Preparation and performance of ultrafine grained WC-10Co alloys with added La2O3

Abstract La2O3/WC-10Co mixed-powders with different amounts of La2O3 were prepared by ball milling. Then, the powders were pressed and consolidated by microwave sintering. The microstructure and mechanical properties of the La2O3/WC-10Co alloys with different La2O3 contents were investigated. The experimental results show that addition of an appropriate amount of La2O3 can suppress WC grain growth and narrow the grain size distribution. With the addition of a small amount of La2O3, the nanosize La2O3 particles mainly distribute at the interfaces between the WC and Co phases. However, excessive addition of La2O3 leads to aggregation, forming large particles with a size of approximately 200 nm. Two types of interface relationships were observed between the La2O3 and WC phases in the samples. One is that of the well-coherent interface, and the other is that of the poorly coherent interface where structural disorder is found in the 1–3 nm wide region between the La2O3 and WC phases. However, this structural disorder does not occur in the interfaces between Co and La2O3 phases. Addition of a minor amount of La2O3 into the alloys has less effect on the relative density of the La2O3/WC-10Co alloys. Regarding the mechanical properties, when the La2O3 content is 0.8 wt% (the mass ratio of La2O3 in Co), the Rockwell hardness and fracture toughness of the La2O3/WC-10Co alloys reach 91.8 HRA and 13.44 MPa m1/2, respectively. The transverse rupture strength (TRS) has a maximum value of 2359 MPa when the La2O3 content is 1.2 wt%.