Abstract
We describe and study the thermal profiles experienced by various age-hardenable alloys during laser additive manufacturing (LAM), employing two different manufacturing techniques: selective laser melting and laser metal deposition. Using scanning electron microscopy and atom probe tomography, we reveal at which stages during the manufacturing process desired and undesired precipitation reactions can occur in age-hardenable alloys. Using examples from a maraging steel, a nickel-base superalloy and a scandium-containing aluminium alloy, we demonstrate that precipitation can already occur during the production of the powders used as starting material, during the deposition of material (i.e. during solidification and subsequent cooling), during the intrinsic heat treatment effected by LAM (i.e. in the heat affected zones) and, naturally, during an ageing post-heat treatment. These examples demonstrate the importance of understanding and controlling the thermal profile during the entire additive manufacturing cycle of age-hardenable materials including powder synthesis.
Highlights
Many classes of alloys owe their high strength to the presence of finely dispersed second phase particles
We describe and study the thermal profiles experienced by various agehardenable alloys during laser additive manufacturing (LAM), employing two different manufacturing techniques: selective laser melting and laser metal deposition
Using examples from a maraging steel, a nickel-base superalloy and a scandiumcontaining aluminium alloy, we demonstrate that precipitation can already occur during the production of the powders used as starting material, during the deposition of material, during the intrinsic heat treatment effected by LAM and, naturally, during an ageing post-heat treatment
Summary
Many classes of alloys owe their high strength to the presence of finely dispersed second phase particles (i.e. phases different from the matrix phase) Since they form by precipitation phase transformations, they are called precipitates, and the materials featuring them, precipitation-strengthened alloys,[1] Examples are most Al alloys,[2,3,4] many Ni-based alloys[5,6,7] and some steels.[8,9,10,11] During conventional processing, these materials undergo two subsequent heat treatments. The material is annealed at a lower temperature, where the remaining solutes that are in a supersaturated state are allowed to precipitate In this age-hardening step, the desired fine dispersion of particles forms. The alloys under investigation are a maraging steel, an Al-Sc alloy and a nickel-based superalloy
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