WC Ni Composites Research Articles

Effect of yttrium oxide addition on the microstructure and mechanical properties of WC–ni composites fabricated from recycled WC and Ni

ABSTRACT WC-Co composites are widely used in cutting tools but are expensive and harmful due to Co in the composites. Alternatives, such as WC-Ni composites have inferior mechanical properties, as a result, WC-Co composites are used in most cutting tools. This study investigated whether adding yttrium oxide (Y2O3) to WC-Ni composites, fabricated from recycled tungsten carbide (WC) and Ni, improved their mechanical properties. Changes in the composites’ microstructure and mechanical properties depended on the amount of Y2O3 added. Y2O3 reacted with WC during sintering, promoting the formation of W and reducing the proportion of C in the composite. The added Y2O3 accelerated the dissolution of W in the Ni matrix, and increased the fractions of the eta phase and solid solution phase. Ni is strengthened by the dissolution of W in Ni, thereby supplementing the low toughness of the eta phase and ultimately yielding WC – Ni with improved hardness and fracture toughness (HV: max. 15.4 GPa, KIC: max. 13.4 MPa∙m1/2) compared to WC – Ni without Y2O3 (HV: 13.5 GPa, KIC: 12.7 MPa∙m1/2). The method for improving the properties of WC – Ni composites by the addition of Y2O3 has a high possibility of commercialization because it does not necessitate process changes.

Manipulation of the thermal conductivity for two-phase WC-Ni composites through a microstructure-based model along with key experiments

Thermal conductivity, one of critical properties for composite materials, constitutes an indispensable part of high-efficient materials design. However, a quantitative model to describe the thermal conductivity of two-phase composites has yet to be developed. In this work, we proposed an effective evaluation framework of a microstructure-based thermal conductivity model with key inputs from CALPHAD-type approach. Two-phase WC-Ni composites with Ni–W solid-solution matrix were used as the target system to validate this framework combined with key thermal conductivity measurements. Calculated thermal conductivities agree well with experimental results within the experimental error of 10%. Applying this well-established framework, thermal conductivities depending on wide ranges of temperature, WC grain size (dWC), and phase constitution are predicted, suggesting some unique features. The thermal conductivity becomes less dependent on dWC when dWC is >3 μm. Additionally, the thermal conductivity of nano-sized WC-Ni shows a quite different temperature-dependent variation tendency in contrast to that of micron-sized WC-Ni. These correlations are found and quantitatively described in the present work. Furthermore, the thermal conductivity for WC-Ni carbide rolls is predicted by the established framework, demonstrating a high accuracy. The present work is expected to guide the design of composite materials with desirable thermal properties efficiently.

Neutron diffraction characterizations of NbC-Ni cemented carbides thermal residual stresses

Cemented carbide materials develop very large micro-stresses due to the coefficient of thermal expansion (CTE) mismatch between the metallic carbide phase and the binder phase. While micro-stresses developed in WC-Co cemented carbides have been investigated, there is very little to no information on the micro-stresses developed in NbC-Ni materials.In this study the thermal stresses developed in NbC-Ni materials as a function of the carbide grain size (from 2.5 μm to 12.8 μm) and the binder content (from 8 vol% to 12 vol%) were characterized by neutron diffraction. It was found that the residual stresses decreased with the increase of the binder content and the increase of the carbides grain size. For both binder and carbide phases, stresses were higher for smaller NbC particles, reaching 4 GPa in Ni at the lowest binder content. In general, stresses were higher than the ones measured in WC-Co or WC-Ni composites. This unexpected finding was attributed to the very different shapes presented by the carbide particles; NbC particles are almost spherical, and WC particles are triangular plates with truncated corners. These different shapes create different strain/stress distributions on the microscopic level around the carbide particles.

