Jüri Pirso

Tallinn University of Technology | TTU · Department of Mechanics

Reactive sintering is a process where synthesis reaction of the ceramic phases is combined with sintering (densification) of the composite. Dense lightweight titanium oxycarbide-aluminium oxide ceramic-ceramic composites were produced from titanium dioxide, carbon black as graphite source and aluminium precursors by high energy attritor milling, fo...

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. Ha...

Armouring vehicles against lower lever threats (such as hand guns) usually implement armour alloy materials including armour steel, titanium and aluminium alloys. These materials are simple to add to vehicles in the form of sheet-metal but for higher threat levels such as 7.62 calibre rounds with an armour piercing core described in NATO STANAG 456...

Fine particles originating from a mixture of erodent particles or being the residues of broken particles, might retain on the surface of an eroded material by electrostatic field. This results in the presence of a fine third body between an attacking original erodent particle and a material surface during collision that leads to higher and more loc...

Structure formation and properties of chromium carbide-based cermets with iron–titanium binder were investigated. Chromium carbide (50–70 wt%), Fe, and Ti (Fe: Ti ratio 4: 1 as the binder phase) powders were milled in an attritor and a ball mill, compacted, and sintered at different temperatures and for different periods in vacuum. The microstructu...

Bimodal WC-Co hardmetals were produced using novel technology-reactive sintering. Milled and activated tungsten and graphite powders were mixed with commercial coarse grained WC-Co powder and then sintered. The microstructure of produced materials was free of defects and consisted of evenly distributed coarse and fine tungsten carbide grains in cob...

Reactive sintering was used to produce titanium carbide cermets with molybdenum as an alloying element and nickel for binder. High energy attritor mill was used to mill the same composition of Ti, C, Ni and Mo powders with different durations. High energy milling significantly reduces the temperatures at which a series of reactions occurs between m...

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...

WC-Co hardmetals are widely known wear resistant materials, their properties depend strongly on the WC grain size; commonly fine grained materials exhibited superior 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 combin...

Titanium carbide based cermets with molybdenum as alloying element and nickel as binding metal were produced using high energy powder milling of elemental powders of Ti, Ni, Mo and C (carbon black) followed by liquid state sintering. Reactive sintering process was applied where the synthesis of (Ti, Mo)C occurs in solid state and the final densific...

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...

Effect of different grain growth inhibitors, such as VC, Cr3C2, TiC and mixtures of them, on the microstructure and mechanical properties of WC-15wt%Co hardmetals were investigated. Hardmetals grades were produced by the reactive sintering, where the synthesis reaction of the carbide phase is combined with the solid and liquid phase sintering and t...

Cermets and hard metals are the materials of interest in applications where wear resistance is important. The examination of worn surfaces of these materials with scanning electron microscope had revealed the presence of mechanically mixed layer (MML). The chromium, titanium and tungsten carbide based cermets were selected for the current study. Ma...

Mechanical properties and microstructure of WC-TiC-Co cemented carbides fabricated by using reactive sintering technology were investigated. In case of reactive sintering the elemental powders of tungsten, titanium, cobalt and carbon are activated through ball-milling and then the synthesis of carbide occurs in the same cycle with the liquid phase...

Investigated WC-Co cermets were produced via reactive sintering. In case of reactive sintering the elemental powders of tungsten, carbon black as graphite source and cobalt at first activated throw high energy milling and then the carbide synthesis is taking place in the same cycle with liquid phase sintering of the cermets. Because there is a lack...

Reactive sintering is a novel process where synthesis reaction of the carbide phase is combined with solid and liquid phase sintering of the cermet during a single heating cycle. Ti-C-Ni-Mo composites were synthesized in situ from elemental powders of Ti, Ni, Mo and C by high energy milling, followed by reactive sintering. The milled powders with t...

A novel recycling technology for the production of bulk WC-Co hardmetals from a mixture of WO3, CoWO4 and graphite powders by way of carbothermal reduction in combination with reactive sintering has been developed. Waste hardmetals parts with 15 wt% Co from hardmetals production were fully oxidized into a mixture of WO3 and CoWO4 powder. To oxide p...

Present paper is focused on abrasive impact wear of tungsten and titanium carbide based cermets with different binder contents. A series of samples of different cermets was tested in experimental impact wear tester DESI using different amounts of granite abrasive to study the wear kinetics. The wear resistance of TiC-NiMo and WC-Co cermets was comp...

