Irina Hussainova

Effect of microstructure on the erosive wear of titanium carbide-based cermets

Abstract In thus study the effects of microstructure on wear of multiphase materials is analyzed with reference to titanium carbide-based ceramic–metal composites. The weight fraction of TiC phase in these cermets varied between 0.5 and 0.8. The solid particle erosive wear behavior of TiC-based cermets with different binder phases was investigated. The microstructure of each material was characterized with scanning electron microscopy (SCM). In this study, the possible modes in which composition and microstructure influence the erosive wear behavior are examined. Results indicate that microstructural parameters play an important role in determining wear resistance of composite materials whereas the bulk hardness and/or toughness seem to be of minor importance.

Assessment of cermets performance in erosive media

Ceramicmetal composites are a success story from the viewpoint of their many applications. However, the lack of design criteria and predictive models for durable applications of cermets poses a significant barrier to their wider application. The main objective of this paper is to review the cermets behaviour in tribological environment for better understanding material performance and durability in erosive media. For this reasons, microstructure of multiphase materials, features of structure development during sintering, fracture mechanisms, interface phenomenon, ability of energy dissipation and thermo-mechanical parameters were analysed with reference to WC-, TiC-, and Cr3C2-based cermets.

Some views on the erosion?corrosion response of bulk chromium carbide based cermets

Chromium carbide/nickel based composites are applicable in many environments involving tribo-corrosion due to their combined ability to resist wear and corrosion. Hence, they are candidate materials for use either in bulk as surface coatings in crude oil (offshore) or in power and marine industries. The aim of this work was to study the effect of material parameters such as composition and surface roughness, together with test conditions such as abrasive particle concentration, applied potential, temperature and time of experiment on the performance of chromium carbide based cermets. Potentiodynamic and potentiostatic tests were carried out as part of this work. SEM studies were also conducted to establish the mechanisms of the material degradation processes. Finally, erosion-corrosion maps were constructed based on the results. Material wastage, synergy and regime maps were developed for these materials and demonstrated that the performance of the cermet depends on the interplay of material and process variables.

Reactive Sintering of ZrC-TiC Composites

Inherently, zirconium carbide (ZrC) suffers from low fracture toughness (~3 MPa*m1/2) and excessive porosity when sintered in vacuum. One way to improve ZrC’s sinterability and fracture toughness is the addition of binder metal or other carbides to increase densification. Using mechanical activated synthesis (MAS) to homogenously mix ZrC and titanium carbide (TiC) powders, followed by sintering at 1900 °C, produces a ZrC-TiC composite with hardness and fracture toughness at 20 GPa & ~7 MPa*m1/2, respectively. 80ZrC-20TiC (wt%) gave the highest fracture toughness value compared to other ratios. Varying TiC ratio from 20 - 50 wt% does little to affect mechanical hardness or densification of the composite. However, fracture toughness appears to increase marginally with decreasing TiC concentration down to ~20 wt%.

Direct CVD Growth of Multi-Layered Graphene Closed Shells around Alumina Nanofibers

In this work, a catalyst-free direct deposition of multi-layered graphene closed shells around highly aligned alumina nanofibers with aspect ratio of 107 is demonstrated for the first time. A single – step chemical vapor deposition process of specified parameters was used for development of hybrid structures of carbon shells around the core alumina nanofibers. Transmission electron microscopy and Raman spectroscopy were used to confirm formation of graphene layers and to understand the morphology of the various structures. The developed routine for growth of peculiar carbon nanostructures opens new opportunities for deposition of the tailored carbon structures on dielectric substrates.

Microstructural Design of Ceramic–Metal Composites for Tribological Applications

The properties, performance, and reliability of a cermet material depend mostly on the intrinsic properties influenced by microstructure that evolves during processing and use. In this study, the effect of microstructure on reliability of multiphase materials in erosive media is analyzed with reference to WC-, TiC-, and Cr3C2 - based ceramic-metal composites. Microstructure of multiphase materials, fracture mechanisms, ability of energy dissipation, thermo-mechanical parameters and erosion resistance are examined. It has been shown that microstructural variables play a very important role in cermets performance. The energetic criterion of non-homogeneous materials selection has been presented.

