O. B. Zgalat-Lozinskii

Nanocomposites Based on Refractory Compounds, Consolidated by Rate-Controlled and Spark-Plasma Sintering (Review)

Rate-controlled sintering and spark plasma sintering are considered the most promising methods to produce dense nanoctructured ceramics. Refractory compounds are used to demonstrate the application of methods for controlling the densification rate and nonlinear heating and loading conditions to produce dense nanocomposites with 30–70 nm grains. The mechanical and tribological properties of ceramics with grains from 50 to 500 nm in size are compared. The effect of increase in the mechanical (5–15%) and tribological (to 50%) characteristics of nanocomposites consolidated by rate-controlled sintering and modified nonlinear spark plasma sintering is studied. Nanocomposites based on refractory nitrides and borides are regarded as promising materials for creating a new generation of cutting tools, as well as wear-resistant ceramics for wide application.

Sintering of Refractory Compound Nanocrystalline Powders. Part 1. Storage and Preliminary Heat Treatment of Titanium Nitride Nanocrystalline Powders

Several approaches are considered for storing and processing finely-dispersed oxygen-free refractory compound powders using the example of titanium nitride nanopowder. The change in composition of nanopowders protected by a surfactant and without protection from oxidation during storage in air, and also during processing in gas atmospheres (nitrogen, hydrogen) and in a vacuum is studied.

Sintering of Refractory Compounds Nanocrystalline Powders. Part 2. Non-Isothermal Sintering of Titanium Nitride Powder

New approaches to the sintering of nanocrystalline powders of refractory compounds are proposed. Titanium nitride-based ceramics with a grain size of 50 nm and nanohardness 28.8 ± 2.47 GPa was obtained by sintering at a controlled rate of densification. Investigation of evolution of the block structure in the material during sintering enabled further optimization of the procedure and reduction of the sintering temperature to 1150°C.

Friction and Wear of the TiB2–30 vol.% B4C Composite Consolidated in Spark Plasma Sintering

The tribotechnical properties of the TiB2–30 wt.% B4C composite material in pair with VK6 hard metal are investigated. The material demonstrates high wear resistance under dry friction conditions: the intensity of linear wear of the friction pair does not exceed 1.83 μm/km, the friction coefficient of the friction pair is 0.5. The analysis of 3D profiles of the sample surface shows the effect of smoothing of the surface of the ceramic composite by transfer of hard metal submicron particles on its surface and formation of tribofilm.

Production of Products of Various Shapes From Si3N4-Based Refractory Compounds by Spark Plasma Sintering

The possibility of manufacturing ball-, cylinder-, and hollow cylinder-shaped products based on Si3N4 and TiN nanocomposites by spark plasma sintering (SPS) is demonstrated. The features of the product properties associated with different conductivity of composites. The mechanical properties of ball- and hollow cylinder-shaped materials measured: HV ~ 11.5 GPa, KIc ~ 4.1 MPa · m1/2 (for Si3N4); and HV ~ 12.7 GPa, KIc ~ 4.8 MPa · m1/2 (for Si3N4–TiN).

Structure of Si3N4–Y2O3–Al2O3 and TiN–AlN Composites Consolidated in Microwaves (2.45 GHz)

The consolidation of nanocomposite powders of refractory nitrides (TiN, Si3N4, AlN) in the microwave field (2.45 GHz) is studied. The structurization of sintered samples with aspect ratio l/h >>5 is examined. The structure and properties of the composites consolidated by microwave and conventional (resistance) heating are compared. The use of microwaves for sintering of bulk parts from Si3N4–Y2O3–Al2O3 and TiN–AlN nanocomposites with a great l/h ratio revealed a number of issues in producing homogenous nanoceramics.

Friction and Wear of TiN–Si3N4 Nanocomposites Against ShKh15 Steel

Spark plasma sintering is used to produce dense silicon nitride nanoceramics with titanium nitride additions and nanofiber-strengthened composites. The sintered nanocomposites demonstrate quite high mechanical properties (HV ≈ 14–16 GPa, KIc≈ 4.8 MPa ∙ m1/2) and low dry friction coefficient (f ≈ 0.65–0.68) and mass wear (~0.2–0.4 mg/km) against ShKh15 steel. The nanocomposite strengthened with 3.8 wt.% silicon nitride nanofibers shows the most balanced mechanical and tribotechnical characteristics.

Thermochemical microwave treatment of refractory nanopowders

Titanium nitride and silicon nitride nanopowders are subjected to microwave treatment to stimulate reduction and nitration reactions. It is established that oxygen content of the nanopowders after microwave treatment is 30–60% lower than that of the starting powders. It is also studied how the efficiency of thermochemical treatment and the particle-size distribution depend on the amount of the phase that absorbs microwave energy.