Mechanical Properties of Silicon Nitride in Different Morphologies: In Situ Experimental Analysis of Bulk and Whisker Structures

Silicon nitride (Si₃N₄) is widely used in structural ceramics and advanced manufacturing due to its excellent mechanical properties and high-temperature stability. These applications always involve deformation under mechanical loads, necessitating a thorough understanding of their mechanical behavior and performance under load. However, the mechanical properties of Si₃N₄, particularly at the micro- and nanoscale, are not well understood. This study systematically investigated the mechanical properties of bulk Si₃N₄ and Si₃N₄ whiskers using in situ SEM indentation and uniaxial tensile strategies. First, nanoindentation tests on bulk Si₃N₄ at different contact depths ranging from 125 to 450 nm showed significant indentation size effect on modulus and hardness, presumably attributed to the strain gradient plasticity theory. Subsequently, in situ uniaxial tensile tests were performed on Si₃N₄ whiskers synthesized with two different sintering aids, MgSiN₂ and Y₂O₃. The results indicated that whiskers sintered with Y₂O₃ exhibited higher modulus and strength compared to those sintered with MgSiN₂. This work provides a deeper understanding of the mechanical behavior of Si₃N₄ at the micro- and nanoscale and offers guidance for the design of high-performance Si₃N₄ ceramic whiskers.