Analytical modeling to calculate the hardness of ultra-fine WC–Co cemented carbides (original) (raw)
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International Journal of Refractory Metals and Hard Materials, 2001
Mechanical properties and microstructures of nanocrystalline WC±10Co cemented carbides were investigated. The nanocrystalline WC±10Co cemented carbide powders were manufactured by reduction and carbonization of the nanocrystalline precursor powders which were prepared by spray drying process of solution containing ammonia meta-tungstate (AMT) and cobalt nitrate. The WC powders were about 100 nm in diameter mixed homogeneously with Co binder phase and were sintered at 1375°C under a pressure of 1 mTorr. In order to compare the microstructures and mechanical properties with those of nanocrystalline WC±10Co, commercial WC powders in a diameter range of 0.57±4 lm were mixed with Co powders, and were sintered at the same conditions as those of nanocrystalline powders. TaC, Cr 3 C 2 and VC of varying amount were added into nanocrystalline WC±10Co cemented carbides as grain growth inhibitors. To investigate the microstructure of Co binder phase in the WC±10Co cemented carbides, Co± W±C alloy was fabricated at the temperature of sintering process for the WC±10Co cemented carbides. The hardness of WC±10Co cemented carbides increased with decreasing WC grain size following a Hall±Petch-type relationship. The fracture toughness of WC±10Co cemented carbides increases with increasing HCP/FCC ratio of Co binder phase by HCP/FCC phase transformation. Ó
International Journal of Refractory Metals and Hard Materials, 2006
Microstructure and mechanical properties of WC-TiC-10 wt%Co cemented carbides fabricated by sintering with hot isostatic pressing (Sinter-HIP) process were investigated. The WC/TiC grain size ratio of WC-TiC-10 wt%Co cemented carbides was controlled by changing the average size of WC powders ranged from 0.5 to 4 lm, with keeping the average size of TiC powder as 1 lm. The microstructures of sintered WC-TiC-10 wt%Co cemented carbides were sensitively dependent on the WC/TiC grain size ratio. In WC-TiC-10 wt%Co cemented carbides with WC/TiC grain size ratio of 0.5, the TiC/(Ti, W)C core-rim phases were distributed in WC/Co matrix. While, in WC-TiC-10 wt%Co cemented carbides with WC/TiC grain size ratio above 0.8, the WC and TiC/(Ti, W)C core-rim phases were surrounded by Co binder phase. Hardness of WC-TiC-10 wt%Co cemented carbide increased with decreasing the WC/TiC grain size ratio from 4 to 0.8 following the modified Hall-Petch type equation. However, the hardness of WC-TiC-10 wt%Co cemented carbides with WC/TiC grain size ratio of 0.5 shows much higher values than that expected by modified Hall-Petch type equation. Transverse rupture strength of WC-20TiC-10 wt%Co cemented carbides increases with decreasing the WC/TiC grain size ratio.
International Journal of Refractory Metals and Hard Materials, 2016
In this paper the influence of the consolidation process and sintering temperature on the properties of near nanoand nano-structured cemented carbides was researched. Samples were consolidated from a WC 9-Co mixture by two different powder metallurgy processes; conventional sintering in hydrogen and the sinter-HIP process. Two WC powders with different grain growth inhibitors were selected for the research. Both WC powders used were near nanoscaled and had a grain size of 150 nm and a specific surface area of 2.5 m 2 /g. Special emphasis was placed on microstructure and mechanical properties; hardness and fracture toughness of sintered samples. Consolidated samples are characterised by different microstructural and mechanical properties with respect to the sintering temperature, the consolidation process used and grain growth inhibitors in starting powders. Increasing sintering temperature leads to microstructure irregularities and inferior hardness, especially for samples sintered in hydrogen. The addition of Cr 3 C 2 in the starting powder reduced a carbide grain growth during sintering, improved microstructural characteristics, increased Vickers hardness and fracture toughness. The relationship between hardness and fracture toughness is not linear. Palmqvist toughness does not change with regard to sintering temperature or the change of Vickers hardness.
Magnetic Properties and Hardness of Nanostructured WC-Co Cemented Carbide
Materials Science Forum, 2012
Nacrystalline WC-10wt.%Co powders were prepared by high energy milling and liquid phase sintered. The powders with different milling time were characterized by X-ray diffraction and SEM. After sintered the WC-10wt.%Co cemented carbides exhibits ultra fine grain sizes. Coercitive field and Vickers hardness measurements on the consolided samples detected a significant increase and decrease Vickers hardness with the milling time increase in sintered samples.
