Spark Plasma Sintering Behavior and Structural Stability of 2D- WS2 Nanosheets

The sintering behavior and structural stability of two-dimensional (2D) WS2 nanosheet powder under high-temperature pressure-assisted spark plasma sintering (SPS) were investigated. Transformation of the 2D particle morphology to coarse WS2 platelets was observed during sintering at a higher temperature of and above 1000 degrees C. Particle coarsening was caused by diffusion bonding of multiple 2D-WS2 nanosheet particles on the basal plane surface. Consolidation of the 2D-WS2 nanosheet particles at lower sintering temperatures primarily involved particle-particle interlocking and limited particle-particle diffusion bonding. About 94% of the theoretical density was achieved without any sintering additives on SPS at 1200 degrees C. The WS2 stoichiometry was retained even at 1200 degrees C with no indication of any thermal degradation. A fraction of the hexagonal 2H-type structure of the 2D-WS2 transformed to rhombohedral 3R phase during SPS at and above 800 degrees C. The as-sintered 2D-WS2 showed a low coefficient of friction in the range of 0.06-0.1. The observed tribological behavior was correlated with its thermo-mechanical properties and sintering characteristics at different temperatures.