Fabrication of diamond enhanced WC-Ni composites by spark plasma sintering

Wear resistance of the rock drill bit is one of the important factors affecting drilling efficiency and exploration cost. Hence, the development of tool materials with high wear resistance has been widely concerned by researchers. The composites of cemented carbides and Ti-coated diamond (Ti/Dia) were successfully prepared by spark plasma sintering with excellent wear resistance. The characterization of microstructure and phase composition revealed that diamond particles distributed homogeneously without obviously graphitization. With 2–6 wt% Ti/Dia, the relative density, hardness and flexural strength of the composites were all improved. However, with the further increase in Ti/Dia content, the relative density and flexural strength sharply decreased. The composites with 2 wt% Ti/Dia shown the best wear resistance and the wear rate was reduced by 50 times compared with that of the sample without diamond addition. The diamond plays an important role in the rock cutting and grinding for the sample with 2 wt% Ti/Dia. However, for the samples with 18 wt% Ti/Dia, the cutting edge is easy to fracture and the diamond is more likely to pull-out whole because of the weak retention ability of the matrix to diamond.

Improved mechanical performance and wear resistance of Ti-coated cBN–WC–Ni composites

Abstract

Effect of Ni Content on Microstructure and Properties of WC-Ni Composites Prepared by Electroless Plating and Powder Metallurgy

WC-Ni composite powders were prepared by electroless plating with a simplified chemical method. The morphologies of original, pretreated WC powder, WC-Ni powders and surface morphologies, fracture surface and composition of WC-Ni composites were analyzed by FE-SEM. EDS and XRD. Different contents of Ni doped WC composites were prepared after sintering. The relative density and properties of the WC-Ni composites were also discussed. Results show that the WC powder is uniformly covered by Ni particles. After powder metallurgy (PM), the fabricated composites perform a well-dispersed surface morphology. With the increasing of Ni content bending strength enhances without reducing hardness. Trans-granular fractures are observed on the fracture surface of the WC-Ni composites.

Influence of different reinforcing particles on the scratch resistance and microstructure of different WC–Ni composites

WC composites are largely used in many engineering and industrial fields such as mining, cutting tools, and underground works. This interest in WC materials is related to their high wear resistance due to their convenient mechanical properties and controllable microstructures. However, the abrasive behavior of WC materials is very complicated because they are formed from several phases and their damage mechanism involves numerous parameters and factors that may be related to the composites themselves and the external environment. Reinforcing particles play a critical role in the achievement of wear-resistant materials. In this study, the impact of the presence of different types of reinforcing particles in the chemical makeup of WC–Ni composites on their resistance to scratch formation is highlighted through experimental abrasion tests by a single diamond tip.

Highly toughened dense TiC–Ni composite by in situ decomposition of (Ti,Ni)C solid solution

A highly-toughened TiC–Ni composite was produced by the in situ decomposition during sintering of a nonequilibrim (Ti,Ni)C solid-solution phase. The solid solution was synthesized by the mechanical milling of Ti–Ni alloy/graphite mixtures, which then decomposed to finely dispersed TiC and Ni upon heating in a vacuum. To take advantage of the fine microstructure, samples were sintered to facilitate the in situ decomposition. Densification of the (Ti,Ni)C during the sintering was achieved through the coalescence of fine particles and the concurrent decomposition of the nonequilibrium (Ti,Ni)C phase. Additional densification was obtained through liquid-phase sintering by the eutectic melting of Ni. The fracture toughness of the sintered TiC–Ni composite was notably higher than that of conventional TiC/Ti(CN)–Ni or of comparable Ti(CN)–WC–Ni composites. Its fine and dense microstructure is believed to account for the enhanced toughness. The method suggested here might represent a valuable option for the preparation of TiC–Ni composites with desirable mechanical properties.

Mechanical properties of (Ti,V)C–Ni composite prepared using ultrafine solid-solution (Ti,V)C phase

(Ti,V)C–Ni composite was sintered using ultrafine (Ti,V)C solid-solution powders prepared by mechanically alloying a Ti–V alloy/graphite powder mixture. The (Ti,V)C–Ni powders were sintered to full density at 1400°C, which is significantly lower than that required for the conventional liquid-phase sintering of TiC–Ni or Ti(CN)–Ni powders. The examination of linear shrinkage curve during sintering revealed that the consolidation of the (Ti,V)C–Ni composite proceeds in three distinct steps. Firstly, it shrinks by the solid-state sintering. Afterwards, it expands by CO gas evolution. Finally, Ni melt penetrates into the pores between carbide particles during the liquid-phase sintering. The fracture toughness values of the (Ti,V)C–Ni composite were notably higher than those of TiC–Ni or even Ti(CN)–WC–Ni composites. The improved fracture toughness of the (Ti,V)C–Ni composites is believed to originate from the solid-solution effect of TiC and VC in addition to the lack of core/rim structure, which is common in Ti(CN)–WC–Ni composite.

