Fracture characterisation of vertically build functionally graded 316L stainless steel with Inconel 718 deposited by directed energy deposition process

Functionally graded materials (FGM) are a very promising group of technical materials. The potential of FGM was increased recently by Additive manufacturing (AM) techniques. This is due to the possibility of automatisation of the entire process and achievable variable material structure by controlled deposition parameters. The defects and unexpected structure formation are crucial for the performance of additively manufactured components. Conventional compositionally graded multi-material systems are characterised by horizontally oriented interfaces located within the XY plane of the deposition system. This paper deals with the fabrication of a graded material based on 316L and IN718 in combination with vertically oriented interfaces between single materials zones. Critical defects were observed in the microstructure as a result of solidification cracking. Mini tensile test results showed that the 316L/IN718 interface and 316L in ZYX (vertical) orientation are the weakest points of the produced material. Fractographic analysis revealed that all specimens in the YZX testing direction exhibit the solidification cracking propagated along the grain boundaries with a detrimental effect on the strength of the 316L/IN718 interface. Results of the current study were confronted with previous results obtained for horizontally deposited combination of materials.