Received 9 September 2012, revised 2 November 2012, online published 12 November 2012 Defence Science Journal, Vol. 62, No. 6, November 2012, pp. 382-389, DOI: 10.14429/dsj.62.2666  2012, DESIDOC 1. INTRODUCTION The growing threats due to the increase in use of small calibre armor piercing projectiles are posing continuous threat to personnel on the battlefeld. With the advancement in technology, newer explosives and explosive based projectiles have been introduced, which demand the development of new lightweight armor systems 1 . A good armor material must possess high hardness, elastic modulus, fracture toughness, compressive strength 2 and Hugoniot Elastic Limit (HEL). Also, the desired armor material should have multi-hit capability i.e. the material should be able to resist multiple bullets. The currently available body armor materials include ceramics, laminated composite structures and ballistic fabrics. Some of the structural ceramics as B 4 C, SiC, Al 2 O 3 , aluminium nitride, TiB 2 and Syndie (synthetic diamond composite) 3-6 are considered as potential materials for armor applications for both personnel and vehicle protection, owing to their low density, reliability, superior hardness, compressive strength and greater energy absorption capacity, which enable effective erosion and defeat of the projectiles. These structural ceramics exhibit favorable properties such as high impact velocity for dwell/penetration transition and deformation induced hardening 7,8 . Therefore, as soon as the projectile hits the ceramic target, projectile gets shattered. If during impact the ceramic gets pulverized, the pulverized particles help in abrading the projectile further. However, ceramics being brittle usually lack multi-hit capability i.e. they cannot sustain successive impacts without quickly losing much of their strength property. Hence, they are susceptible to failure during service. Also, due to brittleness, when a projectile enters a ceramic, the entrance channel of the shaped projectile becomes ragged, as compared to that while penetrating a metal (ductile). The ragged channel cause asymmetric pressures and disturbs the geometry of the projectile 9 . The asymmetric pressures also cause great irregularities in the ceramic itself, leading to failure. Therefore, tougher composites need to be developed, which can cause effective crack defection as well as lower projectile penetration by shattering, bending or change of path. Over the years, newer and tougher composites have been developed, which give about fve times the protective value of the monolithic ceramics. These are usually metal matrix composites (MMCs), which have both ceramic and metal. Presently, B 4 C and alumina are being frequently used in armor systems. But, these suffer from drawbacks such as, B 4 C undergoes amorphisation at bullet speeds of 800-900 m/s and alumina has lower hardness and toughness. Therefore, there is a need to develop a new armor material system, which does not possess such disadvantages. TiB 2 being a ceramic, is one of the good choices as armor material as it offers most of the required properties for being an armor material as high hardness, compressive strength, elastic modulus, HEL and ballistic effciency. However, it possesses moderate fracture toughness, which is detrimental for its use as an armor material, as it cannot effectively resist the projectile penetration. Also, in order to attain near theoretical density, Ballistic Studies on TiB 2 -Ti Functionally Graded Armor Ceramics Neha Gupta * , V.V. Bhanu Prasad # , V. Madhu # , and Bikramjit Basu *,! * Indian Institute of Technology Kanpur, Kanpur- 208016, India # Defence Metallurgical Research Laboratory, Hyderabad- 500058, India ! Indian Institute of Science (IISc), Bangalore-560012, India * E-mail: nehgupta@iitk.ac.in ABSTRACT The objective of this paper is to discuss the results of the ballistic testing of spark plasma sintered TiB 2 -Ti based functionally graded materials (FGMs) with an aim to assess their performance in defeating small-calibre armor piercing projectiles. We studied the effcacy of FGM design and compared its ballistic properties with those of TiB 2 -based composites as well as other competing ceramic armors. The ballistic properties are critically analyzed in terms of depth of penetration, ballistic effciency, fractographs of fractured surfaces as well as quantifcation of the shattered ceramic fragments. It was found that all the investigated ceramic compositions exhibit ballistic effciency (η) of 5.1 -5.9. We also found that by increasing the thickness of FGM from 5 mm to 7.8 mm, the ballistic property of the composite degraded. Also, the strength of the ceramic compositions studied is suffcient to completely fracture the nose of the pointed projectile used. Analysis of the ceramic fragments (2 µm-10 mm) showed that harder the ceramic, coarser were the fragments formed. On comparing the results with available armor systems, it has been concluded that TiB 2 based composites can show better ballistic properties, except B4C. SEM analysis of the fragments obtained after testing with FGM showed formation of cleavage steps as well as presence of intergranular cracks, indicating that the FGM fractured by mixed mode of failure. It can be concluded that the FGM developed has lower ballistic properties compared to its monolith TiB 2 -20 wt.% Ti. Keywords: TiB 2 -Ti FGM, SPS, depth of penetration, ballistic effciency, fractography 382