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Design of Cemented Carbides and Cermet

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A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (20 December 2019) | Viewed by 35359

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Prof. Dr. Yadir Torres Hernández

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Department of Engineering and Materials Science and Transport, University of Seville (US), 41004 Seville, Spain
Interests: design and manufacture of porous materials; surface modification (physical and chemical); biofuntional (osseointegration, cells, and bacterial response) and tribo-mechanical (instrumented micro-indentation, fracture, fatigue, scratch resistance, and wear) behavior; biomaterials; tool materials (cemented carbides, cermet’s, and multi-layered: alumina-zirconia, WC-Co/WC-Co, and Cermet/WC-Co); powder metallurgy (conventional and space-holder technique)
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Dear Colleagues,

Cemented carbides and cermets are families of ceramic–metal composites used as materials for quite diverse applications: Forming and cutting tools, structural components and wear parts, all of them involving severe and complex service conditions. In this context, the design and manufacturing of novel materials with enhanced tribological and thermo-mechanical behaviours are continuous and challenging demands. They include the development of new hard composite bulk materials and coatings (with modified composition, microstructure and phases), implementation of advanced processing routes (reduction of energy, costs and environmental impact) alternative to conventional ones, as well as the improvement of resistance to fracture, fatigue, wear, oxidation, etc.

This Special Issue’s scope includes contributions of experimental and theoretical analysis, aiming to rationalize and improve the relationship among microstructure, processing and properties of cemented carbides, cermets, high entropy alloys (HEAs), as well as functional gradient materials (FGMs), multilayered designs, hard coatings, etc. In general, research papers are recommended, but the Special Issue is not limited them and include powder synthesis and production technologies, powder compaction (conventional and isostatic), sintering techniques (vacuum, field-assisted and hot consolidation), as well as coating deposition routes to optimize the properties and functionalities of the materials under consideration.

Prof. Dr. Yadir Torres Hernández
Guest Editor

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Keywords

Cemented carbides and cermets
Powder technology
Field assisted sintering
Coatings and surface modification techniques
Mechanical and tribo-corrosion behaviour
Chemical stability at high temperature

Published Papers (11 papers)

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Research

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12 pages, 2420 KiB

Open AccessArticle

Influence of the Test Configuration and Temperature on the Mechanical Behaviour of WC-Co

by Luis M. González, Ernesto Chicardi, Francisco J. Gotor, Raul Bermejo, Luis Llanes and Yadir Torres

Metals 2020, 10(3), 322; https://doi.org/10.3390/met10030322 - 29 Feb 2020

Cited by 1 | Viewed by 2140

Abstract

In this work, the effect of the test configuration and temperature on the mechanical behaviour of cemented carbides (WC-Co) with different carbide grain sizes (d_WC) and cobalt volume fractions (V_Co), implying different binder mean free paths (λ_Co), was studied. The mechanical strength was measured at 600 °C with bar-shaped specimens subjected to uniaxial four-point bending (4PB) tests and with disc specimens subjected to biaxial ball-on-three-balls (B3B) tests. The results were analysed within the frame of the Weibull theory and compared with strength measurements performed at room temperature under the same loading conditions. A mechanical degradation greater than 30% was observed when the samples were tested at 600 °C due to oxidation phenomena, but higher Weibull moduli were obtained as a result of narrower defect size distributions. A fractographic analysis was conducted with broken specimens from each test configuration. The number of fragments (N_f) and the macroscopic fracture surface were related to the flexural strength and fracture toughness of WC-Co. For a given number of fragments, higher mechanical strength values were always obtained for WC-Co grades with higher K_Ic. The observed differences were discussed based on a linear elastic fracture mechanics (LEFM) model, taking into account the effect of the temperature and microstructure of the cemented carbides on the mechanical strength. Full article

(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)

