Modification of NiCoCrAlY with Pt: Part Ⅱ. Application in TBC with pure metastable tetragonal(t’) phase YSZ and thermal cycling behavior

A thermal barrier coating system comprising Pt-modified NiCoCrAlY bond coating and nanostructured 4mol.% yttria stabilized zirconia(4YSZ, hereafter) top coat was fabricated on a second generation Ni-base superalloy. Thermal cycling behavior of NiCoCrAlY-4 YSZ thermal barrier coatings(TBCs) with and without Pt modification was evaluated in ambient air at 1100?C up to 1000 cycles, aiming to investigate the effect of Pt on formation of thermally grown oxide(TGO) and oxidation resistance. Results indicated that a dual layered TGO, which consisted of top(Ni,Co)(Cr,Al)_2O_4 spinel and underlying α-Al_2O_3, was formed at the NiCoCrAlY/4 YSZ interface with thickness of 8.4μm, accompanying with visible cracks at the interface. In contrast, a single-layer and adherent α-Al_2O_3 scale with thickness of 5.6μm was formed at the interface of Pt-modified NiCoCrAlY and 4 YSZ top coating. The modification of Pt on NiCoCrAlY favored the exclusive formation of α-Al_2O_3 and the reduction of TGO growth rate, and thus could effectively improve overall oxidation performance and extend service life of TBCs. Oxidation and degradation mechanisms of the TBCs with/without Pt-modification were discussed.

Benefits of Zr addition to oxidation resistance of a single-phase (Ni,Pt)Al coating at 1373 K

A single-phase (Ni,Pt)Al coating with lean addition of Zr was prepared by co-electroplating of Pt-Zr com posite plating and subsequent gaseous alum inization treatm ents. Isotherm al and cyclic oxidation behavior of the Zr-doped (Ni,Pt)Al coating sam ples was assessed at 1373K in static air in comparison with plain nickel alum inide (NiAl) and norm al (Ni,Pt)Al coatings. Results indicated th at Zr-doped (Ni,Pt)Al coating dem onstrated a lower oxidation rate constant and reduced tendency of oxide scale spallation as well as surface rumpling, in which the enhanced oxidation perform ance was m ainly attributed to the segregation of Zr at oxide scale grain boundaries and the im proved Young's modulus of the coating. Besides, the addition of Zr effectively delayed oxide phase transform ation of Al2O3 from θ phase to α phase in the early oxidation stage and coating degradation of β-NiAl to γ'-Ni3Al in the stable oxidation stage.

A general strategy towards improving the strength and thermal shock resistance of glass-ceramics through microstructure regulation

Glass-ceramics are usually obtained through controlled crystallization.In this work,we propose a new strategy to add an appropriate amount of oxide particles to the parent glass to improve the performance of glass-ceramics.Different amounts of Al_(2)O_(3) or/and CeO_(2) particles were added into a SiO_(2)-Al_(2)O_(3)-ZnOCaO-ZrO_(2)-TiO_(2)based glass,and crystallization behavior,fracture strength,and thermal shock behavior were systematically evaluated.The results indicate that with the addition of Al_(2)O_(3) or/and CeO_(2) particles of moderate amount,the unfavorable needle-like ZrSiO_(4),Zn 2 SiO_(4),and CaTiSiO_(5) crystals were largely inhibited when annealed at 900℃ .Accordingly,fracture strength is maintained high after heating at high temperatures.The thermal shock resistance is also enhanced drastically.The additive Al_(2)O_(3) is thermodynamically favorable to react with the glass,forming particulate ZnAl_(2)O_(4) instead of precipitating the needle-like crystals of Zn_(2)SiO_(4) and CaTiSiO_(5);while CeO_(2) will combine with ZrO_(2) to form a solid solution and promote the precipitation of primary crystal CaZrTi_(2)O_(7) that will not transform to ZrSiO_(4) with prolonging thermal exposure.

Microstructure and Improved Thermal Shock Behaviour of an In Situ Formed Metal-Enamel Interlocking Coating

A novel metal-enamel interlocking coating was designed and prepared in situ by co-deposition of Ni-enamel composite layer and subsequent air spray of enamel with 10 wt% nanoscale Ni. During the firing process, the external enamel layer was melted and jointed with the enamel particles at the upper part of the Ni-plating layer to form the enamel pegs. Thermal shock tests of pure enamel, enamel with 10 wt% Ni composite and metal-enamel interlocking coatings were conducted at 600 °C in water and static air. The results indicated that the metal-enamel interlocking showed superior thermal shock resistance to both pure enamel and enamel with 10 wt% Ni composite coatings. The enhanced performance was mainly attributed to the advantageous effects of mechanical interlocking of the enamel pegs formed at the enamel/Ni-plating interface. Meanwhile, during thermal shock test, big clusters formed by nanoscale Ni agglomerations were oxidised to be a Ni/NiO core–shell structure while small single nanoscale Ni grains were oxidised completely, which both improved the thermal shock resistance of enamel coating significantly.