Study of wear behavior of nitride layers in Fe–Mn–Al–C alloys

The wear behavior of high toughness austenitic Fe–30Mn–(2, 5, 6 and 9 wt.%)Al–0.7C–(3Cr) alloys with/without nitriding in pure nitrogen were studied by a TE77 frictional test machine in a reciprocating sliding mode. Microstructures of alloys were also examined. The results showed that AlN was the major product of the nitriding process at 1050 °C for 25 h. Acicular AlN was found at the subsurface to be part of the morphology of all specimens. The hardness of the raw metal in the Fe–Mn–Al alloy system increased with increasing aluminum content in alloys. When oxide film was absent on the worn surface, wear resistance increased with increasing hardness of the raw metal. The wear loss of Fe–30Mn–xAl–0.7C–(3Cr) alloys (x⩾5) decreased one order of magnitude after nitriding due to AlN supporting an oxide film. The nitride layer is beneficial for enhancing hardness of Fe–30Mn–xAl–0.7C–(3Cr) alloys (x⩽7.5), to improve wear resistance of alloys due to the fact that the hardness of AlN is much higher than that of the matrix. When oxide is produced on the worn surface, the governing wear mechanism is tribooxidation. On the contrary, when oxide is absent on the worn surface, the governing wear mechanisms are abrasion, surface fatigue and shear fracture or delamination.