Corrosion-Induced Damage and Residual Strength of WC-Co,Ni Cemented Carbides: Influence of Microstructure and Corrosion Medium

Yafeng Zheng,Olivier Lavigne,Elaine Armelin,Gemma Fargas,Luis Llanes

doi:10.3390/met9091018

Abstract

The corrosion behavior of cemented carbides with binders of different chemical nature (Co and Ni) and carbides with distinct mean grain size (ultrafine and coarse) was studied. The investigation also included corrosion media (acidic and neutral solutions containing chlorides and an alkaline solution) as experimental variables. Immersion tests were performed to induce corrosion damage in a controlled way. Electrochemical parameters were measured together with a detailed inspection of the corroded surfaces. Microstructural influence on the tolerance to corrosion damage was evaluated in terms of residual strength. Results pointed out that corrosion rates were lower in the alkaline solution. In contrast, acidic media led to higher corrosion rates, especially for cemented carbides with Co regardless the influence of carbide mean grain size. Corrosion damage resulted in strength degradation due to the formation of surface corrosion pits in acidic solution. In neutral and alkaline solutions, much less pronounced effects were determined. Focused Ion Beam (FIB)/ Field Emission Scanning Electron Microscopy (FESEM) results revealed differences in corrosion-induced damage scenario. In acidic solution, corrosion starts at binder pool centers and evolves towards binder/WC interfaces. Meanwhile, corrosion in alkaline solution is initially located at binder/WC interfaces, and subsequently expands into the ceramic particles, developing a microcrack network inside this phase.

Highlights

Cemented carbides, usually referred to as hardmetals, are preeminent material choices for extremely demanding applications, such as cutting and forming tools, mechanical seals, and mining bits
It has been found that nickel, nickel-chromium, and nickel-cobalt binder exhibit higher corrosion resistance compared to plain cobalt one, especially in acidic and neutral media
This result is in agreement with previous studies which pointed out that during sintering chromium dissolves into the binder, resulting in a beneficial effect against corrosion [26]

Summary

Introduction

Usually referred to as hardmetals, are preeminent material choices for extremely demanding applications, such as cutting and forming tools, mechanical seals, and mining bits. The main reason behind this is the unique combination of hardness, toughness, and wear resistance they exhibit It results from their two-phase interpenetrated network as well as the intrinsic properties of the ceramic particles and the metallic binder [1,2,3,4,5]. It has been found that nickel, nickel-chromium, and nickel-cobalt binder exhibit higher corrosion resistance compared to plain cobalt one, especially in acidic and neutral media. Under these conditions, metallic binders are preferentially attacked, while ceramic phase is the one corroded in alkaline solution [10,11]. The fact that neither materials nor the electrolytes were the same in these studies, increases the uncertainty about this issue

Methods

Results

Conclusion