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12 pages, 2685 KiB

Open AccessArticle

Electrochemical Corrosion Resistance of Ni and Co Bonded Near-Nano and Nanostructured Cemented Carbides

by Tamara Aleksandrov Fabijanić, Marin Kurtela, Irbas Škrinjarić, Johannes Pötschke and Markus Mayer

Metals 2020, 10(2), 224; https://doi.org/10.3390/met10020224 - 6 Feb 2020

Cited by 7 | Viewed by 2455

Abstract

The advantages of nanostructured cemented carbides are a uniform, homogenous microstructure and superior, high uniform mechanical properties, which makes them the best choice for wear-resistant applications. Wear-resistant applications in the chemical and petroleum industry, besides mechanical properties, require corrosion resistance of the parts. Co as a binder is not an optimal solution due to selective dissolution in an acidic environment. Thus, the development of cemented carbides with alternative binders to increase the corrosion resistance but still retaining mechanical properties is of common interest. Starting mixtures with WC powder, grain growth inhibitors GGIs; VC and Cr₃C₂, and an identical binder amount of 11-wt.% were prepared. GGIs were added to retain the size of the starting WC powder in the sintered samples. The parameters of the powder metallurgy process were adapted, and samples have been successfully consolidated. A very fine homogeneous microstructure with relatively uniform grain-size distribution and without microstructural defects in the form of carbide agglomerates and abnormal grain growth was achieved for both Ni-bonded and Co-bonded samples. Achieved mechanical properties, Vickers hardness, and Palmqvist toughness, of Ni-bonded near-nanostructured cemented carbides are slightly lower but still comparable to Co-bonded nanostructured cemented carbides. Two samples of each grade were researched by different electrochemical direct current corrosion techniques. The open circuit potential E_corr, the linear polarisation resistance (LPR), the Tafel extrapolation method, and the electrochemical impedance spectroscopy (EIS) at room temperature in the solution of 3.5% NaCl. From the carried research, it was found that chemical composition of the binder significantly influenced the electrochemical corrosion resistance. Better corrosion resistance was observed for Ni-bonded samples compared to Co-bonded samples. The corrosion rate of Ni-bonded cemented carbides is approximately four times lower compared to Co-bonded cemented carbides. Full article

(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)

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11 pages, 10313 KiB

Open AccessArticle

Corrosion-Induced Damage and Residual Strength of WC-Co,Ni Cemented Carbides: Influence of Microstructure and Corrosion Medium

by Yafeng Zheng, Gemma Fargas, Elaine Armelin, Olivier Lavigne and Luis Llanes

Metals 2019, 9(9), 1018; https://doi.org/10.3390/met9091018 - 19 Sep 2019

Cited by 16 | Viewed by 2700

Abstract

The corrosion behavior of cemented carbides with binders of different chemical nature (Co and Ni) and carbides with distinct mean grain size (ultrafine and coarse) was studied. The investigation also included corrosion media (acidic and neutral solutions containing chlorides and an alkaline solution) as experimental variables. Immersion tests were performed to induce corrosion damage in a controlled way. Electrochemical parameters were measured together with a detailed inspection of the corroded surfaces. Microstructural influence on the tolerance to corrosion damage was evaluated in terms of residual strength. Results pointed out that corrosion rates were lower in the alkaline solution. In contrast, acidic media led to higher corrosion rates, especially for cemented carbides with Co regardless the influence of carbide mean grain size. Corrosion damage resulted in strength degradation due to the formation of surface corrosion pits in acidic solution. In neutral and alkaline solutions, much less pronounced effects were determined. Focused Ion Beam (FIB)/ Field Emission Scanning Electron Microscopy (FESEM) results revealed differences in corrosion-induced damage scenario. In acidic solution, corrosion starts at binder pool centers and evolves towards binder/WC interfaces. Meanwhile, corrosion in alkaline solution is initially located at binder/WC interfaces, and subsequently expands into the ceramic particles, developing a microcrack network inside this phase. Full article

(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)

