Cell Structure in LPBF 316L-Microstructural Heterogeneity, Thermal Stability, and Mechanical Properties

Area of Science:

• Materials Science
• Additive Manufacturing
• Metallurgy

Background:

• Additive manufacturing (AM) of 316L stainless steel results in a hierarchical microstructure.
• Microstructural features like cell structures and dislocations significantly influence mechanical properties.
• Understanding the thermal stability of these microstructures is crucial for AM part performance.

Purpose of the Study:

• To investigate the microstructural heterogeneity in laser powder bed-fused (LPBF) 316L stainless steel.
• To analyze variations in cell and dislocation structures along the build direction.
• To assess the impact of post-processing heat treatments on microstructure and hardness.

Main Methods:

• Analysis of microstructure variations through sample thickness in as-built LPBF 316L.
• Investigating thermal stability of cell structures after heat treatment at 500 °C and 800 °C.
• Microhardness testing across different layers and conditions.

Main Results:

• Significant variations in dislocation density were observed, with higher density in bottom layers.
• Cell structures showed different stabilities upon heat treatment, with notable dissolution at 800 °C, especially at the top.
• Microhardness measurements confirmed higher hardness in bottom layers, consistent with microstructural findings.

Conclusions:

• As-built 316L parts exhibit significant through-thickness microstructural heterogeneity.
• This heterogeneity impacts mechanical properties and the response to post-processing heat treatments.
• LPBF process parameters influence microstructure, necessitating careful control for consistent material properties.