An in situ (W,Ti)C–Ni composite fabricated by SHS method

The combustion synthesis reaction was combined with liquid phase sintering to fabricate net-shape TiC–Ni and TiC–WC–Ni composites in a single processing operation. When Ti and C powders used for in situ production of TiC–Ni cermet, the final product was porous and had low strength. By the addition of fine W powder with W/Ti=1 molar ratio, the product contained (Ti,W)C, W2C and mix compounds of type Ni2W4C. Using W with W/Ti=2 molar ratio results in a dense high strength product containing (Ti,W)C and WC.

A magnetorheological polishing-based approach for studying precision microground surfaces of tungsten carbides

Abstract Surface features of tungsten carbide composites processed by bound abrasive deterministic microgrinding and magnetorheological finishing (MRF) were studied for five WC–Ni composites, including one binderless material. All the materials studied were nonmagnetic with different microstructures and mechanical properties. White-light interferometry, scanning electron microscopy, and atomic force microscopy were used to characterize the surfaces after various grinding steps, surface etching, and MRF spot-taking. It was found that the peak-to-valley (p–v) microroughness of the surface after microgrinding with rough or medium abrasive size tools gives a measure of the deformed layer depth. MRF spots revealed the true depth of the grinding-induced deformed surface layer.

Comparison of sintering behavior and mechanical properties between WC−8Co and WC−8Ni hard materials produced by high-frequency induction heating sintering

The sintering behavior and mechanical properties of WC-Co and WC-Ni hard materials produced by high-frequency induction-heating sintering (HFIHS) were compared using ultra fine WC, WC-Co, and WC-Ni powders. HFIHS allows very quick densification to near theoretical density and prohibits grain growth in nano-structured materials. Highly dense WC, WC-Co, and WC-Ni with a relative density of up to 99.2% could be obtained with simultaneous application of 60 MPa pressure and induced current within 2 min without significant change in grain size. The hardness and fracture toughness of the dense WC, WC-Co, and WC-Ni composites produced by HFIHS were also investigated.

Effects of WC size and amount on the thermal residual stress in WC–Ni composites

Effects of WC particle size and volume fraction on the magnitude and distribution of thermal residual stresses (TRS) in WC–Ni cemented carbide composites were studied by neutron powder diffraction. Samples of high (0.3) and low (0.1) Ni volume fraction and coarse (1.7μm) and fine (0.5μm) WC particle size were employed. Thermal residual strain and stress values were obtained at temperatures between 100 and 900K. The magnitude of the mean (compressive) WC stress increased as WC fraction decreased, while the mean (tensile) Ni stress did the opposite. For both phases, stresses were highest for fine WC particles, reaching over 3GPa in Ni. Elastic strain distributions, due to the sharp edges and corners of WC particles, were characterized by analyzing diffraction peak widths. The range of stress increased with the magnitude of the TRS. Even though the mean TRS is compressive in WC, regions of tension exist, and, for Ni, regions of compression are present.

Field-activated, pressure-assisted combustion synthesis of tungsten carbide–nickel composites

The field-activated, pressure-assisted combustion synthesis (FAPACS) process, which combines the simultaneous synthesis and densification of materials, was utilized to produce WC–10 wt.% Ni composites from reactant mixtures of W, Ni, and different carbon sources. The product composition, density, and microhardness of WC–Ni composites fabricated through the FAPACS process were investigated. The results show that the Vickers microhardness and toughness were 1287 kg/mm 2 and 7.8 MPa m 1/2 for the product made with activated carbon, and 1424 kg/mm 2 and 5.9 MPa m 1/2 with carbon black.

