| The application of non-magnetic materials has become increasingly widespread in oil exploration, aerospace, abrasive, mechanical chemical industry and other fields. In these areas, materials with high hardness, high strength, wear resistance, corrosion resistance and other conditions can also need to satisfy the nature of non-magnetic. Ordinary cemented carbide although have some characteristics such as high hardness, but it is ferromagnetic material. Laser cladding technology belongs to the cross discipline with laser technology and new materials. The non-magnetic material with wear resisting and corrosion resistant can be prepared on the surface of the workpiece when used this technology. When compared with laser cladding WC-Fe based cemented carbide with non-magnetic, laser cladding WC-NiCrMoAl cemented carbide with non-magnetic can not only improve the corrosion resistance but also increase the service life of the workpiece. We mainly study the non-magnetic mechanism of laser cladding WC-NiCrMoAl cemented carbide based on the first principle. To establish the mechanism of laser cladding non-magnetic materials and optimize the process of laser cladding WC-NiCrMoAl cemented carbide with non-magnetic, we discussed the influence on magnetism because of interface reaction, which include the interface reaction between the melting and diffusing tungsten carbide particles and alloy elements in powder, and the interface reaction between the substrate material and WC- NiCrMoAl composite coating under the effect of high energy laser beam. On the whole, we study the magnetic property of various phases and the solid solution and then analyze the electronic interaction between atoms and the magnetism of each phase on the influence of magnetism.First of all, WC- NiCrMoAl composite coating is prepared under the appropriate process parameters and then using scanning electron microscope and energy spectrometer, X-ray diffraction to detect the laser cladding coating composition and phase analysis. The results show that under the effect of laser, tungsten carbide particles melt and spread and then interface fusion reaction occur with the powder substrate. The edge of the WC particles has formed a certain amount of η compounds, mainly Ni2W4 C and Ni3Mo3 C. Of course, W2 C also exist because of the decomposition of WC particles. Ni3 Al, Fe3 Al, Al4C3 and other phase precipitated in the coating with the addition of Mo, Al and other alloy elements. Between the coating and the non-magnetic alloy steel, large amounts of Fe flow into the coating because of the liquidity of molten pool under the action of laser and then Fe3 Al, γ-Ni and other phase formed.The second, we study the magnetic property of laser cladding coating with the vibrating sample magnetometer(LakeShore740). The results show that the hysteresis area of the sample is very small and have good non-magnetic property when the WC content is low. With the increase of WC content, the hysteresis area gets bigger when the WC content reached 45%. It suggests that the laser cladding coating began to precipitate a certain amounts of ferromagnetic phase or weak magnetic phase.Finally, we completed the magnetic calculation of phase with CASTEP package based on density functional theory. The calculated results show that some phases are non-magnetic such as WC, W2 C, Al4C3, Mo2 C, Ni2W4 C and other phases are magnetic such as Ni3Mo3 C, Ni4 C, Ni3 Al and Fe3 Al. Then, we calculated the magnetic moments of Ni3MC(M=Fe、Cr)in which Fe and Cr atoms replace Ni atoms in Ni4 C crystal structure. The magnetic moment of Ni4 C is 0.46μB. The calculated results suggest that Ni3 MC is magnetic but the spin state changed around the Fe and Cr atoms in Ni3 FeC and Ni3 CrC because of the difference of magnetic state about Fe and Cr atoms which Fe is ferromagnetic element and Cr is antiferromagnetic element. Furthermore, in my point of view for the laser cladding coating with different ratio of powder, which lead to the different macroscopic magnetic. |
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