Fretting Wear Behavior Of NC30FE Nickel-Based Alloy Under Alternating Load Conditions

Steam generator (SG) tube is a key component of nuclear power heat exchanger equipment, whose fretting wear had seriously affected the operation safety of nuclear power plants. The research on the fretting wear test of the heat exchanger tube under alternating loads and different environment conditions is not only of significance to explore the complex fretting wear characteristics and damage mechanism under special conditions, but also can provide theoretical supports and practical guides for the operation safety of nuclear power.The fretting wear test of NC30Fe alloy and Incone1690alloy respectively in contact with solid cylindrical sample1Cr13has been investigated under alternating load conditions in this paper. The experiment have been carried out under the following conditions: tangential displacement amplitude range at100μm,150μm and200μm, tangential fretting frequency at2Hz, cycle number at20000times, normal rated loads at20N,50N and100N, normal excitation force at Fnl=16sinωt(N), normal excitation frequencies at10Hz and50Hz, test environments at25℃in air,300℃in air and300℃in nitrogen. Based on the test data the fretting wear characteristics and damage mechanism of NC30Fe alloy and Incone1690alloy under alternating loads have been studied by using optical microscopy (OM),3D/2D dual-mode profilometer, scanning electron microscopy (SEM) and some other microscopic analysis tools. The main research conclusions are listed as follows:Compared with the fretting wear characteristics under the same conditions, worn surface damage of NC30Fe alloy was turned to be much more serious. NC30Fe alloy wear scar surface morphology appeared as blocks which leaded to bigger peeling pits. Incone1690alloy surface spalling damage was relatively minor which looked like flaky peeling in the shape of smaller pits.The comparison on wear scar cross-section morphology was carried out under the same conditions. The result is that the debris layer of wear scar cross-section of Incone1690was more thicker, which accumulated more alternating excitation energy so as to buffer and protect the materials beneath the layer. Therefore, the accumulated damage of Incone1690 was relatively slighter as well as the fatigue spalling degree on wear scar surface.The numerical analysis of the contact pair was processed under Ansys. It focused on the study of Mises stress situation of the same point which locateed on the contact surface or the area beneath the surface, respectively under the situation of static loads and dynamic loads. It was proved that the stress amplitude of material was greater.Under alternating load conditions, the alternating stress amplitude imposed on the material became stronger. Therefore, the alternating excitation energy was accumulated in the contact area, thermal disturbance became obvious and accumulated damage became serious. The micro-crack initiation and propagation were easier to emerge beneath the contact surface with certain degree of depth and it finally led the material to peel off so as to develop into spalling pits. So the fatigue spalling became more obvious and extended as the main damage form during the middle and late of the fretting stages.