An experimental study on fretting wear behavior of cross-contacting Inconel 690 tubes

A fretting wear test rig employing a piezoelectric actuator has been developed, which is equipped with a heating and water circulation system. The fretting wear tests of cross-contacting Inconel 690 tubes, which is widely used for power plant steam generator, have been carried out in room temperature ambient and 80 °C in-water conditions. Maximum normal load was 55 N, and the sliding amplitude was below 50 μm. Scars of the mixed-slip and the gross-slip fretting wear have been measured in terms of scar diameter and wear volume. From the relationship between the work rate and the wear rate, a threshold of work rate has been defined, and this is found to be closely related with fretting wear regimes. The wear coefficients have been evaluated in the gross-slip regime. Distinct fretting wear mechanisms have been observed for the two different test conditions from SEM microphotographs. The crack formation, large particle separation and resulting third body effect were significant in room temperature ambient condition. The protective nature of the tribologically transformed layers coupled with non-uniform contact results in the lower wear coefficient while smooth wear scar and extensive abrasion produces higher wear volume in the other condition.