A novel double ceramic layered (DCL) CaZrO 3 /Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) was designed for improved service life against sulfate vanadate hot corrosion as compared with that of YSZ single layered coating. The hot corrosion behavior of DCL CaZrO 3 /YSZ coatings was studied at 950°C after dry spreading 50%Na 2 SO 4 +50%V 2 O 5 mixture onto a coated surface.The CaZrO 3 as the topmost layer in DCL CaZrO 3 /YSZ coatings, served as a sacrificial layer during sulfate vanadate hot corrosion protecting the underneath YSZ coating. The corrosion reactions in this case were sluggish due to the initial formation of low melting point meta-calcium vanadate (CaV 2 O 6 ) that isothermally transformed to higher melting point calcium vanadates having higher calcia (CaO) content. The corrosion reaction products sealed the top surface, impeding the oxygen movement and eventually retarded the thermally grown oxide (TGO) growth.
Two alloys of varying contents of tantalum (Ta) and tin (Sn) were prepared and homogenized to evaluate their microstructural and electrochemical characteristics. The microstructural features were revealed through optical microscopy and X-ray diffraction methods. The formation and stability of passive film was studied by open circuit potential, potentiodynamic polarization and electrochemical scratch tests. The electrochemical impedance spectroscopy results simulated with equivalent electrical circuit suggested bilayer structure of outer porous and inner barrier oxide films. The quantitative data showed thick inner barrier oxide film retarded electrochemical reactions at low 'Ta' and 'Sn' concentration. The increased percentage of 'Ta' and 'Sn' deteriorated barrier properties by agglomeration of Ta 2 Sn 3 and Ta 0.15 Ti 0.85 precipitates within grains and at the grain boundaries.
Demand of special combination of different properties of the materials instigated the development of metal matrix composite. The carbon nanotubes being renowned for their excellent physical and mechanical properties are one of the major choices as strengthen material for metal matrix composites. To benefit their properties, the carbon nanotubes should be thoroughly dispersed and have wetting with the matrix. In the present study, a precursor of aluminum-carbon nanotubes was prepared by coating the nanotubes with titanium and used to fabricate the composite by induction melting. The precursor provided easy wetting, while induction melting facilitated dispersion of the nanotubes readily. Consequently, the composite exhibited noticeable augmentations in yield and tensile strength from 64 to 193 MPa and 81 to 227 MPa, respectively.
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