Microstructure and mechanical properties of Fe-C alloy produced by mechanical alloying and spark plasma sintering

Abstract

Nanocrystalline Fe with carbon concentrations of 0.2 wt.% and 0.4 wt.% was prepared by the mechanical alloying technique. The grain size after milling for 100 h was 22 and 17 nm for 0.2 and 0.4 wt.% C, which shows the carbon addition is beneficial in getting smaller nano-crystalline grain size. Consolidation into bulk shape with a relative density above 98% was performed with the spark plasma sintering technique at 650, 675, 700 and 730 °C. A maximum compression strength of approximately 2000 MPa was obtained for 650 °C consolidation sample with an absolute lack of plasticity, whereas a strength to plasticity balance could be obtained by increasing the temperature. Detailed microstructural analysis has been done with scanning electron microscopy and transmission electron microscopy. The microstructure shows a bimodal grain size distribution with a fine dispersion of oxide particles having a size ranging from 20 to 200 nm and cementite particles having a size range from 100 to 500 nm depending on the sintering temperature. The presence of oxide particles along with bimodal grain distribution resulted in a high yield strength value of 1620 MPa and high plasticity of 45%.