WO2014074198A2

WO2014074198A2 - Method for making ballistic products from titanium preforms

Info

Publication number: WO2014074198A2
Application number: PCT/US2013/055680
Authority: WO
Inventors: Gopal Subray REVANKAR; Kenneth Edward Johnson
Original assignee: NI Industries Inc
Current assignee: NI Industries Inc
Priority date: 2012-08-30
Filing date: 2013-08-20
Publication date: 2014-05-15
Anticipated expiration: 2015-02-28
Also published as: WO2014074198A3

Abstract

An apparatus and process are described which are used in the production of a ballistic product such as an armor plate, which begins with titanium preform in the form of a thick sheet and which is submerged in a molten A1 bath. By submerging Ti preform in a volume of molten A1, a layer of intermetallic compound titanium aluminide (TiA1₃) is formed into the Ti preform, resulting in a dimensional (primarily thickness) increase; this dimensional (thickness) increase is due to a slightly lower density of the Titanium aluminide (TiA1₃) compared to that of the titanium metal. It is therefore required to choose starting dimensions (primarily thickness) of the titanium preform to accommodate the dimensional changes so as to achieve a final net shape (primarily thickness) for the ballistic product.

Description

METHOD FOR MAKING BALLISTIC PRODUCTS

FROM TITANIUM PREFORMS

BACKGROUND

Metal intermetallic laminate (MIL) composites, such as Ti-Ti aluminide, have been fabricated using alternating Ti and Al metal foil layers. One example of a MIL composite is the Ti- T1AI₃ composite which is made by stacking alternate layers of Ti and Al foils and treating the stack under heat and pressure for extended periods of time. For the Ti-Al system, atomic diffusion and the associated metallurgical reaction at the Ti-Al interface result in the formation of a region of titanium aluminide (T1AI₃) on the Ti metal under select process (primarily temperature) conditions.

Before going into the proposed process details it is important to define some terms used in the following description of the process:

Titanium preform: Usually a 1-3 mm thick titanium part with a desired shape and geometrical dimensions, which is immersed into molten Al bath to form a surface layer of the intermetallic compound T1AI3. However, solids of titanium such as rods, tubes, gears and other parts are included in this definition.

Titanium sheet: This definition is the same as the Titanium preform definition except that this definition refers to a flat sheet.

Reacted Titanium preform/sheet: Titanium perform/sheet after formation of

T1AI₃ surface layer.

Final product: The final product for commercial application formed by stacking reacted Titanium sheets and interfacially welding them to form a product which is many times thicker than a single reacted Titanium sheet. It may also be a product used as reacted and used without interfacial welding, such as rod or tube

Titanium foil: A thin sheet of titanium which is 0.2 mm or less thick. Aluminum foil: A thin sheet of aluminum which is 0.2 mm or less thick.

Currently available technologies and related methodologies for producing the types of MIL composites mentioned above, using foils, are considered too time consuming and expensive and hence make their commercial applications cost prohibitive. Also when foil stacks are thick it may be difficult to ensure uniformity of temperature and pressure throughout the stack volume and this may affect uniformity of final product quality. Further, the current methodologies require the use of thin foils of materials, which limit the final composition of MIL composites only to materials that are readily able to be formed into foils at the outset. The present disclosure sets forth a simpler and less complex approach, and the apparatus and method which are described herein are intended to help produce the same MIL composites at a lower cost and in less time while still providing improved quality control. The disclosed apparatus and method are therefore envisioned to make the resulting products (armor plate, for example) more commercially acceptable, and applicable to a variety of shapes, material compositions and thicknesses. The process uses Ti preforms with starting thicknesses greater than those of Ti foils used in the previous art, while still maintaining desired quality of the final MIL product. These reacted Ti preforms are then interfacially welded to form the required thickness of the final product.

