Study On Phase Equilibrium Of Ni-Al-Cr-Y Quaternary System And Related Ternary System

MCrAlY coatings are widely used on industrial gas turbine hot end components because of their excellent high temperature oxidation and thermal corrosion resistance.Appropriate adjustment of the composition of MCrAlY coating under different service conditions can effectively improve the service life of the coating.The phase relationships of Ni-Al-Cr-Y alloy system to provide theoretical guidance for the design of MCrAlY coatings with better composition ratio.In this paper,the equilibrium alloy method combined with scanning electron microscopy(SEM),energy spectrometry(EDS)and X-ray diffractometry(XRD)were used to observe the microstructure and analyze the composition and phases of the samples.The isothermal section and partial liquid phase projection of the Ni-Cr-Y ternary system at 900°C,partial isothermal section of the Ni-Al-Y ternary system at 900°C and isothermal section of the Ni-Al-Cr-Y quaternary system with 55 at.%Ni at 900°C were studied,and the main conclusions were obtained as follows:Nine three-phase regions exist in the isothermal section of the Ni-Cr-Y ternary system at 900°C,and eight three-phase regions were experimentally determined:Ni₁₇Y₂+Ni₅Y+(Ni),(Ni)+Ni₅Y+(Cr),Ni₅Y+Ni₄Y+(Cr),Ni₇Y₂+Ni₃Y+(Cr),Ni₃Y+Ni₂Y+(Cr),Ni₂Y+Ni Y+(Cr),L+Ni Y+(Cr),L+(Y)+(Cr).A three-phase region Ni₄Y+Ni₇Y₂+(Cr)was speculated.And the maximum solubility of Cr in Ni₇Y₂,Ni₅Y,Ni₄Y,Ni₇Y₂,Ni₃Y,Ni₂Y,Ni Y,L,(Y)phases is:41.8 at.%,1.0 at.%,9.9 at.%,3.3 at.%,5.0 at.%,2.8 at.%,1.5 at.%,0.8 at.%,0.7 at.%,0.2 at.%,respectively.The maximum solubility of Ni in(Cr)and(Y)phases is 6.3 at.%and 0.3 at.%.Y is barely soluble in(Ni)and(Cr)phases.In the determination of the liquid phase projection of the Ni-Cr-Y ternary system,there are six primary phases:Ni₅Y,Ni₃Y,Ni₂Y,(Ni),(Cr)and(Y),and a ternary eutectic reaction L?Ni₂Y+(Cr)+Ni Y.Three three-phase regions were measured in the partial isothermal section of the Ni-Al-Y ternary system at 900?:?₁+Ni Y+Ni₂Y,Ni Y+?₁+?₂,?₁+Ni₅Y+Ni₃Y,and the composition range of?₁ was determined to be Ni_52.8-55.2Al_15.7-18.0Y_29.0-29.4.Six quaternary regions:Ni₃Al+(Cr)+(Ni)+Ni₅Y,Ni₃Y+(Cr)+?₁+Ni₅Y,Ni₂Y+(Cr)+?₁+Ni Y,Ni₃Y+Ni₂Y+?₁+(Cr),Ni₅Y+Ni₇Y₂+Ni₃Y+(Cr),Ni₃Al+Ni₅Y+Ni Al+(Cr)were measured in the isothermal sections of the Ni-Al-Cr-Y quaternary system with 55 at.%Ni at 900°C.A four-phase region Ni₅Y+Ni₄Y+Ni₇Y₂+(Cr)was speculated.In this work,no new ternary or quaternary compound was found.