Thermal oxidation treatment of iron aluminide for improved tribological properties

Abstract

A major setback in the industrial applications of high strength to weight ratio iron aluminides is their poor tribological properties under dynamically loaded conditions. A surface modification technique, namely thermal oxidation (TO) treatment, was developed in the present study toimprove the load bearing capacity and tribological properties of a B2 structured iron aluminide (Fe40Al). The treatment was performed at 1000°C for various time from 10 to 150 h. The composition, microstructure and mechanical properties of the TO treated surfaces were characterised bya number of analytical techniques. The load bearing capacities and antiscuffing properties of the TO treated samples were evaluated by an Amsler block on wheel machine. The tribological properties of the TO treated and untreated iron aluminide were investigated using a pin on disc wear tester.It was shown that a hard and dense α-Al₂O₃ layer is formed on the iron aluminide surface after TO treatment, which has an increase in surface hardness from 5.5 GPa to 26.3 GPa and in elastic modulus from 200 GPa to 340 GPa. The improved hardness, reduced value ofE_r/H and the ceramic nature of the oxide layer has considerably improved the load bearing capacity and tribological properties of the iron aluminide. The coefficient of friction of the TO treated alloy is low and stable, and the wear rate for the TO treated alloy canbe more than 16 times less than that for the untreated alloy.