The Experimental And Simulation Study Of Wear-Corrosion Characteristics Of TC4 Alloy

With the rapid development of China’s aerospace industry,the use of crucial components made from TC4 alloy in extreme environments has significantly increased.Although TC4alloy has excellent mechanical properties,it has poor wear resistance.Moreover,the components regularly suffer from wear,corrosion,fatigue damage,and other damages,which severely threatening the safety and reliability of aircraft devices.Therefore,researching on the failure mechanisms of TC4 alloy,reducing the wear of components,and improving component service life have become key problems waiting to be solved in the aerospace field.The frictional wear mechanism of the TC4 alloy was studied under different service conditions using the Anton Paar TRB³ pin-disk frictional wear tester.The frictional wear mechanism of the alloy GCr15/TC4 was investigated under four different service conditions,including dry friction,distilled water,artificial seawater,and artificial acid rain.The corrosion-wear interactions and wear mechanisms of three water-based mediums were investigated.To investigate the formation mechanism of the plastic deformation layer and the damage mechanism of the contact cross-section,the relationship between cracking and wear at the wear cross-section was investigated.The influence of hardness and counterpart materials on TC4 alloy frictional wear was investigated using four coupled balls（GCr15,TC4,Si₃N₄,Al₂O₃）with TC4 alloy specimens to discover the evolution of the contact interface and wear debris during the wear process.Aimed to study the frictional wear mechanism,behavior,and evolution of GCr15/TC4 under different normal loads and cycles,the finite element method（FEM）was used to characterize the wear mechanism.The wear model based on frictional dissipation energy was established.The variable friction coefficient and realistic slip distances coupled with modified FEM element,and accelerated calculations were used in the model to improve the accuracy of the model.The evolution of cracks was investigated by the development of Abaqus with fluid penetration into the cracks.A two-dimensional crack fluid-filled model for disc-plane contact was established to explore the influence of fluid on crack propagation in different geometries.The major research components and results of this paper are shown as follows.The dry friction wear experiments show that the friction coefficient curve of GCr15/TC4in the initial stage rises sharply and then decreases rapidly.The mean friction coefficients in the stable phase were found to be 0.35,0.47 and 0.57 for loads of 2 N,4 N and 10 N,respectively.Furthermore,the wear volume exhibited a linear increase with the increase of loads and cycles.The wear mechanism at the edge of the wear scar is abrasive wear and adhesive wear,while the center shows abrasive wear,adhesive wear,and fatigue peeling,which are accompanied by plowing and oxidation.The typical adhesive wear and plastic deformation layer appears at the wear cross-section edge,and cracks propagate to the centeral wear scar.The crack propagation direction in the bottom plane of the wear scar is primarily parallel to and vertical to the contact interface.When the wear rate exceeds the crack growth rate,the wear reduces crack propagation,whereas the crack propagation promotes wear.The wear mechanism of the four friction counterparts（TC4/TC4,GCr15/TC4,Si₃N₄/TC4,and Al₂O₃/TC4）is adhesive wear and abrasive wear at the wear edge,while abrasive wear,adhesive wear,and fatigue peeling are combined in the center of the wear scar.With the increase of elasticity factor and load,the cutting plasticity ratio increases as well as the abrasive wear gradually dominates the wear,and the microscopic damage mechanism of the wear interface is dominated by micro-cutting and followed by micro-plowing.Significant central wear and edge scratches occur on the wear scars of the GCr15,Si₃N₄,and Al₂O₃ balls,whereas the wear planes appear on the TC4 ball with the greatest area of wear scars.The size and elemental distribution of wear debris under the four friction counterparts are different.The flaky debris of GCr15/TC4 is caused by the peeling of GCr15 balls,however,the flake debris of the other friction counterpart are the oxidation of the wear debris during the wear process.Powdered debris and flake debris can reduce wear,however,abrasive particles formed by small size debris can accelerate wear.The wear mechanisms of GCr15/TC4 in three water-based mediums are different.Adhesive wear dominates wear in distilled water,fatigue delamination is most serious in seawater,and abrasive wear is most significant in acid rain.The friction coefficients of seawater and acid rain are slightly lower than distilled water.The length,width,and depth of wear scars in acid rain are greater than that of seawater and water.The wear volume of TC4alloy in acid rain is higher than in seawater,and it increased linearly with the cycles and loads increases.It reveals that GCr15/TC4 is the most sensitive to acid rain and suffers the most serious damage.The TC4 alloy corrosion wear interaction ratios in the three mediums are listed in decreasing order by acid rain,saltwater,and distilled water trends.The TC4 alloy material loss in water is driven by mechanical factors,while in seawater and acid rain it is dominated by the interaction of corrosion-wear and mechanical factors.As the load increases the lubrication ratio in distilled water decreases,as the mechanical factors influence the wear.Serious oxidation and corrosion of GCr15 balls occur in three mediums,but the wear of the spherical surface is lower than dry friction conditions,while the loss of spherical material is dominated by corrosion.The wear profiles of FEM and experiment are in approximate agreement,and the maximum errors of wear depth and width are less than 15%.It shows that the finite element model is in good agreement with the experimental results.The maximum contact pressure between the contact interfaces of the GCr15/TC4 friction counterpart increases with the cycles increases,however,it decreases with the normal loads increase.With small loads or low cycles,the contact interface deforms plastically in the local region,but enters completely plastic deformation for large loads or high cycles.As the load increases,the accumulated plastic deformation at the contact interface becomes more severe,and the accumulated frictional dissipation energy increases.When the contact stress states are elastic,the wear between the friction interfaces are dominated by material shear.The contact state is plastic when the load raises to 10N,the wear is dominated by plasticity at this moment.The plastic deformation and material loss ratio of GCr15/TC4 is negatively related to the cycles,but positively related to the loads.An increase in the density and height of the micro-convex body enhances the fatigue effect of the contact surface,while the maximum principal stress and tangential stress at the contact surface show a trend of rising and then slightly decreasing.A cavity structure is formed by the contact surface of the crack surfaces and the disc plane.The movement of the disc deforms the crack surface and decreases the volume of the cavity increasing the pressure inside the cavity,which accelerates the propagation of the surface crack under the high pressure of the cavity.The cavity formation,sealing,leakage,and the cavity failure consist of the fluid filled process.The pressure of the cavity is less than the maximum pressure of the circle-plane at the crack mouth.The fluid pressurization effect is significantly enhanced with the increase of crack geometry,and the crack propagation mode transforms from II to I with the increase of crack length and width.In the case of long cracks,the dynamic self-sealing and leakage phenomenon occurs when the liquid leakage from the cavity.Lubricating medium and frictional motion have less influence on the crack propagation mode,but the stress intensity factor of the sliding condition is larger than the rolling condition.