As disclosed herein, one (1) processing embodiment places a titanium preform in a molten Al bath. Once the titanium preform is submerged in the molten Al bath, an intermetallic reaction occurs over time at the surface of titanium. This reaction results in the formation of a titanium aluminide surface layer integrated into the underlying titanium metal. The formation of the titanium aluminide surface layer causes a noticeable increase to the starting thickness of the titanium preforms. This thickness increase due to the Ti-Al reaction can be accommodated since the thickness changes can be predicted for a given part of titanium under a given set of process parameters, and therefore, the starting preform thickness can be chosen to obtain the final desired thickness. This (final) net thickness so obtained would be such that the processed sheet (or other performs) typically would not need any additional forming or modification in order to fabricate a final part, such as an armor plate or a shaped panel for armored protection of a vehicle, as examples.

SUMMARY

The disclosed process (or method) and apparatus include the use of a heated crucible containing molten aluminum (Al). One or more titanium (Ti) preforms (in the form of sheets of various thicknesses and shapes are suspended in the molten Al. As such, the heated crucible becomes a containment vessel for the molten Al and for the Ti forms which are suspended in the melt. The thickness and shape of preforms are not limited by the disclosed process. The apparatus and the process are able to accommodate a wide variety of sizes, and shapes including flat, honeycombed, curved, rods, sheets and any other complex forms.

A metallurgical reaction between Al and Ti is allowed to take place over a period of time. The temperature of the molten Al bath is held at the desired level. This metallurgical reaction creates a titanium aluminide surface layer which forms an integral part of the titanium preform. A noticeable or measurable dimensional increase to the titanium preform occurs uniformly over the entire surface in contact with the molten Al, due to formation of titanium aluminide. This dimensional increase can be calculated and controlled so that the dimensions (primarily thickness) for the starting titanium preform can be selected to yield a net desired dimension (primarily thickness) of the preform at the end of the reaction period. In another related embodiment the metallurgical reaction is allowed to continue until the Al or Ti is consumed, either partially or completely, in order to obtain the desired product. The desired product of this related embodiment is based on the intended application and the process can be controlled to produce one (1) of two (2) MIL composites Al + TiAl₃ and Ti + TiAl₃, or only TiAl₃.

The prior art relating to Ti-Al composites contemplates the use of very thin sheets (foils) of Ti and Al, or their alloys, which are stacked in alternating sequence, in order to form a thicker stack. This stack of alternating foil layers is held under pressure and is heated in air in order to melt the Al. The individual Al foil layers are intended to react with their adjacent Ti foil layers in order to form the TiAl₃ intermetallic compound. The reaction, according to the prior art, continues until the Al is consumed in whole or in part and the final product is a composite consisting of alternating layers of Ti metal and TiAl₃ intermetallic compound. This fabricated stack would form a flat panel to be used for ballistic products such as armor plates.

As noted above, the prior art processes for making these Ti-TiAl₃ MIL composites are affected by factors such as difficulty in maintaining uniformity of temperature and pressure, especially in thick stacks, problems in material selection (since all materials cannot be produced in the form of thin foils) and unacceptably long processing times, and make these prior art processes and methodologies expensive and less attractive for commercial applications. In contrast to this, the only required control for the process of the present disclosure is that of temperature of the molten Al. This type of temperature control is simpler and easier to maintain and results in a better quality control for the disclosed process as compared to prior art process. Also the proposed process does not have restrictions regarding material selection unlike the prior art process which requires materials in the form of thin foils.

