The combination of IN718-316LSS has been well-known for its mechanical properties and corrosion resistance at high temperatures and aggressive environments, making it a familiar pair in conventional welding methods. In recent years, extensive research has been conducted to explore the potential advantages of additive manufacturing techniques. Thus, the aim of this study is to investigate the feasibility and development of the IN718-316LSS bi-metal structure on a preformed substrate and assess the resulting fusion zone under various processing parameters using the laser powder bed fusion method. Initially, nine IN718-316L samples were produced on a preformed substrate of 316L stainless steel using three power levels (100, 175, and 250 W) and three scanning speeds (0.4, 0.6, and 0.8 m/s) without any variations in scanning strategy, hatch distance, and layer thickness. Subsequently, mechanical properties eva‎luations were conducted on samples produced under three optimized specific processing parameter sets based on the results of defects and microstructure analysis. Microstructural investigations were performed using optical and electron microscopy, X-ray diffraction, and phase stability calculations, while mechanical properties were characterized through microhardness measurements and “tensile-shear” tests. The results showed that an increase in energy density, irrespective of different power and speed combinations, led to an increase in penetration depth, dilution, and thickness of the chemically affected zone. Speed variations, especially in the “keyhole mode”, influenced penetration depth. Furthermore, within the linear energy density range of 292 to 312 J/mm, noticeable changes in the dimensions of the fusion pool were observed, resulting in transitional states and geometry alterations of the fusion pool. Mixing degrees in the chemically affected region varied with energy density; lower energy inputs corresponded to incomplete melting with synergistic effects on density reduction in the build direction, while higher energy inputs revealed “keyhole porosity” attributed to material evaporation. In addition to the mentioned process defects, solidification cracks were observed at the maximum energy density of 625 J/mm in the type 1 interface. The high input energy, associated with homogenic iron, molybdenum, and niobium distribution in the matrix, which had led to extension of the solidification range, resulting in Mo-rich laves formation in solidification grain boundaries, and an increased likelihood of solidification cracks. Conversely, type 2 interface exhibited significant mixing, preventing homogeneous iron distribution within the nickel matrix, reducing segregation, and limiting potential crack growth paths. The dimensions of the grains and microstructure scale were influenced by energy density. The microstructure of type 2 interface samples consisted of equiaxed sub-layer steel grains, and equiaxed columnar grains in the mixing zone and columnar grains in the IN718 zone, respectively. The combination of equiaxed and columnar grains in the mixing zone of type 2 interface samples resulted in improved strength and significantly better ductility according to tensile-shear test results. Hardness results and grain size calculations in the steel region showed no significant changes in the heat affected region. The achievement of optimal processing parameters for these dual metals, in terms of relative build density, metallurgical defects, and mechanical properties, represents one of the key findings of this study.

احمد رضائيان , محسن بدرسماي

احمد كرمانپور

بهزاد نيرومند , مسعود عطاپور