| As the first choice of aerospace materials,superalloy plays a very important role in the development of modern aviation industry.The use of superalloy requires the formation of a stable and protective oxide under high temperature service conditions,and requires that the oxide can prevent further oxidation of the alloy.Therefore,it is very necessary to study the high temperature oxidation behavior and oxidation resistance of nickel base superalloys and high niobium superalloys,it provides reliable guarantee for alloy application at higher temperature.In this paper,the laboratory equipment was used to simulate the temperature and atmosphere environment of alloy in the actual service process,characterizes the changes of phase,hardness,quality and roughness of alloy under different oxidation conditions,constructs the oxidation behavior characteristics of two kinds of alloy,provides important experimental parameters for the practical application and in-depth study of alloy,its specific research content was follows:（1）Firstly,the high temperature oxidation behavior of nickel-based superalloy was studied.The oxidation layer did not fall off during the cyclic oxidation for 10 h in the air environment of 700℃～1100℃,and the alloy belonged to the complete oxidation resistance level below 1000℃.At the early stage of oxidation,local oxides are mainly Cr2O3 and Ni O,and later Ni Cr2O4 and Si O2 will be formed.At 1000℃and above,the diffusion rate of Cr ion in Cr2O3 layer increases,promoting the formation of continuous compact Cr2O3 oxide film on the surface.With the increase of oxidation temperature,the thickness of continuous oxide layer increases from 0.29μm to 2.84μm.Its hardness values fluctuate in the range of 215 HV～238HV.Alloy at 1200℃in air environment circulation after 1 h oxygen oxidation,oxidation layer on the surface of the alloy has clearly fall off,but still can be observed in continuous oxide layer thickness from 28.38μm to 82.89μm growth.The oxidation products were mainly Cr oxides and a small amount of Ni O and Si O2.At the initial stage of oxidation,the hardness decreases greatly,but as the cycle oxidation time increases to 40 h,new oxides were formed on the surface of the alloy,and there was a lot of Cr2O3 with high hardness,so the hardness of the alloy begins to rise slowly.（2）Subsequently,the high temperature oxidation behavior of high niobium alloy in the air environment was studied.After the cyclic oxidation at 600℃～800℃and the cyclic oxidation at 700℃,the oxide layer did not fall off.The local oxides formed in the early oxidation stage were mainly Ti O2,Al2O3,Nb2O5,Al Nb O4,etc.With the increase of oxidation temperature,cross section thickness of oxide layer increases by 0.24μm to 0.78μm,change trend consistent with increased weight per unit area.The overall hardness of the oxidized alloy surface was slightly higher than that of the matrix,and fluctuates in the range of 378.66HV～407.25HV.10 h～110 h after 700℃circulating oxidation,oxidation layer thickness from 0.31μm to 1.42μm growth.On the dynamics,increase weight per unit area follows the parabola change rule,oxidation rate constants of Kp=6.6877×10-4(mg2·cm-4·h-1),belongs to the level of antioxidant.At high temperature oxidation,oxides with higher hardness will be formed continuously.Solid solution strengthening of alloying elements and grain refinement at high temperature lead to slight increase of alloy hardness.（3）Finally,the high temperature oxidation behavior of high niobium alloy at different oxygen partial pressures was studied.The local oxides formed by the alloy at 700℃for 50 h were mainly Ti O2,Al2O3,Nb2O5,Al Nb O4,etc.The surface roughness increases with the increase of oxygen partial pressure.Cross section thickness of oxide layer gradually increases from 0.71μm to 0.97μm.The hardness of the sample has no great change and was slightly higher than that of the alloy matrix. |
PDF Full Text Request