Abstract
Additive manufacturing has been around for many years, yet the underlying physics of thermal gradients, local pressure environment, and other non-steady state manufacturing conditions are not fully understood. A Multi-University Research Initiative (MURI) is currently ongoing to measure liquid/solid and solid/solid interface stabilities in AM Ti-6Al-4V. Samples were produced with different beamscanning strategies in order to study the role of thermal gradients on the resulting microstructure. The motivation is to determine which beam-scanning strategy leads to desired grain size and texture. Orientation at different length scales (from mm to nm) can be quantified and compared with a combination of techniques including Precession Electron Diffraction (PED), Electron Backscatter Diffraction (EBSD) and Neutron diffraction. This new information will help predict properties of additively manufactured parts.
Highlights
A principal advantage of manufacturing parts by Addi ve Manufacturing (AM) system is the ability to obtain complex geometries, different types of composites/alloys or even gradients of composi on in the same part, as it follows a layer-by-layer build up approach
A recent semi-analy cal heat model has been developed at Oak Ridge Na onal Laboratory Manufacturing Demonstra on Facility (ORNL MDF), to tackle the above-men oned complexi es [11], based on a transient solu on, to construct a temperature field for an arbitrary beam path, from which informa on can be extracted regarding thermal gradients and interphase growth veloci es of a layer of a build, both essen al in understanding the microstructural features of the build such as phase selec on, morphological features of the phase
The goal of this Mul disciplinary University Research Ini a ve (MURI) funded by the Office of Naval Research is to understand how the varia on of composi on and thermal gradients, both spa ally and temporally, will result in differences in liquid-solid interface veloci es, thermal gyra ons and elas c-plas c stress/strain gradients as a func on of geometry and energy deposi on while manufacturing the part; in other words understanding how the build parameters influence local condi ons that result in specific microstructural features, defects and heterogenei es
Summary
A principal advantage of manufacturing parts by Addi ve Manufacturing (AM) system is the ability to obtain complex geometries, different types of composites/alloys or even gradients of composi on in the same part, as it follows a layer-by-layer build up approach. The Rosenthal equa on [10] gives the three-dimensional steady state temperature field for a point source While it is a straight forward analy cal solu on, it does not account for complex boundary condi ons and non-steady state condi ons, nor for latent heat of fusion or convec on. The proper es of AM parts, as with any other manufacturing process, are a func on of composi on, microstructure (phases, grain size and morphology, etc.), orienta on, texture, defects (created during the manufacturing process) and superficial characteris cs [7] The goal of this Mul disciplinary University Research Ini a ve (MURI) funded by the Office of Naval Research is to understand how the varia on of composi on and thermal gradients, both spa ally and temporally, will result in differences in liquid-solid interface veloci es, thermal gyra ons and elas c-plas c stress/strain gradients as a func on of geometry and energy deposi on while manufacturing the part; in other words understanding how the build parameters influence local condi ons that result in specific microstructural features, defects and heterogenei es
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