Formation of a Tribologically Transformed Surface (TTS) on AISI 1045 Steel by Friction Stir Processing

Superficial nanostructuration by friction stir processing (FSP) experiments has been carried out on samples of AISI 45 steel. Sixteen tests were carried out, with a traverse speed in the range of 10–70 mm/min and 900–1800 N for the normal force at a constant rotational speed of 2000 rpm, in order to determine the optimal conditions for the process applied to this material and to test its feasibility. The results obtained have shown that FSP in this range of parameters leads to the formation of a stirred layer of small grains (30 times smaller than the initial grains) with high hardness (approximately doubled). When the load is higher than 1500 N and the traverse speed is superior to 50 mm/min, a white layer (WL) with very high hardness can be produced. It has also been determined that the increase of the stirred layers’ thickness is almost linked to the increase of the normal force.