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P. Barriobero Vila, J. Gussone, J. Haubrich, S. Sandlöbes, J. da Silva, P. Cloetens, N. Schell, G. Requena:
"Inducing Stable α + β Microstructures during Selective Laser Melting of Ti-6Al-4V Using Intensified Intrinsic Heat Treatments";
Materials, 10 (2017), 268; 1 - 15.

Selective laser melting is a promising powder-bed-based additive manufacturing technique for titanium alloys: near net-shaped metallic components can be produced with high resource-efficiency and cost savings. For the most commercialized titanium alloy, namely Ti-6Al-4V, the complicated thermal profile of selective laser melting manufacturing (sharp cycles of steep heating and cooling rates)usually hinders manufacturing of components in a one-step process owing to the formation of brittle martensitic microstructures unsuitable for structural applications. In this work, an intensified intrinsic heat treatment is applied during selective laser melting of Ti-6Al-4V powder using a scanning strategy that combines porosity-optimized processing with a very tight hatch distance. Extensive martensite decomposition providing a uniform, fine lamellar α + β microstructure is obtained along the building direction. Moreover, structural evidence of the formation of the intermetallic α2-Ti3Al phase is provided. Variations in the lattice parameter of β serve as an indicator of the microstructural degree of stabilization. Interconnected 3D networks of β are generated in regions highly affected by the intensified intrinsic heat treatment applied. The results obtained reflect a contribution towards simultaneous selective laser melting-manufacturing and heat treatment for fabrication of Ti-6Al-4V parts.

additive manufacturing; selective laser melting; intrinsic heat treatment; titanium alloys; metastable phases; phase transformations; martensite decomposition; element partitioning; high energy synchrotron X-ray diffraction; synchrotron holographic X-ray

http://dx.doi.org/10.3390/ma10030268