Preparation of Electro-deposited Ni-Mo-Al Coating and Its Properties
Ni-Mo-Al coatings were prepared on Ni alloy by electrodeposition method. The effects of current density, frequency, duty cycle and electrodeposition time on mass percentages of Al of Ni-Mo-Al coatings were researched, respectively. The properties of wear weight loss and friction coefficients were investigated respectively. Ni-Mo-Al coatings were characterized with inductively coupled plasma-atomic emission spectroscopy (ICP-AES), energy-dispersive analyses of X-ray (EDAX), scanning electron microcopy (SEM), and X-ray diffraction (XRD) techniques, respectively. When electro-deposition parameters: current density 18.5 A/dm 2, frequency 5000 Hz, duty cycle 0.5 and electrodeposition time 20 min, mass percentages of Al of Ni-Mo-Al coating is as high as 2.04%. Ni-Mo-Al coatings show higher wear weight loss and lower friction coefficient compared with those of Ni-Mo coatings. The wear weight loss of Ni-Mo-Al coating is 1.27 times higher than that of the Ni-Mo coating. The friction coefficient of Ni-Mo and Ni-Mo-Al coatings are 0.816 and 0.540 respectively. The Ni-Mo and Ni-Mo-Al coatings have similar nodular microstructure. The nodules of Ni-Mo-Al coating are smaller than those of the Ni-Mo coating. The parts of nickel are replaced by Mo and Al respectively in the Ni lattice.
Bending fatigue failure of atmospheric-plasma-sprayed CoNiCrAlY + YSZ thermal barrier coatings
Abstract Bending fatigue failure of conventional atmospheric-plasma-sprayed CoNiCrAlY + ZrO2–8 wt.% Y2O3 thermal barrier coatings with/without the thermally grown oxide layer generated between the bond coat and the top coat was experimentally studied at room temperature. Microscopical and profilometrical characterization of as-received and fractured specimens and a simplified finite element study of cooling thermal stresses show that the same fatigue strength of both the as-coated and the oxidized specimens (i.e. its insensitivity to the presence of the thermally grown oxide) is most likely caused by a preferential through-the-thickness cracking of the thermally grown oxide layer. Moreover, the bond-coat/substrate interface is identified as the weakest part of the studied thermal barrier system under both low and high crack growth rates.
High performance nanostructured ZrO2 based thermal barrier coatings deposited by high efficiency supersonic plasma spraying
Abstract In this paper, the nanostructured zirconia (ZrO 2 ) based thermal barrier coatings (TBCs) deposited by high efficiency supersonic atmospheric plasma spraying (SAPS), were described. The phase composition, microstructure, thermal conductivity and thermal shock resistance of as-sprayed coating were studied. The results revealed that the as-sprayed coating was composed of tetragonal zirconia and consisted of some unmelted nanoparticles (30–50 nm) and nanograins (60–110 nm), and the latter was the main microstructure of the coating. The nanograins and homogeneously distributed micro-cracks of coating resulted in not only low thermal conductivity, but also high thermal cycling lives. Besides, the failure process of coating during thermal cycles was also investigated in the present work.