Intensified Intrinsic Heat Treatments during Selective Laser Melting of Ti-6Al-4VWednesday (08.11.2017) 12:20 - 12:40 Part of:
Metallurgy plays a central role to advance the understanding of laser additive manufacturing (LAM) owing to the complex, currently uncontrollable thermal history that determines the microstructure and, hence, the structural performance of components. For titanium alloys, selective laser melting (SLM) represents a promising manufacturing method. This powder-bed-based LAM technique allows near net-shape manufacturing of metallic components with high resource-efficiency and promising cost savings. However, the sharp cycles of steep heating and cooling rates associated with the SLM process usually hinder the manufacturing of components in a one-step process. This promotes formation of brittle microstructures containing martensite that render poor ductility, poor fatigue resistance and are unsuitable for structural applications. Our investigations analyse the effect of the intrinsic heat treatment applied during selective laser melting of Ti-6Al-4V powder using scanning strategies that combine porosity-optimized parameters. The results obtained show that extensive martensite decomposition leading to lamellar α + β microstructures can be formed along the building direction. Synchrotron holographic X-ray computed tomography shows that interconnected 3D networks of the β matrix percolate through this microstructure, while the degree of stabilization of this phase is indicated by changes in the lattice parameter of β obtained from bulk analysis using high energy synchrotron X-ray diffraction. Moreover, structural evidence of the formation of the intermetallic α2-Ti3Al phase is provided. This is a step leading to simultaneous selective laser melting-manufacturing and heat treatment for fabrication of Ti-6Al-4V parts.