of 14 W/in.sup.2, with rotation and time the
same for the calibration runs and yielded a deposition rate of 9 nm
per pass. All work is done under Ar atmosphere of 3 milliTorr.
[0036] The sputter cathodes allow fast change-out of the source
material, for easy target changes, and use of a variety of
alternate materials combinations when desired. The sputter cathodes
are equipped with high strength magnets (rare earth type magnets),
which can be arranged in a number of magnetic field configurations.
Also, the small source size, each coupled with a 500 W DC power
capability, gives the ability to use a sputter power density up to
150 W per square inch. This high power density, coupled with the
higher strength magnetic field, (and therefore higher plasma
density) results in significant increase in sputter deposition
rates, which is important with deposition of magnetic materials
like Inconel.
[0037] Also, a motor controller with adjustable speed control was
installed on the deposition system. This allowed for control of the
individual layer thickness comprising the multilayers by setting
and holding consistent drum rotation speeds. Layer thickness is
controlled by power density and rotation speed of the drum holding
the "targets".
[0038] Once the system was set-up and equipment calibrated, several
runs of samples were produced to record and understand the impact
of power density, rotation speed, cooling cycle of samples between
deposition layers, and impact of substrate on the multi-layer
properties. Higher sputter deposition power was feasible with the
equipment upgrades, so additional calibration process runs were
completed.
[0039] Another calibration processing was completed using a silicon
wafer for the base substrate masked by a coverslide to create the
"step" differential thickness that when removed provided a clean
interface to measure the thickness of the deposited layer on the
substrate. Drum rotation speeds were varied between 45
seconds/revolution and 73 seconds/revolution.
[0040] The impact of varying the substrate, onto which the
multi-layers were deposited, was evaluated by comparing DSC
results. Substrates used included glass, aluminum foil, and copper
foil. Parameter development work also revealed that a cooling cycle
of 5 minutes between deposition layers was beneficial for reducing
the diffusion of multiple layers together. Diffusion of the two
elements would reduce the reactivity of the multi-layer.
[0041] Final parameters were established to be 200 W for nickel
alloy, 250 W for aluminum, drum rotation rate of 73
seconds/revolution onto copper foil substrates. These parameters
produced consistent alternating layers of 7.5 nm of nickel and 7.5
nm of aluminum totaling 17 microns thick in final form.
[0042] The processing parameters for Ta--Al were established using
the same approach as for the Ni--Al system. Calibration methods
were utilized to determine a rate of deposition of tantalum.
Preliminary PVD runs were made of Ta/Al multilayer foils, using
power settings of 300 W/200 W, respectively. To expedite the
processing of initial Ta/Al multilayers for DSC evaluation and
reactive initiation properties, calibration data obtained for the
previous Ni/Al deposition, in conjunction with sputter gun
manufacturer's data on relative deposition rates of various metals,
the initial multilayers were deposited with an estimated bilayer
thickness of 5 nm/7.5 nm
[0043] Cooling cycles were incorporated into the process to allow
approximately 5 min target off per each hour of run time, to insure
adequate substrate cooling during sample deposition. Tantalum
deposition still resulted in more heat generation, and therefore
higher substrate temperature, during deposition as compared to
either Al or Ni processing. Substrate rotation speed of 0.8 rev/min
(73 sec per drum revolution) was again used for the initial
multi-layer sample deposition. Copper foil substrates,
3''.times.7''.times.25 mil thickness were used. Deposition was
conducted for a total run time of 4 hours, after which the
multi-layer Ta/Al foil material was removed by flexing the copper
substrate to cause delamination. Initiation of the foil was
initiated with a butane lighter flame. Vigorous initiation of this
material was observed, with a white shade of visible light given
off, compared to the orange characteristic light present in
initiation of Ni/Al multilayer foils.
[0044] Greater substrate heating was present in the Ta deposition,
presumably due to less sputtered material per Watt input to the
sputter gun, as well as tantalum's thermal properties resulting in
a higher temperature at the sputter target surface. This effect
resulted in two distinct deposition zones on the coated copper
substrate, with a more vigorous initiation given by the outer
"cool" zone as compared to the center "hot" zone, which may have
partially inter-diffused during deposition. Samples of material
from each zone is currently underwent DSC analysis.
