| The Mo-Cr-B-Fe system alloy taken ternary boride as hard phase has excellent wear and corrosion performance, which is a promising new material. In this paper, we designed and prepared alloy powder block of diverse Mo-Cr-B-Fe system, then fabricated deposited metal using argon and carbon arc welding process, studied the effect Mo/B ratio, C content, WC content and different welding processes on the microstructure and properties of deposited metal by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction, microhardness and wear test, analyzed theoretically formation mechanism of hard phase and phase transition of deposited metal. The results showed that the Mo-Cr-B-Fe system alloy could be prepared by the welding process.The deposited metal with different Mo/B ratios consisted of Mo2FeB2, M3B2 (M: Mo, Fe, Cr) and Fe-based solid solution. The coatings with Mo/B ratio of 0.34 and 0.44 would form Cr2B and Fe2B eutectic boride. Hard phase and the matrix contained Mo, Fe and Cr elements, the highest percentage of Mo in the hard phase, and the highest content of Fe in the matrix. When Mo content is the same, microhardness of the deposited metal increased with the increasing of B content, up to 1350HV, and Rockwell hardness was 67.7HRC. Microhardness of the deposited metal with Mo/B ratio of 0.9,1.0 and 1.1 increased with the increasing of Mo/B ratio, up to 1000HV, and Rockwell hardness was 58.5HRC. The deposited metal with Mo/B ratio of 0.34 had the best wear resistance.The deposited metal with different C contents consisted of Mo2FeB2 and M3B2 hard phase, Cr2B eutectic and Fe-based solid solution. When the C content exceeded 2% in alloy powder block, deposited metal still contained (Fe, Cr)7C3, Fe23(B, C) 6 coarse carbides and borides. Mo, Fe and Cr atomic ratio of the hard phase in argon arc deposited metal was (5-7):2:1, Mo, Fe and Cr atomic ratio in carbon arc deposited metal was (5-8):3:1. Microhardness of the deposited metal firstly increased, and then decreased with the increasing of C content, which was up to 1080 HV for argon arc deposited metal and 1300HV for carbon arc deposited metal.When the WC content was less than 10% in alloy powder block, deposited metal consisted of a large number of (Fe, Cr)?C3, Fe3(W, Mo)3C and W2(B, C), a small amount of M3(B, C)2 (M:Mo, W, Cr, Fe) and Fe-based solid solution. When WC content of 15%, contents of Mo, Fe, Cr and W in the hard phase were 57.1%,22.3%, 6.2% and 14.4%, respectively, and atomic ratios of 7.5:5:1.5:1. Microhardness of deposited metal increased with the increasing of WC content, the maximum value was 980HV, and Rockwell hardness was 62.7HRC.The calculated results of Mo-Fe-B system ternary phase diagram showed that under equilibrium conditions its organization was mainly Mo2FeB2, binary borides and Fe-based solid solution at room temperature. Result of Gibbs free energy revealed that the formation free energy of MoB, MoB2, FeB, Fe2B and CrB2 borides was negative, indicating that these binary borides could form under the thermodynamic conditions. M3B2 phase was composed by diffusion reaction between high temperature binary boride and liquid phase. The surface of β-MoB phase would form a liquid film. M3B2 particles were precipitated. M3B2 were produced by the reaction between Fe2B phase and a liquid phase with the temperature decreasing. Finally, M3B2 particles grow and form the square, elongated and cross-blossom shape. At the same time, binary boride particles precipitated surrounding M3B2 particles from the eutectic liquid phase, and the remaining liquid form Fe-based solid solution. |
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