Graphene-augmented nanofiber scaffolds demonstrate new features in cells behaviour.

Three-dimensional (3D) customized scaffolds capable to mimic a native extracellular matrix open new frontiers in cells manipulation and advanced therapy. The major challenge is in a proper substrate for in vitro models on engineered scaffolds, capable to modulate cells differentiation. Here for the first time we demonstrate novel design and functionality of the 3D porous scaffolds of aligned, self-assembled ceramic nanofibers of ultra-high anisotropy ratio (~107), augmented into graphene shells. This unique hybrid nano-network allows an exceptional combination of selective guidance stimuli of stem cells differentiation, immune reactions variations, and local immobilization of cancer cells, which was not available before. The scaffolds were shown to be able to direct human mesenchymal stem cells (important for stimulation of neuronal and muscle cells) preferential orientation, to suppress major inflammatory factors, and to localize cancer cells; all without additions of specific culture media. The selective downregulation of specific cytokines is anticipated as a new tool for understanding of human immune system and ways of treatment of associated diseases. The effects observed are self-regulated by cells only, without side effects, usually arising from use of external factors. New scaffolds may open new horizons for stem cells fate control such as towards axons and neurites regeneration (Alzheimer’s disease) as well as cancer therapy development.

Hybrid Syntactic Foams of Metal – Fly Ash Cenosphere – Clay

This paper addresses an innovative syntactic foam produced out of metal powder (Fe), fly ash cenospheres (CS) and clay ceramic syntactic foams composite material (CM). Due to the low density of CS (bulk density - 0.38 g/cm3), the average density of these foams is about 2.6-2.9 g/cm3. It was found that CS undergoes phase transformation during thermal treatment at a temperature of 1200°C. Microstructural observations reveal a uniform distribution of CS and Fe particles in the composite. Compressive strength, and friction coefficient of obtained Fe/CS CM are in the range between 149 - 344 MPa and 0.15 - 1.1, respectively. Dependence of compressive strength on firing temperature is demonstrated exhibiting the maximum at 344 MPa; however, dependence of coefficient of friction on a material properties, obtained at different firing temperature exhibits the minimum value of 0.15 at the firing temperature of 1150 °C. The obtained syntactic form was shown to be a candidate for wear resistant applications.

Influence of Cr, Ti and Zr Oxides Formation on High Temperature Sliding of NiAl-Based Plasma Spray Coatings

In this study, the tribological characteristics of plasma thermal spray coatings are studied with particular interest on formation and performance of Cr, Ti and Zr oxides under dry sliding at 500 °С with Pin-On-Disc configuration against NiAl. Plain Cr2O3, TiO2 and ZrO2 coatings were tested to trace the difference between performance of original and in-situ formed oxides. Friction surfaces were examined using SEM and X-ray spectral analyses. The highest wear resistance of NiAl-CrB2 composite coatings can be related to the formation of Cr2O3 during the tribosynthesis process.

Synthesis of ZrC-TiC Blend by Novel Combination of Sol-Gel Method and Carbothermal Reduction

Titanium Carbide and zirconium carbide binary mixtures (ZrC – TiC) were prepared by sol-gel processing followed by carbothermal reduction. Solution-based synthesis was applied to achieve a molecular dispersion of the reactants. Titanium – (IV) – and zirconium – (IV)butoxides were used as metal sources and hydroquinol was used as carbon source for precursor preparation. Mixture of titanium and zirconium carbides was synthesized by carbothermal reduction at temperatures up to 1500 o C in argon and vacuum environment. The structural transformation of the polymeric materials into the carbides was characterized by SEM, X – ray diffraction analysis and Raman spectroscopy. Characterizations of heat treated samples at 800 o C to 1500 o C in argon and vacuum has showed that the carbothermal reduction of the binary solid carbide mixture (ZrC – TiC) polymeric precursor began in vacuum at lower temperature (1100 o C) than in argon environment.