Effect of Mechanical Surface Treatments on the Surface State and Passive Behavior of 304L Stainless Steel

At a Glance

Metadata	Details
Publication Date	2021-01-12
Journal	Metals
Authors	Kathleen Jaffré, Benoît Ter-Ovanessian, Hiroshi Abe, Nicolas Mary, Bernard Normand
Institutions	Université Claude Bernard Lyon 1, Matériaux Ingénierie et Science
Citations	24
Analysis	Full AI Review Included

Technical Analysis & Documentation: Surface State Control for High-Reliability Applications

Source Paper: Effect of Mechanical Surface Treatments on the Surface State and Passive Behavior of 304L Stainless Steel (Metals 2021, 11, 135)

Executive Summary

This research rigorously demonstrates that the mechanical surface finishing of 304L Stainless Steel (SS) critically dictates the stability, defect density, and corrosion resistance of its passive film, a finding highly relevant to high-reliability engineering, such as nuclear applications.

Surface Quality Correlation: Corrosion resistance is inversely correlated with surface disorder (roughness, residual stress, and subsurface defects).
Optimal Finish: The best corrosion performance was achieved by the smoothest surface (1 µm diamond polished, Ra 16 nm RMS), which produced the thickest (3-3.5 nm) and most stable passive film with the lowest defect density (NA 2.2 x 10²⁰ cm^-3).
Detrimental Effects: Dry grinding resulted in high roughness (1300 nm RMS), high compressive stress (-432 MPa), and a thin, unstable passive film (1.4-1.6 nm) with the highest defect density, leading to enhanced reactivity and poor pitting resistance in chloride environments.
Semiconductive Behavior: Passive films exhibited dual semiconductive behavior: p-type (associated with Cr vacancies in the inner layer) at low potentials (< -0.76 V vs. MSE) and n-type (associated with oxygen vacancies in the outer layer) at higher potentials.
6CCVD Value Proposition: This study underscores the necessity of ultra-precise surface control. 6CCVD provides MPCVD diamond materials (SCD and PCD) with surface roughness specifications (Ra < 1 nm) that far surpass the performance achieved by the optimal SS polishing, offering superior stability for extreme environments.

Technical Specifications

The following data points were extracted from the analysis comparing the three surface preparations of 304L SS.

Parameter	Grinding (Worst Performance)	1 µm Polishing (Best Performance)	Unit	Context
Surface Roughness (RMS)	1300 ± 200	16 ± 4	nm	Measured by 3D optical profilometer
Residual Compressive Stress	-432 ± 17	-110 ± 84	MPa	Measured by XRD (cosα method)
Ultrafine Grain Layer Thickness	150 - 280	150	nm	Subsurface modification (TEM/FIB)
Passive Film Thickness (δ)	1.4 - 1.6	3 - 3.5	nm	Determined by EIS/Complex Capacitance
Acceptor Density (N_A)	8.0 x 10²⁰	2.2 x 10²⁰	cm^-3	Highest defect density (Mott-Schottky)
Donor Density (N_D)	6.0 x 10²⁰	3.8 x 10²⁰	cm^-3	Lowest defect density (Mott-Schottky)
Semiconductive Transition	-0.76	-0.76	V vs. MSE	Potential where behavior shifts from p-type to n-type
Passive Current Density (0.5 V vs. MSE)	0.03	0.15	mA·cm^-2	Lower current indicates better passivation
Electrolyte pH	9.2	9.2	-	Borate buffer solution (H₃BO₃/Na₂B₄O₇)

Key Methodologies

The study employed a comprehensive suite of material science and electrochemical techniques to characterize the surface state and passive film behavior.

Surface Preparation:
- Grinding: Dry grinding using Green Ace Gold (#46) followed by Mac flat disc (#60).
- Polishing: Sequential polishing down to 2400 SiC emery paper.
- Fine Polishing: Sequential polishing down to 1 µm diamond paste.
Microstructural and Mechanical Characterization:
- Surface Roughness: Measured using a MICROMAP 3D optical profilometer (RMS parameter preferred over Ra).
- Subsurface Analysis: Transmission Electron Microscopy (TEM) on Focused Ion Beam (FIB) cross-sections to characterize the ultrafine-grained layer and plastic deformation zone.
- Residual Stress: X-ray Diffraction (XRD) using the cosα method (penetration depth ~10 µm).
Electrochemical Testing (Borate Buffer, pH 9.2):
- Immersion: 24 hours monitoring Open Circuit Potential (OCP).
- Passivation Ability: Potentiodynamic polarization curves (-0.8 V to 1.2 V vs. MSE) at 0.5 mV·s^-1 scan rate.
- Semiconductive Properties: Multi-frequency Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky (MS) analysis (potential scan -1.40 V to 0.00 V vs. MSE).
Corrosion Resistance Confirmation:
- Cyclic Potentiodynamic Polarization (CPP) in aggressive 2.5 M NaCl solution to determine pitting potential (E_p) and repassivation potential (E_rp).