A comparison of two-body abrasive wear behaviour of WC-Co hardmetals in both wet and dry environments is presented. Five different composites were studied. Two-body abrasive wear tests were conducted on a block-on-ring tester, described in the ASTM B611-85. The steel wheel was replaced with an alumina grinding wheel. The wet environment promoted lo...

The present paper is focused on three-body abrasive wear of cermets on the base of tungsten, titanium and chromium carbides with different contents of binder phase. A series of samples of different cermets was tested using a block-on-ring test machine by the method of ASTM B611 using normal loads of 40 and 200 N. Silica sand was used as the abrasiv...

Cr<sub align="right"> 3 </sub>C<sub align="right"> 2 </sub>-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...

The mechanism of three-body abrasive wear of TiC-base cermets was studied. The wear rate of a series of cermets with different percentage of NiMo binder phase (20–60 wt%) was studied. Silica sand was used as an abrasive. The wear rate of the cermets decreases with the increase of TiC and Mo content, which corresponds to the increase in the bulk har...

The aim of the study was to investigate the effect of oxidation on the behaviour of TiC-based cermets with Ni-Mo binder under low intensity wear conditions in silica sand medium. Three types of material performance maps were constructed: oxidation rate map, wear rate map and map showing the effect of oxidation on wear. Discussion on the performance...

In this paper the friction and sliding wear of WC-Co cemented carbide with free graphite content are studied. The influence of the mixing parameters of the initial powders to the graphite distribution and wear rate is presented. The aim of the study was to develop a new bearing material based on the conventional WC-Co. Friction and wear tests were...

There is increasing demand for adequate materials to handle in erosive slurries. Titanium carbide based cermets, due to their corrosion resistance, are perspective material to use in corrosive and abrasive environments. Present paper covers slurry erosion corrosive wear properties of titanium carbide based cermets with different binder contents and...

The aim of the current study was to investigate the effect of oxidation on behaviour of TiC-based cermets with Ni-Mo binder under low intensity wear conditions in silica sand medium. Three types of material performance maps were constructed: oxidation rate map, wear rate map and map showing the effect of oxidation on wear. Discussion on the perform...

Composite materials produced by powder metallurgy provide a solution in many engineering applications where materials with high abrasion and erosion resistance are required. The actual wear behaviour of the material is associated with many external factors (particle size, velocity, angularity, etc.) and intrinsic material properties (hardness, toug...

The resistance of Ti(Mo)C–Ni cermets of different binder content to solid particle erosion was evaluated at 25, 350 and 650°C. The elevated temperature erosion of cermets containing 40, 50, 60, 70 and 80wt.% of titanium carbides and produced from the powder of initially different ratios of Ni to Mo were tested with the help of specially designed ce...

Wear j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / w e a r a b s t r a c t The present paper concerns the two-body dry abrasive wear phenomenon of a series of cermets on the base of titanium and chromium carbides with different composition, using a "block on abrasive grinding wheel" test machine. WC–Co hardmetals w...

Chromium carbide based cermets, due to their high corrosion resistance, are perspective material to use in corrosive and abrasive environments. Present paper covers slurry erosion corrosive wear properties of chromium carbide based cermets with different chemical compositions (10-40% of Ni). Widely used WC-Co cermets are used as reference material....

Chromium carbide based cermets are perspective materials to use in aggressive and abrasive conditions. Present paper considers the impact wear properties of chromium carbide based cermets with different chemical compositions (10 wt%-50 wt% ofNi). The investigated chromium carbide based cermets were produced by a novel method reactive sintering and...

TiC-base cermets have been elaborated from Ti-C-Ni-Mo powders by mechanical attrition following reactive sintering. This simple and low cost method allows producing sub-micron TiC-base cermets. The influence of carbon black in initial powder mixture on the microstructure formation and properties of TiC-NiMo cermets are studied. With the increase of...

Present paper considers the sliding wear properties of chromium carbide based cermets, produced by different methods and with different chemical compositions (10-30% of Ni), under different wear conditions. Sliding wear properties depend on the chemical composition and microstructure of cermets and although on wear conditions. Sliding wear under no...

