| Hydrogen-induced plastic damage and vibration fatigue fracture are the typical failure modes of titanium alloy components in deep sea service.As an emerging surface treatment process,laser peening(LP)can effectively prolong the vibration fatigue life of key metal structural parts in a marine hydrogen-rich environment by inducing stress strengthening and tissue strengthening effects.In this paper,TC4 titanium alloy was taken as the research object.The combination of theoretical analysis and experimental research was used to study the effect of LP on the residual stress,microstructure,modal parameters,vibration fatigue performance and fracture morphology of hydrogen-charged samples.The mechanism of hydrogen embrittlement resistance and vibration fatigue life extension of TC4 titanium alloy hydrogen filled samples strengthened by LP is deeply analyzed.The main work is as follows:(1)Based on the hydrogen embrittlement mechanism of titanium alloys,the analysis of residual compressive stress,grain refinement of the two-phase structure and different dislocation structures were used to study the mechanism of hydrogen embrittlement resistance of titanium alloys by LP.In addition,comprehensively considering the influencing factors of natural frequency and damping ratio,the mechanism of the effect of LP on the fatigue limit,fatigue crack growth threshold and stress intensity factor of hydrogen-charged samples was explored.The relationship between the total life of the hydrogen-charged vibration fatigue samples after LP is derived,and the mechanism of anti-vibration fatigue life extension in the hydrogen-rich environment of LP was revealed.(2)The effect of laser peening TC4 titanium alloy sample surface integrity was studied.The laser peening test,the electrochemical hydrogen charging test and the nano-indentation test were carried out respectively to analyze the residual stress distribution,microstructure evolution,nano-hardness and elasticity of the surface and depth direction of different laser peening power density on the surface and depth direction of the hydrogen-charged sample The influence of modulus.The results show that the value of residual compressive stress and the depth of its influence layer increase with the increase of laser power density;after laser peening,the ?-phase and ?-phase grains are refined,the dislocation density increases,and the hydrogen concentration per unit grain boundary decreases The number of hydrogen capture sites increases;the nano-hardness value,the depth of the affected layer,and the elastic modulus increase with increasing laser power density.The TC4 titanium alloy's resistance to hydrogen embrittlement,fatigue limit and crack growth threshold are worth improving.(3)The modal parameter test and vibration fatigue test of typical TC4 titanium alloy vibration fatigue standard samples were carried out to analyze the vibration fatigue fracture morphology(crack initiation zone,crack propagation zone and crack transient fracture zone).The test results show that the natural frequency and damping ratio of the TC4 titanium alloy hydrogen-charged sample increase with the increase of laser power density.After LP,the vibration fatigue life of hydrogen-filled specimens increased significantly.LP promoted the initiation of fatigue crack initiation of hydrogen-filled specimens from the surface to the interior of the specimen,reducing the size of the quasi-cleavage surface in the crack initiation area;As the laser power density continues to increase,the fatigue band spacing in the fatigue crack growth area continues to decrease,and the crack propagation path is more tortuous;the craters in the transient fracture area become larger and deeper,showing better fracture toughness. |
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