Yanbo Liu

Formation and corrosion behavior of Fe-based amorphous metallic coatings prepared by detonation gun spraying

Amorphous metallic coatings with a composition of Fe48Cr15Mo14C15B6Y2 were prepared by detonation gun spraying process. Microstructural studies show that the coatings present a densely layered structure typical of thermally sprayed deposits with the porosity below 2%. Both crystallization and oxidation occurred obviously during spraying process, so that the amorphous fraction of the coatings decreased to 54% compared with fully amorphous alloy ribbons of the same component. Corrosion behavior of the amorphous coatings was investigated by electrochemical measurement. The results show that the coatings exhibit extremely wide passive region and low passive current density in 3.5% NaCl (mass fraction) and 1 mol/L HCl solutions, which illustrates excellent ability to resist localized corrosion.

Oxidation of Ni-based single crystal after grit-blasting during exposure at high temperature

Abstract The effect of grit-blasting on the oxidation of Ni-based single crystal at 1150 and 1250 °C was studied. The oxide scales formed on the samples with or without grit-blasting were characterized by SEM, XRD, EDS, and EPMA. The results indicate that grit-blasting introduces a plenty of oxide nodules with lamellar structure into the oxide scale of samples after oxidation. The oxide nodule is composed of external and internal part. The external part is multi-layered with outer Cr2O3 layer, inner Al2O3 layer and transitional layer. The internal part includes several alternative alloy layers lack of Al and Al2O3 layer. Hf and Ta segregate at the oxide/alloy and oxide/oxide interface in two parts. Two recrystallized grains are formed under the blasted alloy surface after grit-blasting and heat exposure. The formation of oxide nodules accelerates the development of equiaxed recrystallization. Grit-blasting introduces abundant paths of oxygen diffusion and residual stress into the alloy, promoting the formation of oxide nodules and recrystallization.

Study on high power CW laser’s irradiation effect on yttria-stabilized zirconia coating

With the increasing in laser power, it is necessary to prepare protective coatings for components and devices under high power laser irradiation environment. Yttria-stabilized zirconia has high melting point, good stability and low thermal conductivity, and is often used as thermal barrier coating material. However, the study on its anti high power CW laser performance is rare. In this paper, the yttria-stabilized zirconia coating was deposited using atmospheric plasma spraying. The spectrophotometer, X-ray diffraction, scanning electron microscope and energy dispersive spectrometer were used to characterize the coating before and after high power CW laser irradiation. The temperature of substrate in back side was measured during irradiation. The results show that under the 2000 W/cm 2 laser power density continuously irradiated for 20 s, the back temperature is only 250 °C. Even continuously irradiated for 60 s under this power, no obvious damage appears on the coating. Only the phenomenon of micro melting in the irradiation center was observed under scanning electron microscope. The coating shows excellent anti-laser irradiation ability.

Chemical Stability between NiCr2O4 Material and Molten Calcium-Magnesium-Alumino-Silicate (CMAS) at High Temperature

NiCr2O4 as a potential protection for thermal barrier coatings (TBCs) against the attack of molten calcium-magnesium-alumino-silicate (CMAS) was studied by a CMAS-contacting experiment. Atmospheric plasma sprayed coatings and sintered bulk materials were fabricated, covered with CMAS deposits, and exposed to 1200 °C for 24 h. Nano-sized CMAS-NiCr2O4 mixed powder was manufactured by ball milling and then conducted heat treatment under the same condition. The results show that no reacting product was found at the border between molten CMAS and NiCr2O4 and no element transportation occurred. It can be inferred that NiCr2O4 has outstanding chemical stability with the molten CMAS.

Preparation of Mo(Si,Al)2 feedstock used for air plasma spraying

Abstract In order to prepare high quality Mo(Si,Al) 2 feedstock characterized with C40 phase, higher Al doping amount and excellent flowability, Mo(Si 1– x ,Al x ) 2 with different Al contents ( x =0, 0.1, 0.2, 0.3, 0.4, 0.5) were synthesized by self-propagating high-temperature synthesis first and Mo(Si 0.6 ,Al 0.4 ) 2 was confirmed as the suitable material through X-ray diffraction analysis. A series of tests with different parameters of induction plasma spheroidization were applied to improving the flowability of feedstock. Mo(Si,Al) 2 feedstock with excellent flowability (26.2 s/50 g) was prepared through adding hydrogen into sheath gas and decreasing the powder feeding rate. The composition segregation occurred in the spheroidized powder after Al consumption and oxidation. The inhomogeneous structure of the same particle was caused by the asymmetric heating and cooling when particle passed through the plasma jet.