Kristjan Juhani

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.

Phase evolution, microstructure characteristics and properties of Cr 3 C 2 -Ni cermets prepared by reactive sintering

Cr 3 C 2 -Ni cermets are perspective materials to operate in aggressive and abrasive environment. Recently a novel method – reactive sintering of chromium carbide based cermets – was invented. Elemental powders of chromium, nickel and carbon black were milled in a high-energy ball mill (attritor) to nanocrystalline size and pressed to compacts. The thermal treatment (sintering) caused at first the formation of chromium carbide grains in situ and following liquid phase sintering of alloy in one cycle. Since the reactive sintering has not been used for the production of Cr 3 C 2 -Ni cermets before, the influence of chromium to carbon ratio and the influence of different alloying elements on the microstructure and properties of the chromium carbide based cermets was investigated. It is shown that mechanical properties and abrasive erosion wear resistance depend on the chromium to carbon ratio, alloying additives and sintering method.

Influence of Pressurized Sintering on Performance of TiC-Based Cermets

This paper discusses the effect of advanced sintering technologies – sinter + hot isostatic pressing (HIP) and sinter/HIP on the performance of TiC-based cermets. The performance was evaluated by strength (transverse rupture strength), adhesive wear resistance and durability. Adhesive wear was performed by a turning method (turning of mild steel at low speed) while durability was evaluated by functional testing – wear of tools during blanking of sheet metal. It was found that sinter/HIP ensures a higher positive effect than sinter + HIP in different cycles.

Developments in cermet design, technology and performance

This paper reviews developments in the research of cermets, related technologies and their mechanical and tribological (erosion abrasive wear resistance) characterisation. The aim is to enhance the performance and reliability of cermets and widen their application areas. Cermet technologies (ceramic-metal composites), such as TiC-based bonded with Ni- and Fe-alloys and Cr3C2-based bonded with Ni-alloys, are analysed. Focus is on the influence of different sintering modes: vacuum sintering, sinter/HIP and sinter + HIP (in different cycle) on the performance and reliability of TiC- and Cr3C2-based cermets. The structure, mechanical characteristics (hardness, transverse rupture strength) and wear resistance (erosive and abrasive wear) of the developed cermets are characterised.

Microstructural and Mechanical Characteristics of in Situ Synthesized Chromium-Nickel-Graphite Composites

Cr-C-Ni composites were synthesized in situ from elemental powders of Cr, Ni and C by high energy milling followed by reactive sintering. The milled powders with the grain size in nano-scale were pressed to compacts and sintered. During the thermal treatment that was performed after the pressing the chromium carbide was formed first and then the Cr3C2-Ni cermets were sintered in one cycle. The interface between the binder phase and the carbide grains of the in situ composite has a good bonding strength as it is not contaminated with oxidation films or other detrimental surface reactions. The microstructure of such cermets is fine-grained and more homogeneous than that of cermets produced by conventional method. As a result the cermets have higher hardness, transverse rupture strength and 1.2-2 times higher wear and erosion resistance.

The Influence of Processing Parameters on Mechanical Properties of Spark Plasma Sintered Chromium Carbide Based Cermets

Present paper discusses the influence of spark plasma sintering (SPS) on the microstructure and perfomances of chromium carbide based cermets. The effect of SPS parameters (temperature, pressure) is discussed. It is shown that SPS enables to produce more fine grained chromium carbide based cermets compared to conventional liquid phase sintering. Hardness and fracture toughness are exhibited.

Three-Body Abrasive Wear of Reactive Sintered WC-Co Hardmetals with Grain Growth Inhibitors

WC-Co hardmetals are widely known wear resistant materials, their properties depend strongly on the WC grain size; commonly fine grained materials exhibited higher properties. One opportunity to produce fine grained materials is reactive sintering. Reactive sintering is a novel processing method, where the synthesis of the carbide phase is combined with solid and liquid state sintering of the composite during a single heating cycle. WC-co hardmetals where synthesized in situ from the elemental powders of W, Co and C. To investigate the influence of grain growth inhibitors the Cr3C2 and VC were also included to powder mixtures. To investigate the influence of carbon content composites with different amounts of C were produced. The microstructures, hardness and three-body abrasive wear resistance of reactive sintered WC-Co hardmetals with grain growth inhibitors depending on carbon content in initial powder mixture is exhibited.

Erosion Wear of Reactive Sintered WC-TiC-Co Cermets

WC-5TiC-15Co cermets were prepared via novel technology – reactive sintering. In case of reactive sintering the elemental powders of tungsten, titanium, cobalt and carbon black are activated through ball-milling and then the synthesis of carbide occurs in the same cycle with the sintering of the cermet. Carbon content in initial powder mixture has crucial effect on properties of reactive sintered WC-based cermets. This paper investigates the erosion wear of the WC-5TiC-15Co cermets. Wear resistance dependent on the carbon content as well as wear mechanism of reactive sintered and conventional cermets are exhibited.

Effect of Sinter/HIP Technology on Properties of TiC-NiMo Cermets

The present work is a study on the argon gas pressure effects of Sinter/HIP sintering on microstructure and strength of different grades of TiC-NiMo cermets. Titanium carbide in the composition of different grades of TiC-NiMo cermets was ranged from 40 to 80 wt.% and the ratio of nickel to molybdenum in the initial powder composition was 1:1, 2:1 and 4:1 respectively. On the sintered alloys, the main strength characteristic, transverse rupture strength (TRS) and erosion wear resistance were measured. Furthermore, the microstructure parameters of some alloys were measured and the pressure effect on pore elimination was evaluated. All the results were compared with common, vacuum sintered alloys. The TRS values of TiC-NiMo cermets could be considerably improved by using Sinter/HIP technique, for high-carbide fraction alloys and for alloys sintered at elevated temperatures. The results provide new possible application fields for Sinter/HIP-ed TiC cermet materials to areas where, in addition to wear performance, higher strength properties are demanded.