Atom probe, AFM, and STM studies on vacuum-fired stainless steels

Area of Science:

• Materials Science
• Surface Science
• Vacuum Technology

Background:

• Understanding the surface properties of stainless steels is crucial for applications involving vacuum environments.
• Thermal treatments like vacuum annealing significantly impact material surface morphology and composition.
• Outgassing behavior in vacuum systems is strongly linked to surface characteristics.

Purpose of the Study:

• To investigate the surface morphology and elemental composition changes in 304L and 316LN stainless steels after low-temperature bake-out and vacuum annealing.
• To correlate surface microstructure and composition with outgassing behavior.
• To compare the effects of thermal treatment on 304L and 316LN stainless steels.

Main Methods:

• Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) were used to analyze surface morphology.
• Atom Probe (AP) depth profiling was employed to determine local elemental composition.
• Samples included 304L and 316LN stainless steels subjected to vacuum annealing.

Main Results:

• Vacuum annealing induced significant changes in surface structure and topology for both steel grades.
• Recrystallization and surface reconstruction were less pronounced in 316LN stainless steel compared to 304L.
• Atom Probe analysis revealed notable nickel enrichment on the surface of 304L samples after annealing.

Conclusions:

• The surface microstructure and composition of stainless steels are significantly altered by vacuum annealing.
• These surface modifications, particularly nickel enrichment in 304L, strongly influence hydrogen recombination and outgassing behavior.
• Grade 316LN shows greater stability in surface structure after thermal treatment, suggesting different outgassing characteristics.