Improvement in corrosion resistance of 304 stainless steel using anodizing process

Dissertant

Bakr, Yaqub Muhsin

Thesis advisor

Ujayl, Sami Abu al-Nun

University

University of Technology

Faculty

-

Department

Department of Production Engineering and Metallurgy

University Country

Iraq

Degree

Ph.D.

Degree Date

2010

English Abstract

The research objective is to investigate the formation of oxide layer on the metal surface of stainless steel type 304 by using anodizing process at different variables positive and negative current density, nitric and sulfuric acids concentration, time and temperature of electrolyte).

A power supply with an asymmetric AC square waveform is used with voltage control.

It was found that the best conditions as follow positive current density of 0.1A / cm2, negative current density 0.003A / cm2, nitric acid concentration 17 Vol.

Sulfuric acid concentration 8 Vol., time of exposure 10 mins.

And temperature of electrolyte 10 oC.

The electropolishing process is carried out before anodizing process by using mixture acids baths for stainless steel.

It was found that the best brightness.

Smoothness and weight loss measurements are observed with applied current density of 0.55 A / cm2 and temperature 95 0C for time of 10 mins.

The X-ray diffraction and SEM investigation are carried out on surface after anodizing process.

X-ray diffraction phase analysis of the oxide layer on the 304 stainless steel specimens is proved the presence of (NiCr2O4) oxid layer on the surface and SEM micrograph shows the dark spots on the surface which indicates that anodizing process dissolves the intermetallic particles to the solution.

These spots are covered with oxide film formed.

The hexagonal cells clearly appear in anodic film.

The surface roughness and microhardness measurements are provided on electropolishing and anodizing surface.

The surface roughness measurements (Ra) using (AFM) after electropolishing process decreases by dissolving process to irregularities regions and values of Ra = 4.240 nm (X- axes), Ra = 1.411 nm (Y- axes), Ra = 3.094 nm (Z- axes), while the surface roughness (Ra) after anodizing process increases by oxide layer growth on the surface and values of Ra = 30.30 nm (X- axes), Ra =18.50 nm (Y- axes), Ra = 27.60 nm (Z- axes).

The microhardness of stainless steel type 304 decreases with electropolishing and anodizing processes respectively due to the increase in chromium to iron ratio and the presence of nickel in the oxide film.

The present work is also aimed to investigate the corrosion behavior of 304 stainless steels by using open circuit, polarization and cyclic polarization tests at room temperature in sea water (3.5 % NaCl, pH 6.7).

These tests are done for unprotected, electropolishing and anodizing specimens.

Improvement in corrosion resistance is clearly observed for specimens after anodizing process that shown, Ecorr = -359.6 mV and Ecorr=3.83μA/cm2, while the specimen after electropolishing, Ecorr = -398.8mV and Ecorr = 4.69μA / cm2, and specimen before treated, Ecorr = -419.9 mV and Ecorr = 5.56Μa / cm2, and pitting potential increases in positive direction.

Main Subjects

Materials Science , Minerals

Topics

• Stainless steel

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305050