The Influence of the Sintering Temperature on the Grain Growth of Tungsten Carbide in the Composite WC-8Ni (original) (raw)
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Acta Metallurgica Slovaca, 2019
In this research, WC-7(Ni,Fe) hard alloys were prepared by ball milling, cold compaction and finally consolidated by hot isostatic pressing. The effect of binder composition and sintering temperature were investigated in term of the microstructure, density and mechanical properties of sintered samples. Density of hard alloys was measured by the Archimedes' principle while the microstructure was observed using a scanning electron microscope. The Vickers hardness was investigated at load of 30KG and the fracture toughness was calculated based on the Palmqvist crack method. The results revealed that the density of sintered samples was obtained in the range of 14.65 to 14.8 g/cm3 meanwhile the measured Vicker hardness and fracture toughness were respectively achieved from 1260 to 1520 HV30 and 11,7 to 17,5 MPa.m1/2 depending on the binder composition and sintered temperature.
Microstructural Evolution of Composite 8 WC-(Co, Ni): Effect of the Addition of SiC
Defect and Diffusion Forum, 2017
Tungsten carbide (WC) based cemented carbides, also called hardmetals, are a family of composite materials consisting of carbide ceramic particles embedded in a metallic binder. They are classified as metal matrix composites (MMCs) because the metallic binder is the matrix that holds the bulk material together [1]. WC based composites are used in applications where a good combination of hardness and toughness are necessary [2]. It is usual to add more components to tailor the microstructure of the WC-(Co, Ni) system. The hardness for the cemented carbides based on nickel, increases significantly because of the addition of reinforcements like SiC nanowhisker [3]. In this work, the SiC was considered as an additional component for the composite WC-8(Co, Ni). Four mixtures were prepared with SiC contents ranging from 0 to 3.0 wt%. These mixtures were pressed (200 MPa) and green samples with 25.2 mm of diameter and 40 g were produced. Sintering was carried out in Sinter-HIP furnace (20 ...
Effect of high energy milling on the microstruture and properties of wc-ni composite
Materials Research, 2010
Hard metal is a composite material used in several areas of machining, mining and construction. It can be applied directly on oil and gas drilling equipment components. The main objective of this work was to apply a high energy milling technique to produce the WC-Ni composite and study the effects of milling time in the material properties. The milling of hard metal WC-20Ni, was performed for milling times of 1, 2, 4, 8, 16, 32 and 64 hours. The starting powders were characterized by laser sedigraphy, SEM and EDS. Microstrutural analysis of the sintered samples was performed by optical microscopy, microhardness and density by Archimedes. The best results for the WC-20%Ni composite were achieved for 8 hours milling, where the density and hardness reached 97.09% and 1058 ± 54 HV, respectively, after sintering.
Journal of Alloys and Compounds, 2010
The effect of mechanical alloying and the sintering regime on the microstructural and the physical properties of W-SiC composites were investigated. Powder mixtures of W-20 vol.% SiC were mechanically alloyed (MA'd) using a Spex mill for 3 h, 6 h and 24 h. MA'd powders were characterized by Laser Diffraction Particle Size Analyzer, SEM and XRD investigations. MA'd W-20 vol.% SiC powder composites were sintered under inert Ar and reducing H 2 gas conditions at 1680 • C and 1770 • C for 1 h. The microstructural and mechanical characterizations of the sintered samples were carried out by scanning electron microscope (SEM) and X-ray diffraction (XRD) and Vickers Hardness analyses. The addition of SiC remarkably increases the hardness of the composites. Hardness is also increased with decreasing grain size and increasing amount of MA.
Reduction of carbide grain growth in WC–VC–Co by sintering in a nitrogen atmosphere
International Journal of Refractory Metals and Hard Materials, 2009
In order to produce a harder and more wear resistant material than WC-Co, a WC-VC-Co hardmetal was sintered in nitrogen at a pressure of 1 bar to reduce the growth of (W,V)C grains created during sintering. The hardmetal was analysed using scanning and transmission electron microscopy (SEM and TEM), energy dispersive X-ray spectrometry (EDS) and X-ray diffractometry (XRD). The cubic carbonitride (W,V)(C,N) grains were found to be of two types, those with higher vanadium content and the others with lower vanadium content. The presence of nitrogen restricted the growth of the cubic carbide grains giving a much narrower grain size distribution than in a material produced from an identical powder but sintered in vacuum. The nitrogen potential was higher in the bulk than in the sintering atmosphere resulting in outward diffusion of nitrogen and inward diffusion of V. This created a gradient zone of approximately 50 lm depleted of cubic carbonitride and enriched with binder phase. Remarkably, the WC grain size in the gradient zone was not larger than in the bulk.
