| With the rapid development of modem industry, most of machine parts are always working reliably and continuously under a high speed, high pressure, over loading or corrosion circumstance. So wear and corrosion become the main form of failure. In ordinary steel surfaces prepared with high performance composite coating can not only prolong the life of the part, but also create enormous economic value. Fe-based amorphous and nanocrystalline alloys have high hardness, high strength and corrosion resistance, which may have a wide application in the field of material surface modifying. Laser cladding was an advanced and efficient surface engineering technology, which could be easy to focus the beam and produce high energy density. Cladding surface had fine organization, high hardness, little deformation and other advantages. The Fe-based amorphous alloys coating was prepared on the hardened and tempered steel by laser cladding technique, which would improve mechanical properties of surface of parts.In this paper, the factors of GFA and the experience of designing amorphous alloy component which had high plasticity were analyzed comprehensively. The component of the Fe-based amorphous alloys which had high Poisson’s ratio and no metalloid elements was designed from the factors of electronic structure, modulus, formation enthalpy and bond of alloying elements. Fe60Nb20Ti20 and Fe60Nb13Ti13Ta13 alloy powders were finally selected for the study. It was analyzed that the crystallization kinetics and crystallization thermodynamics of the glassy powders with pure metal elements, which were prepared by mechanical alloying method. The Fe-based amorphous alloys coating was prepared by laser cladding technique. Effects of amorphous transition, crystallization kinetics, crystallization thermodynamics and laser cladding parameters on the evolution of microstructure and mechanical properties were systematically investigated.Results showed that the elements of Nb, Ti and Ta gradually spread to the Fe-based when Fe60Nb20Ti20 and Fe60Nb13Ti13Ta13 alloy powders were milled. At the same time, the supersaturated solid solution was produced, and then the lattice was changed resulting in a large amount of distortion energy. Two kinds of amorphous alloys powders when were milled for 70 hours seemed like globular and had great mobility. The study of crystallization kinetics and crystallization thermodynamics showed that amorphous alloys powders had wide supercooled liquid region and high crystallization activation energy. The crystallization kinetics of Fe60Nb20Ti20 and the crystallization thermodynamics of Fe60Nb20Ti20 were 165℃ and 375.98 KJ/mol, while the crystallization kinetics of Fe60Nb13Ti13Ta13 and the crystallization thermodynamics of Fe60Nb13Ti13Ta13 were 172℃ and 386.74 KJ/mol.The findings of laser cladding indicated that the influences of different laser cladding parameters, such as the laser power, the scanning velocity and coating thickness on the microstructure and mechanical properties were investigated. The best craft parameter was that P=350 W, V=240 mm/min, H=0.25 mm, which used the orthogonal testing method to optimize the laser cladding process parameters. The surface of coating was smooth, little crack and little stomata. The coatings have a good metallic bonding with the substrate. The microstructure of coating surface was fine equal crystal and few amorphous particles. The changes of hardness of cladding coating were the obvious stepped distribution, and the hardness of near surface was highest. The average hardness of Fe60Nb20Ti20 amorphous alloys coating was 857 HV, while the average hardness of Fe60Nb13Ti13Ta13 amorphous alloys coating was 873 HV. The findings of friction and wear experiment indicated that the average friction coefficient of Fe6oNb2oTi2o was 0.295, and the average friction coefficient of Fe60Nb13Ti13Ta13 was 0.268, while the average friction coefficient of substrate was 0.309. Therefore, the wear resistance of coating was better than substrate. |
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