Long-range migration behavior of rare earth additives in WC–Co cemented carbides

• 10-year work on migration behavior of rare earth (RE) in hardmetals is summarized.
• Reason behind the instability in quality control of RE doped hardmetals is revealed.
• Mechanism for the migration related phenomena is discussed.
• Measures on how to promote and get control over the migration behavior are suggested.
• Self-lubricating function of RE doped hardmetals can be realized.

Research on cemented carbides with rare earth (RE) additives started in the 1960s. Nevertheless, since then the instability in the quality control has troubled the industry. Our research reveals that a strong long-range migration ability of RE exhibited during the sintering process is the reason behind the instability. It is well established that there is a huge difference (more than 29%) in the atomic radius between La/Ce/Pr/Nd and W and La/Ce/Pr/Nd and Co. For this reason, it is an amazing phenomenon to observe the long-range migration of RE in WC–Co alloys. In the present work, we report the long-range migration phenomena of RE towards the sinter skins (surfaces) during the sintering process, the in situ formation of a layer-structured RE2O2S phase with self-lubricating and high heat-resistance functions on the working surfaces of WC–Co inserts, the mechanism for the formation of the RE containing dispersed phase(s) on the surfaces and the measures on how to promote and get control over the long-range migration behavior to develop self-lubricated function oriented cemented carbides.