Mechanical characterization of composites prepared from WC powders coated with Ni rich binders
International Journal of Refractory Metals and Hard Materials, 2008
In this study composite powders of WC and Ni/Fe/Cr were prepared in an innovative way, which consists of the sputter-deposition of the metallic binder onto the tungsten carbide particles. Compacts of coated powders were sintered by conventional vacuum sintering followed by hot isostatic pressing (HIP) to reach almost full densities. In order to evaluate the mechanical properties of reduced specimens size (microcomponents), depth-sensing indentation equipment was used. This method enabled the evaluation of the hardness, H, Young's modulus, E, and the yield stress, r y , in a non-destructive way, using only one sample. For the composites of sputter-coated WC-Ni/Fe/Cr the results showed an effective reduction of H and E due to the properties of Ni and the binder characteristics of the coated powders, such as uniform distribution and nanometer structure.
The effect of consolidation parameters on the mechanical properties of binderless tungsten carbide
International Journal of Refractory Metals and Hard Materials, 2011
This paper discusses the effect of the process parameters on the mechanical properties of binderless pure tungsten carbide during a GPS (gas protection sintering) process. The result of experiments reveal that the mechanical properties of the material increases with raising the sintering temperature and extending the retention time; however a decreased hardness was observed as a result of abnormal grain growth under higher sintering temperatures. The results of XRD and EDS analyses confirmed the absence of brittle phases such as W 2 C or impurity phases in the microstructure. The optimized process parameters for GPS process are identified as: a mean particle size of 1.03 μm, a sintering temperature of 1860°C and a retention time of 60 min; the resulting mechanical properties are: a relative density of 95.1%, a micro-hardness of 1718 kgf/ mm 2 and a fracture toughness of 5.97 MPa m 1/2. The width of particles size distribution has a significant effect on the density and hardness of the sintered material however the width of particles size distribution is dependent on the original particle size. Finally, ultra-fine particles increase the chance of conglomeration and sub-micron structures. The conglomeration of ultra-fine particles hinders the filling of porosities during sintering and lowers the density and hardness of the material.
Synthesis and characterization of a MoWC-WC-NiC nanocomposite via mechanical alloying and sintering
MoWC-NiC-WC was produced by mechanical alloying at different grinding times as follows: 0, 40, 80, 120, 160, 200 and 240 h. A mixture of elemental powders of W, Mo, C and Ni was submitted to mechanical alloying in a ball mill under an argon atmosphere. The milled powders were sintered at 900°C for 1 h. The phases and morphology at each stage of milling were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD indicated that by increasing the milling time from 0 to 240 h, the nano-structured carbide phases were synthesized with a crystal size ranging from 125.6 to 10.1 nm. The experimental results demonstrated that after sintered milled powder at 240 h, particles with spherical morphology were formed. The elemental maps revealed the formation of heterogeneous spheres which are primarily MoWC. The TEM results of sintered composites that were milled for 240 h showed nanoparticles ranging from 2.5 to 50 nm. As the milling time increased, the microhardness increased from 70 to 248 Hv using the sintered powder milled for 240 h. The surface area specific properties of the milled powders ranged from 21.60 to 88.15 m 2 g −1 .
Comparative studies of WC-Co and WC-Co-Ni composites obtained by conventional powder metallurgy
Materials Research, 2011
The present work reports a comparative study of cemented carbides of compositions WC-6Co, WC-10Co, WC-20Co, WC-6Co-6Ni and WC-12Ni-6Co. The purpose was to study the powder metallurgical production process of these compositions starting from a commercial WC-6Co powder, obtaining the desired compositions by mass balance with pure Co and pure Ni powders. During the process steps mixing, milling, compacting and sintering the powders were described by its apparent density, green density, shrinkage and sintered density. Lower densities were observed in composites with higher binder content. The process was monitored by scanning electron microscopy and EDS analysis to evaluate the homogeneity of the powders, to detect contaminations by the process and to characterize the microstructure of the sintered materials. A finer microstructure was found when the binder contained Ni. Potentiodynamic polarization tests in sulfuric acid revealed pseudo-passive behavior for all the tested hard metals.
NbC as grain growth inhibitor and carbide in WC–Co hardmetals
International Journal of Refractory Metals & Hard Materials, 2008
WC-NbC-12 wt%Co hardmetals with 0.45-60 wt%NbC were prepared by solid state pulsed electric current sintering (PECS), also known as spark plasma sintering (SPS), for 2 min at 1240°C and conventional sintering (CS) for 1 h at 1420°C. The role of NbC as grain growth inhibitor and major carbide addition was investigated in terms of the densification behaviour, the microstructure and mechanical properties. Experimental work revealed that the addition of more than 5 wt%NbC inhibits pressure assisted solid-state densification compared to WC-Co based hardmetals. The addition of NbC limits WC grain growth during PECS and conventional sintering, whereas substantial (Nb, W)C grain growth was observed in the hardmetals with P0.9 wt%NbC addition. The influence of the NbC content on the hardness, strength and toughness of the WC-NbC-12 wt%Co hardmetals was explained in terms of WC grain growth inhibition and the formation of coarse (Nb, W)C grains.