Research On Fretting Wear Of TC4 Alloy In Corrosion And High Temperature Environment

TC4 titanium alloy has excellent performance and is widely used in the manufacture of aero-engine and steam turbine blades.However,TC4 titanium alloy is soft and has poor wear resistance,which makes the connection structure of the blade and rotor prone to micro-movement damage.According to statistics,20% of aero-engine accidents and 30% of steam turbine accidents are caused by the failure of mortise and tenon structure.Up to now,there is still a lack of comprehensive and in-depth understanding of the fretting wear behavior and damage mechanism of TC4 titanium alloy.Therefore,it is of great theoretical significance and engineering application value to study the fretting wear behavior and mechanism of TC4 titanium alloy in different environments.In this paper,optical microscope,laser confocal microscope,scanning electron microscope,micro-area X-ray diffractometer,X-ray energy spectrometer,Raman spectrometer,electrochemical workstation and other means were used to characterize and detect the surface,profile morphology,elements,and electrochemical changes of the wear trace.By establishing a simplified model,the fretting wear behavior of TC4 titanium alloy under different environments and working conditions was systematically studied,and the fretting wear mechanism and tissue damage mechanism were discussed.The following results were obtained.:(1)In air environment,with the increase of displacement amplitude,the fretting region of TC4 titanium alloy changes from partial slip region to mixed region and finally to complete slip region;while with the increase of normal load,the fretting region changes from complete slip region to mixed region and partial slip region.In the partial slip zone,the friction coefficient is small and stable,and the structure of adhesive zone and micro-slip zone is obvious on the surface.The fretting damage of material structure mainly occurs in the micro-slip zone dominated by oxidation wear,adhesive wear and fatigue wear.In the mixed sliding mode,the adhesive zone disappears,and the micro-sliding zone occupies the whole wear mark surface,which is mainly dominated by oxidation wear and fatigue wear,accompanied by serious wear debris accumulation.In the mode of complete slip,the friction coefficient fluctuates sharply and the wear volume increases sharply.The evolution of wear debris has more obvious influence on the fretting process,and the wear mechanism changes into oxidation wear,abrasive wear and fatigue wear with slight adhesion wear.(2)In pure water environment,the influence of displacement amplitude and normal load on fretting running area of TC4 titanium alloy is consistent.In pure water medium,due to the lubrication and cooling effect of water medium,the occurrence of adhesive wear is inhibited and the friction coefficient decreases significantly;The existence of water medium is conducive to the occurrence of abrasive wear,with a significant increase in wear volume and a deep wear profile;Corrosion and wear ratio of the interaction of the negative and the proportion is very mild,shows that the conductivity of pure water is poor,almost no corrosion effect,only the role of lubrication,TC4 alloy material erosion is mainly caused by mechanical wear and abrasive wear.(3)In seawater environment,TC4 titanium alloy has only mixed slip and complete slip operation modes under the same experimental conditions,without partial slip mode;In seawater,chloride lubricating film is formed in the friction process of Cl-in solution,so that it has better lubrication performance than pure water,and the friction coefficient is further reduced.Under the joint influence of mechanical action and Cl-penetration,the material loss is intensified,and the wear volume is further increased compared with pure water.The complex "positive" interaction between wear and corrosion is reflected,and the wear mechanism is mainly abrasive wear and corrosion wear.(4)In the high temperature environment,the friction coefficient and wear volume of TC4 titanium alloy decrease to different degrees and increase with the increase of temperature.Compared with the normal temperature environment,high temperature is conducive to the formation of oxidized wear debris layer,which effectively blocks the direct contact between friction pairs and reduces the degree of wear.The wear mechanism is mainly oxidation wear and adhesive wear.(5)Compared with TC4 titanium alloy,the friction coefficient and wear volume of LSP-TC4 alloy are significantly reduced,and adhesive wear and oxidation wear are in a dominant position,there are no obvious material delamination is found.Laser shock strengthening can cause high-density dislocations on the surface of TC4 titanium alloy,form nanocrystalline layers with high strength and hardness and introduce a large amount of residual compressive stress,it can effectively inhibit the initiation and propagation of fretting cracks and improve the fretting wear resistance of titanium alloy,which is an easy and effective strengthening method.