[0045] Using the parameters established in the calibration and
optimization runs, multiple samples were produced for the
initiation testing. Repeating equal layers of aluminum and Inconel
(7.5 nm/layer) were deposited onto copper foil substrates that were
approximately 6'' tall.times.10'' wide.times.25 mils thick. A grid
was established on the copper sheet using high-temperature,
vacuum-compatible tape (Kapton tape/silicone adhesive) to create
rectangles of multi-layer foil approximately 1''.times.2'' in size
for the initiation testing. After processing, reactive foils with
even alternating layers resulted in 17 mm thick foils for
initiation testing.
[0046] Differential scanning calorimetry (DSC) was performed on
freestanding multi-layer material (material removed from substrate
prior to DSC run). This analysis measured heat flow as a function
of scan temperature of several milligrams of each of the
multi-layer sample materials. Specimens were subjected to a heating
cycle that ramped from ambient temperature up to 700.degree. C. at
a scan rate of 5 deg/min. Relatively large exothermic peaks were
noted at scan temperature from 200 to 300.degree. C., with a double
peak evolving in some of the scans.
[0047] The sharp peak indicates a rapid increase in heat flow
indicating initiation of the exothermic reaction. Sharp peaks
represent fast reaction propagation, while wider peaks, are
indicative of a slower moving reaction.
[0048] For the Ni--Al foils, DSC results were collected for
multi-layer foils deposited on glass, foil and copper substrates.
FIGS. 5-8 show DSC scans for the Ni--Al foils. FIG. 5 is a DSC scan
of Ni--Al on the foil substrate. FIG. 6 is a DSC scan of Ni--Al on
a glass substrate. FIG. 7 is a DSC scan of a sample with relatively
thick bi-layers of Al, resulting in more total heat output. FIG. 8
is a DSC scan of Ni--Al produced with a slower rotation speed,
resulting in lower heat output possibly due to greater heating of
the sample during deposition of the multilayers resulting in more
interdiffusion between the layers. The DSC results varied with this
possibly indicating the heat-sink effect of a metallic substrate is
preferable to the insulating effect of a glass substrate for making
these reactive foils. Also, a scan with proportionally richer
aluminum layers exhibited a different exotherm peak than the sharp
spike typical of the other foils.
[0049] The Ta--Al DSC scans showed a higher peak for the reaction
than the Ni--Al scans. FIG. 9 is a DSC scan of the Ta--Al
multilayer structure from an inner region of the deposited
material. FIG. 10 is a DSC scan for the Ta--Al multilayer from an
outer region of the deposited material. There appeared to be
differences in the outer and inner regions of the deposited target
area. DSC runs were completed on materials from these areas and in
fact do exhibit different behavior.
[0050] The slightly greater peak height seen in the "outer" region
could be a result of more efficient cooling of that area versus the
"inner" region during deposition. More efficient cooling leaves
less chance of inter-diffusion of the layers that can impact the
exothermic reaction.
[0051] Testing was conducted on foils composed of nickel and
aluminum layers with the objective of documenting various levels of
thermal and pulsed energy sources that would cause initiation of an
exothermic reaction. Foils were exposed to standard matches,
electric matches, igniter, and two power levels of EBW detonators.
Results showed that foils of nickel and aluminum multi-layers
materials initiated a reaction from the thermal and energetic
sources. Foils well bonded to a copper substrate are not initiated
by the thermal input from a match, but they are initiated by sparks
form an electric match and shock from a detonator.
[0052] Testing was completed at a ballistic testing laboratory on
an indoor range. Foils of layered material were adhered to a steel
plate and the various initiation sources were mounted at specific
stand-off distances from the foils. These stand-offs were
established in related testing and were selected to ensure samples
were not destroyed, but still exposed to the energy sources. A
flash detector was used to trigger capture of a gated video still
image of the exothermic reaction.
[0053] Foils tested included samples where the foil was backed by
copper plate, which is the condition these samples were
manufactured. Foils were also tested that were removed from the
copper backing and were placed against the steel backing plate and
secured by tape.
[0054] For each initiation source, a still photo of the detonation
action of the source only (no foil in place) was taken to test
instrumentation and also to document any flash and debris
attributed directly to the detonation. For further comparison,
"before" firing images were recorded on the foil set-up prior to
initiation of the initiation sources.
