Effects of (Ti, W)C Addition on the Microstructure and Mechanical Properties of Ultrafine WC-Co Tool Materials Prepared by Spark Plasma Sintering

doi:10.1007/s40195-020-01013-3

Abstract

Abstract:

In this study, powder mixtures containing (Ti, W)C additions (10, 20, 30 and 40 wt%) were prepared and then consolidated at 1200, 1250, 1300 and 1350 °C by spark plasma sintering. The effect of (Ti, W)C additions on the microstructure and mechanical properties of ultrafine WC-Co materials was investigated. The results demonstrate that the (Ti, W)C not only retards the sintering densification but also increases the porosity of sintered samples. The increasing sintering temperature is beneficial to the densification but results in the grain coarsening and the dissolution of W in (Ti, W)C. Moreover, there are no (Ti, W)C grains with obvious core/rim structure in the microstructure. With the (Ti, W)C increasing from 10 to 20 wt%, the hardness increases and fracture toughness changes hardly. However, the hardness and fracture toughness decrease slightly as the (Ti, W)C further increases. The transgranular fracture of (Ti, W)C phases is responsible for the slight reduction in fracture toughness. The sample with 20 wt% (Ti, W)C has high hardness and fracture toughness (H_V: 21.3 GPa, K_IC: 9.8 MPa m ^1/2).

Key words: (Ti, W)C, Cemented carbides, Spark plasma sintering, Microstructure, Mechanical properties

Boxiang Wang, Zhenhua Wang, Juntang Yuan, Bin Yu. Effects of (Ti, W)C Addition on the Microstructure and Mechanical Properties of Ultrafine WC-Co Tool Materials Prepared by Spark Plasma Sintering[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(6): 892-902.

Figures/Tables 13

Table 1 Charactristics of WC, (Ti, W)C and Co raw powders

Powder	Purity (%)	Particle size, d_LPSA	Particle size, d_BET	C content (wt%)	O content (wt%)	Manufacturer
WC	≥ 99.9	60 nm	38 nm	6.13	0.09	Shanghai ChaoWei-Nano Co., Ltd
(Ti, W)C	≥ 99.9	1.5 μm	-	5.19	0.08
Co	≥ 99.9	500 nm	130 nm	-	0.09

Fig.1 SEM images showing morphologies of starting and composite powders: (a) WC, (b) Co, (c) (Ti, W)C, (d) WC-20(Ti, W)C-8Co

Table 2 Compositions and symbols of sintered samples (wt%)

Cemented carbides	Symbol	WC	(Ti, W)C	Co	VC	Cr₃C₂
WC-10(Ti, W)C-8Co	TW10	Bal.	10	8	0.4	0.4
WC-20(Ti, W)C-8Co	TW20	Bal.	20	8	0.4	0.4
WC-30(Ti, W)C-8Co	TW30	Bal.	30	8	0.4	0.4
WC-40(Ti, W)C-8Co	TW40	Bal.	40	8	0.4	0.4

Fig.2 Shrinkage behavior of composite powders with different (Ti, W)C contents: (a) shrinkage displacement, (b) shrinkage rate

Fig.3 Volumetric shrinkage of WC-(Ti, W)C-Co sintered at different temperatures

Fig.4 SEM images showing microstructures of WC-(Ti, W)C-Co: (a) TW10 sintered at 1250 °C, (b) TW10 sintered at 1350 °C, (c) TW20 sintered at 1250 °C, (d) TW20 sintered at 1350 °C, (e) TW30 sintered at 1250 °C, (f) TW30 sintered at 1350 °C, (g) TW40 sintered at 1250 °C, (h) TW40 sintered at 1350 °C

Fig.5 XRD patterns of (a) samples TW10, TW20, TW30 and TW40 sintered at 1250 °C, (b) sample TW20 sintered at 1200 °C, 1250 °C, 1300 °C and 1350 °C

Fig.6 SEM images and EDS line analyses of (Ti, W)C grain in sample TW20 sintered at (a) 1250 °C and (b) 1350 °C

Table 3 SEM-EDS results of (Ti, W)C grains in sample TW20

Area-No		1250 °C				1350 °C
Area-No		C	Ti	W	Ti-to-W ratio	C	Ti	W	Ti-to-W ratio
S1 (rim)	at.%	59.45	24.74	15.81	61:39	55.20	23.16	21.64	52:48
	wt%	14.86	24.65	60.49		11.53	19.26	69.18
S2 (core)	at.%	58.71	24.36	16.93	59:41	54.73	28.99	16.28	64:36
	wt%	14.15	23.40	62.45		13.05	27.56	59.39
S3 (rim)	at.%	60.35	24.58	15.07	62:38	55.35	23.41	21.24	52:48
	wt%	15.52	25.18	59.30		11.68	19.71	68.61

Fig.7 SEM images showing grain morphologies of sample TW20 sintered at (a) 1200 °C, (b) 1250 °C, (c) 1300 °C, (d) 1350 °C

Fig.8 (a) Hardness, (b) fracture toughness of WC-(Ti, W)C-Co with different (Ti, W)C contents

Fig.9 SEM images showing crack propagation morphologies of WC-(Ti, W)C-Co sintered at 1250 °C: (a) TW10, (b) TW20, (c) TW30, (d) TW40

Table 4 Mechanical properties of some ultrafine cemented carbides

TiC additions (wt%)	Binder phases (wt%)	Hardness (GPa)	K_IC (MPa m^1/2)	Sintering technology
16TiC [30]	6Co	20.2	-	Vacuum sintering
5TiC [31]	6Co	19.8	10.1	Hot pressing sintering
25TiC [11]	10Ni	19.5	8.3	Vacuum sintering
[17]	8Co	18.9	9.8	Rapid omni compaction
[1]	8Co	16.2	9.6	-
[1]	8Co	14.5	10.8	-
[18]	8Co	19.0	9.6	-
[16]	12Co	18.0	10.6	Spark plasma sintering
[13]	12Co	18.9	10.2	Spark plasma sintering
[16]	12Co	18.3	10.5	Hot isostatic pressing
20(Ti, W)C^a	8Co	21.3	9.8	Spark plasma sintering

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