Microstructure Development, Nanomechanical, and Dynamic Compression Properties of Spark Plasma Sintered TiB 2 -Ti-Based
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INTRODUCTION
A good armor material should possess properties such as low density, high hardness, elastic modulus, fracture toughness, compression strength and Hugoniot elastic limit[1] along with multi-hit capability to resist multiple bullet impacts. The currently available body armor materials include ceramics, laminated composite structures and ballistic fabrics. Ceramics are one of the good choices for such applications as they provide a combination of low density, high hardness, compression strength and modulus.[1,2] Some commonly used armor ceramics are boron carbide (B4C), silicon carbide (SiC), alumina (Al2O3), aluminum nitride (AlN), titanium diboride (TiB2) and Syndie (synthetic diamond comNEHA GUPTA, Post Doctoral Fellow, is with the Department of Materials Science and Engineering, Indian Institute of Technology (IIT) Kanpur, Kanpur208016 India. VENKITANARAYANAN PARAMESWARAN, Professor, is with the Department of Mechanical Engineering, Indian Institute of Technology (IIT) Kanpur, Kanpur 208016, India. BIKRAMJIT BASU, Associate Professor, is with the Materials Research Centre, Indian Institute of Science (IISc), Bangalore 560012, India. NEHA GUPTA, Post Doctoral Fellow, is with the Aerospace Engineering, Indian Institute of Science (IISc), Bangalore 560012, India. Contact e-mail: [email protected] Manuscript submitted December 18, 2013. Article published online June 17, 2014 4646—VOLUME 45A, SEPTEMBER 2014
posite).[3–6] Among these, TiB2 is one of the materials that exhibit a better combination of specific properties as required for body armor application. However, due to moderate fracture toughness (~5 MPa m1/2), TiB2 usually lacks multi-hit capability i.e., it cannot sustain successive impacts without quickly losing much of its strength and is, therefore, susceptible to premature failure during service. This limits its application as an armor material. Therefore, tougher TiB2 composites are needed to be developed, which can effectively resist/ mitigate the crack propagation upon impact either by deflecting or arresting the crack. Apart from this drawback, TiB2 exhibits poor sinterability due to which higher sintering temperatures [>3273.15 K (3000 C)], pressures and longer holding times are required in order to attain near theoretical density (qth), using conventional sintering techniques.[7– 10] Such extreme processing conditions adversely affect the mechanical properties of TiB2 as they can result in abnormal grain growth and sintering reactions.[11–13] It is well recognized that the restriction in grain growth/ secondary phase formation can be achieved by employing rapid heating rates and decreasing the holding times at elevated sintering temperatures.[14,15] In consideration to the above aspects, the densification and toughness of TiB2 can be improved with the addition of a suitable metallic METALLURGICAL AND MATERIALS TRANSACTIONS A
sinter-aid with the hypothesis that metallic additive will aid in better densification at lower sintering temperatures and can impart good fracture toughness due to
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