Composed of hard tungsten carbide (WC) particles and a soft cobalt (Co) matrix, WC-Co cemented carbides exhibit significant differences in the material removal rates of these phases during metallographic preparation. This disparity, combined with the susceptibility of the soft Co phase to deformation-induced martensitic phase transformation from its face-centered cubic (CoFCC) to hexagonal close-packed (CoHCP) structure, poses substantial challenges for microstructural characterisation. The resulting ambiguity complicates the identification of the pristine Co phase and raises concerns about the presence of preparation-induced artefacts. In this study, we present a detailed comparative analysis aimed at minimizing ambiguities in the characterisation of the pristine Co phases in a series of WC-Co cemented carbides. We quantitatively report on the controllability of various preparation parameters under multiple conditions, for plane-polished cross-sections used in (e.g.) EBSD analysis and for thin-sections such as used in (e.g.) TEM analysis. We report on the interplay between material removal and the deformation-induced martensitic CoFCC-CoHCP phase transformation during metallographic preparation, identifying "GO" and "NO GO" regimes for the unequivocal identification of the pristine Co phase in WC-Co cemented carbides. The optimal metallographic preparation method for the "GO" regime involves an Ar+ ion polishing energy density of similar to 10 MJ/m(2) and a duration of similar to 80 min. This work establishes a robust workflow for accurately determining the pristine Co phase, providing a pivotal aspect for the characterisation of microstructure-property relationships in WC-Co cemented carbides.

WC-Co cemented carbides alloyed with Ru are relevant for the hardmetal industry in spite of their high cost. These alloys are used in applications requiring very demanding thermal properties and good performance in aggressive and abrasive media. For some applications, it is difficult to find an alternative material that could offer a similar performance. Ru containing binders (based on Co, Ni, CoNi and CoNiCr) are analyzed in this work considering carbon contents covering the whole carbon window, and using an equivalent WC-binder Ru-free alloy for comparison. The addition of Ru modifies significantly the chemical composition of the binder which can have important consequences in aspects such as phase formation and grain growth, and also in the final material properties.

Grain boundaries (GBs) generally exhibit complex structural and compositional features that significantly affect material hardness. Here, we establish a methodology to correlate the local hardness contributions of the GBs with their frequency distribution and their structural and compositional characteristics, using a submicron WC-Co cemented carbide as a model. An exceptional local hardness of (14.68 +/- 0.12) GPa is observed from a 90 degrees WC{0001}/WC{1010} GB, unlike the low contributions from other WC/WC GBs. This is linked to pronounced Cr and Co segregation at this GB, due to Cr affinity at the WC{0001}/Co and WC{1010}/Co phase boundaries and Co infiltration during liquid-phase sintering. Density functional theory results indicate that a large lattice mismatch, strong W-C covalent bonding, and Cr and Co accumulation increase the elastic strain field, resulting in strong atomic distortion near the interface and contributing to exceptional strengthening. Our findings highlight the critical influence of GB complexities on material hardness.

In spite of the rather high cost of Ru, CoRu binders are commonly used by the industry for the production of cemented carbides with performance demands at high temperatures. In a recent study it was shown that the solubility of W in Co-binders is considerably increased by the addition of Ru (both at low and at high carbon contents), which can significantly affect aspects such as grain growth inhibition, hardness, corrosion resistance and high temperature strength. The present work has extended the study to further binder chemistries: Co, Ni, CoNi and CoNiCr, which have been evaluated both with and without Ru additions. The results indicate that Ru additions increase the solubility of elements like W and Cr for all binder chemistries, both at low and at high carbon contents. The solubility of W is the lowest in the Cr-containing systems (CoNiCr and CoNiCrRu), however, due to the presence of Cr, the total amount of elements in solution is the highest from all binders. The results clearly demonstrate that the WC growth behaviour is significantly affected by the chemistry of the binder system, i.e. the chemical environment of the growing WC grains, which is strongly linked with the chemical activity of carbon in the system.

