Papers by Author: Jian Min Hao

Abstract: In this work, three cast iron coatings were produced by atmospheric plasma spraying. During spraying, the surface temperature of three coatings (substrate temperature) was controlled to be averagely 50oC, 180oC and 240oC by changing the processing parameters. X-ray diffraction (XRD) was employed to analyze the phase structure of the starting powder and the coatings. The results showed that the powder was mainly composed of (Fe,Cr)7C3 and martensite and both the spraying processing and the substrate temperature exerted no influence on coating phase structure. An optical microscope (OM) was used to characterize the microstructure of the cross-section and surface of the coatings. It was found that the cross sectional hardness increased with the increase of the substrate temperature due to the improvement in interlamellar bonding.

Abstract: The Fe-based amorphous coatings were prepared by Air plasma thermal spraying. X-ray diffraction results show that the coating fabricated at current of 300A has an amorphous structure. The amorphous nanocrystalline composite coatings were obtained at current more than 300A. The friction and wear properties of the coatings were investigated in Ml-10 friction and wear tester at dry friction condition. The results show that the amorphous content is the main influencing factors to wear resistance of coating. The density of coating is another reason to affect the wear resistance of amorphous nanocrystalline composite coating.

Abstract: Three composite coatings were prepared by nitriding-sulfurizing processing of Ti-6Al-4V alloy at different sulfurizing temperatures. The microstructure and phase structure of the coatings were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Furthermore, the hardness of the coatings was measured. The effect of the sulfurizing temperature on microstructure of coatings was investigated. The results indicated that the composite coating was mainly comprised of titanium nitrides, titanium sulfides, and titanium. It was found that the phase composition of composite coating changed with the variation of the sulfurizing temperature.

Abstract: In this work, an experiment was performed to demonstrate the possibility of the metallurgical bonding in plasma-sprayed cast iron coatings at high substrate temperature. A quantitative analysis of splat cooling and rapid solidification of cast iron splat is then presented. The effect of the substrate temperature on the development of melt undercooling within the splat is investigated in detail. The results indicated that the initial substrate temperature has a profound effect on the development of melt undercooling in a splat, the splat bottom melt temperature, and the substrate surface temperature. A high initial temperature of the substrate restrains the cooling of the splat and leads to a high melt temperature that may promote the grain growth directly on cast iron substrate surface to form the metallurgical bonding.