International Journal of Refractory Metals and Hard Materials, 2011
Nanocrystalline tungsten carbide has been obtained by reduction/carburization at low temperature from precursors obtained by freeze-drying of aqueous solutions. Nanocrystalline WC powders with a adequate content of carbon were mixed with submicrometric Cobalt powder (12 wt.%), obtained by same synthesis method, and sintered in vacuum furnace. The cemented carbides fabricated from experimental powders were compared with both commercial ultrafine and nanocrystalline WC-12Co mixtures consolidated by the same route. The synthesised powders were characterized by X-ray powder diffraction, elemental analysis and scanning and high resolution transmission electron microscopy. On the other hand, density, microstructure, hardness and fracture toughness together with X-ray diffraction analysis of the sintered materials were evaluated. The cemented carbides obtained from synthesised powders exhibited a WC platelet-based homogeneous microstructure. This anisotropic growth might be due to the presence of stacking faults parallel to the basal plane in the starting WC powder, which would promote the defectassisted preferential growth. These materials showed excellent mechanical properties, with a superior hardness/fracture toughness combination compared to materials prepared from commercial mixtures.
Influence of VC on the microstructure and mechanical properties of WC–Co sintered cemented carbides
International Journal of Refractory Metals & Hard Materials, 1999
The aim of this work was to evaluate the microstructural aspects and mechanical properties of a series of 90 wt% [1 À yWC± yVC]±10 wt% Co cemented carbides. The microstructural parameters of contiguity (g a ), binder mean free path (v b ) and grain size of carbide phases (v a ) have been evaluated. Contiguity has a maximum value of 0.61 at the 36WC±54VC±10Co (y 0.6) composition. The addition of 8 g 7 resulted in the formation of a c-(W x V y )C solid solution phase inhibiting the appearance of g-(W x Co y )C grains which embrittles the body. Although the indentation fracture toughness value of 18 MPa m 1a2 obtained for y 0.6 is acceptable, it is advisable to strictly control the predominant c±(W x V y )C double carbide grain size in order to achieve higher hardness values. Ó
Tribologia, 2016
This study performs a comprehensive analysis concerning the amount of fine tungsten carbide (WC) grains needed for the appropriate reinforcement of the cobalt (Co) metallic binder in WC-8Co cemented carbides. The goal is to investigate the balance of coarse-to-fine grain distribution to achieve overall improvement of the material’s mechanical and wear properties. All samples possessed the same WC-8Co binder content, therefore, allowing the role of grain size distribution to be tested. It was found that a ratio of 8:1 wt% of coarse to ultrafine grain WC yielded an appropriate balance between material hardness, fracture toughness, and rupture strength. Upon adding grain growth inhibitors vanadium carbide (VC) and chromium carbide (Cr3C2), the overall wear resistance is further improved compared to undoped composites when samples are tested under abrasive wear conditions.
Effect of Carbon Addition on Microstructure and Properties of WC–Co Cemented Carbides
Journal of Materials Science & Technology, 2012
Based on a unique method to synthesize WC-Co composite powder by in-situ reactions of metal oxides and carbon, the effects of the carbon addition in the initial powders on the phase constitution, microstructure and mechanical properties of the cemented carbides were investigated. It is found that with a suitable carbon addition the pure phase constitution can be obtained in the sintered bulk from the composite powder. The mechanical properties of the cemented carbides depend on the phase constitution and the WC grain structure. To obtain the excellent properties of the WC-Co bulk, it is important to obtain the pure phase constitution from the appropriate carbon addition in the initial powders and a suitable grain size.
Spark plasma sintering behavior of nanocrystalline WC–10Co cemented carbide powders
Materials Science and Engineering: A, 2003
Microstructure and mechanical properties of WC Á/10Co cemented carbides fabricated by spark plasma sintering (SPS) process were investigated. Nanocrystalline precursor powders were prepared by spray drying process from solution containing ammonia meta-tungstate and cobalt nitrate, and followed by reduction and carbonization into nanocrystalline WC/Co composite powders by a mechano-chemical process. The WC particles of about 100 nm in diameter were mixed homogeneously with Co binder. The nanocrystalline WC Á/10Co powders were consolidated by SPS process at temperature ranged 900 Á/1100 8C and under a pressure of 50 or 100 MPa, respectively. Optimum consolidation conditions, such as temperature and pressure, were determined by analysing the dimensional changes of powder compact during SPS process. Hardness and fracture toughness of consolidated WC Á/10Co cemented carbide were measured by using a Vicker's indentation test. The solute content within the Co binder phase of WC Á/10Co cemented carbide was evaluated by measuring the saturated magnetic moment. It is found that the hardness of cemented carbide was dependent on the density and grain size of WC. The fracture toughness of cemented carbides increased with increasing the saturated magnetic moment, while decreased rapidly when the liquid Co phase was formed during sintering.
Microstructure and mechanical properties of nanocrystalline WC-10Co cemented carbides
Scripta Materialia, 2001
The intercritical annealing and isothermal bainitic processing response was studied for three Nb and V microalloyed Transformation-Induced Plasticity (TRIP)-assisted 980 MPa grade steels. Their mechanical and microstructural properties were compared to industrially produced TRIP 800 steel. Depending on the isothermal holding temperature and microalloying, the experimental steels reached properties comparable to the reference steel. The retained austenite content did not show direct correlation to elongation properties. Niobium was found to be more effective microalloying element than vanadium in increasing the elongation properties, which were investigated by measuring true fracture strain from tensile test specimens.