Alternative hard materials to traditional WC-Co are one of the main goals in the investigation efforts of both scientific and industrial communities. In this investigation, WC-based materials were designed and processed with different Fe alloys employing a powder metallurgy route. Two candidates were selected: FeCrAl and FeNiCr. The former showed the formation of aluminium oxides, which hindered a homogeneous metal-ceramic distribution. On the other hand, FeNiCr led to dense and optimised samples which were further characterised in terms of their mechanical properties and corrosion resistance. They revealed an excellent combination of hardness and toughness, comparable or even superior to industrial compositions containing Co. Selected Cr addition induced some segregation and formation of secondary carbides –in consonance with thermodynamic simulation results and as evidenced by optical microscopy, XRD and TEM analyses– with a decrease in the TRS value. However, massive nanoindentation tests revealed that it also led to improved intrinsic hardness of binder and composite (metal-ceramic) phases, as well as enhanced corrosion resistance in acidic media compared to Cr-free alternative and reference hardmetals.

The present investigation addresses the mechanical properties, wear behaviour, and high-temperature oxidation of cermets and hardmetals based on either Ti(C,N) or WC and a metal binder based on Fe15Ni or Fe15Ni10Cr. This study also includes a commercial-grade WC-Co for comparative purposes. The production of these materials involved a powder metallurgy and sinter-HIP processing route under identical conditions. It is found that WC-based materials have superior mechanical properties, including hardness, fracture toughness, transversal rupture strength (TRS), and wear response, compared to Ti(C,N)-based materials. However, the latter show better oxidation behaviour than the former. Notably, WC-FeNi exhibits a higher hardness and TRS than the commercial-grade material (an increase of 7% and 9%, respectively). The difference in wear behaviour is due to the difference in wear mechanisms. In this regard, cermets wear through a tribolayer of Ti and Fe oxides, while hardmetals primarily wear through abrasion from ploughing. Thus, hardmetals exhibit a lower coefficient of friction (COF) and wear rate than cermets. Furthermore, Ti(C,N)-based materials form a protective layer of TiO2, which enhances their integrity and reduces mass gain. The addition of Cr to the FeNi binder only appears to have a clear effect on the TRS of the materials.

This study presents a methodology for determining powder systems' Critical Binder Volume Concentration (CBVC), a key parameter in optimizing paste properties for various shaping processes. Leveraging both press and pycnometer density measurements, our approach precisely identifies the CBVC by analysing the pressure-dependency of powder compaction within a confined cavity, reflecting the interplay between internal friction and packing capacity. Through comparative analysis with established techniques, we validate our method using a nano-sized WC-Co powder system combined with two distinct organic binders, linseed oil and a proprietary binder. The method finds the maximum packing fraction more efficiently and utilizes less material than conventional CBVC determination techniques. A zero-pressure density is introduced and its applicability to other powder types, including ceramics and metals, is anticipated.

The influence of sintering temperature, dwelling time at maximum temperature and carbon content on the microstructure and on the mechanical and magnetic properties of WC-6%Co hardmetal was investigated. Samples were sintered according to a central composite design and subsequently analysed with respect to microstructural parameters (average WC grain size, binder mean free path and contiguity), as well as mechanical (hardness, transverse rupture strength and toughness) and magnetic (magnetic saturation and coercivity) properties. Microstructural parameters were determined using a Matlab (R)-based program developed for the evaluation of EBSD images. Results show that in order to maximize both hardness and TRS sintering should be performed in the low temperature range, i.e. < 1400 C-degrees, while dwelling time should not be too short, at least 75 min. This is particularly important for low carbon parts, since longer dwelling times are required to provide the microstructure with the necessary homogeneity required for high TRS.

