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Influence of Substrate Thermal Boundary Conditions on Microstructure and Mechanical Properties of DED-Processed Maraging Steel

📑 10 slides 👁 29 views 📅 1/26/2026
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Title & One-line Pitch

Project aim: control in-situ heat treatment via substrate thermal management.

Title & One-line Pitch
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The Physical Problem

  • Layer deposition produces cyclic reheating of underlying material.
  • Substrate temperature rises substantially during long builds.
  • Repeated reheating acts as an in-situ aging step.
The Physical Problem
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Literature Summary

  • Reports of hardness gradients in DED maraging steel.
  • Evidence for partial in-situ precipitation during builds.
  • Active cooling improves rate but risks instability.
Literature Summary
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Gap I: Stability vs Control

  • Observation studies characterize gradients but lack substrate control.
  • Immersion cooling refines microstructure but introduces instability.
  • Need method preserving stability while controlling thermal boundary.
Gap I: Stability vs Control
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Gap II: Nanoscale Blind Spots

  • Strengthening driven by 5–30 nm precipitates in maraging steels.
  • Most DED studies rely on SEM/EDS — insufficient for nanoscale.
  • No link between thermal boundary and nanoscale precipitation.
Gap II: Nanoscale Blind Spots
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Our Solution

  • Substrate clamped to conductive block with sealed cooling channels.
  • Cooling beneath plate — no fluid contact with melt pool.
  • Converts substrate to controlled thermal boundary (<10 °C option).
Our Solution
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Scientific Logic

  • Controlled cooling → increased local cooling rate.
  • Faster cooling → refined dendritic spacing.
  • Reduced dwell → suppressed coarsening & GB precipitates.
Scientific Logic
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Experimental Matrix

  • DED builds under five substrate thermal conditions.
  • Constant parameters: powder feed, laser power, scan speed.
  • Sample plan: replicate builds for OM/SEM/EBSD/TEM and mechanical tests.
Experimental Matrix
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Multi-Scale Characterization

  • OM/SEM: melt pool geometry, porosity, lack-of-fusion.
  • EBSD: grain size/texture; retained austenite fraction.
  • TEM: nanoscale precipitate presence/size/distribution.
Multi-Scale Characterization
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Timeline & Risks

  • Feb-Mar: DED printing (room & elevated substrates).
  • Apr-May: OM, SEM, EBSD, hardness mapping.
  • May-Jul: Cooled-substrate printing, TEM, tensile tests.
Timeline & Risks
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