[0055] SQ-80 igniters contain 450 mg of a Thermite mix. RP-3
detonators have a small amount of explosive (30 mg of PETN) and are
generally used for situations where minimum fragmenting debris is
desired. The RP-501 detonator is a general-purpose "higher energy"
explosive containing 136 mg PETN for initiation with 227 mg RDX
with binder for output explosive.
[0056] Table 3 below shows data recorded for each test. Each
initiation source was attempted twice on copper backed foils, and
test sequence was repeated on unbacked foils. Initiation sources
included a standard match, electric match, SQ-80 igniter, RP-3
detonator, and RP-501 detonator. There were limited quantities of
RP-3 detonators available for testing, so a repeated test was not
completed on the foil on copper sample using that detonator.
TABLE-US-00003 TABLE 3 Shot-by-Shot Data for Initiation Testing of
Layered Foils Shot Foil Initiation # Configuration Source
Initiation Comment 1 Foil on Cu Match Yes A protruding piece of
foil not touching the copper initiated the reaction 2 Foil only
Match Yes 3 Foil on Cu Match No Full contact with flame was made,
but no initiation resulted 4 Foil only Match Yes 5 Foil on Cu
Electric Yes Electric match was touching foil Match surface 6 Foil
on Cu Electric Yes Electric match touching foil surface Match 7
Foil on Cu Electric Yes 1/2'' offset between match and foil Match
surface 8 Foil only Electric Yes 1/2'' offset between match and
foil Match surface 9 Foil only Electric Yes 1/2'' offset between
match and foil Match surface 10 Foil on Cu SQ-80 Yes 5'' stand-off
11 Foil on Cu SQ-80 Yes 5'' stand-off 12 Foil only SQ-80 Yes 5''
stand-off 13 Foil only SQ-80 Yes 5'' stand-off 14 Foil on Cu RP-501
Yes 6'' stand-off 15 Foil on Cu RP-501 Yes 6'' stand-off 16 Foil
only RP-501 No Foil had breaks in surface prior to detonation. 17
Foil only RP-501 No Foil integrity was good prior to firing, no
apparent reaction occurred 18 Foil on Cu RP-3 Yes 1/2'' stand-off
19 Foil only RP-3 Yes 1/2'' stand-off - foil in pieces, but
appeared to have reacted 20 Foil only RP-3 Yes 1/2'' stand-off,
foil had tape over the front face to hold pieces together. Foil was
reacted under the tape along radial lines from impact point.
[0057] In the data, there are some outliers from the general trend
of initiation of reactions. Using the standard match, the foils on
copper backing did not initiate unless there was a section of foil
not contacting the copper backing. In shots 1 and 3 this difference
was clearly visible in that shot 1 resulted in a reaction, but shot
3 did not.
[0058] The foils subjected to the higher energy RP-501 detonators
also did not show conclusive initiation of foils in shots 16 and 17
where the foil only, (no copper backing), were tested. It is
believed that the explosive force of the detonation physically
separated the foil before any reaction had time to propagate. Foils
on copper backing, shots 14 and 15, did successfully result in an
exothermic reaction initiating.
[0059] This example demonstrates that exothermic reactions were
initiated in layered foils using electric matches, igniters and two
different energy levels of detonators. Reaction of foil on copper
backing was not initiated using a standard match when the foil did
not have "cracks". Foils not backed with copper, were initiated
using standard matches with flames contacting the surface. Foils
that had protruding sections from the plane of the foil, and were
therefore separated from the copper backing, were ignited using a
standard match.
Example 3
[0060] Repeating equal layers of aluminum and Inconel were
deposited onto copper foil substrates that were approximately 6''
tall.times.10'' wide.times.25 mils thick. A grid was established on
the copper sheet using high-temperature, vacuum-compatible tape
(Kapton tape/silicone adhesive) to create rectangles of multi-layer
foil approximately 1''.times.2'' in size for the initiation
testing. After processing, reactive foils with even alternating
layers resulted in 17 mm thick foils for initiation testing. Very
thin 100 micron thick Inconel/Al exothermic multilayer foils
fabricated using the magnetron sputter deposition process achieved
tensile strengths of 300 Mpa.