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11 pages, 3053 KiB

Open AccessFeature PaperArticle

Effects of Boron Addition on the Microstructure and Mechanical Properties of (Ti,Ta)(C,N)-Co Based Cermets

by Ernesto Chicardi and Francisco José Gotor Martínez

Metals 2019, 9(7), 787; https://doi.org/10.3390/met9070787 - 16 Jul 2019

Cited by 6 | Viewed by 3279

Abstract

In this work, a titanium–tantalum carbonitride based cermet, with cobalt as the binder phase and boron as a sintering additive, was developed by a mechanically induced self-sustaining reaction process using two different methodologies. The boron additive was added to prevent the formation of brittle intermetallic compounds generally formed during the liquid phase sintering step due to the excessive ceramic dissolution into the molten binder phase. A systematic study was carried out to understand the effects of boron addition on the nature of the phases, microstructure, and mechanical properties of cermets. With the boron addition, the formation of two different boride solid solutions, i.e., (Ti,Ta)B₂ and (Ti,Ta)₃B₄, was observed. Moreover, the nature of the binder was also modified, from the (Ti,Ta)Co₂ brittle intermetallic compound (for cermets without boron addition) to ductile and tough (Ti,Ta)Co₃ and α-Co phases (for cermets with boron addition). These modifications caused, as a general trend, the increase of hardness and toughness in cermets. Full article

(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)

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13 pages, 6679 KiB

Open AccessArticle

Characterisation and Performance Optimisation of WC-MC/M(C,N)-Co Hardmetals

by Roman Hochenauer and Walter Lengauer

Metals 2019, 9(4), 435; https://doi.org/10.3390/met9040435 - 12 Apr 2019

Cited by 3 | Viewed by 2716

Abstract

WC-MC/M(C,N)-Co hardmetals with 10 wt% Co were prepared in undoped, as well as in either Cr- or V-doped form. The starting formulations contained 5 wt% TiC or 5% (TiC+TiN), the latter with two different TiC/TiN ratios, and 10 wt% (Ta,Nb)C. For each composition, a low-C grade (Ms ≈ 75%) and a high-C grade (Ms ≈ 88%) was adjusted by C or W addition, to end up with 18 different hardmetal formulations, prepared in an industrial process. Model alloys, MC and M(C,N) phases with a composition reflecting the composition of these phases in the hardmetal were prepared, too. A variety of data was collected: binder phase and hard phase compositions of model alloys by wavelength-dispersive electron-probe microanalysis (WDS-EPMA), liquid phase formation temperatures in model alloys with free C and eta by differential thermal analysis (DTA), respectively, thermal conductivities of MC and M(C,N) phases and hardmetals by laser-flash temperature conductivity and heat capacity measurements up to 950 °C, crystallite-size distribution by electron backscatter diffraction EBSD, hardness HV30, Palmqvist-Shetty fracture toughness K_IC, Weibull evaluation of the transverse rupture strength (TRS), oxidation resistance in air as well as milling tests on coated hardmetals with Ti(C,N)/Al₂O₃ and (Ti,Al)N layers. Full article

(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)

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13 pages, 5201 KiB

Open AccessFeature PaperArticle

Sintering of Ti(C,N)-WC/Mo₂C-(Ta,Nb)C-Co/Ni Cermets Investigated by CO and N₂ Outgassing

