Directed Energy Deposition — Laser Powder
LENSLMDDMDDED-LB/PLaser Cladding AMFibre or diode laser, typically 1–6 kW, wavelength 900–1100 nm. Focused to 0.5–4 mm spot diameter at the deposition point. Powder is delivered coaxially (surrounding the laser beam) or laterally (off-axis nozzles) directly to the laser focal zone.
How it works
A focused high-power laser beam creates a melt pool on the substrate or previously deposited material. Metal powder (50–150 µm D50, broader than LPBF) is injected into the melt pool through coaxial or off-axis nozzles entrained in a carrier gas (typically argon). Powder melts on contact with the melt pool and solidifies rapidly as the focal zone moves away. A shielding gas shroud prevents oxidation. The process occurs in an inert atmosphere chamber (for reactive metals like Ti) or with local shielding only (for steels and Ni alloys). DED-LB/P can repair near-net-shape components by depositing only where material is needed, and can deposit multi-material structures by switching powder feeders mid-build.
Parameter envelopes (2 material–machine combinations)
Power
300–2000 W (typ. 800 W)
Scan speed
5–30 mm/s
Layer thickness
300–800 µm
Max O₂
50 ppm
Ti-6Al-4V requires enclosed argon chamber (O₂ < 50 ppm) — local shielding is insufficient. Powder catchment efficiency 60–90%. Deposition rate 5–50 g/min. Typical post-processing: annealing + machining. AMS-7004 covers Ti-6Al-4V ELI DED parts for aerospace.
Power
500–3000 W (typ. 1500 W)
Scan speed
5–25 mm/s
Layer thickness
300–1000 µm
Max O₂
200 ppm
IN718 DED for turbine blade repair and large aerospace components. Local shielding (trailing argon shroud) may be sufficient vs. full chamber. SA+DA heat treatment required post-build. Build rates up to 100 cm³/h possible with multi-nozzle heads.
Defect modes (4)
Oxidation from Insufficient Shielding
Cause
Insufficient inert gas coverage allows atmospheric oxygen or nitrogen to reach the melt pool or hot solidified material. Titanium is especially susceptible: >500 ppm O₂ causes embrittlement and discolouration. Steels and Ni alloys are more tolerant.
Indicator
Blue, gold, or white discolouration on Ti (rainbow oxidation). Increased oxygen or nitrogen content in chemistry test. Reduced ductility and impact toughness. For steels: surface oxide scale.
Prevention
Use enclosed inert atmosphere chamber for Ti. For Ni and steel: trailing and leading shielding gas shrouds. Monitor O₂ level continuously during deposition. Preheat shielding gas flow before initiating the arc.
Detection
- OES (optical emission spectrometry) for O, N content
- visual inspection (Ti colour)
- hardness testing (Ti embrittlement)
Coarse Columnar Grain Structure
Cause
Slow cooling rate (~10² K/s) and epitaxial growth from the substrate promotes large columnar grains aligned with the build direction (Z). Columnar grains can span multiple layers in DED, producing strong texture and anisotropy — more pronounced than in LPBF.
Indicator
EBSD shows strong columnar texture. Tensile anisotropy >20% between XY and Z specimens. Lower Charpy impact energy in Z-direction.
Prevention
Solution anneal + age (SA+DA) heat treatment for Ni alloys. Microstructural manipulation via scan strategy changes, preheat control, or inter-layer forced cooling. Grain refinement additives for Al alloys.
Detection
- EBSD
- optical metallography
- dual-axis tensile testing
Dilution at Substrate Interface
Cause
The first few deposited layers partially melt and dilute the substrate or previously deposited material. In multi-material builds or repair applications, dilution changes the local composition and can produce unintended intermediate alloy zones or brittle intermetallics.
Indicator
EDX (energy-dispersive X-ray) shows compositional gradient at deposit/substrate interface. Hardness measurement shows intermediate zone between substrate and deposit values. Microstructural anomaly (e.g., martensite in a zone not expected to transform).
Prevention
Use buttering layers (deposit a compatible intermediate alloy before the final material). Optimise laser power to minimise dilution depth. Characterise dilution zone by cross-section metallography before qualifying the component.
Detection
- EDX mapping
- hardness traverse
- metallographic cross-section
Residual Stress and Distortion
Cause
Large thermal gradients during deposition, particularly on thin substrates or cantilever geometries. The high deposition rates and large melt pools produce more distortion than LPBF but less than WAAM (wire-arc).
Indicator
Substrate bends or warps during deposition. CMM measurement shows part dimensions differ from CAD. Cracking at substrate attachment point after wire-EDM release.
Prevention
Preheat substrate (100–400°C depending on alloy). Optimise deposition strategy (island scanning, symmetrical build-up). Use process simulation software to predict distortion and apply inverse compensation to CAD geometry.
Detection
- CMM before and after build plate release
- neutron or X-ray diffraction (bulk stress)
- Contour method