The Ti preforms of various shapes for the disclosed process are suspended in molten Al. As a result of this process feature, the diffusion rate of Al into Ti, and TiAl₃, and the reaction rate between Al and Ti, and hence the TiAl₃ formation rate are expected to be much improved. This aspect is expected to reduce the process time required for the formation of a given thickness of TiAl₃ region on the Ti surface. The prior art processes are rather long, approximately 40 hours, which may be, in part, due to decreasing Al concentration at the Ti or TiAl₃ surface, as the TiAl₃ formation process continues. One of the features of the disclosed process is the stirring of the molten Al bath which is considered unique and which results in uniform bath temperature and hence promotes uniform thickness of T1AI₃ region on the entire Ti surface submerged in the molten Al. Additionally, the disclosed process allows several Ti preform shapes such as sheets, rods and cylindrical tubes to be simultaneously suspended in the molten Al bath. Further, the size and shape of those various Ti preforms are not a limiting factor in the disclosed process. Also, the proposed process allows use of preforms with a porous structure where the porous preform is made by compacting the required proportions of Ti and Al powders for the composite formation. Such porous compacts would facilitate penetration of liquid Al metal into the compact, inter-diffusion between Al and Ti particles and consequently the Ti- T1AI₃ reaction rate thus speeding up T1AI₃ formation. It would be nearly impossible to produce similar porous Ti-Al foils for use in the current process. Another advantage of the proposed process is that the process would not be limited to the use of only Ti-Al pair, but can use other pairs of metals such as Ni-Al, Fe-Al and Co-Al where the heavier metals such as Ni, Fe, and Co cannot be easily made into thin foils and are therefore beyond the scope of the current process.

There are several disadvantages in using thin foils for the aluminide reaction: i) Handling is difficult and time consuming

ii) Cleaning and drying before stacking for aluminide reaction is

cumbersome

iii) Cannot be treated easily for creating surface textures to increase surface area to increase aluminide reaction rate

iv) Not all materials can be made into thin foils and this limits the use of the current process

v) Cannot prepare thin porous foils for increasing aluminide reaction rate

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view with a titanium preform submerged in a molten Al bath, according to the present disclosure.

FIG. 2 is a front elevation sectional view of an apparatus which is suitable to be used for the disclosed process.

FIG. 3 is a perspective view of a Ti preform which may be submerged in the molten Al of the FIG. 2 apparatus.

FIG. 4 shows an alternate Ti preform which may be suspended in the molten Al of the FIG. 2 apparatus. FIG. 5 shows an alternate Ti preform which may be suspended in the molten Al of the FIG. 2 apparatus.

DESCRIPTION OF THE SELECTED EMBODIMENTS

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. One embodiment of the invention is shown in great detail, although it will be apparent to those skilled in the relevant art that some features that are not relevant to the present invention may not be shown for the sake of clarity.

Also the following description relates mostly to the processing of thick sheets (to make armor plate, for example) though it would be understood by one skilled in the art that the embodiment described can be used to process any shape or size of titanium preforms which require formation of T1AI3 on the surface.

Referring to FIG.1 there is illustrated one embodiment of the structural basics of apparatus 10 which is suitable for performing the process which is described herein. The described process produces reacted Ti sheets suitable for making armor plate, starting with titanium preforms with a near net thickness. With regard to apparatus 10, the structural basics of this apparatus, in a broad sense, includes a crucible 12 and a volume of molten aluminum (Al) contained in the crucible, i.e. a molten Al bath 14. For the disclosed process, a titanium preform 16 is submerged into the molten Al bath 14. The preform 16 may be virtually any type, style or shape of part which is initially fabricated into a "near" net shape (including both thickness and shape) that would produce the final reacted sheets with the desired thickness and shape after the intermetallic reaction is completed. The phrase, "net shape", as used herein refers to the final shape and thickness of the reacted sheet which is intended to be produced. These net shape parts would be used "as is" or after some minor modification, for further processing such as production of thick armor plates by stacking them and metallurgically bonding them. In this context the "final" shape is also referred to as the "net" shape and these two (2) adjectives may be used interchangeably. Similarly, a "near" net shape refers to a part which is not yet at its desired or intended "net" shape. While the part contours and shape characteristics are all nearly preserved while going through the aluminide reaction process, the thickness of the reacted part is typically slightly larger than the starting "near net" part thickness. In some applications it might be required to remove some of the surface material before using the reacted parts for interfacial welding, to obtain the desired "net" thickness of the final product. In the present disclosure a slight but noticeable increase in the initial titanium preform thickness occurs due to the reaction between titanium and aluminum, and the above mentioned surface material removal would compensate for this dimensional (thickness) increase. Therefore, for this disclosed apparatus and process, "near net" refers to the titanium preform being of smaller thickness than that of the same part after the Ti- Al reaction in the Al bath. The final product such as armor plate which is to be produced from the disclosed process has a target size and shape and a

corresponding acceptable tolerance range for each dimension, and primarily so for thickness. However, it should be understood some parts may not need, from a functional point of view, a close control of near-net shape and net shape; e.g. for producing thick armor plates by stacking and interfacial welding of reacted Ti sheets.

