Titanium Alloy Under High Temperature Fretting Fatigue Behavior And Surface Treatment Technology Research

Weak anti-abrasion property of titanium alloys can bring about early fracture of compressor blade tenon made from titanium alloys during working process because of Fretting Fatigue (FF), so it has become one of the main factors which affect the safe application of titanium alloys at room temperature and elevated temperature in aviation engine. It is important to improve FF resistance of titanium alloy in aeronautic industry and other fields. Due to the complexity of FF loading, FF mechanism is still not quite clear. The trial-and-error approach is usually used to find a way against FF in a given situation. In addition, investigations in FF tests have used different methods. In accordance with above-mentioned problems, an appropriate method of FF is designed by thinking the key annuluses which influence FF behavior of titanium alloy at elevated temperature. The mechanism of FF is discussed by studying the effects of major testing factors. The effects of the three factors of shot peening (SP) and surface coating on fretting fatigue resistance (FFR) are studied through evaluating surface treatment technique and the properties of surface coating. The main contributions are as fellows:(1) The effects of major testing factors, including slip amplitude, contact pressure and temperature, are investigated in the present study. The results indicate that the life of FF is changed non-monotonicly with increasing slip amplitude or contact pressure. Because slip amplitude and contact pressure affect the action of fatigue and wear in FF process, result in the change of crack initiation probability and crack propagating rate. Because the role of oxide etch is aggravated by elevating temperature, the deforming resistance of titanium alloy falls down and creep occurs and the fatigue property of materials is worsening.(2) Shot peening is the most efficient way in improving FF resistance of titanium alloys at room temperature. Working hardening, roughening and compressive residual stress are involved in the shot peened surface. There are different viewpoints on how the three factors of SP work at elevated temperature. The effect of SP on the fretting fatigue behavior of titanium alloys is studied in this paper by separating the three factors of SP. The major part of the three factors of SP for improving FFR at elevated temperature is compressive residual stress, which arrests the crack into closure. The role of working hardening is secondary. The effect of roughening for improving FFR at elevated temperature is bad, which is related with the state of compressive residual stress.(3) The effect of a new kind of surface treatment technique (IBED CrMo and OCr18Ni9 coating) which can be combined with SP on FFR of titanium alloys at elevated temperature has been studied. The properties of the modified surface have been evaluated by X-ray diffraction, SEM, optical spectrum analysis. The results indicate that ion beam enhanced deposition (IBED) can produce coating which has high density, small grain size, small void radio, good bonding strength. But the hardness of IBED CrMo coating is high with poor ductility and the coating is brittle. So the coating is easily broken when fatigue is major factor in the process of FF. Cracks can enter the bulk material quickly so that the FFR of titanium alloy is reducing. IBED CrMo coating combined with SP can not achieve the purpose of improving the FFR of titanium alloy.