Improvement of Mechanical Properties of Hard Metals Using Solid Solution Strengthened Metallic Binder (Co1-xWx)

The metallic binder in WC-Co hard metals was effectively strengthened using the solid solution phases of Co and W. These metallic phases of Co and W (Co1-xWx, x<1), which consist of two kinds of structures (FCC and HCP), were successfully formed by hydrogen reduction of milled oxides mixtures (Co3O4 and WO3) at over 1000 oC. When hard metals are fabricated by pressureless sintering of mixed WC and Co1-xWx, the hard metals containing the WC2 and M6C phases (Co2W4C and Co4W2C) have brittleness, which degrades their mechanical properties, like hard metals fabricated from mixtures of WC, Co, and W. By rapidly sintering the WC-Co1-xWx hard metals for 5 min the WC2 and M6C phases were eliminated, and a two-phase (WC and the metallic phase of Co and W) region was successfully obtained. The mechanical properties of the WC-Co1-xWx hard metals showed higher values for both hardness (max. 18.8 GPa) and fracture toughness (8.5 MPa·m1/2) than conventional WC-Co hard metal (HV: 15.9 GPa, KIC: 6.9 MPa·m1/2). The enhancement in toughness was attributed to the solid solution strengthening of the metallic binder and the elimination of the WC2 and M6C phases. The suppression of grain growth due to the short duration of sintering also played a positive role in improving the hardness of the WC-Co1-xWx hard metals. The phase-controlled solid solution metallic binder could be the key material to enhance the hardness and toughness of hard metals.

Effect of WC and Co on the Microstructure and Properties of TiC Steel-Bonded Carbide

TiC base high manganese steel-bonded carbide was manufactured with conventional powder metallurgy method to service in wear and impact resistant condition. WC was added in the alloy in the form of (W,Ti)C carbides to improve the impact toughness and expand the applications of alloy, meanwhile, cobalt powder was also used to enhance the wettability of the metallic binder on the ceramic phase. Results showed that the impact toughness of the alloy was increased remarkably with the increase of WC content. The impact toughness reached 10.6 J/cm2 when WC content was 10.5 wt.%, while the hardness of the alloy did not decrease. It was indicated that the appropriate content of WC and cobalt can improve impact toughness and wear resistance of the alloy greatly with little increase in the production cost.

Microstructural Evolution of Composite 8 WC-(Co, Ni): Effect of the Addition of SiC

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 bar). Two sintering temperatures were investigated, i.e. 1380 and 1420oC, and the sintering time considered was 60 minutes. The relative density, hardness, linear and volumetric shrinkage were determined. Microstructural evaluation was investigated by optical microscopy and scanning electron microscopy (SEM-FEG). The results showed that the addition of SiC promoted higher densification and grain size growth. The hardness was higher for samples with SiC, so solid solution hardening of the binder was more effective than WC grain size growth.

Percolation of a metallic binder in energy generating composites

Indium is introduced as a metallic binder in energetic composites and is an approach for consolidating the media and providing a highly conductive percolating scaffold for enhancing energy transport.