When the titanium preform 16 is submerged into the molten Al bath 14, a metallurgical reaction occurs creating a generally uniform surface layer of titanium aluminide which is integrated into all exposed portions of the titanium preform. There are additional process parameters which need to be established and monitored such as the temperature of the molten Al bath 14, and the amount of time for the reaction. These parameters can be evaluated, quantified and incorporated into the calculations to be able to predict the dimensional (mostly thickness) increase so as to bring the "near" net thickness to within the tolerance range for the (final) net thickness of the reacted Ti perform (or sheet).

The titanium aluminide layer on the titanium preform, which results from the Ti-Al reaction, provides an increased level of hardness, impact resistance, and also structural rigidity. These properties enable the reacted part which is produced from the titanium preform to be suitable for use in special applications such as an armored panel for a vehicle. The titanium preform embodiment as disclosed herein allows for a wide variety of shapes, such as flat, honeycombed and curved, to be fabricated during a single reaction cycle. The processed (reacted) parts such as sheets for making armor plate which are generally at their desired net shape within the permissible tolerance range, will typically not need any additional forming or modification in order to form a stack and interfacially weld them to have an acceptable armor plate.

The titanium preform can be fabricated by a wide variety of methods using the existing technology. For example, the titanium preform can be fabricated by means of machining, casting, welding or mechanically fastening other shapes and forms together in order to create the desired near net shape configuration with the desired dimensions. Once the titanium preform is fabricated, it is to be cleaned and then immersed in the molten Al bath and held at certain temperatures for prescribed periods of time. These prescribed periods of time and temperatures will determine the reacted thickness of titanium (or, alternatively, thickness of T1AI₃ region). The reaction will initiate at the surface boundaries of the titanium preform and the molten Al bath and then continue penetrating into the Ti preform until the desired T1AI₃ reaction composition is reached.

Referring to FIG. 2 there is illustrated another embodiment of a suitable apparatus 20 for performing the process which is described herein. The FIG. 2 embodiment includes additional equipment details over the more generic form of the FIG. 1 embodiment. FIG. 2 also illustrates how more than one part 28 can be submerged in the molten Al at the same time. The FIG. 2 embodiment is simplified in terms of the form of the titanium part. In FIG. 2 a simple flat sheet 28 is used. This process which is the focus of this FIG. 2 embodiment pertains to producing AI-T1AI₃ and Ti-TiAl₃ composites and T1AI₃. T1AI₃ is an intermetallic compound which is one (1) of several possible titanium aluminide compounds. One contemplated and suitable for commercial application is the T1AI₃ type intermetallic compound for forming the Ti- T1AI₃ composites used in the production of armor plates or other ballistic applications. These armor plates are constructed to be suitable for military vehicles, as one example.

As used herein, an "intermetallic compound" refers to a material composed of two (2) or more types of metal atoms, which exists as a homogeneous material and differs in structure and properties from those of the constituent metals.

Alternative terminology uses the phrase intermetallic phase in place of

intermetallic compound. The properties of intermetallic compounds are distinct from those of the constituent elements and do not have a smooth transition into those of the elements. These compounds form distinct crystalline phases separated by phase boundaries from their metallic components. For example, aluminum possesses a face centered cubic (FCC) lattice structure and titanium a hexagonal Close Packed lattice structure, However, T1AI₃ possesses a unique tetragonal lattice structure unlike the structure of either of the two parent metals.

As used herein, "titanium aluminide" refers to an intermetallic compound formed from the metal atoms of titanium (Ti) and aluminum (Al). There are four (4) main intermetallic compounds which are generically referred to as titanium aluminide. These four (4) intermetallic compounds are T1AI₃, T1₃AI, TiAl₂ and TiAl.

