Mechanical Properties Of WC Research Articles

Effect of WC particle size on the microstructure, mechanical properties and fracture behavior of WC–(W, Ti, Ta) C–6wt% Co cemented carbides

Abstract This study deals with the microstructure and mechanical properties of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides fabricated by conventional sintering. The conventional WC particles of 4 μm size and ultrafine particles of 0.2 μm were introduced in the system with varying ratio. The ratios of conventional WC particles to ultrafine WC particles were 2:1, 1:1, and 1:2. The microstructures of sintered WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides were sensitively dependent on the ratio of conventional WC particles to ultrafine WC particles. The rim phase increased with the increase in the amount of ultrafine particles. Hardness of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbide increased with increase in the amount of rim phase and decrease in the average grain size of WC particles. The bending strength showed the similar trend of the hardness. The fracture morphologies are reported. The fracture behavior changed from mixed mode to transgranular fracture mode, when the ratio of conventional WC particles to ultrafine WC particles was changed from 2:1 to 1:2.

Hard Alloy WC–24% Ni Obtained in the Solid Phase from Ultrafine WC, NiO, and C Powders. Part 2. Mechanical Properties

Mechanical properties of WC–24 mass% Ni alloy prepared by a combination in single stage of metal phase synthesis and compaction of an ultrafine mixture of WC–Ni powders by high-energy compaction and sintering are studied. Tungsten carbide, nickel oxide, and carbon are selected as the starting powders. After milling the initial powders the average particle size is 200-300 nm. Previously compacted briquettes of WC + NiO + C are heated, sintered, and pressed in the range 950-1300°C at vacuum of 0.133 Pa. Briquettes are also sintered in the liquid phase at 1350°C for comparison. Ultimate strength in bending, fracture toughness, ultimate strength in compression, and Vickers hardness are determined for specimens prepared at different temperatures. The dependence of mechanical properties on specimen consolidation temperature is studied. It is shown that these dependences for pressed specimens have a maximum at 1200-1250°C. The high level of properties (ultimate strength in bending 2500 MPa, ultimate strength in compression 3100 MPa, fracture toughness 19 MPa·m1/2, and hardness 10.0 GPa) are achieved for a WC + Ni + C powder mixture to which carbon is added in the form of a liquid carbon-containing compound. Introduction into the mixture of commercial carbon grade P803 leads to low specimen mechanical properties. The effect on mechanical properties of porosity and pore size, and also grain boundary quality between particles is studied.

Microstructure and mechanical properties of WC–C nanocomposite films

WC–C nanocomposite film was prepared by using a hybrid deposition system of r.f.-PACVD and DC magnetron sputtering. W concentration in the film was varied from 5.2 to 42 at.% by changing the CH 4 fraction of the mixture sputtering gas of Ar and CH 4. Hardness, residual compressive stress and electrical resistivity were characterized as a function of W concentration. Raman spectroscopy, XRD and high resolution TEM were employed to analyze the structural change in the film for various W concentrations. In the present W concentration range, the film was composed of nano-sized WC particles of diameter less than 5 nm and hydrogenated amorphous carbon matrix. Content of the WC particles increased with increasing W concentration. However, the mechanical properties of the film increased only when the W concentration was higher than 13 at.%. Structural analysis and electrical conductance measurements evidently showed that the increase in hardness and residual stress occurred as the WC particles were in contact with each other in the amorphous carbon matrix.

Cemented Carbides Alloyed with Ruthenium, Osmium, and Rhenium

A study was made of the structure and mechanical properties of WC ― Co cemented carbides alloyed with Ru, Re, and Os. It was shown that the alloying elements form solid solutions with the binder phase, Co(Ru, W, C), Co(Re, W, C), Co(Os, W, C), which have higher microhardnesses and elastic moduli than the solid solution Co(W, C). Ruthenium, rhenium, and osmium reduce the stacking fault energy of the cobalt phase and promote the transformation of the cubic modification of cobalt to the hexagonal. This results in precipitation hardening of the binder phase. Additions of Ru, Re, and Os increase the hardness, and bend, compression and yield strengths, of WC ― Co alloys. Examples of the successful use of WC ― Co cemented carbide tools alloyed with noble metals for the machining of heat-resistant alloys and high-alloy steels are given.

Mapping of mechanical properties of WC–Co using nanoindentation

High-resolution measurements of mechanical properties are of immense importance in metallurgy. Measuring the intrinsic properties of each phase separately in multiphase materials gives information ...

