Yttria stabilized zirconia(YSZ) was deposited on the line cut β-NiAl substrate by electron-beam physical vapour deposition(EB-PVD), and the cyclic oxidation behaviors of thermal barrier coatings on β-NiAl substrate were investigated in 1 h thermal cycles at 1 200 ℃ in air. The results show that the samples fail after 80?100 cycles. Sub-interface cavitations in the substrate develop due to depletion of Al in forming thermally grown oxides(TGOs). The collapse and closing up of cavities result in the ragged YSZ/TGO/substrate interface. Since the specific crack trajectories are quite sensitive to local geometry, cracks along the YSZ/TGO/substrate interfaces ultimately lead to YSZ spallation.
Thermal barrier coatings (TBCs) were developed to protect metallic blades and vanes working in turbo-engines. The two-layered structure TBCs, consisting of NiCoCrAlY bond coat and yttria stabilized zirconia (YSZ), were deposited on a cylinder of superalloy substrate by the electron beam-physical vapor deposition (EB-PVD). The failure mechanism of the TBCs was investigated with a thermo-mechanical fatigue testing system under the service condition similar to that for turbine blades. Non-destructive evaluation of the coated specimens was conducted through the impedance spectroscopy. It is found that the crack initiation mainly takes place on the top coat at the edge of the heated zones.
CHEN Chen ZHANG Chun-xia GUO Hong-bo GONG Sheng-kai ZHANG Yue
NiAl-0.3Ru and NiAl-30Cr-4Mo alloys were fabricated by arc melting method and then annealed at 1 423 K for 12 h. It has been revealed that NiAl-0.3Ru was in a single-phase with large grain size and NiAl-30Cr-4Mo consisted of multiple eutectic cells. Each cell consisted of alternating plates NiAl and Cr(Mo). The compressive properties including the brittle-ductile transition temperature (BDTT) were tested. NiAl-0.3Ru and NiAl-30Cr-4Mo fractured with a little plastic deformation after yielding below the BDTT, and almost no fracture was found after large deformation up to 60% above the BDTT. Fractograph showed that at the room temperature, the fracture in NiAl-0.3Ru was intergranular and the NiAl-30Cr-4Mo in transgranular along the interface betweenβ-NiAl and Cr (Mo). The compressive properties of NiAl were obviously improved by eutectic alloying with Mo and Cr additions.
