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.
Microstructure and oxidation behavior of conventional and pseudo graded NiCrAlY/YSZ thermal barrier coatings produced by supersonic air plasma spraying process
Abstract In this paper, the microstructure and oxidation behavior of conventional and pseudo graded NiCrAlY/yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) is reported. Both conventional and graded TBCs were produced by supersonic air plasma spraying process. In the pseudo graded TBCs, no interface between bond-coat, graded region and top-coat was observed. The ceramic (YSZ) top-coat in both conventional and graded TBCs was found to exhibit a single phase tetragonal-prime structure. Isothermal oxidation results confirmed the formation of thermally grown oxides (TGO) layer in both conventional and graded TBCs. In graded TBCs, the dispersed metallic phase was also found to be oxidized in the graded region. For oxidation time ≥ 50 h, the TGO thickness in the conventional TBCs was found to be lower than that of the graded TBCs. Further, in graded TBCs, the vertical and parallel cracks were formed in the YSZ coating during oxidation for 5 h. The cracks were enlarged during oxidation at 1200 °C for 200 h. After oxidation (at 1200 °C for 200 h), the parallel cracks in the graded TBC penetrated into the graded/layered region. The evolution of cracks in the graded TBCs led to a constant residual stress (0.62 ± 0.2 GPa) in the TGO. However, owing to the presence of few cracks in the conventional TBCs, the residual stress in the TGO increased with oxidation time. After oxidation at 1200 °C for 200 h, the conventional TBCs have higher residual stress (2.1 ± 0.3 GPa) in the TGO as compared to the graded TBCs.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.