No abstract

Plasma spraying is a well established technique for many industrial applications. In the present study, plasma sprayed Al 2 O 3 z13 wt-%TiO 2 coatings with bond layer of NiCrAl were prepared and characterised by optical microscopy, scanning electron microscopy and X-ray diffraction. Silicone resin sealing treatment was applied to the coating, and the salt spray test and electrochemical testing were conducted to investigate the effect of the sealant on the corrosion resistance of the coatings. It was found that the sealants filled the pores and microcracks in the coating and formed a thin layer with the ceramic, protecting the substrate from corrosion, while the as sprayed coating was subjected to pitting corrosion in the form of electrochemical corrosion at the interface between the bonding layer and the substrate.

Effect of Cr element on microstructure of Al-3.2Mg alloys was investigated using optical microscopy, scanning electron microscopy (SEM) and EDS. Moreover, the tensile and hardness test were carried out. The results show that a minor additive of Cr can refine effectively the secondary dendrite arm spacing and decrease the number of coarse interdendritic structures. In the whole series of the alloys, the secondary dendrite arm spacing of Al–3.2Mg-0.1Cr alloy was the smallest, and the spacing presented an increasing trend with the Cr content. With high levels of Cr, the intermetallic compounds are formed by Cr with Al, Mg and Fe, the shape of the second phase particles were transformed from bulky bone shape to fine bone shape and long striped. The strength and the hardness of Al–3.2Mg alloys were greatly improved when the additions of Cr were 0.05% and 0.1%, but the ductility of the alloys remained at a low level by adding 0.05%Cr. Therefore, combining with the comprehensive properties and the microstructure, the best addition of Cr in the alloy was 0.10% in the whole series.

The plasma spraying Al2O3+13wt. %TiO2 ceramic coating was coated with organic-inorganic hybrid emulsion. The hybrid emulsion prepared through co-hydrolysis and copolycondensation reactions of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES), and methylsilicone resin was added in the emulsion to improve the film-forming properties. The morphologies, chemical compositions and hydrophobicity of the resulting surfaces were analyzed by scanning electron microscopy (SEM), 3-dimensional stereoscopic microscope, energy dispersive X-ray detector (EDX), Fourier transfer infrared spectrometer (FT-IR) and water contact angle measurement. When the mole ratio of TEOS/MTES and the weight ratio of methylsilicone resin were 1:1 and 3.5wt. %, respectively, this surface displayed good film-forming properties. The contact angle was 130.24°, and the contact angle hysteresis was less than 10°.

Formation mechanism of TiC in Al matrix at a rather low melting temperature using in situ technology was studied. And effect of the melting temperature on the microstructure of in-situ TiC/Al composite was investigated. The results indicate that, the resultants of TiC and Al3Ti were found out in the matrix; however, no evidence showed that Al4C3, a resultant phase existed probably in TiC/Al composite in accordance with the relative reference, was found out. Compared to the sample of T750, more TiC and less Al3Ti existed in the sample of T850, and morphography of Al3Ti changed from block to bar with the increasing melting temperature. The melting temperature affected extremely the reaction speed and the resultants.