Shicheng Wei

The study of a novel ultrasonic A-scan signal processing method based on fractal theory

Concerning ultrasonic non-destructive testing of ceramic-lined composite steel pipes, a novel bonding flaw locating method based on fractal dimension is proposed. Ultrasonic A-scan method is used on different positions of the composite steel pipe test piece. The fractal dimension of each curve of ultrasonic vibration signal is calculated. The transformation of each fractal dimension is compared and abnormal positions where bonding defects potentially exist are detected. The result indicates that ultrasonic A-scan signal has an excellent fractal conduct characteristic. It is feasible to compare fractal dimension of signal with the normal range and find out abnormal positions, which can provide basis for follow-up inspections.

Research on wear resistance of plasma remelted FeNiCrAl sprayed coating

To improve the microstructure density of high-velocity arc spraying coating and enhance its adhesive strength and wear resistance, a plasma remelting investigation of the FeNiCrAl sprayed coating was carried out in this study. The microstructure and phase composition of the sprayed coating and the remelted coating were compared by using metalloscope, scanning electron microscope and X-ray diffractometer. The microhardness distribution and friction wear characteristics of the plasma remelted FeNiCrAl sprayed coating were investigated by microhardness tester and CETR sliding friction wear testing machine. The results showed that the remelted coating has more compact microstructure and presents metallurgical bonding with the substrate. The generation of hard phases such as (Fe,Cr)7C3 and Cr23C6 as well as solid solution (Fe,Cr) increases the microhardness of the remelted coating significantly, about 1.4 times higher than that of the sprayed coating. According to sliding friction wear test, the abrasion losses of the sprayed coating under 10 N and 20 N loads are 4.6 and 10.5 times higher than those of the remelted coating, indicating the better wear resistance of the remelted coating.