[0061] Differential scanning calorimetry was performed on
freestanding multi-layer material (material removed from substrate
prior to DSC nm). This analysis measured heat flow as a function of
scan temperature of several milligrams of each of the multi-layer
sample materials. Specimens were subjected to a heating cycle that
ramped from ambient temperature up to 700.degree. C. at a scan rate
of 5 deg/min. Relatively large exothermic peaks were noted at scan
temperature from 200 to 300.degree. C., with a double peak evolving
in some of the scans.
[0062] The sharp peak indicates a rapid increase in heat flow
indicating initiation of the exothermic reaction. Sharp peaks
represent fast reaction propagation, while wider peaks, and hence
more energy as defined by the area under the peak, are indicative
of a slower moving reaction.
[0063] Testing was conducted on nickel-aluminum foils of
approximately 1''.times.1''.times.17 mm with the objective of
determining a boundary for impacts that would cause initiation of
an exothermic reaction. Once this range was determined, shots were
fired to attempt to capture the time between impact and the start
of the exothermic reaction.
[0064] Testing was completed at a ballistic testing laboratory on
an indoor range. Foils of layered material were used as "targets"
against which a 17 grain Fragment Simulating Projectile (FSP)
MIL-P-46593A (MU) was fired at varying velocities. Instrumentation
was used to capture velocity of the projectile, delay between
impact and initiation of the reaction, and still photographs of the
impact. Velocities were controlled using initial positioning of the
projectile in the barrel and different propellant loading.
[0065] Foils tested included samples where the foil was backed by
copper plate. Foils were secured to a brass disk about 3'' diameter
by 1/4'' thick using tape. This brass disk backing was put in place
to eliminate the spark from the projectile hitting the steel
backing plate. This insured the flash detector picked up the flash
of a reaction initiating. The flash detector was tested using a
standard match, which triggered a detection of light. The brass
disk was secured to a steel plate in a frame 4.97 meters from the
firing barrel. The projectiles passed through two sets of screens
triggering chronographs prior to hitting the target. The figures
below show the range set-up. After the minimum velocity at which
reactions initiated was determined, the set-up was modified
slightly to enable capture of the timing between impact and the
start of the exothermic reaction. This involved putting a "make"
screen on top of the foil to indicate a completed circuit when the
projectile contacted it thereby triggering the start of the timing
indicator for the sequence of impact to detection of a flash
indicating initiation of the foil.
[0066] Table 4 below shows the shot-by-shot data recorded for the
testing. The initial shots were fired at a range of 4.97 meters
from end of firing barrel to the front face of the test foil. To
accommodate slower velocities needed to bracket the point of
"go/no-go" for the initiation of the exothermic reaction, the
target was moved closer to 1.98 m.
[0067] The velocity at which foils were ignited by impact ranged
from a slowest of 129.6 m/s to the highest of 628.1 m/s. Velocities
of 111.4 m/s and 111.6 m/s did not result in initiation of a
reaction upon impact. This brackets the velocity to start the
reaction between 111.4 m/s and 129.6 m/s. The velocities reported
are striking velocities as calculated from actual measurement of
the projectile velocity taken while passing through two sets of
triggering screens at specified distances.
[0068] There was one "outlier" in the data for shot number 22 in
which a velocity of 236.8 m/s did not initiate a reaction in the
foil. It is not clear why this was the case for this sample.
However, in the higher velocity impacts, it was evident that the
foils were sometimes separated mechanically (blown apart) from the
impact faster than the reaction could propagate from the initial
impact site. It is believed this result is an artifact of the
testing foil thickness of approximately 17 microns making them
fragile and susceptible to cracking during handling for positioning
for the testing.
[0069] The delay between measure impact and flash detection
indicating initiation of a reaction, varied for the four samples on
which it was measured. The range of delays was between 210
microseconds and 2028 microseconds. Table 5 below shows this data
separately.
