Effects of rare-earth oxides on the microstructure and properties of Fe-based friction materials synthesized by in situ carbothermic reaction from vanadium-bearing titanomagnetite concentrates

Abstract

In this work, we prepared an iron-based frictional material from vanadium-bearing titanomagnetite concentrates by in situ carbothermic reaction with improved tribological properties. Effects of different amounts of rare-earth oxides on the microstructure and properties of the Fe-based friction materials were investigated. The microstructure of the Fe-based friction material consisted of an Fe matrix, hard particles (mainly TiC) and a lubricating phase (graphite). The moderate addition of rare-earth oxides improved the microstructure and properties of the Fe-based friction material significantly. Particularly, the friction coefficient decreased from 0.61 to 0.48–0.56 and the wear rate reduced from 7.8 × 10⁻⁷ cm³ J⁻¹ to 2.6 × 10⁻⁷∼4.9 × 10⁻⁷ cm³ J⁻¹. Addition of La₂O₃ (≤0.2 wt%) or CeO₂ (≤0.4 wt%) contributed to sintering densification and improved the relative density, hardness and wear resistance. The dominant wear mechanism changes from severe abrasive wear and oxidative wear to mild oxidative wear. However, when rare-earth oxide addition was increased further, the microstructure, relative density, hardness, and wear performance of the Fe-based friction materials deteriorated. Consequently, the optimal additions of La₂O₃ and CeO₂ were 0.2 wt% and 0.4 wt%, respectively.