Multimaterial Additive Manufacturing of Graded Laves Phase Reinforced NiAlTa Structures by Means of Laser Metal Deposition

Abstract

Recently, the additive manufacturing (AM) technology laser metal deposition (LMD) has gained a lot of attention for processing crack prone high temperature materials such as nickel-based superalloys or intermetallics. A feasibility study on LMD of a graded transition from binary ß-NiAl to Ni50Al42Ta8 is presented with the aim to show the possibility of manufacturing ß-NiAl-based structures with a spatially resolved microstructure and subsequently tailored mechanical properties. For achieving this, the alloys Ni50Al50 and Ni50Al42Ta8 are coinjected into the process zone and the powder feeding rates are adapted in a layerwise manner. Due to preheating temperatures of up to 1000 °C, the transition can be manufactured with high relative density and a low degree of cold cracking. Scanning electron microscopy of the transition zone shows the formation of a fine dendritic microstructure consisting of ß-NiAl dendritic and NiAlTa interdendritic regions. Large area energy-dispersive X-ray analysis reveals a gradient in NiAlTa Laves phase content with increasing build height. The observed volume fraction of Laves phase corresponds well to reported values from cast ingots. Finally, hardness measurements along the build-up direction show an increase in hardness from 300 HV0.1 to 680 HV0.1 indicating a tremendous increase in tensile strength.