Processing of alloy Ti-6Al-4V and of stainless steel 316L by Laser Beam Melting

Additive manufacturing processes such as Selective Laser Melting (SLM) appear very promising in view of the economic production of near-net-shape, complex and (almost) fully dense parts from metallic materials such as Ti alloys and stainless steels. Practically, in SLM, a metallic powder is deposited layer-by-layer in a powder bed and then molten locally according to the desired shape. An important feature of this process is that the structure undergoes an ultra-fast cooling once the beam leaves the working zone, thus giving rise to strongly out-of-equilibrium microstructures. In the case of Ti alloy Ti-6Al-4V, in particular, the microstructural anisotropy resulting from the epitaxial growth of the newly deposited layer on the material previously solidified has been shown to exert a very strong influence on the mechanical properties [1]
In the present work, the thermophysical behaviour of Ti-alloy Ti-6Al-4V and of stainless steel 316L has been characterised in details, in order to reach a better understanding of the phenomena controlling the microstructures and mechanical properties of parts. In particular, the thermal conductivity of Ti-alloy Ti-6Al-4V and of stainless steel 316L at high temperature has been determined by combining dilatometry, Differential Scanning Calorimetry (DSC) and laser flash diffusivimetry based on Laplace’s equation. Since Ti-alloy Ti-6Al-4V and stainless steel 316L exhibit quite different physical behaviours, their careful comparison is shown to shed more light into the role of phenomena such as epitaxial growth, out-of-equilibrium phase transformations and/or internal stresses in the additive manufacturing of metallic materials.