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The Effect of Tungsten on Microstructures and Properties of Wear Resistant Overlays Prepared by Plasma Cladding

Author: LuFeng
Tutor: LiHuiZuo
School: Shandong University of Science and Technology
Course: Materials Processing Engineering
Keywords: Plasma cladding clad coating in situ synthesis WC microstructure micro-hardness wear resistance
CLC: TG174.4
Type: Master's thesis
Year: 2011
Downloads: 62
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Abstract


By means of plasma cladding, different clad coatings were fabricated on the substrates of Q235 steels by varying the weight percent of W+C from 20 wt.% to 80 wt.% in iron based feedstock powders. The as-prepared clad coatings which were strengthened by in situ carbides of tungsten or chromium were metallurgically bonded to substrates. The microstructures, phase constituents and chemical composition of the clad coatings were studied by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Energy Dispersive X-Ray Spectroscopy (EDS) and electron probe micro-analyzer (EPMA). Hardness of the coatings were investigated by a FM-700 type automatic micro-hardness tester. Wear resistance of the coatings were explored by a MLS-225 type wet sand rubber wheel abrasion tester.All the coatings are metallurgically bonded to the Q235 substrates. In addition, all clad coatings except the one with 75 wt.% W particles are free of voids and pores. Macro cracks which are caused by thermal stress and internal stress induced by rapid solidification can be observed in the coatings; dilution rate of the substrates decreases with the increase of tungsten content.The microstructure of the coating with no tungsten addition is typically hypoeutectic, then, with the increment of W content in the alloy powders, the microstructures of the coatings vary in this way:hypoeutectic→near eutectic→hypereutectic→eutectic→hypereutectic. When the content of W in the feedstock powders is more than 40 wt.%, many unmelted tungsten particles, besides the in situ carbides of tungsten, congregate at the bottom of the molten pool.The hardness of the coating without tungsten ranges from 637.15 HVo.2-863.540.2 HV. The hardness of clad coatings firstly increase with the increment of tungsten in the powders, reaching a maximum at 40 wt.% W, and then decline with the increment of tungsten in the coatings. In the coatings with W more than 40 wt.%, the hardness profiles with big scattering show up trends, which can be contributed to the dispersion and deposition of carbides.The main wear mechanisms of all the coatings are grooving and plowing. Compared with the coating without tungsten, the addition of W in the coatings could improve the wear resistance. Because the in situ carbides can prevents the abrasives from indenting into the coating, the coating with about 40 wt.% W exhibits best wear resistance, and the wear loss of which is about 1.94 times less than the coating with no tungsten.On the basis of Fe-Cr-C alloy powders, this paper found that the coating with about 40 wt.% W exhibited the best performance, which could provide theoretical foundation for the future alloy design.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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