Effect of rare earth elements on the boronizing process

Abstract

Boronizing is a thermo-chemical process consisting on the diffusion of the chemical element boron into metallic substrates, aiming at producing on the metal surface a closed layer of borides, which are elements extremely hard and chemically inert. Steels, for example, exhibit substantially higher hardness values (1,600 to 2,000HV) than nitrided steels (650 to 900HV) due to the formation of iron borides. The combination of high hardness and low friction coefficient of this boride layer greatly contributes to endure the main mechanisms of wear: adhesion, abrasion and superficial contact fatigue. The use of the boronizing process, however, is limited due to the elevated process temperatures. To overcome this limitation, recent studies pointed to the use of rare earth elements as catalysts of the process. This work will present the state of the art of these developments.