Apparatus 20 includes a heated crucible 22 which functions as a containment vessel and contains a volume 24 of molten aluminum (Al). There are no particular size or shape restrictions on crucible 22 so long as a sufficient volume of Al is able to be retained therein and so long as the upper opening 26 is sized and shaped to enable the introduction of the desired titanium (Ti) forms 28. With regard to the requisite size and shape of the upper opening 26, and the desired volume 24 of Al, these variables are influenced by the size and shape of the Ti preforms 28 to be submerged in the molten Al volume 24 as well as by the number of such Ti preforms to be submerged at a time.

FIG. 3 shows one option for a Ti preform which may be submerged in the molten Al volume of FIG. 2 and this Ti preform is in the shape of a generally rectangular, flat sheet 28 which is of particular interest in making armor plates. Another Ti preform is illustrated in FIG. 4 in the shape of a solid rod 28a. Another Ti preform is illustrated in FIG. 5 in the shape of a generally cylindrical hollow tube 28b, wherein opening 29 may extend through the entire length (L) of tube 28b or only partway. Other Ti preforms 28 are contemplated including irregular shapes and complex geometries for specific industrial and military applications.

Reference number 28 in FIG. 2 is being used generically to denote all styles of Ti preforms.

Apparatus 20 in FIG. 2 further includes hollow tube 30 which is constructed and arranged for the introduction of an inert gas into the molten Al for stirring the molten Al. Thermocouple 32 may be inserted into the molten Al in order to monitor and maintain a desired temperature for the liquid Al. The desired temperature may be maintained via a feedback connection from thermocouple 32 to the crucible heating element 34 which is represented by block 34 in FIG. 2. A support 36 is used to suspend the Ti preforms 28 into the volume 24 of molten Al. A suitable flux layer 38 may be maintained on the upper surface 40 of volume 24 of molten Al though an inert gas atmosphere over the molten Al may be used in place of the flux layer 38.

With regard to the use of support 36 and the manner in which the Ti preforms 28 are submerged into the volume 24 of molten Al, it will be understood that any portion of any Ti preform 28 which is not submerged into the molten Al will not have the formation of Ti aluminide on its surface unlike the submerged part of the same Ti preform according to the disclosed process. Consequently, those portions of the Ti preforms which are not submerged in the molten Al would typically be machined off or otherwise removed prior to final processing. In the case of the armor plate example the final processing means stacking individual reacted sheets and welding them together to form a usable thick armor plate.

Another option would be to modify the design of the support 36 so as to include a longer extension means so that the entirety of each Ti preform could be completely submerged in the molten Al beneath the flux layer 38. It should be clear from the foregoing that the proposed process also permits partial surface area of a Ti part to be reacted with Al by partially submerging the Ti preform in the molten Al.

The process, as described herein, produces Ti-TiAl₃ composite sheets so as to form a thick armor plate as mentioned above, without resorting to the use of the alternating thin foils of Al and Ti or their alloys, as disclosed in the prior art. One intended benefit of the disclosed process is to be able to increase the temperature of the molten Al as required, to increase the rate of reaction between the Ti surface layer and the molten Al, and thus improve the rate of T1AI₃ formation. The higher temperature of the molten Al is also expected to further improve the reaction rate due to increased rate of Al diffusion into i) the Ti preform and ii) the T1AI₃ layer formed on the Ti perform. As will be described, the metallurgical modifications to the starting Ti preforms 28 result in an intermetallic compound surface layer as part of the Ti preform due to reaction between Ti and Al. There is a metallurgical modification of the portions of the Ti preform which are exposed to the molten Al, and all of Ti surfaces which are submerged will have a relatively uniform intermetallic compound layer of T1AI₃. If, however, any dimensional changes do occur during the process they can be managed by selecting the starting dimensions such that they would produce the final desired dimensions, as mentioned above.

