Grain Growth Inhibitor on the WC-Co Cemented Carbide Coating

doi:10.15541/jim20160590

Abstract

Abstract:

The ultrafine WC-12Co composite powder was synthesized by in situ reduction and carbonization reactions. Using the composite powder with an addition of 1.0wt% grain growth inhibitor (GGI) i.e. VC, Cr₃C₂ and NbC, as raw materials, the ultrafine-structured cemented carbide coatings were fabricated by the high velocity oxy-fuel (HVOF) spraying method. Prior to thermal spraying, the powders were agglomerated into thermal spray feedstock. The effects of GGI addition on phase constitution, microstructure, hardness, and wear and corrosion properties of the coatings were investigated. The results show that the mean WC particle size of coatings with an addition of 1.0wt% VC or Cr₃C₂ decreases by about 49% as compared to that without GGI. Moreover, hardness of the coatings is significantly improved and the wear rate decreases by 52%-55%. Addition of 1.0wt% NbC has little effect on WC particle size of the coating but leads to formation of (W, Nb)C compound in the Co binder. Thus the corrosion resistance of the coating containing NbC is significantly enhanced. However, its wear resistance is lower than those with VC or Cr₃C₂, due to high brittleness of the (W, Nb)C compound.

Key words: grain growth inhibitor, ultrafine WC-Co composite powder, cemented carbide coating, wear resistance, corrosion resistance

CLC Number:

TQ174

WANG Xue-Zheng, WANG Hai-Bin, LIU Xue-Mei, YANG Tao, SONG Xiao-Yan. Grain Growth Inhibitor on the WC-Co Cemented Carbide Coating[J]. Journal of Inorganic Materials, 2017, 32(8): 813-818.

Figures/Tables 11

Table 1 Contents of grain growth inhibitor in WC-12Co composite powder/wt%

Sample	VC	Cr₃C₂	NbC
N1	1	0	0
N2	0	1	0
N3	0	0	1
N4	0	0	0

Table 2 Spraying parameters of WC-12Co coating

Kerosene /GPH	Oxygen /SCFH	Distance /mm	Carrier gas /SCFH	Feed rate /(r·min^-1)
6.0	2000	340	25	5.5

Fig. 1 XRD patterns of WC-12Co spraying powder (a) and coating (b)

Fig. 2 SEM microstructures of WC-12Co coating(a) Sample N1; (b) Sample N2; (c) Sample N3; (d) Sample N4

Fig. 3 SEM microstructure and WC grain size distribution of WC-12Co coating(a) Sample N1; (b) Sample N2; (c) Sample N3; (d) Sample N4

Table 3 Microhardness of WC-12Co coating

Sample	N1	N2	N3	N4
Microhardness HV_0.3	1313±64	1283±65	1175±99	1120±88

Fig. 4 Wear rate curve of WC-12Co coating

Fig. 5 SEM images of coating scratch(a) (b) Sample N1; (c) (d) Sample N4

Fig. 6 Tafel curves and EIS curves of WC-12Co coatings

Table 4 Corrosion potentials (Ecorr) and current densities (Icorr) of WC-12Co coating

Sample	N1	N2	N3	N4
E_corr /V	-0.42	-0.47	-0.32	-0.47
I_corr/(A•cm^-2)	1.109×10^-5	2.371×10^-5	3.981×10^-6	8.913×10^-5

Fig. 7 EDS analysis of the WC-12Co coating with addition of NbC

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