Improvement of lnconel 600 oxidation resistance by aluminization

Dissertant

Halim, Ali Hubi

University

University of Technology

Faculty

-

Department

Department of Production Engineering and Metallurgy

University Country

Iraq

Degree

Ph.D.

Degree Date

2006

English Abstract

The oxidation and hot corrosion resistance of nickel super alloy Inconel 600 can be improved by enriching the surface composition in Al and Cr using pack cementation process.

In this work, Inconel 600 alloy is coated with two different types of coatings, the first one is Cr-modified aluminize coating and the second is the Y-doped chromium modified aluminize coating.

Aluminum, chromium with and without yttrium were simultaneously deposited by diffusion into Inconel 600 substrate by the pack- cementation process, using a pack mixture containing (10 % Cr203, 10 % Al, 2 % NH4CI, 4 % NaCl and 72 % A1203) and 2 % Y203 (wt %) when required.

It was found that diffusion coating time of eight h at 1050 °C produces coating thickness of 65-80 run and consist mainly of NiAl phase.

Cyclic oxidation tests are conducted on the uncoated Inconel 600 alloy, Cr- modified aluminate coating and on Y- doped chromium modified aluminate coating at a temperature range between 800-1000 °C in (air and in C02), and at 900 °C in water vapor for 100 h at 10 h cycle.

The cyclic hot corrosion tests of Inconel 600 and its coated systems deposited with 2 mg / cm2 NaCl / Na2S04 (100 / 0, 50 / 50, and 0 / 100 wt.

%) deposits initially are conducted at 900 °C in air for 105 h at 15 h cycle.

The oxidation kinetics for uncoated Inconel 600 alloy in air, C02 and water vapor environments are found to be nearly parabolic.

The parabolic rate constant (kP) values obtained at 900 °C in air, C02 and water vapor are : 2.68 x l0'7, 6.30 x l0'7 and 4.16 x l0'7 (mg2 / cm4) / s respectively.

This indicates that the oxidation behavior of this alloy is worsening in C02 environment.

The phases present on the cyclic oxidation of uncoated Inconel 600 alloy surface under most test conditions as revealed by XRD analysis are NiO, (Fe, CrOs, NiFe204 and NiCr04.- The hardness of yttrium- doped chromium modified aluminate coating is about three times higher than that of the substrate alloy after cyclic oxidation in air at 900 °C for 100 h.

The oxidation kinetics for both coated systems in air, C02 and water vapor are found to be parabolic.

At 800 °C, the kP values for both coated systems are one order of magnitude lower than that for the uncoated Inconel 600 cyclic oxidized in air under the same test conditions.

In cyclic hot corrosion test, both coated systems follow the parabolic law when oxidized with 100 % NaCl and with (50 % NaCl + 50 % Na2S04) deposits, whereas the oxidation kinetic of uncoated Inconel 600 follows a linear rate law under the same test conditions.

At 900 °C, the KP values for both coated systems with 100 % Na2S04 deposits are one order of magnitude lower than that for the uncoated Inconel 600 alloy under the same test conditions.

Oxide phases that formed on coated systems during most of the oxidation exposure conditions are A1203 and NiCr04.

Main Subjects

Materials Science , Minerals

Topics

• Oxidation
• Alloys

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305539