Laser Additive Manufacturing (LAM) of Hastelloy-X Thin Walls Using Directed Energy Deposition (DED): Parametric Investigation and Multi-objective Analysis

An experimental investigation and multi-objective analysis is carried out for laser additive manufacturing system-directed energy deposition (LAM-DED) of Hastelloy-X thin walls. The process parameters such as laser power, scan speed and powder feed rate are selected to understand their influence on track width, track height and build rate during LAM-DED of the thin Hastelloy-X walls. The investigation is further extended to develop empirical models defining the parametric influence with good agreement to experimental measurements. Analysis of variance (ANOVA) analysis is performed to find out the significant process parameters affecting the geometry and build rate in LAM-DED. ANOVA analysis shows that the most significant control parameter for track width, track height and build rate are power with a contribution of 85.40%, scan speed with a contribution of 48.07% and powder feed rate with a contribution of 58.77%, respectively. Multi-objective optimization using Grey relational analysis (GRA) derived an optimal process parameter combination of power of 600 W, scan speed of 0.3 m/min and powder feed rate of 11 g/ min for maximum build rate and nominal track width of 1.7 mm. The developed methodology can be extended to LAM-DED of other track widths. The thin walls are successfully built using LAM-DED at the optimized process parameters and the measured track width of built wall is found to be within permissible limits. Macrostructural examination revealed that the built wall is defect-free in terms of cracks, porosity, foreign inclusions and similar defects. Microstructural examination shows fine dendritic growth in the direction of wall building. The work finds applications in building thin walled Hastelloy-X components of ultramodern systems, like Advanced Ultra Super Critical Power Plants involving extreme duty conditions.