Field-activated, pressure-assisted combustion synthesis of tungsten carbide?nickel composites

The field-activated, pressure-assisted combustion synthesis (FAPACS) process, which combines the simultaneous synthesis and densification of materials, was utilized to produce WC–10 wt.% Ni composites from reactant mixtures of W, Ni, and different carbon sources. The product composition, density, and microhardness of WC–Ni composites fabricated through the FAPACS process were investigated. The results show that the Vickers microhardness and toughness were 1287 kg/mm 2 and 7.8 MPa m 1/2 for the product made with activated carbon, and 1424 kg/mm 2 and 5.9 MPa m 1/2 with carbon black.

Parameters investigation during simultaneous synthesis and densification WC–Ni composites by field-activated combustion

The field-activated, and pressure-assisted combustion synthesis (FAPACS) process, which combines the simultaneous synthesis and densification of materials, was utilized to produce WC–Ni composites from powdered reactants, mixtures of tungsten, carbon and nickel. These reactants were subjected to high DC currents and uniaxial pressures. Under these conditions, a reaction is initiated by field activation and completed within a short period of time. Several experimental parameters, such as pulse current, power-controlled mode, temperature-increasing rate, maximum temperature and pressure during FAPACS on the relative densities of products were studied. Finally, the material with nearly complete density was fabricated. The percentage of the total shrinkage occurring before and during the synthesis reaction and addition densification was measured. The relative density of the end product and Vickers microhardness measurement (at 50 kg force) on the dense sample is 99.2% and 1424 kg mm−2, respectively.

Thermal residual stress distribution in WC-Ni composites

The thermal residual stress distributions in a series of WC-Ni composites with WC volume fractions of 0.11, 0.21, 0.41, and 0.60 were measured using neutron diffraction and modeled using finite element (FE) analysis. The FE procedure employed enables the local variation of the residual microstress in a composite microstructure to be studied. The mean (compressive) stresses in WC decrease and the mean (tensile) stresses in Ni increase with increasing WC content. The stress distributions are sufficiently extensive to create regions of tension in the WC and compression in the Ni. The maximum tensile stresses in WC increase in magnitude with WC content. They are located in corners and, for higher WC content, normal to WC/Ni interfaces. High compression occurs in narrow portions of the WC skeleton. Regions of compression in Ni occur at WC/Ni interfaces for low WC content and, for composites of higher WC content, in narrow bands between chains of WC particles. It was also determined that models of actual composite microstructures, rather than geometric arrays, are required in order to properly obtain local residual stress distributions using the finite element analysis procedure.

Use of finite element modeling to interpret diffraction peak broadening from elastic strain distributions

An approach employing the finite element (FE) method to interpret diffraction peak broadening due to elastic strain distributions is presented that provides a model of the local variations of elastic strain and stress in a composite or multiphase microstructure. The method involves averaging elastic strain output from a representative FE model to generate a strain distribution analogous to the averaging taking place in the diffraction process. The procedure assumes that the FE model adequately represents the thermally stressed system, an aspect addressed by comparison of the strain distributions obtained from diffraction data and the FE model. Example applications are presented for thermal residual strain in 11 and 60vol.%WC-Ni composites. The stress in the WC, which is compressive on average, becomes tensile at corners and at locations that are normal to WC-Ni interfaces. The Ni stress, which is tensile on average, is compressive in narrow bands between WC particles. In addition, asymmetry of the Ni distribution on the high strain side, due to localized plastic flow, is successfully modeled for the 60vol.%WC-Ni. Composition effects are also represented. Uniqueness aspects and limitations of the procedure are discussed.

Thermodynamics of isolated pores filling with liquid in sintered composite materials

In model studies of the dispersed solid-liquid-vapor system, thermodynamic functions were found which describe changes in the energy of the system when an isolated pore is filled with liquid. From an analysis of these functions, a class of composite materials was isolated in which there exists the migration pressure which has a physical meaning of suction pressure. In these compositions, the liquid in a pore is acted upon by two opposing forces: capillary pressure and migration pressure. Depending on the ratio of these pressures, the liquid may not fill the pore or may first migrate from the composition into the pore, fill it, and then migrate from the pore into the composition, homogeneous structure being formed in the place of the pore. In compositions which are free from the migration pressure, the liquid fills pores of any size. Pores provide a place for the lakes of liquid. Theoretical conclusions were confirmed by our experiments with WC-Co, WC-Ni, WC-Cu, Cr3C2-Cu, and other composites .