In the present study, for the first time, a new method for the synthesis of MAX phases of the composition Ti3SiC2, combining high-temperature sintering and hot pressing, was proposed and implemented, ...and this made it possible to obtain the purest material with a Ti3SiC2 phase content equal to 99.2%. The Ti3SiC2 MAX phases are extremely promising materials for protection of containers and fuel cladding of nuclear reactors taking into consideration their high values of mechanical properties and the unique ability of successful radiation resistance. According to this task, the synthesis methods and formation conditions of the Ti3SiC2 MAX phases are considered in the present study involving the following approaches. Among them the second was used for the first time. Various mixtures from initial powders Ti/Si/C, Ti/Si/TiC, Ti/SiC/C and Ti/SiC/TiC were used to synthesize ternary titanium-silicon carbide (Ti3SiC2) by sintering followed by hot pressing. The powder Ti/SiС/TiC is the best among all powder mixtures for synthesis Ti3SiC2. The relative density of the samples synthesized and consolidated by the hot pressing method reaches 99.4%. It is shown that practically single-phase Ti3SiC2consists of elongated laminar grains. The influence of time and temperature of sintering on the formation of the MAX-phase Ti3SiC2 from original powders Ti/Si/C was determined. Titanium carbide, as an intermediate phase, is always present in final products. Excess silicon contributes to the greatest phase formation Ti3SiC2. The high content of the Ti3SiC2 phase in the samples makes it possible to predict their high mechanical properties and resistance to radiation, as well as to consider these materials as the most promising for the further protection of containers and casings of fuel elements of nuclear reactors.
•Dense materials with the Ti3SiC2 phase were obtained by high-temperature synthesis.•Stages of the Ti3SiC2 synthesis from Ti/Si/C compounds were identified.•The microstructure of the synthesized materials contains elongated laminar grains (Ti3SiC2 phase).
The results of studying the crack resistance of reaction-sintered B
4
C–SiC composite materials impregnated with liquid silicon with identification and fracture methods are presented. With an ...increase in the amount of B
4
C in the reaction-sintered material, its fragility increases. The crack resistance of the material can be increased from 3.40 to 4.02 MPa·m
1/2
(when tested by different methods) by adding to the composite material up to 30 wt.% SiC. The material is destroyed mainly by the intercrystalline (intergranular) mechanism. Ceramics containing more than 90 wt.% B
4
C, is partially destroyed by the transcrystalline mechanism.
This research analyzes the methods for producing silicon nitride and the properties of initial powders. The main methods for obtaining materials based on silicon nitride are described. Liquid-phase ...sintering and hot pressing were used to develop dense materials based on silicon nitride. As a sintering additive, 3 – 10 wt.% and 5 – 20 wt.% of yttrium-aluminum garnet were used for hot-pressed and sintered materials, respectively. The mechanical properties (modulus of elasticity, bending strength, fracture resistance, and Vickers hardness) of sintered and hot-pressed materials have been studied. Maximum properties were obtained with sintered materials containing 15% oxides and hot-pressed materials containing 10% oxides.
The influence exerted by the conditions of the preliminary synthesis of Si
3
N
4
by nitridation at 1350 and 1400°С and additional high-temperature sintering at 1800 and 1900°С on the properties of ...reaction-bonded silicon nitride was studied. Secondary silicon nitride (β-Si
3
N
4
) formed in the course of nitridation consists of needle-like grains, which reinforce the material and impart to it additional mechanical strength. The microstructure and phase composition of the silicon nitride material at different initial ratios of silicon and silicon nitride were studied. The materials obtained approach liquid-phase-sintered and hot-pressed silicon nitride in the mechanical properties.
A review of the literature is presented, including a description of the crystal structure and morphological features of graphite-like hexagonal boron nitride, as well as the preparation of materials ...based on it. The mechanical and dielectric properties of pyrolytic, hot-pressed (hexagonal and turbostratic modification) and reactive sintered boron nitride are presented. The positive effect of impregnation of porous samples based on boron nitride with organoboron and organosilicon compounds, followed by pyrolysis, on the level of physicomechanical characteristics is shown.
Information on the temperature coefficient of linear expansion (TCLE) of materials based on silicon carbide is presented. It is shown that the different polytypes 3C (cubic modification) and 4H and ...6H (hexagonal modifications) are characterized by different thermal expansions, the difference between the values of which increases with increasing temperature. The TCLEs of reaction-sintered, liquid-phase-sintered, and hot-pressed silicon carbide materials are determined in the range 20 – 1800°C.
Dense composite materials Al
2
O
3
–SiC
w
with a whisker volume fraction of up to 30 vol% were formed by the methods of liquid-phase sintering and hot pressing. In the presence of 10 vol % SiC
w
, ...the density of liquid-phase sintered and hot-pressed materials is decreased to 97.3 and 98.0% of the theoretical density, respectively. For liquid-phase sintered materials, the compositions Al
2
O
3
20 vol % SiC
w
have maximum characteristics: σ
ben
= 416 ± 15 MPa and
K
1C
= 4.74 ± 0.12 MPa m
1/2
. The introduction of 30 vol % SiC
w
impedes active compaction of the materials (ρ
rel
= 89.3% of the theoretical density). For hot-pressed materials, the highest characteristics were determined at 30 vol % SiC
w
: σ
ben
= 774 ± 15 MPa and
K
1C
= 5.94 ± 0.12 MPa m
1/2
. For higher volume fractions, the strength of the Al
2
O
3
–SiC
w
composite materials decreases.
A diamond – silicon carbide composite material has been obtained. The reaction-diffusion mechanism of Turing sintering is investigated. The conditions for the growth of SiC grains on diamond ...particles during formation of the composite are shown. The process of graphitization of diamond particles during reaction sintering has been investigated. The mechanical characteristics of the diamond – silicon carbide composite have been studied.
An explanation of the physical nature of the experimentally determined concentration dependences of the electrical conductivity of ceramic composite materials of the SiC–TiN (ZrN) system is proposed. ...A model of the structure and a method for calculating the electrical conductivity of composite materials, as well as experimental dependences of the electrical conductivity of sintered ceramics of the SiC–TiN(ZrN) system are presented.
Initial powders of Zr, Al, C and Zr, Al, ZrC were used for the synthesis of MAX phases of the compositions Zr
2
AlC and Zr
3
AlC
2
. The highest content (50.4 vol %) of the MAX phase Zr
3
AlC
2
was ...obtained using the initial powders Zr/Al/ZrC in the ratio of components 1 : 1.5 : 2 with the addition of 5 vol % of Al. The optimal temperature for the synthesis of a material based on the MAX phase Zr
2
AlC is 1525°C, and that of the material based on Zr
3
AlC
2
—1575°C. The structure of the synthesized MAX materials includes elongated grains of the compositions Zr
2
AlC and Zr
3
AlC
2
, which determines their high strength. Zirconium carbide, as an intermediate phase, is always present in the final products. Due to the considerable evaporation of aluminum, the ZrO
2
phase is also present in the synthesis products. Excess aluminum contributes to the maximal formation of Zr
2
AlC and Zr
3
AlC
2
phases during synthesis.
