Role of Co Content on Densification and Microstructure of WC-Co Cemented Carbides Prepared by Selective Laser Melting

doi:10.1007/s40195-021-01195-4

Abstract

Abstract:

WC-Co cemented carbides, well-known as the conventional tooling materials, have not been successfully produced by one step additive manufacturing processes such as selective laser melting (SLM) yet. The microstructure evolution as well as WC grain growth behavior has rarely been investigated in detail during SLM process. In this study, the WC-Co cemented carbides with different Co contents (12-32 wt%) were prepared by optimized SLM processes for comparative investigation of densification behavior, microstructure characterization and mechanical property. The increase in Co content in feedstock carbide granules can improve the densification behavior during SLM process. The SLM processed WC-12Co shows larger average WC grain size and higher percentage of coarser WC grains as compared with both WC-20Co and WC-32Co. The microstructure characterization, combined with finite element simulation, shows the WC grain growth mechanisms include agglomeration and dissolution-deposition of WC during SLM process and agglomeration of WC is an important mechanism especially for WC-Co cemented carbides with Co content as low as 12 wt%. The comparison between horizontal (perpendicular to the SLM laser beam) and vertical (parallel to the SLM laser beam) cross sections of carbides shows that SLM process introduces a certain degree of microstructure and mechanical behavior anisotropy for WC-12Co, WC-20Co, and WC-32Co.

Key words: Cemented carbides, Selective laser melting, Microstructure, Densification behavior, Finite element simulation

Jinyang Liu, Jian Chen, Li Zhou, Bingyao Liu, Yang Lu, Shanghua Wu, Xin Deng, Zhongliang Lu, Zhipeng Xie, Wei Liu, Jianye Liu, Zhi Qu. Role of Co Content on Densification and Microstructure of WC-Co Cemented Carbides Prepared by Selective Laser Melting[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(9): 1245-1254.

Figures/Tables 12

Fig. 1 Morphologies and EDS spectra of feedstock WC-Co granules: a WC-12Co, b WC-20Co, c WC-32Co

Table 1 Three sets of SLM process parameters optimized specifically for three carbides

Process parameter	WC-12Co	WC-20Co	WC-32Co
Laser power (J/s)	289	260	212
Laser spot size (µm)	100	100	100
Scan speed (mm/s)	350	350	350
Scan line spacing (µm)	50	50	50
Powder layer thickness (µm)	30	30	30

Fig. 2 Schematic illustration of SLM process. Both the vertical (parallel to the laser beam) and horizontal (perpendicular to the laser beam) cross sections were used for microstructural analysis

Table 2 Properties of feedstock WC-20Co granule and SLM process parameters for FEM

Property/SLM process parameters	Value
Laser absorptivity of the powder (%)	0.69
Density of WC-12Co (g/cm³)	14.38
Density of WC-20Co (g/cm³)	13.62
Density of WC-32Co (g/cm³)	12.62
Thermal conductivity of WC-12Co (W/(m K))	117.24
Thermal conductivity of WC-20Co (W/(m K))	102
Thermal conductivity of WC-32Co (W/(m K))	77.64
Thermal capacity of WC-12Co (J/(kg K))	272.8
Thermal capacity of WC-20Co (J/(kg K))	288
Thermal capacity of WC-32Co (J/(kg K))	310.8
Ambient temperature (K)	300
Liquidus temperature (K)	1647
Laser spot diameter (µm)	150
Powder layer thickness (µm)	30

Fig. 3 Relative density of SLM processed cemented carbides

Fig. 4 Microstructures of vertical cross sections of SLM processed cemented carbides: a WC-12Co, b WC-20Co, c WC-32Co

Fig. 5 Backscattered electron microstructure of horizontal and vertical cross sections, a horizontal cross section of WC-12Co, b vertical cross section of WC-12Co, c horizontal cross section of WC-20Co, d vertical cross section of WC-20Co, e horizontal cross section of WC-32Co, f vertical cross section of WC-32Co

Fig. 6 WC grain size distribution of SLM processed WC-12Co, WC-20Co, and WC-32Co cemented carbides, a horizontal cross section, b vertical cross section

Fig. 7 Average WC grain size (D50) of both horizontal cross sections and vertical cross sections of SLM processed WC-12Co, WC-20Co, and WC-32Co

Fig. 8 High magnification SEM of WC grains from SLM processed WC-12Co cemented carbide

Fig. 9 FEM simulation results: a three-dimensional finite element model, b the horizontal/vertical temperature distribution profile of liquid phase sintering pool during SLM process, c temperature contour plots of (b), sintering temperature/heating-cooling rate versus time at the center of liquid phase sintering pool surface for d WC-12Co, e WC-20Co, f WC-32Co

Fig. 10 Vickers hardness of SLM processed cemented carbides in both horizontal and vertical cross sections: a WC-12Co, b WC-20Co, c WC-32Co

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