The Effect Of Ultrasonic Surface Rolling And Plasma Nitriding On Organization And Performance Of Inconel 690TT Alloy

Steam generator becomes an indispensable part of PWR nuclear power plant,and heat transfer in primary and secondary loop is completed by heat transfer pipe in steam generator.Since the advent of PWR nuclear power plant,the heat transfer pipe material by austenitic 304 stainless steel,Inconel 600 alloy,Incoloy 800 evolution,finally determined to applied Inconel 690TT,whose corrosion resistance performed well in high temperature,as the third generation of heat transfer pipe material.However,the wear resistance of Inconel 690TT alloy can not fully meet the service requirements of PWR nuclear power plants.Therefore,this paper focuses on the above problems and aims to explore a new process to improve the performance of Inconel 690TT.Ultrasonic surface rolling and plasma nitriding technology are applied on the surface of Inconel690TT alloy to explore the change of wear resistance of materials after single and composite treatment surface modification,and the following results are obtained:(1)According to the results,the influence of different static pressure,current,feed rate and rolling reduction on the surface morphology and hardness of Inconel 690TT alloy in ultrasonic surface rolling process,the optimal morphology shows different static pressure,current,feed rate and rolling reduction are 0.5 MPa,0.5 A and 1500mm/min,and the rolling reduction is decided as the main investigation parameters.Therefore,the effects of ultrasonic surface rolling treatment on the microstructure,mechanical properties and wear resistance of Inconel 690TT alloy with the rolling redution values of 0.2 mm,0.4 mm and 0.6 mm were studied.Compared with the surface hardness of the untreated Inconel 690TT sample,the surface hardness of the 0.2mm,0.4 mm and 0.6 mm samples is increased to 337 HV0.05,363.75HV0.05 and382.4HV0.05,respectively.When the pressure is 0.2 mm.The elongation and tensile strength of the untreated samples are 100.53%and 424.68MPa,respectively.While the elongation of the pressed samples of 0.2 mm,0.4 mm and 0.6 mm are 47.53%,30.3%and 27.68%,respectively.However,the tensile strength increased by 558.57 MPa,704.17 MPa and 814.58 MPa,respectively.The XRD peaks and peaks of the samples with different rolling reduction keep the same,and the diffraction intensity and half-peak width are change.According to the Debye-Scherrer formula,the average nano-grain sizes of the samples with 0.2 mm,0.4 mm and 0.6 mm are 25.6nm,22.0nm and20.7nm,respectively.The nano grains of the severely plastic deformed layer are consisted of ultrafine twin nano grains,twin nano grains,lamellar nanocrystals and equiaxial nanocrystals.The wear resistance test results of different pressure-downs show that compared with the volume wear and volume wear rate of untreated samples,the pressure-downs of 0.2 mm samples decrease to 76.14%.The pressure-downs of 0.4mm and 0.6 mm samples increase to 250%and 344.44%,respectively.The wear mechanism is oxidation wear,fatigue wear and abrasive wear.Therefore,ultrasonic surface rolling treatment has the best wear resistance improvement effect when the reduction amount is 0.2 mm sample.(2)The best gas ratio and air pressure have been determined.The optimal nitriding temperature and nitriding time are determined by the surface hardness of samples at different nitriding temperatures and times.The effect of gradient nanostructure on the wear resistance of Inconel 690TT alloy is better than that of other different nanostructures.Finally,400?+8 h is determined as the best nitriding temperature and time.The thickness of nitriding layer of plasma nitriding sample and composite surface nitriding sample is 4.4?m and 5.2?m,respectively.Compared with the wear volume and wear rate of untreated Inconel 690TT samples,plasma nitrided samples and composite surface treated samples were only 1.75%and 0.72%of untreated samples,respectively.Plasma nitriding can greatly increase the surface wear resistance of the alloy.The wear mechanism can not change with the process change,which are oxidation wear,abrasive wear and fatigue wear.(3)Study on fretting wear behavior of Inconel 690TT alloy surface by using ultrasonic surface rolling,plasma nitriding and composite surface treatment.The results show that the surface hardness of untreated samples is 195.1HV0.05,the surface hardness of ultrasonic surface rolling,plasma nitriding and composite surface treatment is 337HV0.05,498.5HV0.05 and 588.6HV0.05,respectively,and the surface hardness is greatly increased.Compared with the XRD peak intensity and the position of the diffraction peak of the untreated samples,the XRD peak of plasma nitriding and composite surface treatment showed that a new phase-?_N was produced.Compared with the untreated sample wear volume and wear volume rate,composite surface treatment,plasma nitriding and ultrasonic surface rolling were respectively to reduce the wear rate to 73%,70%and 84%.The results show that the composite surface treatment has the best improvement effect on fretting wear behavior of Inconel 690TT alloy,followed by plasma nitriding treatment and ultrasonic surface rolling treatment.The wear mechanisms of the four samples are oxidation wear,fatigue wear and adhesion wear respectively.