La2O3 addition for improving the brazed joints of WC-Co/1Cr13

The effects of lanthanum oxide (La2O3) as an interlayer component on microstructures and mechanical properties of brazed joints of tungsten carbide/cobalt (WC-Co) cemented carbides and the 1Cr13 stainless steel are investigated by an integrated experimental and computational thermodynamics approach. A carbide solid solution phase (CSSP) is experimentally identified adjacent to the detrimental eta phase (Co3W3C) due to the addition of La2O3. Such a CSSP is observed to suppress the formation of eta phase. The underlying inhibition mechanism is then explained thermodynamically by comparing the Gibbs free energy of the austenite, CSSP and eta phases. The added La2O3 is also found to effectively promote the heterogeneous nucleation of the austenite phase, which results in the grain refinement and the uniform distribution of the austenite phase. The shear strength (similar to 340 MPa) of the brazed joints with La2O3 addition outperforms the counterparts without La2O3.