6CCVD Solutions & Capabilities

The findings of this research emphasize that surface quality and defect control are paramount for achieving stable material performance in demanding environments. 6CCVD’s MPCVD diamond materials offer a path to surpass the limitations of even the best mechanically polished stainless steel.

Applicable Materials for Advanced Electrochemical and High-Reliability Studies

Research Requirement	6CCVD Material Solution	Technical Advantage
Stable Electrochemical Platform	Boron-Doped Diamond (BDD)	BDD electrodes are chemically inert, possess a wide potential window, and are highly resistant to corrosion and fouling, making them ideal for replicating or extending the EIS/Mott-Schottky analysis without the confounding variable of passive film instability.
Ultra-Low Defect Surfaces	Optical Grade Single Crystal Diamond (SCD)	Achieves surface roughness of Ra < 1 nm, significantly lower than the optimal 1 µm polished SS (Ra 16 nm RMS). This minimizes surface defects and maximizes stability for high-purity applications.
Large-Area High Stability	Polycrystalline Diamond (PCD)	Available in large plates/wafers up to 125mm diameter, with polishing down to Ra < 5 nm for inch-size components, suitable for scaling up corrosion studies or integrating into large systems.

Customization Potential for Research Replication and Extension

The complexity of the surface treatments studied (grinding, SiC polishing, diamond paste polishing) highlights the need for precise material control. 6CCVD offers specialized services to meet these exacting standards:

Precision Polishing: 6CCVD provides proprietary polishing techniques to achieve ultra-smooth surfaces (Ra < 1 nm for SCD), ensuring minimal subsurface damage and defect density, directly addressing the core finding of this paper.
Custom Dimensions and Thickness: We supply SCD and PCD materials with precise thickness control, ranging from 0.1 µm to 500 µm (and substrates up to 10mm), allowing researchers to tailor material geometry for specific experimental setups (e.g., TEM sample preparation or sensor integration).
Integrated Metalization: For electrochemical setups requiring robust electrical contacts, 6CCVD offers in-house deposition of standard and custom metal stacks, including Au, Pt, Pd, Ti, W, and Cu, ensuring reliable integration of diamond components into potentiostat systems.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of diamond for extreme environments. We can assist researchers and engineers in selecting the optimal diamond material (SCD, PCD, or BDD) and surface finish required for projects involving:

High-temperature/high-pressure fluid handling.
Advanced electrochemistry and sensing.
Corrosion resistance in aggressive media (e.g., simulated nuclear primary water, as mentioned in the paper’s ongoing work).

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The effect of dry grinding on 304L stainless steel’s passive behavior is compared to two other surface finishing (mechanical polishing down to 2400 with SiC emery paper and 1 µm with diamond paste, respectively). The characterization of the surface state was performed using scanning electron microscopy, transmission electron microscopy, 3D optical profilometer, and X-ray diffraction. Results indicate that each surface treatment leads to different surface states. The ground specimens present an ultrafine grain layer and a strong plastic deformation underneath the surface, while an ultrafine grain layer characterizes the subsurface of the polished specimens. Grinding induces high residual compressive stresses and high roughness compared to polishing. The characterization of the passive films was performed by electrochemical impedance spectroscopy and Mott-Schottky analysis. The study shows that the semiconductor properties and the thickness of the passive films are dependent on the surface state of the 304L stainless steel.

Tech Support

Original Source

DOI: https://doi.org/10.3390/met11010135

References

2002 - Semiconducting properties of oxide and passive films formed on AISI 304 stainless steel and Alloy 600 [Crossref]
2000 - Chemical composition and electronic structure of the oxide films formed on 316L stainless steel and nickel based alloys in high temperature aqueous environments [Crossref]
1995 - Electrochemical and surface studies of the passive layers grown on sputter-deposited nitrogen-stainless steel alloys in 1M H2SO4 solution [Crossref]
1998 - EIS and XPS study of surface modification of 316LVM stainless steel after passivation [Crossref]
2006 - Electrochemical & optical characterisation of passive films on stainless steels [Crossref]
1998 - Examination of the Role of Molybdenum in Passivation of Stainless Steels Using AC Impedance Spectroscopy [Crossref]
2014 - Passivity of Sanicro28 (UNS N-08028) stainless steel in polluted phosphoric acid at different temperatures studied by electrochemical impedance spectroscopy and Mott-Schottky analysis [Crossref]
2003 - Passive films on stainless steels—Chemistry, structure and growth [Crossref]
1978 - Composition of passive films on ferritic 30Cr stainless steels in H2SO4 [Crossref]
2019 - Behavior of hardened steel grinding using MQL under cold air and MQL CBN wheel cleaning [Crossref]