The disclosed process begins with the fabrication of apparatus 20 including a suitable volume 24 of molten Al and the process "controls" including stirring tube 30, thermocouple 32, heating element 34 and flux layer 38. The next step in the described process is to select the number and style or shape of Ti preforms 28 to be submerged into the volume 24 of molten Al. These Ti preforms 28 are attached to support 36 and submerged into the volume 24 of molten Al. As noted, virtually any type of Ti preform 28 can be selected and submerged, including irregular shapes and more complex geometries, including the examples of FIGS. 4 and 5 which show a rod and a tube. In the exemplary embodiment of FIG. 2, the two (2) illustrated Ti preforms 28 are rectangular sheets (see FIG. 3). These generally rectangular sheets are considered to be "thick" in the comparative context relative to the prior art which uses alternating "thin" foils of the Al and Ti metals. While a "foil" is typically thought of as being of a thickness which is less than 0.2 mm, the "thick" sheet 28 of FIG. 3 may have a thickness of approximately 2 .0 mm or slightly greater without imposing limitations on the process results, and this exemplary thickness is not limiting. However this exemplary thickness may depend of the application of the final product.

The temperature of the molten Al which is contained within crucible 22 is monitored and closely controlled by means of thermocouple 32 and heating element 34. The molten Al may be protected from direct contact with ambient air by the use of a suitable flux layer 38. An alternative to the use of flux layer 38 is to use a non-reacting gas shield. Whichever approach is used, either a suitable flux layer or a non-reacting gas shield, or a combination thereof, the objective is to protect the molten Al from direct access of ambient air, mainly oxygen, in order to reduce Al oxidation as much as possible.

The flux which is used to create flux layer 38 is provided in a sufficient volume based on the size of the exposed upper surface 40 so as to result in a layer thickness for the flux which does not break open due to moderate surface turbulence. The gas bubbles, which are used for stirring the molten bath of Al exit from stirring tube 30, and may need to escape through the flux layer 38. However, if the flux layer has a sufficient thickness it will close back as the gas bubbles escape and any exposure of the molten Al to ambient air is kept to a minimum.

The molten Al may be stirred using a jet flow of a suitable inert gas via stirring tube 30. As the gas exits from the lower end of the stirring tube 30, turbulence is created within the molten Al and this imparts a stirring motion to the molten Al so as to continuously expose the outer surface of each Ti preform 28 which is submerged, to a "fresh" supply of molten Al, thus maintaining a uniform temperature of Ti surface submerged in the molten Al. Another option for imparting a stirring motion to the molten Al is to use a ceramic stirrer which is powered by either compressed air or by electric power, both of which can be arranged outside of the embodiment 20 in FIG. 2. With one or more Ti preforms 28 submerged in the molten Al, according to the apparatus of FIG. 2, and while the molten Al is being stirred, a metallurgical reaction between Al and Ti occurs. This metallurgical reaction is allowed to take place over a period of time which is expected to be shorter than the period of time required for the prior art to form the same aluminide thickness, due to the ability to increase the Al melt temperature and also to keep it uniform over the whole volume of the Al melt due to stirring action, as explained above. The stirring action to maintain the uniformity of temperature becomes important when a large number of Ti performs are suspended in the Al melt at the same time. According to the exemplary embodiment, this metallurgical reaction continues until the Al or Ti is consumed partially or completely in order to obtain the final product containing either:

(i) a composite of Al and T1AI₃;

(ii) a composite of Ti and T1AI₃;

(iii) a composite of Ti, Al, and T1AI₃ or,

The selection of one of the above diffusion products would depend on the application. Since the only required temperature control is that for the molten Al, this control requirement is simpler and easier than what is required for the prior art which requires stacking of alternating Al and Ti foils and multi-spot temperature control of the stack. Accordingly, when the exemplary embodiment is compared to the prior art, it is clear that the exemplary embodiment includes a simpler quality control of the process and hence improved quality for the final product.

