Mechanical properties of the hypereutectoid Fe-Cr-C hardfacing coatings with different nano-Y2O3 additives and the mechanism analysis

The hypereutectoid Fe-Cr-C hardfacing (harden-surface-welding) coatings with four nano-Y2O3 additives were developed. The effect of nano-Y2O3 additive on the mechanical properties of the hardfacing coating was researched systematically, and the influence mechanism was analyzed using first-principle calculations. The results indicate that, with the increase of the nano-Y2O3 additive, the dimension of the primary austenite grain decreases gradually, and the mechanical properties of the coating improve obviously. When the nano-Y2O3 additive is 0.76 wt%, the primary austenite grain is the smallest (average diameter is 17 μm), and all the mechanical properties are the most excellent, in which, the hardness is HRC 62.9, the tensile strength and yield strength are 1209 MPa and 989 MPa respectively, the impact energy is 26 J/cm2, the weight loss rate is 0.12 g/h, the numbers of thermal fatigue crack are 0, 0, 4 and 6 after 100, 200, 300 and 400 thermal fatigue cycles. In all the Y inclusions, the free energy of YAlO3 is the smallest (−755,103.18 J/mol), which indicates that it is formed most preferentially. For the YAlO3(001)/austenite(100) interface with O-terminated structure, when ΔμY is in the range of −11.46 eV to −11.04 eV, the interfacial energy is in the range of 0-0.204 J/m2, which meets the energy requirements as the heterogeneous nucleation interface. Therefore, the effectiveness of YAlO3 as the heterogeneous nucleus of austenite can be confirmed.