Mechanical properties of the hardfacing alloys with different La2O3 additives and the mechanism analysis by first-principles calculations

The harden-surface-welding (hardfacing) alloys with different La2O3 additives were developed. The microstructure was observed and the phase structure was determined. Meanwhile, the hardness and wear resistance were measured, respectively. Moreover, the tensile strength, yield strength and impact toughness were measured too. In addition, the fractograph of the hardfacing alloy was observed. On this basis, the LaO-doped C terminated interface was taken, in which, the interfacial energy of LaAlO3 (100)/austenite (100) interface was calculated and the effectiveness of the LaAlO3 as the heterogeneous nucleus of austenite was analyzed by first-principles calculations. The experimental results indicate that, with the increase of the La2O3 additive, the primary austenite grain dimension of the hardfacing alloy decreases obviously. Meanwhile, the hardness, strength, toughness and wear resistance of the hardfacing alloy increase simultaneously. When the La2O3 additive is 3.32 wt%, all of the mechanical properties are the largest, the hardness is HRC 50, the tensile strength and yield strength are 1502 MPa and 1334 MPa respectively, the impact toughness is 7.1 J/cm2 and the wear resistance is 1.29 mg/min. The calculated results show that, for the LaAlO3 (100)/austenite (100) interface with LaO-doped C terminated structure, the interfacial energy is high when the La chemical potential ΔμLa and C chemical potential ΔμC are low. However, with the increase of the ΔμLa and ΔμC, the interfacial energy decreases gradually. When the ΔμLa and ΔμC meet the condition of −3.792 eV≤0.543ΔμLa+0.311ΔμC≤−3.588 eV, the interfacial energy of LaAlO3 (100)/austenite (100) interface is in the range of 0–0.204 J, which meets the requirements of the heterogeneous nucleation interfacial energy. Therefore, LaAlO3 can be the heterogeneous nucleus of austenite.