As described and illustrated, each Ti preform 28 which is submerged in the molten Al is held there during the metallurgical reaction. Since, in the proposed process, the temperature of the molten Al can be quickly and uniformly increased as desired it is recognized that the diffusion rate of Al i) into Ti in the early stages of the Ti- T1AI₃ reaction, and ii) through the initial T1AI₃ reaction layer once the latter is formed, is increased and hence the overall T1AI₃ formation rate is also improved. As such, the process time for the formation of T1AI₃ can be reduced as compared to the corresponding process time for the prior art using alternating Al and Ti foil layers.

The rate of T1AI₃ formation in the early stage of the formation process is controlled by the Ti- T1AI₃ reaction rate, and is then controlled mostly by the rate of Al diffusion through the initially formed T1AI₃ layer, to the Ti- T1AI₃ interface; both these rates are facilitated by higher temperatures of the Al melt. As such, using higher temperatures of the Al melt, the overall process time for the formation of the required T1AI₃ layer thickness can be reduced. Using higher reaction temperatures or changing temperatures of foil stack during the reaction process would not be practical in the prior art process. The described apparatus and process of the exemplary embodiment permits several Ti sheets, rods, tubes (see FIGS. 3-5) and other Ti preforms 28 to be simultaneously suspended in the molten Al (see FIG. 2). The size, shape and number of Ti preforms which can be suspended in a volume of molten Al are not limited and only require a suitable crucible 22 and a sufficient volume of molten Al. The option of having and using various Ti preforms of random shapes and sizes, some of which could be at or close to a final form, is not available in the prior art which is limited generally to alternating Al and Ti flat foil layers of a similar geometrical size. Since the outer surface portions of the Ti preform 28 which are actually submerged are subjected to the reaction, a single TiAl₃ surface layer is formed as part of the Ti preform 28 at the end of the process. This single layer covers all of the exposed surfaces of the Ti preforms 28 which are submerged, thereby creating a uniform covering layer regardless of the shape of the Ti preform 28. A more complex part shape 16 is illustrated in FIG. 1 as a starting titanium preform.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes, equivalents, and modifications that come within the spirit of the inventions defined by following claims are desired to be protected. All publications, patents, and patent applications cited in this specification are herein incorporated by reference as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated by reference and set forth in its entirety herein.

Claims

1. A ballistic product component which begins as a titanium preform in the form of a thick sheet includes a surface layer of titanium aluminide and is produced by the following process which comprises these steps:

providing a titanium preform of near net shape;

providing and maintaining a molten Al bath at a desired reaction temperature;

submerging the titanium preform into the molten Al bath;

maintaining the titanium preform in the molten Al bath for a desired reaction time period;

allowing a Ti- T1AI3 reaction to occur and thereby cause a dimension (primarily thickness) increase to the titanium preform so as to bring the titanium preform from said near net shape to a net shape (primarily thickness); and

making the final ballistic product by stacking the reacted Ti sheets and interfacially welding them

2. The process for producing a reacted Ti sheet of claim 1 which further includes the step of determining the desired reaction time period, and the temperature of the Al melt by considering thickness of the required Ti aluminide layer and the magnitude of the dimension (primarily thickness) increase.

3. The process for producing a reacted Ti sheet of claim 1 wherein the titanium preform is constructed such that it can be used to produce the final ballistic product of required shape and thickness, after the Ti-Al reaction.

4. The process for producing a reacted Ti sheet of claim 1 wherein the shape of the titanium preform is selected from the group consisting of flat, corrugated, curved, honeycombed, and others.

5. The process for producing a reacted Ti sheet of claim 1 wherein the fabrication technique for the titanium preform is selected from the group consisting of machining, casting, cutting, welding, mechanical fastening and other similar means.

6. A method of producing a reacted Ti sheet from a starting titanium preform comprises the following steps:

providing a titanium preform of near net shape;

providing and maintaining a molten Al bath at the desired temperature;

submerging the titanium preform into the molten Al bath;

allowing a Ti-Al reaction to occur and thereby cause a dimension (primarily thickness) increase to the titanium preform so as to bring the titanium preform from said near net dimension to a net dimension (primarily thickness);

and making the final ballistic product by stacking the reacted Ti sheets and interfacially weld them

7. The method for producing a reacted Ti sheet of claim 6 which further includes the step of determining the desired reaction time period by considering the thickness of the reaction layer and the magnitude of the dimension (primarily thickness) increase.