by Viktoria Schwarz, Fabio Scagnetto and Walter Lengauer

Metals 2019, 9(4), 427; https://doi.org/10.3390/met9040427 - 10 Apr 2019

Cited by 7 | Viewed by 2882

Abstract

Cermets of the type Ti(C,N)-WC/Mo₂C-(Ta,Nb)C-Co/Ni with changing [Mo]/([Mo] + [W]) ratio were subjected to an investigation of outgassing of CO and N₂ upon sintering. Quantification of CO and N₂ was performed by gas calibration, measurement of masses 12 (¹²C), 14 (¹⁴N) and 28 (²⁸CO and ²⁸N₂), as well as C, N, O analysis of the samples before and after sintering. The formation of CO occurs at lower temperatures than that of N₂, both gases being completely evolved already at solid-state sintering conditions. If pre-alloyed powders are employed in the starting formulation, the amount of evolved gases is substantially reduced, because part of the formation of mixed hard phases is anticipated. Changing binder composition from Co:Ni = 1:1 to 2:1 and 3:1 does not change the outgassing characteristics, while different batches of nominally the same Ti(C,N) powder can have significant influence. Mass spectrometry is a most valuable in situ tool for getting insight into the metallurgical reactions occurring upon sintering. These reactions result in the typical microstructure and influence the properties of cermets. Full article

(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)

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14 pages, 5937 KiB

Open AccessArticle

Effect of Graphene and Carbon Nanotubes on the Thermal Conductivity of WC–Co Cemented Carbide

by Kui Chen, Wenkai Xiao, Zhengwu Li, Jiasheng Wu, Kairong Hong and Xuefeng Ruan

Metals 2019, 9(3), 377; https://doi.org/10.3390/met9030377 - 24 Mar 2019

Cited by 17 | Viewed by 4152

Abstract

In recent years, it has been found that the service life of cemented carbide shield machine tools used in uneven soft and hard strata is substantially reduced in engineering practice. The study found that thermal stress is the main reason for the failure of cemented carbide shield tunneling tools when shield tunneling is carried out in uneven soft and hard soil. To maintain the hardness of cemented carbide, improving the thermal conductivity of the shield machine tool is of great importance for prolonging its service life and reducing engineering costs. In this study, graphene and carbon nanotubes were mixed with WC–Co powder and sintered by spark plasma sintering (SPS). The morphology was observed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The Rockwell hardness, bending strength, and thermal conductivity of the samples were tested. The results show that adding a small amount of graphene or carbon nanotubes could increase the bending strength of the cemented carbide by approximately 50%, while keeping the hardness of the cemented carbide constant. The thermal conductivity of the cemented carbide could be increased by 10% with the addition of 0.12 wt % graphene alone. Full article

(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)

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13 pages, 4619 KiB

Open AccessArticle

Interlaboratory Measurements of Contiguity in WC-Co Hardmetals

by Ken P. Mingard and Bryan Roebuck

Metals 2019, 9(3), 328; https://doi.org/10.3390/met9030328 - 14 Mar 2019

Cited by 7 | Viewed by 2889

Abstract

The contiguity of a hardmetal is a measure of the proportion of the carbide grain boundaries that are in direct contact with other carbide grain boundaries. Recent analysis of data available in the literature shows a large scatter in results and a significant difference in values measured from scanning electron microscope (SEM) images and from electron backscatter diffraction (EBSD) mapping. An interlaboratory exercise has been carried out with the measurement of a range of WC-Co hardmetal grades. For each grade, SEM images were acquired from both an etched surface and an ion beam polished surface and EBSD maps with two different processing routes. These maps and images were provided to the participants for measurement to eliminate variability from sample preparation and image acquisition. It was shown that measurement of contiguity from EBSD maps is likely to lead to an overestimation of contiguity, largely because EBSD maps do not have the resolution of SEM images to identify small binder phase regions between WC grains. Ion beam polishing combined with backscattered electron imaging was found to provide the best images of the microstructure to underpin a confident measurement of contiguity. However, high resolution SEM images of etched surfaces gave values close to those from ion beam polished samples so it is recommended that, as etching is much more widely available, high-resolution imaging of a lightly etched WC surface should be promoted as the preferred method for measurement of contiguity, in combination with backscattered imaging where possible. Even with good images, variation between operators can give uncertainties of approximately ±10%. Full article

(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)

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14 pages, 5061 KiB

Open AccessArticle

Hard Metal Production by ERS: Processing Parameter Roles in Final Properties

by José María Gallardo, Iñigo Agote, Raquel Astacio, Thomas Schubert, Jesús Cintas, Juan Manuel Montes, Yadir Torres and Francisco G. Cuevas