The processes of direct recycling hardmetal scrap by oxidationreduction technique have been investigated in details. The hardmetal scrap was oxidized in rotary tube furnace. The oxide powders were milled with graphite powder in ball mill. The carbon content was 6, 8 10, 11, 13 and 15wt%. The mechanism of the reduction of CoWO4 and WO3 with carbon (...

This paper is on comparison of the abrasive and erosive wear resistance of chromium carbide based and nickel bonded cermets prepared by two different methods: conventional powder metallurgy sintering and the new developed one—reactive carburizing sintering. The nickel content was varied at the weight percents of 10, 20 and 30%. Results indicate tha...

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 a...

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 Cr...

The bearing and seals operate often in the conditions of sliding wear. The present paper is an overview, concerning various aspects of cermet-metal dry sliding. The sliding wear is more of a surface phenomenon than abrasion, making it difficult to predict the wear from bulk properties. The wear rate of these cermets was found to be slightly depende...

In the present study WC-Co feedstock powder was produced by the process termed mechanically activated synthesis (MAS). The main characteristics of the powder (particle/granules size, size distribution, morphology, chemical composition and granules microstructure) were determined. The material was sprayed by the HVOF process to investigate the prope...

Reactive carburizing sintering is a novel process where synthesis reaction of the carbide phase is combined with liquid phase sintering of the Cr3C2–Ni cermet. This recently developed method is compared with traditional cermet industry routine. Powder of chromium, nickel, and carbon black were milled in a high-energy ball mill (attritor) to nanocry...

The friction and wear behaviour of cermets/steel rubbing pairs were investigated. Friction and wear tests were carried out using three different crèmets on the base of tungsten, titanium and chromium carbides under dry sliding conditions against steel disk (0.45% C). Sliding wear tests were carried out using modified block-on-ring equipment at a sl...

The paper considers two-body dry abrasive wear of a series of chromium carbide base cermets with different amounts of Ni binder (10-50 wt%) using a "block on abrasive grinding wheel" test machine. The wear coefficient of the cermets reduces with the increase of Cr 3C2 content in the composite, which corresponds to an increase in the bulk hardness....

This article focuses on the characterization of WC-based composite spray powders produced by mechanically activated synthesis. The main characteristics of the powder (particle/granules size, size distribution, morphology, chemical composition and granules microstructure) were determined. Chemical composition of powder particles by energy-dispersive...

The friction and wear properties of TiC–NiMo/steel rubbing pairs were investigated under dry condition. The sliding wear tests were carried out on the testing device at a velocity of 2.2 m/s and a load of 40 N. The volume wear increases with increase of the sliding distance as predicted by Archard’s equation. The wear coefficient of the cermets red...

In this paper the friction and sliding wear of WC–Co cemented carbides are studied. Friction and wear tests were carried out using six different WC–Co alloys (Co ranging from 6 to 20wt.%) under unlubricated conditions against steel (0.45wt.% C) disk. Tests were performed at sliding velocity of 2.2ms−1 and normal load of 40 and 180N. Sliding wear te...

The erosive wear resistance of cermets with different composition, structure and properties has been investigated. It has been shown that cermets erosive wear resistance cannot be estimated only by hardness, characterised by resistance to penetration. The differences in wear resistance between cermet materials with equal hardness level can be attri...

TiC-base cermets are in advantage compared with WC-base hardmetals because of their lower friction coefficient and higher oxidation resistance. At the same time, the diversity of alloys based on TiC, wear and loading conditions contributes substantially to problems in material selection. Present research focuses on testing of TiC-based cermets of d...

The relatively good erosion and corrosion resistance of chromium carbide-bare alloys are well known however in source applications their mechanical properties are not sufficient and their wear-resistance falls behind that of the tungsten-carbide alloys. In order to improve their properties, the effect of the various production parameters and alloyi...

High-resolution measurements of mechanical properties of composites produced by powder metallurgy techniques are of immerse importance for reliable materials production. Measuring the intrinsic properties of each phase separately in multiphase composites gives the information on the spatial heterogeneity in local material properties and serves as a...

The article gives an overview of methods suitable for describing WC-Co powder granules and coatings for thermal spray powder development and production. Composite powder particles and microstructure grains vary from a few nanometres to hundreds of micrometers. It is therefore necessary to combine different analysis methods. In the granule and parti...

Thesis (doctoral)--Tallinn Technical University, 1996.