Multi-Material Additive Manufacturing of Dual-Steel Complex Internal Geometries

Multi-material additive manufacturing is a technique gaining popularity to produce parts, optimised through use of multiple materials, to create very specific properties. It offers dimensional freedom to create complex geometries, between the different alloys, that were previously impossible to manufacture by any other method. This can lead to properties which are not achievable in conventional single alloy parts, by manipulation of alloy placement. In this case, manufacture of parts such as this is achieved using a selective powder deposition device, produced by Schaeffler Aerosint. Where powders are adhered, through a negative pressure, to drums and then selectively deposited using an ejection of Argon gas. The resulting geometries manufactured are therefore limited by the resolution of the recoater, the alignment between the powders, and alignment of the powders with the laser. As well as part size being limited by the time taken for the powder deposition. In this work, 316L and 17-4PH stainless steels are used to create multi-material parts with differing internal geometries between the alloys. The aim is to manipulate strength, ductility, and toughness, through production of metal ‘composite’ structures, containing material layers or fibres. The geometries are designed, such that material features are as fine as possible, within the available resolution of the recoater. This also allows for maximising the number of repeated patterns within the samples, which are small enough to be manufactured within a continuous build job. The resulting microstructure for each geometry is then analysed, to assess the accuracy of the interfaces produced. The samples are then heat-treated, subjected to mechanical testing, and compared to their single-material counterparts. The influence of varying material geometry on strength, toughness and crack propagation is then discussed.