Optimization of Co-Cr Alloys Fabricated by DMLS Using Multi-Objective Grey Relational Analysis

Objectives: To optimize Direct Metal Laser Sintering (DMLS) parameters for Co-Cr alloys to simultaneously enhance microhardness and compressive strength using multi-objective Grey Relational Analysis (GRA). Method: Co-Cr alloy specimens were fabricated using DMLS by varying laser power, scan speed, and hatch spacing based on a Taguchi L9 orthogonal array. Microhardness and compressive strength were measured as performance responses. Signal-to-noise ratios were calculated and normalized for GRA to obtain the grey relational grade (GRG). ANOVA was performed to determine the significance of process parameters, and confirmation experiments were conducted to validate the optimal parameter combination. Findings: The multi-objective optimization results showed that laser power was the most influential parameter with a contribution of 76.21%, followed by hatch spacing (11.17%) and scan speed (10.37%). The optimal parameter combination was identified as 200 W laser power, 1200 mm/s scan speed, and 0.10 mm hatch spacing. Under these conditions, the Co-Cr alloy exhibited a microhardness of 438 HV and compressive strength of 827 MPa with a GRG of 0.961. The confirmation experiment showed a very low error of 0.3%, confirming the accuracy of the optimization model. Compared to the initial experimental run, the optimized parameters significantly improved both hardness and compressive strength due to improved densification and melt pool stability. The results are consistent with previous studies that reported improved mechanical properties at optimal energy density; however, this study uniquely demonstrates simultaneous optimization using GRA for DMLS-fabricated Co-Cr alloys. Novelty: This study presents multi-objective optimization of DMLS-fabricated Co-Cr alloys using Taguchi-GRA with experimental validation for simultaneous improvement of hardness and compressive strength. Keywords: Direct Metal Laser Sintering, Co-Cr alloy, Multi-objective optimization, Grey Relational Analysis, Mechanical properties