Metal-ceramic materials

#This invention relates to metal-ceramic composite material and bodies formed therefrom. Particularly, the invention relates to metal infiltrated and/or metal encapsulated ceramic materials, and ballistic armor structures produced therefrom. The present inventive composite materials provide high damage tolerance, multi-hit protective capability, light weight (i.e. aerial density of about 4 lb/ft2 for standard SAPI armor), and relatively low cost, each of which is especially attractive for applications in lightweight armor.

#In many armor applications, weight is not a critical factor, and thus traditional materials, such as steel, can offer some level of protection from ballistic projectiles and shell fragments. Steel armors also offer the advantage of low cost and can serve as structural members of the equipment into which they are incorporated. In recent decades, certain hard ceramic materials have been developed for certain armor applications. These ceramic-based armors, such as alumina, boron carbide, silicon carbide, and titanium diboride ceramics provide the advantage of being lighter in mass than steel (up to ⅓ density of steel) and provide higher ballistic stopping power as steel for the same mass. Thus, in applications in which having an armor design having the lowest possible mass is important, such as (human) body armor and aircraft armor, low specific gravity armor materials are highly desirable. Also, in ceramic armor, the lower the density, the greater the thickness of armor that can be provided for the same areal density. In general, a thick ceramic armor material is more desirable than a thinner one because a greater volume of the armor material will be engaged in attempting to defeat the incoming projectile. Moreover, the impact of the projectile on a thicker armor plate results in less tensile stress on the face of the plate opposite that of the impact than would result on the back face of a thinner armor plate. Thus, where brittle materials like ceramics are concerned, it is important to try to prevent brittle fracture due to excessive tensile stresses on the back face of the armor body; otherwise, the armor is too easily defeated. By preventing such tensile fracture, the kinetic energy of the projectile can be absorbed completely within the projectile, e.g. ideally causing complete projectile self-destruction at the surface of the armor body, or more typically, the kinetic energy absorption of the projectile manifests itself as the creation of a very large new surface area within the armor material in the form of a multitude of fractures, e.g., shattering of the ceramic while the projectile undergoes self-destruction as its kinetic energy goes to zero.

#Current state-of-the-art body armor is the Small Arms Protective Insert (SAPI). The SAPI provides ballistic protection from specific 5.56 mm and 7.62 mm rounds when it is worn in the pocket of the appropriate tactical vest. The current SAPI, which includes both a ceramic strike face and a fiber reinforced plastic backing, weighs 5.1 lb/ft2. Marines wear both a front and back plate, for a total of weight of about 11 pounds. Currently, field SAPIs can be made using a variety of materials including sintered alumina (Al2O3)), silicon carbide (SiC), boron carbide (B4C), or titanium diboride (TiB2) ceramic or hot pressed or reaction bonded ceramics, such as silicon carbide (SiC) or boron carbide (B4C). Ballistic impact with the SAPI plate results in extensive fragmentation damage to the internal ceramic plate so that further ballistic protection is either seriously compromised or eliminated entirely necessitating use of additional textile fabric like Kevlar™ as a soft armor backing. In fact, occasional drops of the SAPI ensembles often result in breaking of the ceramic armor rendering the entire armor system ballistically degraded to the point of being inoperable. At this point, the SAPI ensembles are discarded and new inserts are required, resulting in considerable field replacement cost. For higher performance multi-hit applications, SAPI ensembles based on individual overlapped small tile or disc shaped mosaics can provide the necessary control to limit ballistic induced crack damage to single or adjacent tiles especially when multi-hit repeatability of less than 3 inches is needed. However, whether as single piece or tile mosaic, monolithic ceramics are still very brittle and therefore susceptible to breakage through occasional drops during general field use, also resulting in considerable field replacement as the unitized construction the entire plate must be replaced.

#FIG. 1a is a photograph showing the ballistic damage of a boron carbide tile;

#FIG. 1b is a photograph showing the ballistic damage of encapsulated magnesium-boron carbide composite with carbon reinforcing fiber;

#FIG. 1c is a photograph showing the ballistic damage of encapsulated magnesium-boron carbide composite;

#The present invention provides lightweight composite materials that have high impact damage tolerance and multi-hit protective capability, which can be produced at relatively low cost. The potential applications of the present composites include, but are not limited to, lightweight structures, cutting tools, hot and cool parts of turbine engines, impact resistant structures, abrasive and wear resistant and impact resistant materials, semiconducting devices, and armor.

#In one embodiment, the material contains a ceramic preform infiltrated with a metal. The material is produced by the steps of placing the metal or its alloy on top of the ceramic, and heating to a temperature above the melting point of the metal. The molten metal then infiltrates the ceramic material and forms a continuous matrix in the pores of the ceramic material. After cooling and solidification, the result is a composite material of the present invention. Preferably, the process takes place in an inert environment having minimal oxygen content, preferably Argon.

#In a second embodiment of the present invention, the ceramic material is reinforced with an adjacently placed fiber prior to infiltration by the metal. In this embodiment, the metal is melted over a layer of ceramic placed on the backing fibers to infiltrate into the ceramic and the backing fibers, thereby bonding the ceramic and the fiber being bonded together by the metal phase. The fibers can be in the back of the ceramic as well as in the front of the ceramic, or both. The fiber backing due to its higher strength, higher modulus and higher fracture toughness imparts to the metal-ceramic composite enhanced strength, stiffness and impact resistance (toughness) to the material. As a result of increased material strength, the ceramic composite can be made thinner further reducing weight while retaining bending strength. As a result of increased material stiffness, the aerial density of the composite can be reduced further reducing weight of the armor. As a result of increased impact resistance, the composite will be more resistant to incidental damage during use (e.g. resistance to breakage by casual dropping of the armor material). The reinforcing fiber can be, but is not limited to, titanium, tantalum, Ni-chrome, boron, silicon carbide, and carbon, with carbon being the preferred reinforcing fiber.