| Inconel718 alloy has excellent fatigue resistance,corrosion resistance and oxidation resistance at 650 ?,which is widely used in various parts of aerospace.However,with the upgrading of aerospace equipment,higher requirements have been put forward for its friction and wear properties.In order to improve the friction and wear properties of Inconel718 Alloy,Ultrasonic Roller Burnishing(URB)technology was used.Based on the poor plasticity of high-strength alloy,the temperature field and ultrasonic burnishing was used to strengthening,namely Ultrasonic Roller Burnishing Coupled with Warm Treatment(URB/WT),to further enhance the surface strengthening effect of Inconel718.The surface morphology and roughness,microhardness,grain size and residual stress were selected as the characteristic parameters of surface integrity.The influence of URB/WT technology on the final formed surface integrity of Inconel718 was studied by comparing the traditional finish turning and normal temperature URB processing.On this basis,the influence mechanism of the three processing technologies on the yield strength,creep behavior,friction and wear resistance of the specimens was further studied.The main research contents and conclusions are as follows:(1)The effects of traditional finish turning,URB and URB/WT treated on the surface integrity of Inconel718 alloy were studied.The surface integrity of the specimens by different processes were measured and compared.The results show that,in the experimental range,URB and URB/WT can improve the surface integrity characteristic parameters of the specimens in different degrees compared with the turning specimens.At the same time,the surface strengthening effect of URB/WT is better than that of URB.Similar to shot peening and other mechanical surface strengthening technologies,Sever Plastic Deformation(SPD)is the main strengthening mechanism of urb and URB/WT processes.In the process of URB/WT,the temperature field and the ultrasonic vibration field act on the processed material together,which further reduces the difficulty of material deformation.Therefore,the greater plastic deformation is achieved under the same static pressure,which is the main reason for the better process effect.(2)Based on the finite element analysis method,the internal stress-strain field of material during URB and URB/WT processing is analyzed.The finite element analysis model of Inconel 718 ultrasonic rolling burnishing was established.The accuracy of the model was verified by comparing the experimental data.The stress propagation and instantaneous stress-strain distribution in the material during the processing of the two strengthening processes were compared and analyzed.Compared with the conventional rolling process,the application of high-frequency mechanical vibration significantly changes the internal stress propagation behavior of the material during the URB machining process,which makes the internal stress propagation of the processed material present the characteristics of oscillation and propagation in depth.At the same time,during the URB/WT processing,the oscillating stress wave will form and propagate faster from the inside of the material.on the other hand,the theory of oscillating stress wave can explain the better surface strengthening effect of URURBB/WT.In other words,the oscillating stress wave is the expression of ultrasonic plasticity.In URB/WT processing,the assistance of temperature field can enhance the effect of ultrasonic plasticity and further reduce the deformation resistance of the processed material.The results of stressstrain field analysis also show that the equivalent plastic strain of URB/WT specimens increases and the thickness of deformation layer increases compared with that of URB specimens.(3)Based on nanoindentation test,the yield strength and creep properties of different processed specimens were calculated and analyzed.The P-h curve was measured and the yield strength of different specimens was calculated by reverse analysis.The creep stress index is calculated by the logarithmic curve of hardness-creep strain rate.The results show that the yield strength of turning specimens,URB processed specimens and URB/WT processed specimens are 872.41 MPa,974.78 MPa and 997.46 MPa respectively,which means that the yield strength of the two kinds of strengthened specimens are significantly improved.Meanwhile,the creep stress index calculation results also show that the creep resistance of URB/WT processed specimens is the best.The increase of mechanical properties of the two strengthened specimens is the result of the improvement of surface integrity.With the increase of microhardness,the plastic flow of the material in service decreases and the deformation resistance increases.Meanwhile,the compressive stress layer introduced on the surface and subsurface of the material during the strengthening process is also beneficial to avoid stress concentration and reduce crack propagation.(4)The effects of different strengthening processes on the friction and wear of specimens at room temperature and high temperature was studied.By using the experimental method,the friction coefficient,wear morphology,wear amount and wear rate of different specimens at normal temperature and high temperature(600°C)were measured and analyzed,and the wear mechanism was analyzed.The results show that the friction coefficient and wear rate of URB and URB/WT specimens are lower than those of the ordinary finish turning specimens under normal temperature,and the wear mechanism is abrasive wear.Compared with URB processed specimens,URB/WT processed specimens show better wear resistance.Under the condition of high temperature friction,the experimental results are consistent with those at room temperature.However,in terms of wear mechanism,the fine turning specimens show severe abrasive wear and oxidation wear,while the URB and URB/WT specimens mainly show oxidation wear and abrasive wear.The good friction and wear behavior of URB/WT specimens depends on their better surface integrity and mechanical properties. |
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