Effect of La2O3 on microstructure and properties of Fe-based alloy coatings by laser cladding

One of the challenges limiting the application of laser cladded Fe-based coatings is the coarse columnar grains formed during the process. In order to improve the microstructure homogeneity of laser cladded coatings, Fe-based alloy (Fe78.5Cr15.6Ni4.0Si0.7) composite coatings with different La2O3 additions were prepared on the surface of 45-steel substrate by laser cladding. The effect of La2O3 content on the microstructure and properties composite coatings were systematically studied. X-ray diffractometer (XRD) and scanning electron microscope (SEM) were used to analyze the phase structure and microstructural evolution of Fe-based alloy composite coatings, and the hardness and tribological properties were measured by the microhardness tester and ball on disc wear tester, respectively. The results show that the addition of La2O3 plays the role of grain refinement, and certain amount of addition can completely eliminate the coarse columnar grains. Due to the fine-grain strengthening and dispersion strengthening of La2O3, the hardness and wear resistance of Fe-based alloy composite coatings have been improved. Especially, when the content of La2O3 is 1 wt%, the hardness increases to 3.1 times and the wear loss decreases to 27.7%, compared with the substrate material. The wear surface of composite coating with 1 wt% La2O3 suffered minor damage, and the wear mechanism is slightly abrasive wear. In contrast, higher amount of 2 wt% La2O3 addition has less effective grain refining where some columnar grains appear on the interface, and the hardness and wear resistance of composite coatings decrease as well. Meanwhile, the wear mechanism is transformed into a mixed mode of abrasive wear and adhesive wear.