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• A NiCoCrAlYTa coating was synthesized successfully onto a Ni-based superalloy by arc ion plating (AIP) technology. • During the oxidation process, the oxide scales formed a multi-layer structure, consisting of an outer layer of mixed oxides, namely α-Al 2 O 3 , Cr 2 O 3 , and NiO, and an inner dense α-Al 2 O 3 layer with columnar microstructure. • Ta-riched oxide and (Al0.9Cr0.1) 2 O 3 were detected after 100 and 200 h of oxidation, respectively. • The effect of the changes in the interfacial microstructure of the coating on the growth of the oxide scales layer was investigated closely. A NiCoCrAlYTa coating was synthesized successfully onto a Ni-based superalloy by arc ion plating (AIP) technology. After accomplishing the coating, a vacuum heat treatment was carried out and the coating was then subjected to isothermal oxidation in air at 1050 °C for up to 200 h. The microstructural evolution and interface diffusion behavior were studied systematically using transmission electron microscopy (TEM) and scanning transmission electron microscopy-energy dispersive X-ray microanalysis (STEM-EDX) combined with other characterization methods, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS). The results revealed that the thickness of the obtained NiCoCrAlYTa coating was 60–70 μm and the coating was primarily composed of γ-Ni and γ'-Ni 3 Al phases. During the oxidation process, the Al content was gradually reduced and the oxide scales eventually formed a multi-layer structure, consisting of an outer layer of mixed oxides, namely α-Al 2 O 3 , Cr 2 O 3 , and NiO, and an inner dense α-Al 2 O 3 layer with columnar microstructure. More particularly, after 100 and 200 h of oxidation, a Ta-riched oxide and (Al0.9Cr0.1) 2 O 3 were detected, respectively. The finding provides solid experimental evidence demonstrating that the external diffusion of cations during the growth of oxide scales plays a greater role in the oxidation of the coating compared with the internal diffusion of oxygen. [ABSTRACT FROM AUTHOR]

The shear thinning and shear thickening rheological properties of PCC/PEG suspension were investigated with the increase of oscillatory amplitude stress at different constant frequencies. The results show that the complex viscosity was initially independent of stress amplitude and obvious shear thinning occurred, then dramatic shear thickening took place after reaching the minimum viscosity. Typically, in a constant frequency of 5 rad/s, the elastic modulus, viscous modulus, and tanδ (δ is the out-of-phase angle) vs. the stress amplitude was investigated. It is found that the elastic modulus initially appeared to be independent of stress amplitude and then exhibited a rapid decrease, but the viscous modulus was independent of amplitude stress at lower amplitude stress. After reaching the minimum value the viscous modulus showed a rapid increase. On the other hand, tanδ increased from 0.6 to 92, which indicates that the transition from elastic to viscous had taken place and tanδ showed a steep increase when shear thickening occurred. Lissajous plots are shown for the dissipated energy vs. different maximum stress amplitude in the shear thinning and shear thickening regions. The relationship of dissipated energy vs. maximum stress amplitude was determined, which follows a power law. In the shear thinning region the exponent was 1.91, but it steeply increases to 3.97 in the shear thickening region. [ABSTRACT FROM AUTHOR]

The influence of non-isothermal melt crystallization on thermal behavior and isothermal melt crystallization kinetics of poly-L-lactide (PLLA) were investigated by differential scanning calorimetry (DSC), polarizing micrograph (POM) and x-ray diffraction (XRD). Crystallization performed at lower cooling rates (2°C·min-1) is accompanied by a variation of the kinetics around 118°C. The glass transition temperature of PLLA decreases with increase of cooling rate, and the crystallinity at the end of crystallization increases with decreasing cooling rate. The size of PLLA spherulites increases with a decrease in the cooling rate, and PLLA becomes almost amorphous cooled at rapid rate (>10°C·min-1). PLLA exhibits an Avrami crystallization exponent n = 3.01±0.13 in isothermal crystallization in the range from 90°C to 140°C. According to Hoffman-Lauritzen theory, two crystallization regime are identified with a transition temperature occurring at 118°C, and the value of Kg(II)/Kg(III) is 2.17 [Kg(II) = 6.025 × 105K2, Kg(III) = 1.307 × 106 K2]. [ABSTRACT FROM AUTHOR]