This study shows the results of mechanical properties (hardness, toughness, TRS), oxidation behavior against high temperature and wear resistance of composite materials based on a ceramic phase –Ti(C,N) or WC– and a metal binder (Fe15Ni10Cr). These hard metals were produced through a powder metallurgy process that included mechanical milling, uniaxial pressing, and sinter-HIP. Standardized cylindrical specimens were used for TRS tests, and oxidation tests were conducted on broken specimens in static air at temperatures up to 1000 ºC. Wear behavior was analyzed through reciprocal sliding tests using WC-Co balls as counter material with loads up to 30 N and test times up to 150 min. This study recorded the friction coefficient during and after the tests, the mass variation, the width, and depth of the wear tracks analyzed by an optical profilometer.

The influence of Si concentrations on AlTiN and AlTiCrN coatings deposited by PVD has been investigated by using high-resolution characterization techniques: TEM, Dynamic SIMS, Atom Probe Tomography (APT) analyses and nano hardness measurements. First, investigations focus on crystallographic phase stability, microstructural observations and micromechanical studies to understand the effect of the Si addition on these two nitride coatings. Second, the oxidation mechanisms and the kinetics of oxide growth at 950 C-degrees for various durations are examined. Results indicate that the addition of Si introduces high compressive stresses in both coating groups, reaching values in the range of -6 GPa. However, the behavior of Si content differs for AlTiN coatings with and without chromium. In AlTiSiN coatings, increasing Si addition leads to reduce residual stresses, while no significant change is observed for AlTiCrSiN coatings. This stress evolution is associated with a decrease in crystallinity density of the TiAlN coatings due to Si addition, but this structural phenomenon is not observed when Si is added to the quaternary metallic coatings TiAlCrN. Si content also influences the nanohardness, but the variation among coating is not substantial, with values around 34 + /-2 GPa, and an elastic-modulus around 443 + /-40 GPa. Regarding oxidation resistance at 950 C-degrees, the addition of Si in AlTiN coating results in the formation of an external alumina oxide layer and beneath it, a nanometer sized TiO2 anatase crystallites layer. After the growth of this bi-layer oxide scale, the inward cationic diffusion of the oxygen is very significantly reduced, and it can explain its high oxidation resistance. In contrast, for AlTiCrSiN coatings, the oxide scale morphology is different, consisting of a pure TiO(2 )rutile outer layer, followed by an Al-rich oxide and a mixed oxide region of (AlCr)(2)O-3 with small islands of TiO2. The growth of this last oxide scale shows a regular increase over time, primarily driven by inward oxygen diffusion at the nitride coating interface.

Uniaxial die pressing is a commonly used shaping technique in powder metallurgy. The initial step within the compression cycle is the filling process of the cavity with granular materials. Here, the goal is to have a reproducible cavity filling to manufacture compressed parts of consistent quality. Besides effects linked to the geometry of the cavity and the mechanisms of filling, the flowability of the granular material plays a major role. Therefore, a deeper understanding of the flow behaviour is in the centre of the present study. In order to assess the flowability, two different experimental methods are used. Granular materials of the same composition but different granular size distributions are characterised by angle of repose (AOR) and mass flow rate measure-ments. The two methods deliver a set of parameters that are compared using the granular Bond number. Based on the empirical findings, a modification of the granular Bond number is suggested.

The mass flow of granular matter through orifices can be described by the well-known Beverloo law. It depends on particle and orifice sizes, interparticle and particle/container interaction forces, particles’ surfaces - to name a few influences on the mass flow rate. We present an experimental study of the flow of a set of ready-to-press (RTP) hard metal powders through orifices of varying diameter. The obtained parameters of the Beverloo law are compared with angle of repose measurements. The interplay between attractive interparticle forces and gravitational forces are discussed for both types of experimental measurements and related to the difference between particle and orifice size.

We present a comparative study on determining the critical binder volume concentration (CBVC) of a hard metal paste using the following techniques: theoretical calculation, density method, oil titration, binder titration, and Reddy's model. The theoretical calculations involve density measurements to discern the carbide powder-free volume. The titration methods consist of a stepwise increase of the organic content while the mixer torque is recorded. In contrast, Reddy's model requires the preparation of several feedstocks at varying solid loadings, which are tested in a capillary rheometer to obtain the CBVC. The paste consists mainly of nano-sized tungsten carbide-cobalt (powder phase) and a macromolecular multiphase system (organic phase). The accuracy and expenditure of experimental work of the different methods are discussed.

