Study On The Fretting Behavior Of Tc4Titanium Alloy And Its Shot Peening Treatment

TC4titanium alloy has been widely used in aviation structure, however, the fretting wear damage becomes more and more serious and has become one of the main obstacles of its application. The fretting wear and fretting fatigue behavior of TC4titanium alloy before and after shotpeening treatment have been studied. This paper mainly studied four aspects:(1) The fretting wear behavior of TC4titanium;(2) The fretting wear behavior of TC4titanium after shot peening treatment;(3) The fretting fatigue behavior of TC4titanium;(4) The fretting fatigue behavior of TC4titanium after shot peening treatment. The results were as follows:Under the stationary normal load, with the displacement amplitude increasing from20μm to150μm, the fretting wear regime access to partial slip regime, mix slip regime, slip regime respectively. In the partial slip regime, only at the edge of wear scar has slightly damage; in the mix slip regime, due to the stress distribution at the contact surface was inhomogeneous, the wear mechanism in the centre of the wear scar was adhesive wear, but the edge of the scar was in slip regime, and the damage was serious than any other parts of the scar; in the slip regime, the wear damage was serious, and due to the adhesive wear and accommodation of wear debris, the friction coefficient had a large fluctuation.The wear mechanism of TC4titanium included delamination wear, oxidation wear, abrasive wear, and adhesive wear, and in different fretting wear stage, different wear mechanism occupied a leading role. At the early stage of fretting wear, the wear mechanism was plastically deformation and adhesive wear; at the later stage of fretting wear, the mechanism was delamination wear, a large number of wear debris was produced and oxidized, wear debris prevented the direct contact of friction pair, the mechanism changed from adhesive wear to abrasive wear and oxidation wear.The wear volume of TC4titanium increased with the increasing of cycles, normal load, displacement amplitude; but the wear volume decreased with the increasing of frequency. Shot peening treatment had little influence on the friction coefficient under different conditions, because of the shot peening treatment leaded to the increasing of roughness, and the friction coefficient of shot peening specimen increased a little, also because of the shot peening treatment leaded the increasing of surface brittleness, the wear volume of treated specimen was greater than untreated ones. The existence of the fretting wear greatly reduced the fatigue life of TC4titanium alloy. Residual stress layer formed at the surface of TC4titanium by the shot peening treatment, which greatly improved the conventional and fretting fatigue life.Fretting fatigue fracture morphology of TC4titanium included crack source zone, fatigue propagation zone, fatigue fracture zone. The crack source zone was the wear scar caused by fretting wear, and the stress gradient and stress concentration in the fretting wear promoted the crack initiation. After crack initiation, wear occurred between the two parts of fracture surface under the fatigue load, and there were obvious wear scar and wear debris in the crack source zone. Typical fatigue striation and secondary crack formed in the fatigue propagation region, also the borderline between the fatigue propagation zone and fatigue fracture zone could be seen very clear. The fracture morphology of fatigue fracture zone was dimple fracture, but at some conditions, the fracture morphology of fatigue fracture zone was quasi-cleavage fracture.