Effect of Y2O3 Addition on High-Temperature Oxidation of Binderless Tungsten Carbide

Jinfang Wang,Zhibiao Tu,Xiao Lin,Liu Zhu,Weiwei Li,Xiaoqiong Zhang,Yinan Wu,Dunwen Zuo

doi:10.3389/fmats.2021.645612

Abstract

High-temperature oxidation tests were carried out on binderless tungsten carbide (WC) with different Y2O3 contents (0, 1, 2, 3, and 4 wt.%) and on YG3 cemented carbide. Results demonstrated that the addition of Y2O3 led to a significant improvement in the high-temperature oxidation resistance of binderless tungsten carbide compared with those of YG3 cemented carbide and pure tungsten carbide. After oxidation at 800°C for 120 min, the oxidation weight gain of binderless tungsten carbide with 1 wt.% Y2O3 was 58.54 mg cm−2, corresponding to the reduction by 47.7% compared with YG3 cemented carbide. In the high temperature oxidation process, WC in the triangle grain boundary was first oxidized to Y2WO6 due to the high activity of Y2O3 which is present mainly in the WC grain boundaries. The transport of W4+ outward along the grain boundary and the diffusion of O2− inward along the grain boundary were hindered by Y2WO6 with the high ionic radius and thus the antioxidant capacity of binderless tungsten carbide was improved. Meanwhile, the adhesive ability of oxidation layer on the substrate was enhanced with the “pinning effect” of Y2WO6, which also led to the improvement of oxidation resistance. With the Y2O3 content increasing from 1 to 4 wt.%, the antioxidant properties of binderless tungsten carbide gradually declined, and the antioxidant performance of binderless tungsten carbide with 1 wt.% Y2O3 was found to be the best.

Highlights

Tungsten carbides with metallic binder cobalt are widely used for cutting tools and wear applications due to their excellent mechanical properties (Kim et al, 2004; Xiao et al, 2010; Ou et al, 2012; Zhang et al, 2016; Liu et al, 2018)
The oxidation resistance of the WC cemented carbide was determined by measuring the weight change after the oxidation at the temperatures of 600°, 700°, 750 ° and 800°C respectively
The binderless tungsten carbide doped with Y2O3 has good oxidation resistance, we suggest as follows: (1) Oxidation product Y2WO6 distributed at the triangle grain boundaries prevents the inward diffusion of O2− and the outward diffusion of W4+

Summary

Introduction

Tungsten carbides with metallic binder cobalt are widely used for cutting tools and wear applications due to their excellent mechanical properties (Kim et al, 2004; Xiao et al, 2010; Ou et al, 2012; Zhang et al, 2016; Liu et al, 2018). For applications for cutting tools, because the highest temperature at tool/chip interface may vary between 600 and 1000°C (Bhaumik et al, 1999; Majumdar et al, 2005; Sutter and Ranc, 2007), oxidation of cemented carbides will take place in dry and high speed cutting (Basu and Sarin, 1996; Voitovich et al, 1996; Campo et al, 2009; Chen et al, 2015; Chen et al, 2016), which will result in the degradation of mechanical properties and decreasing of their service lifetime. The O content in Co phase increases quickly while there is no change of O content in WC phase because no oxidation takes place

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