The angle of repose is a quantity that delivers direct information about the flowability of granular material. It is therefore desirable to have a reliable experimental method for its determination. Based on the well-established funnel method with continuous mass flow, an extension is introduced which allows increasing the precision and reproducibility of the angle of repose measurements. A modified experimental setup is presented which exploits asymmetries in the alignment of the mechanical setup to gain more precision in the determination of the angle of repose. This experimental setup is combined with an evaluation method based on automated image analysis. First results for a set of metal powders are presented.

The fundamental reason for analysing the microstructure of a material is to achieve a higher degree of understanding of the microstructural mechanisms governing its mechanical properties and to use this knowledge as a tool for further developments. In this study, Ti(C,N)-based cermets were sinter-HIP’ed at different temperatures, the mechanical properties of the samples were measured and the obtained microstructures were analysed by light optical and electron microscopy. A tailored python-based image processing tool was developed to combine and analyse the microstructures obtained by EBSD and BSE. The goal of the study was to determine the influence of the sintering temperature on the microstructural features of the cermets.

In this investigation, Ti(C,N)-FeNiCr systems were designed using Thermo-Calc? software. Materials were processed by conventional powder metallurgy, employing different carbon additions to study a wide range of the phase diagram as well as the effect of C in the sintered samples. Specimens were extensively characterised in terms of density, magnetic and mechanical properties, and microstructural features. Simulation approach was validated by means of Differential Thermal Analysis (DTA) and High-Temperature X-Ray Diffraction (HT-XRD), from room temperature up to 1200 ?C for each composition, comparing phases obtained for each temperature and composition with predicted ones. Results showed excellent consonance between Thermo-Calc? and XRD phases, except for precipitation of secondary carbides, which appeared in the simulation but not in the sintered samples. Moreover, variation of C content demonstrated to have a direct effect in the microstructural homogenization of the final specimens.

Processing route is a determining factor that affects the properties of hard materials. Although processing routes are well defined for WC-Co hardmetals, a complete study is needed to understand the factors influencing the properties when alternative compositions are developed. In this investigation, Ti(C,N)-Fe15Ni10Cr cermets were produced following conventional powder metallurgy routes. Two types of milling – attritor and planetary, using different vessel/ball materials – and of sintering regimes – sinter-HIP and high-vacuum – were used to process the specimens and compare their final properties. Carbon content was also included in the study as experimental variable. Density, porosity, microstructure, mechanical and magnetic properties, and corrosion behaviour of the resulting cermets were determined by using a wide range of characterization techniques. Optimization of their production led to materials with a competitive hardness-toughness combination, comparable to those exhibited by plain WC-Co grades. Evaluation of corrosion confirmed the improved resistance when Cr is included as alloying element and also compared to cobalt, as well as the superior corrosion response of Ti(C,N) with respect to WC.

