Microwave sintering of chessboard-structured TiN–Si3N4  nanocomposites reinforced by nanofibers

  

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Omeliana Pritsaka str.,3, Kyiv, 03142, Ukraine
zgalatlozynskyy@gmail.com
Powder Metallurgy - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2022, #01/02
http://www.materials.kiev.ua/article/3379

Abstract

The microstructural design of composite nanomaterials for microwave sintering applying chessboard structurization is proposed. Since single-phase and composite nanoparticles and nanofibers are distributed according to the chessboard principle in the mixture and the Si3N4–TiN powder composites acquire a combined microstructure formed by components that significantly differ in the depth of microwave penetration into the volume, the consolidation process in the electromagnetic microwave field at a ratio of ~50 : 50 can be improved significantly. The effectiveness of the above principles was proved by producing high-density (~99% relative density) composites in the Si3N4–TiN system and composites reinforced with nanofibers. The chessboard-structured Si3N4–TiN composites were consolidated in a microwave furnace at a frequency of 2.45 GHz in a nitrogen flow at T = 1500 °C. In situ mixtures of TiN–40 wt.% Si3N4 and TiN–20 wt.% Si3N4 plasma-chemical powders with 7 and 20 wt.% silicon nitride nanofibers incorporated by mechanical mixing and preliminarily covered with titanium nitride were used. Microstructural analysis of the TiN–40 wt.% Si3N4 composite revealed that titanium nitride grains coarsened to 100–200 nm, while silicon nitride grains remained 30–50 nm in size. This indicates that the electromagnetic microwave energy is predominantly absorbed by titanium nitride grains resulting in their self-heating. The mechanical properties of the TiN–40 wt.% Si3N4 nanocomposite were as follows: HV = 21.2 ± 0.5 GPa and KIc = 4.9 MPa × m1/2. Reinforcement of the composites with silicon nitride fibers, with their surface being covered with a titanium nitride layer, increases the fracture toughness to 5.5 MPa × m1/2 at ~ 20 GPa hardness. Increase in the number of Si3N4 nanofibers from 7 to 20 wt.% did not improve the mechanical characteristics of the composite, indicating that the optimal amount of silicon nitride nanofibers needs to be determined in the composite.


CHESSBOARD, MICROWAVE SINTERING, NANOFIBERS, NANOPOWDERS, SI3N4, STRUCTURE, TIN