Tungsten carbide hardfacing offers superior wear resistance in a wide range of oil and gas applications. However, for designs of complex geometries, trade-offs often need to be made between manufacturing robustness and service lifecycle based on limited choices of conventional deposition processes. An additive manufacturing (AM) functionally graded tungsten carbide using laser directed energy deposition (L-DED) is developed in an integrated numerically controlled multi-axis machining center with multi-material feeding capability. Essential process parameters are optimized using design of experiment (DOE). Graded structure is shown to reduce crack density. Erosion performance of the L-DED tungsten carbide is on par with commercial high velocity air fueled (HVAF) tungsten carbide coating. The study demonstrates that L-DED-based graded material strategy can significantly improve the robustness of the fabrication process and the expected service reliability. It opens up opportunities involving other hard materials, transition materials, grading strategy by thickness and/or by location.