Effects Of Lu On The Adherence Of ?-Al₂O₃(0001)/?-NiAl(110) Interface From First-principles Calculations

With the increasing temperature of the turbine inlet,the traditional MCrAlY materials has not been able to meet the requirements of the development of high-performance aero-engines.The intermetallic compound ?-NiAl is a promising material for high temperature utilizations,especially as the bond coat in a thermal barrier coatings(TBCs)due to its excellent properties,including high melting temperature,high strength,low density and good oxidation resistance,etc.However,its application remains restricted owing to its relatively poor cyclic oxidation performance.During thermal cycling,the protective oxide film scale(?-Al₂O₃)formed on the NiAl surface has poor adhesion and is prone to premature spalling,resulting in the coating failure eventually.A amount of studies have shown that the modification of NiAl alloy and coating with trace reactive elements(Hf,Y,Zr)can significantly promote the cyclic oxidation resistance,especially in the aspect of improving the adhesion of oxide film.Recent experimental studies have shown that the reactive element Lu can also significant improving the spallation resistance of the oxide film on the NiAl surface.However,the mechanism of Lu in improving the interfacial adhesion of Al₂O₃/NiAl is not still clear.In this thesis,the first-priciples methods were adopted to investigate the interactions between the doped reactive element Lu and the trace impurity element S in NiAl alloy,as well as the effect of Lu on the interface bonding strength of Al₂O₃/NiAl.The main conclusions are as follows:(1)The preference site,the solid solubility of Lu and S in NiAl are calculated by combining first-principles method with the Schottky model.The results show that both Lu and S are tend to occupy the Al sublattice site,and the solid solubility of Lu is greater than that of S.(2)The interactions between the doped Lu and the impurity element S in NiAl,and the heats of segregation are calculated by using first-principles method.The results show that Lu has strong affinity for the impurity S in NiAl by forming Lu-S bonds with S,which plays a role in binding S and decreasing the interface segregation of S.Moreover,Lu can prioritize segregation to the interface and occupy Al substitutional sites at the interface to inhibit the segregation of S to the interface since Lu has a higher heats of segregation than S.(3)The effects of undoping and single Lu-doping and(Lu+Lu)co-doping on the binding strength of ?-Al₂O₃(0001)/?-NiAl(0001)interface are compared by first-principles method.The results show that both single Lu-doping and(Lu+Lu)co-doping can improve the bonding strength of the interface,but the effect of(Lu+Lu)co-doping is more obvious due to the formation of more chemical bonds such as Lu-O and Lu-Ni at the interface.