The sulfur-free expansible graphite and expanded graphite were prepared by induction heating method at different temperature using natural flake graphite, nitric acid and phosphoric acid as the raw materials. Expansion effect and heating mechanism has been analyzed. The microstructure of expansible graphite and expanded graphite has been analyzed by means of a scanning electron microscope and an energy spectrum analyzer. The result shows that the expanded volume of the expansible graphite can reach 200mL/g. Expanded graphite is characterized by vermicular structure and more developed pore structure where the pore of internal level basically maintains the original layer appearance of natural flake graphite.
The in situ synthesized ZrC particulate reinforced metal matrix composite coating was fabricated on AISI1020 steel by gas tungsten arc (GTA) cladding powder mixture of Nickel, Zirconium and Graphite. The microstructure and wear resistance of the composite coating were investigated. It is shown that the coating is bonded metallurgically to the substrate and has a homogeneous fine microstructure containing both approximate cubic ZrC particle uniformly dispersed in matrix of (Fe,Ni) solid solution. Compared to a substruate, the hardness of the composite coating was increased by a factor of 6, could achieve a Vicker microhardness of HV0.21100. And the wear resistance in a block on ring test against YG8 was increased by a factor of 10. This is attributed to the presence of in situ synthesized ZrC particles and their well distribution in the coating.
Nanostructure WC composite coatings were prepared on surface of Q235 steel by argon arc cladding injection using microstructure WC feeding which were prepared by nanostructure WC powder. The microstructure of the coating were analyzed by scanning electron microscopy (SEM). Phase of the coating were analyzed by energy dispersive spectrometer and X-Ray diffract meter, moreover, microhardness and wear resistance were texted by Microhardness tester (HVST-1000) and friction wear testing machine (MMS-2A). The results show that the combination of coating and substrate is metallurgical bonding. and no Pores and cracks were founded in bonding area. aggregated nanostructure WC particles and nanostructure WC particles uniformly distributed in the coating. The maximum hardness of the coating is 1461 HV. Compared with the Q235 steel, the wear resistance of the coating increased about 15 times.
Micro-nanostructured WC composite coatings were successfully fabricated by induced heating sintering method on the surface of Q235 steel .The microstructure, micro-hardness and the wear resistance of the composite coatings were studied .The results show that the microstructure of induced heat layer is mainly composed of Ni-based solid solutions and WC particles. And there exists excellent
metallurgical bonding between coating and substrate. The wear resistance of micro-nanostructured WC Composite Coatings is increased by 1.5 times on an average as compared with that of micron.
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