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Mo alloying Fe-based coating was fabricated on the surface of Q235 steel by using 6 kW fiber laser. The effects of Mo additions on the microstructure, microhardness and wear resistance of the cladding layer were studied by means of optical microscopy (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), Vickers hardness tester and M-200 ring block wear tester. Research results showed that the microstructure of Mo-free cladding layer mainly consisted of matrix and eutectic structure. The matrix was martensite and retained austenite. The eutectic structure mainly consisted of M2(B,C) and M7(C,B)3 type of eutectic borocarbides. With the increase of Mo content, there was no significant change in the matrix. However, the eutectic structure was transformed from M2(B,C)- and M7(C,B)3-type borocarbides into M2(B,C)-, M7(C,B)3- and M23(C,B)6-type borocarbides. When the content of Mo is 4.0 wt.%, the Mo2C-type carbide appear on the matrix, and parts of the borocarbide networks are broken. The change of microhardness of the cladding layer was not obvious with the increase of Mo content. But the increase of Mo content increases the wear resistance of the cladding layer. The wear resistance of cladding layer with 4.0 wt.% Mo is 2.4 times as much as the cladding layer which is Mo-free. [ABSTRACT FROM AUTHOR]

In this work, the microstructure, alloying element distribution, and borocarbide mechanical properties of high-boron multi-component alloy with Fe-2.0 wt.%B-0.4 wt.%C-6.0 wt.%Cr-x wt.%Mo-1.0%Al-1.0 wt.%Si-1.0 wt.%V-0.5 wt.%Mn (x = 0.0, 2.0, 4.0, 6.0, 8.0) are investigated. The theoretical calculation results and experiments indicate that the microstructure of high-boron multi-component alloy consists of ferrite, pearlite as a matrix and borocarbide as a hard phase. As a creative consideration, through the use of first-principles calculations, the comprehensive properties of borocarbide with different molybdenum concentrations have been predicted. The calculations of energy, state density, electron density and elastic constant of Fe2B crystal cell reveal that substitution of the molybdenum atom in the Fe2B crystal cell can remarkably improve its thermodynamic stability, bond strength, and covalent trend. For verifying the accuracy of this theoretical calculation, nano-indentation testing is carried out, the results of which indicate that the actual properties of borocarbide present favorable consistency with the theoretical calculations. [ABSTRACT FROM AUTHOR]

Two-body abrasive wear behavior and mechanism of Fe B alloys with different Mo contents have been systematically investigated. The results show that the Mo addition can promote the formation of Mo-rich and Cr-rich M 2 B in Fe B alloys, and the Mo-rich and Cr-rich M 2 B possess the higher H (hardness) and δ A (plasticity factor) compared to the Fe-rich M 2 B. Meanwhile, with the increase of Mo content, the V Mo+Cr / V Fe increases slightly firstly and then increases rapidly (Where the V Mo , V Cr and V Fe represents the volume fractions of Mo-rich, Cr-rich and Fe-rich M 2 B, respectively, and the V Mo+Cr shows the volume fractions of V Mo and V Cr). The wear results reveal that the wear rate decreases greatly with the increasing V Mo+Cr / V Fe , especially when the V Mo+Cr / V Fe < 0.42. During the two-body wear process, the main wear mechanism is microcutting, and the Mo-rich and Cr-rich M 2 B provide better resistance to the SiC abrasive relative to the Fe-rich M 2 B. In this case, the increasing V Mo+Cr / V Fe induced by the Mo addition contributes to the improvement of the abrasion resistance of Fe B alloys effectively. • The Mo addition results in the formation of Mo-rich and Cr-rich M 2 B in Fe-B alloy. • The Mo-rich and Cr-rich M 2 B possess higher H and δ A compared to the Fe-rich M 2 B. • The Mo-rich and Cr-rich M 2 B can provide better resistance to the SiC abrasive compared to the Fe-rich M 2 B. • The increasing V Mo+Cr / V Fe induced by the Mo addition facilitates the improvement of the abrasion resistance of Fe-B alloy effectively. [ABSTRACT FROM AUTHOR]