Self-propagating high-temperature synthesis of advanced ceramics MoSi2–HfB2–MoB

This study focuses on the investigation of the macrokinetic features of SHS (combustion synthesis) of elemental mixtures Mo–Hf–Si–B, in particular the mechanisms of structure and phase formation in the combustion front as well as the structure and properties of consolidated ceramics. Two routes for the fabrication of the composite SHS powder in system MoSi₂–HfB₂–MoB were used: (1) synthesis using Mo–Si–B and Hf–B mixtures followed by mixing of the combustion products and (2) synthesis using the four-component Mo–Hf–Si–B mixture. Dense ceramic samples with a homogeneous structure and low residual porosity (0.8–3.6%) were prepared by hot pressing of SHS powders. Although the particles size distribution and phase composition of SHS powders are similar for both synthesis routes, the structure and properties of both the composite SHS powders and hot-pressed ceramics differ considerably. Synthesis using the four-component Mo–Hf–Si–B mixture allows one to produce hierarchically ordered nanocomposite material with improved mechanical properties: hardness up to 17.6?GPa and fracture toughness up to 7.16?MPa?m^1/2.     

Reactive,nonreactive, and flash spark plasma sintering of Al2O3/SiC composites—A comparative study

The influence of different SPS-based methods, that is, conventional spark plasma sintering (SPS), flash SPS (FSPS), and reactive SPS (RSPS) on the properties of Al₂O₃/SiC composite was investigated. It was shown that the application of preliminary high energy ball milling of the powders significantly enhances the sinterability of the ceramics. It was also demonstrated that FSPS provides unique conditions for rapid, that is, less than a minute, consolidation of refractory ceramics. The Al₂O₃-20 wt% SiC composite produced by FSPS possesses the highest relative density (~99%), fracture toughness (7.5 MPa m^1/2), hardness (20.3 GPa) and wear resistance among all ceramics produced by other SPS-based approaches with dwelling time 10 minutes. The RSPS ceramics hold the highest Young's modulus (390 GPa). Substitution of micron-sized Al₂O₃ particles by nano alumina does not lead to measurable enhancement of the mechanical properties.     

Features of Synthesizing Ceramic Composites Discretely Reinforced by Carbon Fibers and SiC Nanowires Formed in situ in the Combustion Wave

Russian Journal of Non-Ferrous Metals - A new method is proposed for the engineering of SiC-based ceramic-matrix composite materials strengthened by discrete carbon fibers and single-crystal...     

A critical review on spark plasma sintering of copper and its alloys

Journal of Materials Science - Copper and its alloys have been in the service of humankind earlier than any other metal throughout history. In the present review, all aspects of the SPS of copper...     

Peculiarities of the Synthesis of High-Temperature TaSi2–SiC Ceramics Reinforced in situ by Discrete Silicon Carbide Nanofibers

Russian Journal of Non-Ferrous Metals - The possibility of increasing the mechanical properties of the ceramic material of the TaSi2–SiC system by reinforcing it with silicon carbide...     

Theoretical and experimental study of combustion synthesis of microgradient ULTRA high-temperature ceramics in Zr-Ta-Si-B system

The macrokinetic features and phase and structure formation mechanisms are investigated in the Zr-Ta-Si-B system in the framework of the fractal theory of combustion. The reaction mechanisms are explored using ab initio grand potential modeling and Ellingham diagrams and then verified via direct in situ time-resolved XRD and quenching of combustion fronts in a copper block. The tendency of the Zr-TaSi-B system to form tantalum boride Ta₃B₄ and a transient tantalum silicide Ta₅Si₃ and release elemental Si and Zr in the combustion front is suggested based on the developed models and verified using a quenched combustion front and timeresolved XRD analysis. Investigation of hot-pressed combustion products shows that despite slightly higher relative density, TaSi₂-rich ceramics have relatively lower mechanical properties and oxidation resistance under plasma torch as compared to single-phase (Zr,Ta)B₂ solid solution.     

Self-propagating high-temperature synthesis of nanocomposite ceramics TaSi2-SiC with hierarchical structure and superior properties

This study focuses on the investigation of the combustion kinetics and mechanisms, as well as the phase and structure formation processes, during elemental self-propagating high temperature synthesis of ceramics in Ta-Si-C system.Thermodynamic and kinetic features of SHS are discussed. Thermodynamic calculations, time-resolved XRD and investigation of stopped combustion front suggest the following chemical reactions sequence in combustion wave for the Ta-Si-C system: Ta + Si_solid + C → TaC + Si_solid + C → TaC + SiC + Si_liquid + C → TaC + TaSi₂ + Ta₅Si₃ + SiC + Si_solid + C → TaSi₂ + SiC.Significant microstructure refinement occurs due to the formation of SiC within the TaC, Ta₅Si₃ and TaSi₂ particles during the SHS. Combustion products consist of agglomerated SiC and TaSi₂ particles with the size of individual grains equal to 15–50 nm. Hot pressing of TaSi₂-SiC powders at 1600 °C produces the bulk nanocomposites with a relative density of 97%. In comparison to similar materials reported in the literature, bulk SHS composite TaSi₂-30%SiC exhibits superior hardness (19.1 GPa) as well as fracture toughness (6.7 MPa m^1/2) and shows a great potential for application as a structural material and as a precursor for ion-plasma deposition of high-temperature tribological coatings.     

Influence of Ti and TiH2 Additives on the Structure and Properties of Copper Alloys for Diamond Cutting Tools

Russian Journal of Non-Ferrous Metals - The influence of titanium and titanium hydride additives on the structure, mechanical properties, and wear resistance of copper alloys intended for use as a...