8. The method for producing a reacted Ti sheet of claim 6 wherein the titanium preform is constructed to be used as an element (part) of the final ballistic product after the Ti-Al reaction.

9. The method for producing a reacted Ti sheet of claim 6 wherein the shape of the titanium preform is selected from the group consisting of flat, corrugated, curved, honeycombed, and others.

10. The method for producing a reacted Ti sheet of claim 6 wherein the fabrication technique for the titanium preform is selected from the group consisting of machining, casting, welding, cutting, mechanical fastening and other means.

11. A composite material (a reacted titanium sheet in this case) which includes as part of its composition the intermetallic compound titanium aluminide, said composite material being used in the production of ballistic products and said composite material being prepared by a process comprising the steps of;

a) providing a containment vessel;

b) providing a volume of molten Al within said containment vessel; c) providing a Ti preform;

d) suspending said Ti preform within said volume of molten Al; e) maintaining a molten condition for said molten Al; and f) enabling the formation of a single thickness of intermetallic compound titanium aluminide fully or partially into said Ti preform.

12. The composite material of claim 11 wherein said process includes the additional step of providing said containment vessel with heating means for maintaining said molten condition of said molten Al at a predetermined

temperature which is well above the melting temperature of Al but well below the boiling temperature of molten Al.

13. The composite material of claim 12 wherein said process includes the additional step of inserting a thermocouple into said molten Al, said

thermocouple being electrically connected to said heating means.

14. The composite material of claim 13 wherein the process further includes the step of inserting stirring means into said molten Al for imparting a stirring motion to said molten Al.

15. The composite material of claim 14 wherein said stirring means is a tube and wherein said process includes the additional step of imparting said stirring motion by forcing an inert gas flow through said tube into said molten Al.

16. An apparatus for the production of a composite material, including titanium aluminide, said apparatus comprising:

a containment vessel;

a volume of molten Al in said containment vessel; a support structure which is constructed and arranged to suspend a

Ti preform from said support structure into said volume of molten

Al;

a heating element; and temperature sensing means cooperatively arranged with said heating element for maintaining said volume of molten Al in a molten condition at the desired temperature.

17. The apparatus of claim 16 wherein said temperature sensing means is a thermocouple which is suitably positioned in said volume of molten Al.

18. The apparatus of claim 17 which further includes stirring means inserted into said volume of molten Al, said stirring means being constructed and arranged for imparting a stirring motion to said volume of molten Al.

19. The apparatus of claim 18 wherein said stirring means is a tube constructed and arranged to allow an inert gas introduced into said volume of molten Al.

20. A process for the production of a composite material, including titanium aluminide, comprising the following steps:

a) providing a containment vessel;

b) providing a volume of molten Al within said containment vessel;

c) providing a Ti preform; suspending said Ti preform within said volume of molten Al;

maintaining a molten condition at a desired temperature for said molten Al; and

enabling the formation of a single thickness of intermetallic compound titanium aluminide into said Ti preform.

21. The process of claim 20 which includes the further step of providing said containment vessel with a heating means for maintaining said molten condition of said molten Al.

22. The process of claim 21 which includes the additional step of inserting a temperature sensor into said molten Al, said temperature sensor being electrically connected to said heating means.

23. The process of claim 22 which includes the additional step of inserting stirring means into said molten Al for imparting a stirring motion to said molten Al.

24. The process of claim 23 wherein said stirring means is a tube and said imparting stirring is accomplished by forcing an inert gas flow through said tube into said molten Al or said imparting stirring is accomplished by means of a ceramic stirrer which is powered by either compressed air or by electric power, both of which can be arranged outside of the embodiment 20 in FIG. 2.