Influence of VC on the microstructure and mechanical properties of WC–Co sintered cemented carbides

The aim of this work was to evaluate the microstructural aspects and mechanical properties of a series of 90 wt% [(1− y)WC– yVC]–10 wt% Co cemented carbides. The microstructural parameters of contiguity ( C α ), binder mean free path ( L β ) and grain size of carbide phases ( L α ) have been evaluated. Contiguity has a maximum value of 0.61 at the 36WC–54VC–10Co ( y=0.6) composition. The addition of V 8 C 7 resulted in the formation of a γ-(W x V y )C solid solution phase inhibiting the appearance of η-(W x Co y )C grains which embrittles the body. Although the indentation fracture toughness value of 18 MPa m 1/2 obtained for y=0.6 is acceptable, it is advisable to strictly control the predominant γ–(W x V y )C double carbide grain size in order to achieve higher hardness values.

Nanocrystalline WC and WC/a-C composite coatings produced from intersected plasma fluxes at low deposition temperatures

Low temperature vacuum deposition of tungsten carbide coatings, W1−yCy with compositions that varied from y=0 to 0.9, was investigated. Special attention was given to the production of nanocrystalline carbides with coatings of y>0.5. Previous attempts at producing WC with excess carbon at near room temperatures resulted in the formation of amorphous phases. In this study, crystalline WC was produced at 45 and 300 °C by the intersection of plasma fluxes from magnetron sputtering of tungsten and laser ablation of graphite. At both temperatures, formation of WC chemical bonding and nanocrystalline cubic β-WC1−x was observed using x-ray photoelectron spectroscopy and grazing angle x-ray diffraction when the carbon content was increased more than 30%. Increasing the substrate temperature to 300 °C did not affect the percentage of WC bonding, but it did promote considerable crystallization of cubic WC. As the carbon content was increased to more than 50%, a second phase consisting of amorphous carbon (a-C) was observed together with amorphitization of β-WC1−x. The a-C phase was identified as amorphous diamond-like carbon (DLC) by Raman spectroscopy. At 60–80 at. % C, a two phase structure was produced, which was composed of nanocrystalline β-WC1−x with 5–10 nm grains and amorphous DLC. The hardness of the WC/DLC composites was about 26 GPa based on nanoindentation tests. Correlation of the chemistry, microstructure, and mechanical properties of WC and WC/a-C coatings is discussed.

Analytical Electron Microscopy of (W,Ti)C

Addition of titanium to tungsten carbide changes its structure from hexagonal to NaCl type in the single phase region of the W-Ti-C ternary. This results in a change of the slip systems active during deformation. It Is thus possible to improve the mechanical properties of WC (especially toughness) by the alloying addition of Ti. The purpose of this study is to identify the appropriate deformation mechanisms, using TEM techniques. The present report deals with investigations on deformed and undeformed single phase ternary carbides. The bulk (W,Ti)C samples were obtained by arc melting presintered pellets of mechanically mixed WC and TiC powders with a nominal composition of 22.5% W, 32.5% Ti, and 45% C (atomic). Three millimeter dia. discs of 100 μm thickness were obtained from these samples by spark cutting and further mechanical grinding. The deformation was introduced by creating a square array of micro-indentations. The discs were then ion-beam thinned.

WC-Co超硬合金の機械的性質に及ぼす表面研削の影響

The effects of surface-grinding, i.e., γ→ε′ transformation and residual compressive stress (σr), on the mechanical properties of WC-(6∼30)%Co alloy were investigated in detail. The specimen almost free from the ε′ phase and the residual stress was prepared by sufficiently polishing the ground specimen so as to remove the surface-layer containing ε′ and σr (the thickness is about 30 μ).The results obtained were as follows: (1) The hardness of the alloy and in particular that of the binder phase were increased by grinding. (2) The binder phase contracts by a small amount due to the γ→ε′ transformation, whereas the residual compressive stress was formed in the surface layer by grinding. (3) One set of crack length around Vickers indentation and frequency of crack path in the binder phase were larger in the orientation perpendicular to the grinding direction than in the orientation parallel to it. These were considered to be due to the anisotropy in the formation of a plate-shaped ε′ phase in relation to the grinding direction. (4) The contribution of σr to the transverse-rupture strength appeared to be neglected in common alloys, but it became considerably large in high-strength alloys. The amount of the contribution was considered to depend on the perfection of specimens, the surface state and distribution of σr, etc.