TABLE-US-00004 TABLE 4 Shot-by-Shot Data for Impact Initiation
Testing of Layered Foils Shot Distance to Velocity Initia- # Target
(m/s) tion Comment 1 4.57 m 340.4 Yes Steel backer plate 2 4.57 m
557.9 Yes Steel backer plate 3 4.57 m 554.9 N/A No foil -
instrumentation test 4 4.57 m 628.1 Yes Steel backer plate 5 4.57 m
337.0 N/A No foil - instrumentation test 6 4.57 m 541.1 N/A No foil
- instrumentation test 7 4.57 m 549.5 N/A No foil - instrumentation
test 8 4.57 m 338.8 N/A No foil - instrumentation test 9 4.57 m
310.0 Yes Brass disk mounting started 10 4.57 m 545.0 Yes 11 4.57 m
332.0 Yes 12 4.57 m 184.2 N/A Missed sample 13 4.57 m 170.5 N/A
Missed sample 14 4.57 m 165.3 N/A Missed sample 15 1.98 m 234.3 Yes
16 1.98 m 192.4 Yes 17 1.98 m 111.4 No 18 1.98 m 111.6 No 19 1.98 m
129.6 Yes 20 1.98 m 237.9 Yes Delay = 1802 microseconds 21 1.98 m
243.9 N/A No foil - instrumentation test 22 1.98 m 236.8 No Outlier
relative to other tests 23 1.98 m 228.2 Yes Delay = 2028
microseconds 24 1.98 m 232.9 Yes Delay = 1519 microseconds 25 1.98
m 380.7 Yes Delay = 210 microseconds 26 1.98 m 377.8 Yes Delay =
321 microseconds 27 1.98 m 380.5 Yes No flash reading 28 1.98 m
386.8 Yes No flash reading
TABLE-US-00005 TABLE 5 Impact to Flash Detection Delay Comparisons
Shot # Velocity (m/s) Delay (microseconds) 20 237.9 1802 23 228.2
2028 24 232.9 1519 25 380.7 210 26 377.8 321
[0070] Impacting bodies at a striking velocity of 129.6 m/s had
sufficient energy to initiate an exothermic reaction of layered
nickel and aluminum foils 17 microns thick.
[0071] Impacting bodies at a striking velocity of 111.5 m/s did not
have sufficient energy to initiate an exothermic reaction of
layered nickel and aluminum foils 17 microns thick.
[0072] At higher velocities (>370 m/s), the integrity of the
foil after impact appeared to have an impact on the ability of the
exothermic reaction to propagate through the test foil.
[0073] The time delay between impact and the detection of the flash
indicating initiation of an exothermic reaction varied with the
striking velocity of the impacting body. More data would be
required to determine the validity of this correlation.
Example 4
[0074] The sensitivity to initiation of exothermic multilayer
structures can be controlled by varying thermal state during
deposition. Multilayer structures were deposited on glass, aluminum
foil, and copper foil substrates. Parameter development work
revealed that a cooling cycle of 5 minutes between deposition
layers is also beneficial for reducing the diffusion of multiple
layers together. Diffusion of the two elements reduces the
reactivity of the multi-layer. Using the parameters established in
calibration and optimization runs, multiple samples were produced
for the initiation testing. Layers of aluminum (7.5 nm/layer) and
Inconel (7.5 nm/layer) were deposited onto substrates. DSC results
were collected for Ni--Al multi-layer foils deposited on glass,
foil and copper substrates. The DSC results showed that the
sensitivity was higher when a thermally conductive metallic
substrate was used.
Example 5
[0075] A water-cooled rotation stage was installed in a PVD system.
The sputter guns were re-mounted and oriented so as to deposit onto
the rotating cooled mandrel. A stainless steel shield, with a
cutout to accommodate the deposition mandrel, was positioned so as
to have incident deposition from each sputter source onto separate
sides of the mandrel, while rotating. This setup allows for
reactive multilayer structures, comprised of alternating layers of
two metals, to be deposited onto the mandrel. By varying the
rotation speed of the mandrel and the deposition rate of the
individual metals, bilayer thickness and the ratio of the two
materials can be controlled. The cooled mandrel will insure that
interdiffusion between the layers is minimized. Alternatively, by
varying the mandrel temperature (by controlling coolant
temperature) differing levels of multilayer interdiffusion can be
achieved.
[0076] Whereas particular embodiments of this invention have been
described above for purposes of illustration, it will be evident to
those skilled in the art that numerous variations of the details of
the present invention may be made without departing from the
invention.
* * * * *