An Experimental Study on the Rotational Fretting Wear Behavior of LZ50 Steel

Rotational fretting tests in a configuration of ball-on-flat have been successfully realized by developing a new fretting device based on an ultra-low-speed reciprocating rotational driver. The rotational fretting tests of LZ50 steel flats against 52100 steel balls were performed under different testing parameters, i.e. the angular displacement amplitudes of 0.25 degrees to 1 degrees and the normal loads of 5 N to 20 N. The frictional kinetics of rotational fretting and the characteristic of wear damage for LZ50 steel were discussed in detail. The results showed that the rotational fretting behavior of the LZ50 was strongly dependent upon the angular displacement amplitude and normal load. Friction force-angular displacement (F-t-theta) curves can be used to characterize the rotational fretting running behavior, which exhibited three basic types of the parallelogram, elliptical and linear cycles by varying the angular displacement amplitudes or normal loads. Under the condition of the angular displacement amplitude of 0.25 degrees and the normal load of 10 N, the rotational fretting run in the regime of partial slip, which corresponding elastic deformation coordination at the contact interface. With the increase of the angular displacement amplitude and the decrease of normal load, the fretting running state transferred from the partial slip to the gross slip. The micro-examinations indicated that the plastic deformation, abrasive wear, oxidative wear and delamination were the main damage mechanism for LZ50 steel under the gross slip conditions. A special phenomenon which different from that observed in the tests of the normal reciprocating fretting (tangential fretting), i.e. wear debris generated was accumulated in the centre zone of the wear scar under the condition of gross slip, was observed in this paper.