TiAlN single layer coatings deposited by High-Power Impulse Magnetron Sputtering (HiPIMS) on carbide and Si-wafers substrates were performed. They were characterized in order to study the effects of different process parameters on the film stoichiometry, microstructure and morphology and finally their mechanical and tribological properties were investigated. For comparison, the properties of the same composition Ti50Al50N coatings produced by Cathodic Arc Evaporation (CAE) were also studied. Only the most influential process parameters, which are the effects of duty cycle, pressure, power and bias for the HiPIMS process are here discussed. High-resolution TEM images were used to investigate the microstructure of CAE and HiPIMS coatings and the observations indicate that both processes produced high density Ti50Al50N coatings with a fine fibrous structure, and a similar grain size. XRD analyses showed that TiAlN coatings deposited by CAE and by HiPIMS have a single-phase cubic structure with respectively the (200) and (111) reflection peaks as a preferred orientation. Furthermore, the residual stresses determined by XRD for the HiPIMS coated samples show that it can be possible to tune them from tensile (+500 MPa) to high compressive stresses (-4000 MPa) by adjusting the process parameters. Independently of their intrinsic stress level, the HiPIMS coatings show similar hardness and the values obtained are in the same range of CAE coatings (30-35 GPa) with same composition and thickness. However, during ball-on-disc tests in dry condition using a steel ball against the coated carbide substrate, the behaviour of similar Ti50Al50N as deposited coatings produced by these two processes was different. Lower friction coefficients (-30%) but, higher abrasion kinetic of the steel ball as counterpart during pin-on-disk test (+50%) were recorded for the Ti50Al50N HiPIMS coatings. In conclusion, it is proposed that, for HiPIMS coatings with high compressive stresses (<-5000 MPa), having also low surface roughness and (111) main texture orientation, high tribological properties can be achieved.

The sintering behaviour of cemented carbides based on WC-ZrC-Co-Cr3C2 powder mixtures have been analyzed by dilatometric and calorimetric methods for different cobalt contents and WC/ZrC ratios. As expected, powder oxide reduction in these compositions is mainly of carbothermic nature. However, depending on the milling conditions, some highly stable Zr-rich oxides are retained in the binder phase after sintering. Hot isostatic pressing (HIP) cycles have been successfully applied for closing residual porosity after vacuum sintering. For a fixed amount of binder phase and a WC/ZrC ratio, the hardness of these materials depends on the amount of residual porosity and WC grain growth control. The best combination of hardness and toughness is found for alloys with 8 wt%Co and WC/ZrC wt. ratios of 6.46. HIP treatments induce the formation of a compact and well adhered layer mainly comprised of Zr oxides and WC grains. The cobalt binder phase migrates from this layer towards the sample bulk likely due to the loss of wettability on these Zr rich oxides. Hot hardness is higher for the alloy with higher WC/ZrC ratio suggesting that this property depends on both the volume fraction of (ZrxW1-x)C and WC phases and their degree of contiguity.

Recently, there has been increasing interest in cemented tungsten carbide hardmetals and titanium carbonitride cermets with binders of multi-component alloys (>= 4 elements) or high entropy alloys (>= 5 principal elements in equimolar ratios). Property improvements have been reported, such as increased ambient and elevated temperature hardness, as well as greater oxidation resistance. This study has thoroughly investigated model cemented carbides manufactured using coarse WC with a binder content of 20 wt% (32-37 vol%) from three different (Al)CoCrCuFeNi high entropy alloys (HEM) and at different carbon levels (low, medium and high). Binder alloys were manufactured by both planetary ball milling of elemental powder mixtures and gas atomizing. Sintering was performed in vacuum for 2 h at different temperatures between 1200 degrees C and 1500 degrees C. Post-HIP treatments were also applied in some cases as all systems were difficult to densify without residual porosity. Detailed analyses were performed on the as-manufactured binder alloys, sintered binder alloys (without WC) and the actual sintered cemented carbides (WC + HEA). Various analysis methods were used to examine the materials. These included thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) to determine the melting behaviour; X-Ray Diffraction (XRD), Electron Backscatter Diffraction (EBSD) and Energy-Dispersive X-Ray Spectroscopy (EDS) to identify the type, crystal structure and exact composition of the phases present; and light optical microscopy (LOM) and scanning electron microscopy (SEM) for microstructural characterization. Additionally, the hardness and Palmqvist indentation toughness of each composition were also measured. 2-Phase WC-HEA microstructures could not be obtained using the investigated high entropy alloys. Several solid solution binder alloys and numerous carbide phases were present after sintering, formed by segregation and reaction. The type and quantity of the phases depend on the carbon balance. For the compositions containing aluminium, it was found that aluminium forms oxides and intermetallic phases during sintering. The paper presents these findings in detail.