Optimization of processing and post-heat treatment parameters for direct energy deposited Ti-6Al-4 V alloy: a dual-stage Taguchi approach for freeform fabrication and repair
摘要
Direct Energy Deposition (DED) offers a sustainable and cost-effective alternative for the fabrication and repair of complex Ti-6Al-4 V components. However, achieving mechanical homogeneity remains a challenge for critical structural applications. In particular, DED-repaired components may exhibit process-induced defects, microstructural heterogeneity, and mechanical-property mismatch between the deposited region, heat-affected zone, and base material. This study employs a dual-stage Taguchi design of experiments to optimize both DED processing and post-heat-treatment parameters for Ti-6Al-4 V freeform fabrication and turbine-blade repair. In the first stage, laser power, scanning speed, and powder feed rate were optimized using porosity volume fraction as the response criterion. In the second stage, solution heat-treatment temperature, cooling method, aging temperature, and aging time were optimized using compressive yield strength for freeform-fabricated samples and hardness homogeneity for repaired samples as response criteria. Experimental specimens were evaluated using optical and electron microscopy, SEM-EDS analysis, microhardness profiling, and compression testing to assess defect density, microstructural evolution, and mechanical response. The optimum DED processing condition, 300 W laser power, 1200 mm/min scanning speed, and 1 g/min powder feed rate, produced deposits with a relative density above 99.9%. The optimum post-heat-treatment route, involving solution treatment at 1050 °C followed by water quenching and aging at 600 °C, produced a mean hardness of 416 HV0.2 and a yield compressive strength of 1306 MPa. These results demonstrate that a reduced-experiment DoE workflow can efficiently link DED processing, post-heat-treatment design, microstructural evolution, and mechanical homogeneity in Ti-6Al-4 V repair applications.