Mitigating Solidification Cracking in LPBF-Processed K418 Superalloy via Substrate Preheating and Layer Thickness...

Area of Science:

• Materials Science
• Additive Manufacturing
• Metallurgy

Background:

• Solidification cracking is a critical defect in laser powder bed fusion (LPBF) of nickel-based superalloys.
• K418 nickel-based superalloy is prone to hot cracking during additive manufacturing.
• Controlling process parameters is essential for achieving high-density, defect-free components.

Purpose of the Study:

• To systematically investigate the impact of layer thickness and substrate preheating on solidification cracking in LPBF of K418 alloy.
• To identify optimal process parameters for minimizing hot cracking.
• To understand the microstructural mechanisms underlying cracking.

Main Methods:

• Laser Powder Bed Fusion (LPBF) was used to fabricate K418 nickel-based superalloy samples.
• Varying layer thicknesses (30 μm and 60 μm) and substrate preheating temperatures (200 °C and 350 °C) were employed.
• Microscopic analysis (e.g., optical microscopy, SEM) was performed to examine crack propagation and microstructural features.
• Relative density measurements were conducted.

Main Results:

• A layer thickness of 30 μm with 350 °C preheating and a volumetric energy density (VED) of 60-80 J/mm³ effectively suppressed cracking, achieving >99% relative density.
• Preheating to 200 °C offered limited crack suppression.
• At a 60 μm layer thickness, preheating became detrimental, increasing cracking due to thermal accumulation and shrinkage stress.
• Cracks propagated along high-angle grain boundaries, associated with low-melting-point element segregation (O, B, Si, C).

Conclusions:

• 350 °C substrate preheating is a crucial parameter for mitigating solidification cracking in LPBF of K418 alloy.
• Moderate VED combined with optimal preheating and layer thickness enables the production of high-density, crack-minimized K418 components.
• Understanding the role of thermal stress and grain boundary segregation is key to controlling cracking in LPBF superalloys.