Study On The Oxidation Behavior Of TiAl Based Multielement Alloys In Different Environments

TiAl-based alloys are widely used in aerospace and gas turbine engines due to their low density,high strength and excellent high temperature oxidation resistance.Ordinary binary TiAl alloy has good oxidation resistance at 700?and below,but when the service temperature is higher than 800?,its oxidation resistance will be greatly reduced.Previously,domestic and foreign scholars have carried out some studies on the influence of a single additive element on the oxidation resistance of TiAl alloys,but few considered the synergistic effect of multiple additive elements and the influence of the oxidation environment.This article uses simultaneous thermal analyzer,scanning electron microscope(SEM)and X-ray diffractometer(XRD)to analyze the oxidation kinetics,oxidation cross-section morphology,and element distribution of oxide scale elements of the three multicomponent TiAl alloys Ti-44Al-4Nb-4Mn-1B?Ti-44Al-4Nb-4Zr-1B and Ti-44Al-8Nb-1B(at.%)in argon oxygen,air and air-water vapor environments.Based on the above,the oxidation behavior of the alloy was discussed.The oxidation behavior of three multicomponent TiAl alloys in an argon-oxygen environment was studied.In this environment,TiAl-based alloys tend to form Al-poor regions at the subsurface.The addition of Nb element will increase the activity of Al in the TiAl matrix and inhibit the diffusion of Ti,thereby further aggravating the depletion of Al in the subsurface area and even induce internal oxidation.The addition of Mn will enhance the diffusion of Ti and stabilize the Z phase to a certain extent,thereby alleviating the Al-poor condition of the subsurface and hindering the formation ofa₂ phase.However,the oxide scale of TiAl alloy containing Zr is obviously peeled off.The oxidation behavior of three multicomponent TiAl alloys in air environment was studied.Due to the presence of nitrogen in the air environment,the Al-poor condition of the TiAl-based alloy subsurface has been greatly improved.In this environment,The presence of Nb in TiAl will promote the formation of protective Al₂O₃ and Ti N layers in the oxide scale,while Mn will accelerate the formation of non-protective Ti O₂.Through theoretical calculations,it is found that the thermal stress and growth stress caused by the rapid growth of Ti O₂ are the main reasons for the oxide scale peeling of the 4Nb4Mn and 8Nb alloys in the air environment.The reason for the more serious peeling of the oxide scale of 4Nb4Zr alloy is the phase transformation stress caused by Zr O₂.The oxidation behavior of three multicomponent TiAl alloys in air-water vapor environment was studied.This study shows that TiAl alloy has a very high oxidation rate in this environment,and the morphology and structure of the oxide scale are significantly changed compared with argon oxygen and air environment,and this is mainly due to the existence of hydrogen defects in the air-water vapor environment.In addition,the addition of Nb,Mn,and Zr will significantly affect the oxidation behavior of TiAl alloy in air-water vapor environment.Among them,the Nb element will aggravate the Al depletion on the subsurface of the alloy and cause internal oxidation to deteriorate the oxidation resistance of the alloy;Mn element has the effect of stabilizing the Z phase,which is expected to improve the oxidation resistance of the TiAl alloy to a certain extent;The Zr element will promote the formation of a dense Al₂O₃ oxide layer in the oxide scale,greatly improving the oxidation resistance of TiAl-based alloys in this environment.