Synthesis And Thermal Stability Of Homogeneous Nanostructured Fe3C (Cementite)

Mechanical alloying (MA) of blended elemental Fe and C powder mixtures corresponding to the stoichiometric composition of Fe3C (cementite) was carried out in a high-energy SPEX 8000 shaker mill. The phase evolution and thermal stability of the phases produced were determined. A supersaturated solid solution of C in Fe (α-Fe) formed in the early stages of milling. The solid solubility increased on continued milling and reached the maximum value of about 0.6 wt% C on milling the powders for 10 h. The Fe3C (cementite) phase started to form on milling the powders for 15 h and a homogeneous Fe3C phase formed on milling the powders for 30 h. Spark plasma sintering (SPS) of the milled powders at 600 °C and 70 MPa for 15 min led to the formation of homogeneous nanocrystalline bulk Fe3C with a very high hardness value of over 900 HV. Annealing of this sample at 900 °C for 1 h resulted in the decomposition of Fe3C to form a mixture of α-Fe and Fe3C and a reduced hardness value. The results confirm that MA of pure Fe and C powders, followed by SPS, can be successfully utilized to synthesize nanocrystalline bulk Fe3C with good mechanical properties and good thermal stability