A Study of the Impact of Graphite on the Kinetics of SPS in Nano- and Submicron WC-10%Co Powder Compositions

Eugeniy Lantcev,Kseniya Smetanina,Nataliya Isaeva,Artem Murashov,Maksim Boldin,Vladimir Chuvil’Deev,Nataliya Malekhonova,Pavel Andreev,Yuriy Blagoveshchenskiy,Aleksey Nokhrin

doi:10.3390/ceramics4020025

Eugeniy Lantcev, Kseniya Smetanina + Show 8 more

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https://doi.org/10.3390/ceramics4020025

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Journal: Ceramics	Publication Date: Jun 10, 2021
Citations: 9	License type: CC BY 4.0

Affiliation: Baikov Institute of Metallurgy and Materials Science

Abstract

This study investigates the impact of carbon on the kinetics of the spark plasma sintering (SPS) of nano- and submicron powders WC-10 wt.%Co. Carbon, in the form of graphite, was introduced into powders by mixing. The activation energy of solid-phase sintering was determined for the conditions of isothermal and continuous heating. It has been demonstrated that increasing the carbon content leads to a decrease in the fraction of η-phase particles and a shift of the shrinkage curve towards lower heating temperatures. It has been established that increasing the graphite content in nano- and submicron powders has no significant effect on the SPS activation energy for “mid-range” heating temperatures, QS(I). The value of QS(I) is close to the activation energy of grain-boundary diffusion in cobalt. It has been demonstrated that increasing the content of graphite leads to a significant decrease in the SPS activation energy, QS(II), for “higher-range” heating temperatures due to lower concentration of tungsten atoms in cobalt-based γ-phase. It has been established that the sintering kinetics of fine-grained WC-Co hard alloys is limited by the intensity of diffusion creep of cobalt (Coble creep).

Highlights

Hard alloys based on tungsten carbide and containing a readily fusible metallic binder lend themselves to a wide range of industrial applications [1,2,3,4,5,6,7,8,9,10,11,12]
The X-ray diffraction (XRD) results show that each initial composition contains hexagonal α-WC tungsten carbide and hexagonal α-core (α-WC)-shell (Co) (Figure 2c, the black line).The peaks corresponding to the W2 C phase were absent in the XRD curves
It has been demonstrated that an increased concentration of graphite leads to a shift of the shrinkage curves towards lower heating temperatures, to a lower fraction of η-phase particles, and to a decreased size of abnormally large grains in specimens of WC-10Co hard alloys obtained by liquid-phase spark plasma sintering (SPS)

Summary

Introduction

Hard alloys based on tungsten carbide and containing a readily fusible metallic binder (usually cobalt) lend themselves to a wide range of industrial applications [1,2,3,4,5,6,7,8,9,10,11,12]. Depending on the under- or oversaturation of carbon relative to the equilibrium concentration (C0 = 6.14 wt.% [1]), the WC-Co alloys may, in addition to the two main phases, contain ternary carbides (η-phase) or graphite, respectively [2,3,4,5,6]. An increased oxygen concentration in the tungsten carbide powders favors the formation of unwanted phases in the sintered hard alloys (α-W, η-phase, WOx ) [1,59,60]

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