Growth Inhibition of Nano WC particles in WC-Co Alloys during Liquid-Phase Sintering

Abstract

WC-10Co-xVC alloys were produced using two different sizes of WC powders (200 nm and 4.4 mm) via planetary milling and a liquidphase sintering technique. When VC was added to the WC-Co alloys, the growth of WC particles was effectively suppressed. However, this process was dependent on the amount of additive used. Since the average WC particle size became less than 1 mm, the system experienced a significant loss in carbon, resulting in the formation of an undesirable phase. The goal of this study was to determine the role of VC in controlling growth and to verify its effectiveness as a function of average WC size and inhibitor content. It was found from XRD and HREM studies that the (W,M)C phase was formed in WC-10Co-xVC-C systems. The effect of V or VC on the solubility of W in the Co matrix was also examined using HREM/EDS. The findings indicate that the presence of VC tends to reduce the solubility of W in a Co melt, thus inhibiting the dissolution and growth of WC.

First-principles calculations of the phase stability and the elastic and mechanical properties of η-phases in the WC–Co system

“…In particular, hardness measured by indentation methods strongly depends on the testing load and time [16]; thus, the hardness of a sample can vary. Dense WC sintered bodies are also difficult to obtain by general vacuum sintering, and several studies have reported that carbon-deficient phases, such as W 2 C, that are softer than WC are frequently detected in WC sintered bodies [13,16,17,44]. Therefore, the experimental hardnesses are lower than the calculated hardnesses.…”

Abrasion wear, thermal shock and impact resistance of WC-cemented carbides produced by PECS and LPS

“…Additionally, reduced hardness with increased binder content is less in cemented carbides with finer WC grains than with micron-sized WC [5]. Fine grain sizes have high sintering rates because of the large interfacial surface area between the WC particles and the binder [3,6].…”

Sintering of nano-sized WC–Co powders produced by a gas reduction–carburization process

“…Several explanations for the role of the grain growth inhibitors have been proposed, e.g. the preferential segregation of V or Cr [16,17], the lower surface energy of WC due to the presence of V or Cr [18], and the inhibiting effect of those carbides on the dissolution of WC in a Co melt [19]. Even though grain growth inhibitors are able to maintain the small size of WC, the addition of VC and Cr 2 C 3 promotes the formation of a phase (W 3 Co 3 C), (W,V)C [20] and an M 7 C 3 -type carbide [21], both of which degrade the mechanical properties.…”