The method of simulating the wear performance under working conditions using a high-temperature ultra-high-speed wear testing machine was adopted to study the effect of feed rate variation on the wear behavior and scraping performance of the AlSi/hBN sealing coating and TC4 simulated blades. The macro and micro morphology of the coating and blades were analyzed by stereomicroscope and scanning electron microscope (SEM). The phase composition of the coating was analyzed by energy dispersive spectrometer (EDS) and X-ray diffraction. The results showed that, under the conditions of temperature of 450°C, line velocity of 300m/s, and feed depth of 500μm, the change in feed rate significantly affected the macro and micro morphology and wear mechanism of the AlSi/hBN sealing coating-TC4 simulated blades. At low feed rates, severe wear occurred, mainly manifested as grooving, adhesion transfer, and overheating mechanisms. At medium to high feed rates, good machinability was observed, mainly manifested as cutting and transfer of coating material to the blades.

Ductile iron pipes (DIP) have been used worldwide since 1960s for water transmission and distribution mains. By 1979, ductile iron pipe largely replaced cast iron as the predominant material in water industry. Zn and Zn/Al 85/15 coatings applied by thermal spray technique are used for the protection of the ductile iron pipe against corrosion in heterogeneous soil conditions. In this study, heat treated and non-heat treated ductile iron pipe samples were coated with Zn and Zn/Al 85/15 in optimum spray parameters by twin wire electric arc (TWEA) spraying technique. The coatings were investigated by optical microscopy, scanning electron microscopy (SEM), and analyzed by energy dispersive spectrometer (EDS). Both Zn and Zn/Al 85/15 coatings showed fairly good lamellar structure with acceptable amount of internal porosities and oxides. Annealing oxides available on pipe surface helped the bonding of coatings. The protection performance of the coatings was compared with accelerated corrosion (salt spray) test according to the ASTM B 117 and corrosion products were analyzed by SEM and EDS technique. Salt spray test results showed that Zn/Al 85/15 coatings have better corrosion resistance than Zn coatings and annealing oxide on ductile iron pipe acts as a good corrosion resistant protective layer.

Hot corrosion tests have been conducted on Ni- and Cr-based laser coatings, a high-velocity oxy-fuel (HVOF) sprayed coating and various wrought alloys covered with a synthetic salt of Na 2 SO 4 -V 2 O 5 and exposed at 650°C for 1000 h in air. Coating microstructures and reaction product layers were analyzed with scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The hot corrosion resistance of tested specimen was evaluated by measuring its mean thickness loss. Generally, wrought alloys, HVOF coating and Cr-based laser coatings suffered from selective corrosion beneath salt film, that is, distinct Cr-depleted layer was formed at alloy/salt interface. Cr-based laser coatings exhibited extended solid solubility and they transformed towards equilibrium condition. Cr-rich phases enriched further with Cr and they were prone to corrosion. Low diluted laser coatings and HVOF coating were more resistant to hot corrosion than commonly used industrial standard alloy, Nimonic 80A. Ni-based laser coating exhibited resistance equivalent to Cr-based coatings and superior to corresponding wrought alloy.