High Temperature Erosion Characteristics Of GH4738 Alloy Affected By Long-term Service

During long-term service,the hot-end components of aero-engine will experience damage behaviors such as high-temperature oxidation,creep,and erosion.Based on the actual service conditions of the hot-end components(compressor,turbine rotor)under long-term service,using GH4738 superalloy prepared by the vacuum induction and electroslag remelting process as the research object,we designed an accelerated alternating high-temperature erosion-oxidation simulation test for the long-term service samples.And then,combined with surface analysis techniques such as scanning electron microscope,transmission electron microscope,X-ray diffractometer,and metallographic microscope,as well as mechanical performance tests such as room temperature hardness test and high-temperature hardness test,we studied the damage behaviors of long-term high-temperature oxidation/erosion,and high-temperature creep/erosion,to provide theoretical support for actual damage assessment.The growth pattern of the oxide layer during long-term high-temperature oxidation of GH4738 alloy and its different oxidation forms are systematically analyzed.The long-term high-temperature oxidation experiment is divided into three stages for analysis:initial stage(50-200h),middle stage(250-650h),and final stage(700-1000h).it shows that in long-term high-temperature oxidation,the initial oxide layer is mainly composed of four kinds of oxides of Cr₂O₃,Al₂O₃,Ti O₂,and Ni O.Ni Cr₂O₄ spinel-like oxide occurs in the middle term,and in the final stage,there have no new oxide components.The average thickness of the oxide layer formed on samples during the 0-650h high-temperature oxidation increased by approx.6.52?m.In comparison,the average thickness of that during 650-1000h decreased to 5.50?m.In addition,some delamination occurred on the oxide layer of the sample during350-1000h.Then,the high-temperature erosion experiment was carried out for the long-term high-temperature oxidized specimens,and the variation rule of its erosion rate was analyzed.It finds that the high-temperature erosion rate of the original sample is 0.0447 cm³/kg.In 0-150h interval of high-temperature oxidation,the erosion rate of the specimen increased by33.6%,and at 200h,its erosion rate decreased by 5.7%.In 200-400h intervals,the erosion rate increased by 11.9%.However,in 400-600h intervals,the sample's erosion rate fluctuated steadily around 0.0605 cm³/kg on average.Then,the erosion rate decreased by15.9%during600-700h.At 750h,the erosion rate increased by 10.5%.While in 750-950h intervals,it dropped sharply by 22.2%,and the erosion rate at 1000h increased again by 24.8%.The correlations of hardness near the worn surface,the density,continuity,and thickness of the oxide layer to its evolution law of oxidation wear are analyzed.The results show that the oxide layer of the sample characterized poor compactness and continuity initially,and its average thickness is also thin.In the middle stage,the average thickness of the oxide layer has increased,but its continuity and compactness are still lacking.The hardness of the original specimen was 392 HV.The hardness of the high temperature oxidation 0-150h sample decreased by 16.9%,and at 200h,the hardness increased by 11.5%.In 200-400h intervals,the hardness dropped by 8.4%.In 400-550h intervals,the hardness fluctuated steadily around 336 HV on average.Then,in 550-650h intervals,the hardness of the sample dropped by 9.3%.Therefore,the oxide layer of specimens during the initial and mid-stage has little resistance to high temperature erosion,and the changing trend of high temperature erosion rate is consistent with the hardness.In the final oxidation stage,the hardness of the sample fluctuates steadily around 306 HV in the 650-850h interval,and the hardness of the specimen drops by 2.5%at 900h,the hardness of the specimen in 900-1000h interval fluctuates steadily around 295 HV on average.That is,the hardness at the final stage changes little.However,although the thickness of the oxide layer at 700-950h interval decreased by 1.02?m,its density and continuity increased strongly.This phenomenon is consistent with the change in the high-temperature erosion rate,indicating that the increase of the densification and continuity of the oxide layer improves the wear resistance and reduces erosion rate.In addition,the reason for the rise in the high-temperature erosion rate at 1000h is that the overall oxide layer cracked at 1000 hours,making the resistance to high-temperature erosion became weak so that the high-temperature erosion rate rebounded.In addition,in the high-temperature creep-erosion experiment,the crystal grains,dislocation forms,and hardness changes of the high-temperature creep samples are studied,and the damage mechanism of high-temperature creep-erosion is analyzed.The results show that the final erosion rate of the specimen is 59.0%higher than that of the original specimen.The reason is that the grain orientation of the high-temperature creep specimen is consistent with the direction of the loading force,and there are a large number of parallel dislocations,which accelerates the generation of plastic deformation;At the same time,the increase of subgrain boundaries reduces the interface energy and increases the possibility of grain fracture.What's more,the hardness is reduced by 10.2%compared with the original sample,which further accelerates the damage caused by high-temperature erosion.