Microwave Sintering of Chessboard-Structured TiN–Si3N4 Composites Reinforced by Nanofibers

• Published in: Powder metallurgy and metal ceramics Vol. 61; no. 1-2; pp. 32 - 39
• Main Authors: Zgalat-Lozynskyy, O.B., Ragulya, A.V.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-05-2022; Springer Nature B.V
• Subjects: Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Composites; Fracture toughness; Glass; Grains; Materials Science; Mechanical properties; Metallic Materials; Microstructural analysis; Microstructure; Microwave sintering; Mixtures; Nanocomposites; Nanofibers; Nanomaterials; Nanoparticles; Natural Materials; Particulate composites; Principles; Silicon nitride; Sintering (powder metallurgy); Specific gravity; Theory and Technology of Sintering; Thermal and Thermochemical Treatment; Titanium; Titanium nitride; nanopowders; silicon nitride; microwave sintering; chessboard; titanium nitride; nanofibers; structure
• ISSN: 1068-1302; 1573-9066
• DOI: 10.1007/s11106-022-00292-y

The microstructural design of composite nanomaterials for microwave sintering using chessboard structurization is proposed. As single-phase and composite nanoparticles and nanofibers are distributed according to the chessboard principle in the mixture and the Si
3
N
4
–TiN powder composites acquire a combined microstructure consisting of 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 principle was proved in the production of high-density (~99% relative density) Si
3
N
4
–TiN composites and composites reinforced by nanofibers. The chessboard-structured Si
3
N
4
–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.% Si
3
N
4
and TiN–20 wt.% Si
3
N
4
plasma chemical powders with 7 and 20 wt.% silicon nitride nanofibers incorporated by mechanical mixing and preliminarily coated with titanium nitride were used. Microstructural analysis of the TiN–40 wt.% Si
3
N
4
composite revealed that titanium nitride grains coarsened to 100–200 nm, while silicon nitride grains remained 30–50 nm in size. This indicates that microwave energy is predominantly absorbed by titanium nitride grains, which leads to their self-heating. The mechanical properties of the TiN–40 wt.% Si
3
N
4
nanocomposite were as follows: HV = 21.2 ± ± 0.5 GPa and K
Ic
= 4.9 MPa ⋅ m
1/2
. Reinforcement of the composites with silicon nitride fibers coated with a titanium nitride layer increased the fracture toughness to 5.5 MPa ⋅ m
1/2
at ~ 20 GPa hardness. Increase in the amount of Si
3
N
4
nanofibers from 7 to 20 wt.% did not improve the mechanical characteristics of the composite, indicating that the optimal amount of silicon nitride nanofibers in the composite needs to be determined.