Preparation And High Temperature Oxidation Properties Of （MoSi₂-CoNiCrAlY） Composite Coating On GH4169 Alloy By Plasma Spraying

The general thermal barrier coatings applied in the aviation industry aremainly composed by the adhesive layer and the ceramic layer. There are problems such as thebonding strength gradually weakened with time, the complex process and high cost. In thisthesis, a new proposal to make the(Mo Si2-Co Ni Cr Al Y) composite coatings was put forward:firstly, the Mo Si2 powder and Co Ni Cr Al Y powder were compounded by high energy ballmilling; and then, the(Mo Si2-Co Ni Cr Al Y) composite coatings were directly prepared byplasma spraying process with the composite powder.An analysis of the Mo Si2-Co Ni Cr Al Y composite powder prepared by the high energyball milling was made. The result showed that the grain size of the composite powder wasabout 30 nm after 30 h ball-milling. The formation of the Mo Si2-Co Ni Cr Al Y compositepowder has experienced 4 stages: mixing stage, composite stage, deformation stage andcrushing stage, respectively. And the formation of the flocculent powder marked thebeginning of composite stage.The phase analysis of(Mo Si2-Co Ni Cr Al Y) composite coatings prepared by the plasmaspraying showed that the(Mo Si2-Co Ni Cr Al Y) composite coatings were composed of γ-Co,γ’-Ni3 Al, Mo Si2 and Mo5Si3. The thickness of the composite coating was about 130μm, thehardness reached 855.6Hv, the fracture toughness was as high as 5.07MPa·m1/2, the bondingstrength exceeded 10 MPa.HB5258-2000 aviation industry standard was used to guide the experiment design. Themicrostructure characteristics and the static isothermal oxidation behavior under 1000℃ ofthe Co Ni Cr Al Y single coatings and the(Mo Si2-Co Ni Cr Al Y) composite coatings werecontrasted through SEM, XRD and other testing methods. The results showed that the coatingweight gain curves of Co Ni Cr Al Y single coatings and(Mo Si2-Co Ni Cr Al Y) compositecoatings were both satisfied with the parabolic law. The Co Ni Cr Al Y single coatings werecomposed of Ni Cr2O4 and(Co,Ni) Cr2O4 in the initial stage of oxidation; Cr2O3 and α-Al2O3 phases became the main oxide after 120 h oxidation. The(Mo Si2-Co Ni Cr Al Y) compositecoatings were composed of Cr2O3 and(Co,Ni) Cr2O4 in the initial stage of oxidation, and Si O2,Cr2O3 and α-Al2O3 phases became the main oxide after 120 h oxidation.The two coatings showed different oxidation mechanism. 1) The Co Ni Cr Al Y singlecoatings showed obvious stages in the oxidation process. The initial oxidation stage was fastoxidation stage, the Ni Cr2O4 and(Co,Ni) Cr2O4 formed by the combination of Ni O, Cr2O3 andCo O. In the stable oxidation stage, it tended to form the main phase α-Al2O3 dense film byselective oxidation. 2) The(Mo Si2-Co Ni Cr Al Y) composite coatings was covered by of themain mixed oxide Cr2O3 in the initial stage of oxidation; with increasing the oxidation time,the Si O2 was covered on the coatings; in the end of the oxidation, the double oxide film wasformed, that is, Si O2 coated on the surface, Cr2O3 and Al2O3 mixed oxide in the bottom ofSi O2.