Effects of micro/nano CeO2 on the microstructure and properties of WC-10Co cemented carbides
Introduction
WC-Co cemented carbide prepared by powder metallurgy process is a kind of material with ideal hardness, excellent anti-wear ability, high transverse rupture strength and fracture toughness, which is applied to mining tools, molds, wear-resistant parts and etc. [[1], [2], [3]]. However, the hardness and strength of cemented carbides are contradictory to each other under normal circumstances. In addition, with the development of industrial technology, the traditional WC-Co cemented carbides can not meet the rigorous working conditions [4]. It was found that when the grain size of WC decreased to micron or nanometer, the hardness and strength of cemented carbides would be improved significantly, and showed a good comprehensive properties [5]. Nowadays, superfine or nanocrystalline cemented carbides has become a hotspot. However, the excessive pursuit of superfine or nanocrystalline WC powders preparation will dramatically increase the cost. Besides, the grain growth in the sintering process of cemented carbide produced by powder metallurgy is difficult to control. The use of micron WC raw material and the addition of grain inhibitors can not only inhibit the grain growth of cemented carbide during sintering process, but also improve the mechanical properties of cemented carbide and save the cost [[6], [7], [8], [9], [10]].
As is known to all that rare earth elements have good inhibition effects among many additives of grain inhibitor [[11], [12], [13], [14], [15], [16], [17], [18]]. WC-Co cemented carbides with Y2O3 additives were prepared by powder metallurgy technology, and the microstructure and properties of alloys were investigated by literatures [5,10,[12], [13], [14]]. The results indicated that the additive of Y2O3 showed good ability to inhibit the growth of WC grain and increased the comprehensive properties of cemented carbides to a certain extent. In addition, the effect of Y2O3 on the corrosion resistance of cemented carbide was also investigated by previous studies [5,10]. The results showed that the corrosion resistance of cemented carbide was enhanced when the content of Y2O3 was 1.0 wt%. Huang et al. [13] pointed out that WC-10Co cemented carbides with Y2O3 and CeO2 presented obvious tendency of grain spheroidization, and the degree of adjacency between WC and WC grains decreased from 0.6 to 0.39, which could improve the properties of the alloys.
At present, the influence of rare earth additives on the microstructure and properties of cemented carbide mainly focus on the types and the amount of rare earth elements. Research on the effects of rare earth additives with different grain sizes and the composite additive of rare earth and other metal elements is limited. Therefore, the core goal of the work is to analyze the effects of CeO2 additives with different grain sizes on structure as well as performances of these alloys.
Section snippets
Preparation
WC (≥99.6%, −0.5 μm, Fig. 1a) and Co powders (≥99.6%, −1.2 μm, Fig. 1b) were selected as raw materials. Some micron CeO2 powders (≥99.5%, −5 μm, Fig. 1c) and nanometer CeO2 powders (≥99.5%, 100 nm, Fig. 1d) were added into WC-10Co cemented carbides. The nominal compositions of WC-10Co cemented carbides were listed in Table 1. Composite powders mixed with 2 wt% paraffin were subjected to wet ball-milled by a three-roller grinder system for 60 h. Meanwhile, the ball-to-material ratio is 6:1 as
Composition and microstructure
The XRD patterns of the as-sintered cemented carbides with different contents of CeO2 were shown in Fig. 2. Through observation, hard and binder phases could be observed in all samples, and the phase composition of all samples was similar. Meanwhile, the Ce-related phases were not found in the results. By comparison, for a mixture multi-phases of CeO2 doped WC-10Co alloys, the volume of a phase irradiated by X-rays was the volume fraction in the sample [19], which could be calculated by formula:
Conclusions
(1) The grain size of WC decreased with the addition of micro/nano CeO2. In addition, the refining effects of nano CeO2 on WC grain size were better than that of micro CeO2, which led to higher hardness and stronger wear resistance.
(2) The hardness, TRS and fracture toughness increased with the increase of CeO2 additives, and then followed a decrease trend when then content of CeO2 exceeded 0.8%.
(3) Comprehensive analysis showed that the addition amount of nano CeO2 strongly affected the
Suggestions for Further Work
In this work, the sliding wear is used to evaluate the wear resistance of WC-Co cemented carbides. However, the sliding wear method has many uncertainties, which will affect the test results. In order to characterize the relationship between wear characteristics and toughness of alloy, the abrasion testing such as ASTM G65 and ASTM B611 should be used to characterize the wear characteristics if condition permit [[40], [41], [42]].
Credit Author Statement
This article was completed with the joint efforts of several authors. In detail, Huang Cai and Wenwen Jing are responsible for writing and revising manuscript, Lei Liu, Ying Ye, Yan Wen, Yunxuan Wu, Shuilong Wang, Xing Huang, Jianbo Zhang are responsible for experimental preparation and testing, Shengda Guo is responsible for analysis and guidance. All data are authentic and reliable. It has not been published in other journals or submitted for publication.
Declaration of Competing Interest
We are submitting our original research paper entitled “Effects of micro/nano CeO2 on the microstructure and properties of WC-10Co cemented carbides” for the possible publication in International Journal of Refractory Metals and Hard Materials. All authors have read and approve this version of the article, and due care has been taken to ensure the integrity of the work. I and co-authors state: no part of this paper has been published or submitted elsewhere, and no conflict of interest exits in
Acknowledgements
The work was financially supported by the Natural Science Foundation of China (51904126), the Key project of Natural Science Foundation of Jiangxi Province (20202ACBL214012), the Scientific Research Foundation of Jiangxi University of Science and Technology (jxxjbs18041), the Postdoctoral Research Foundation of Jiangxi Province (2019KY29) and the Innovation Training Foundation for College Students of Jiangxi University of Technology (DC2019-032).
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