Metals 2019, 9(2), 172; https://doi.org/10.3390/met9020172 - 2 Feb 2019

Cited by 6 | Viewed by 3536

Abstract

Cemented carbide is a hard composite material, used widely in a variety of industries. The value of the global tungsten carbide market is expected to grow by 4.4% (compound annual growth rate) from 2017 to 2022. One of the main markets is in metal cutting and wear parts, where small pieces (or inserts), a few grams in weight, are used. Field-assisted sintering technique (FAST) technologies allow for the production of small blanks in a single step from powder, which are near final dimensions. Production cycles are very short. In this paper, one of the FAST processes, the ERS technology, is applied to obtain WC10Co parts. A review of the process variable effects on the final properties of the parts is accomplished. Final properties of a range of conventionally produced inserts are obtained, using 100 MPa compacting pressure, 80 MA/m² of current density, and processing times of around 800 ms. Full article

(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)

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Review

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9 pages, 1300 KiB

Open AccessFeature PaperReview

In-Depth Understanding of Fatigue Micromechanisms in Cemented Carbides: Implications for Optimal Microstructural Tailoring

by Luis Llanes

Metals 2019, 9(9), 924; https://doi.org/10.3390/met9090924 - 23 Aug 2019

Cited by 6 | Viewed by 2318

Abstract

The fatigue mechanics and mechanisms of cemented carbides (composites usually referred to as hardmetals) are reviewed. The influence of microstructure on strength lessening and subcritical crack growth for these ceramic-metal materials when subjected to cyclic loads are highlighted. The simultaneous role of the ductile metallic binder as a toughening and fatigue-susceptible agent for hardmetals results in a tradeoff between properties measured under monotonic and cyclic loading: fracture strength and toughness on one hand, as compared to fatigue strength and crack growth resistance on the other one. Toughness/fatigue–microstructure correlations are analyzed and rationalized on the basis of specific crack–microstructure interactions, documented by the effective implementation of advanced characterization techniques. As a result, it is concluded that the fatigue sensitivity of cemented carbides may be reduced if either toughening mechanisms beyond ductile ligament bridging, such as crack deflection, are operative, or strain localization within the binder is suppressed. In this regard, grades exhibiting metallic binders of a complex chemical nature and/or distinct microstructural assemblages are proposed as options for effective microstructural tailoring of these materials. Full article

(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)

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26 pages, 5550 KiB

Open AccessReview

Small-Scale Mechanical Testing of Cemented Carbides from the Micro- to the Nano-Level: A Review

by Annamária Naughton-Duszová, Tamás Csanádi, Richard Sedlák, Pavol Hvizdoš and Ján Dusza

Metals 2019, 9(5), 502; https://doi.org/10.3390/met9050502 - 29 Apr 2019

Cited by 19 | Viewed by 5095

Abstract

In this overview, we summarize the results published to date concerning the small-scale mechanical testing of WC–Co cemented carbides and similar hardmetals, describing the clear trend in the research towards ever-smaller scales (currently at the nano-level). The load-size effect during micro/nanohardness testing of hardmetals and their constituents and the influence of the WC grain orientation on their deformation, hardness, indentation modulus, fracture toughness, and fatigue characteristics are discussed. The effect of the WC grain size/orientation, cobalt content, and testing environment on damage accumulation, wear mechanisms, and wear parameters are summarized. The deformation and fracture characteristics and mechanical properties, such as the yield and compression strength, of WC–Co composites and their individual WC grains at different orientations during micropillar compression tests are described. The mechanical and fracture properties of micro-cantilevers milled from WC–Co hardmetals, single WC grains, and cantilevers containing WC/WC boundaries with differently-oriented WC grains are discussed. The physical background of the deformation and damage mechanisms in cemented carbides at the micro/nano-levels is descri and potential directions for future research in this field are outlined. Full article

(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)

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