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Research Papers: Nuclear Power

High Temperature Aging and Corrosion Study on Alloy 617 and Alloy 230

[+] Author and Article Information
Kun Mo

Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801kunmo2@illinois.edu

Gianfranco Lovicu

Dipartimento di Ingegneria Chimica, Chimica Industriale e Scienza dei Materiali, Universitá di Pisa, Pisa 56126, Italyg.lovicu@ing.unipi.it

Hsiao-Ming Tung

Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801htung2@illinois.edu

Xiang Chen

Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801xchen24@illinois.edu

James F. Stubbins

Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801jstubbin@illinois.edu

J. Eng. Gas Turbines Power 133(5), 052908 (Dec 13, 2010) (9 pages) doi:10.1115/1.4002819 History: Received July 02, 2010; Revised July 03, 2010; Published December 13, 2010; Online December 13, 2010

Abstract

The very high temperature gas-cooled reactor (VHTR), with dual capacities of highly efficient electricity generation and thermochemical production of hydrogen, is considered as one of the most promising Gen-IV nuclear systems. The primary candidate materials for construction of the intermediate heat exchanger (IHX) for the VHTR are alloy 617 and alloy 230. To have a better understanding of the degradation process during high temperature long-term service and to provide practical data for the engineering design of the IHX, aging experiments were performed on alloy 617 and alloy 230 at $900°C$ and $1000°C$. Mechanical properties (hardness and tensile strength) and microstructure were analyzed on post-aging samples after different aging periods (up to 3000 h). Both alloys attained increased hardness during the early stages of aging and dramatically soften after extended aging times. Microstructural analysis including transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and electron backscatter diffraction was carried out to investigate the microstructure evolution during aging. A carbide particle precipitation, growth, and maturing process was observed for both alloys, which corresponds to the changes of the materials’ mechanical properties. Few changes in grain boundary character distribution and grain size distribution were observed after aging. In addition, high temperature corrosion studies were performed at $900°C$ and $1000°C$ for both alloys. Alloy 230 exhibits much better corrosion resistance at elevated temperature compared with alloy 617.

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Figures

Figure 12

TEM analysis of alloy 230 aged at 1000°C for 1000 h (zone axis [001])

Figure 13

EBSD and CSL boundaries analysis of alloy 617 aged at 900°C for 1000 h

Figure 14

Hardness of the as-received and aged alloy 617

Figure 15

Hardness of the as-received and aged alloy 230

Figure 16

YS of the as-received and aged alloy 617

Figure 17

UTS of the as-received and aged alloy 617

Figure 18

Oxidation of alloy 617 at 1000°C for 300 h

Figure 19

Oxidation of alloy 230 at 1000°C for 300 h

Figure 20

EDS analysis of the corrosion layer of alloy 617

Figure 11

TEM analysis of alloy 617 aged at 1000°C for 1000 h (zone axis [001])

Figure 10

Intergranular precipitates in alloy 230 aged at 1000°C for 3000 h

Figure 9

Intergranular precipitates in alloy 617 aged at 1000°C for 3000 h

Figure 8

Microstructure characteristics of alloy 230 aged at 900°C for 30 h

Figure 7

TEM analysis of a small precipitate of alloy 617 aged at 900°C for 30 h (zone axis [111])

Figure 6

Microstructure characteristics of Alloy 617 aged at 900°C for 30 h: (a) precipitation, (b) diffusion-control precipitate coarsening on a grain boundary, and (c) diffusion-control precipitate coarsening on phase boundaries

Figure 5

Inclusions in the Alloy 230 in the as-received condition

Figure 4

Inclusions in the Alloy 617 in the as-received condition

Figure 3

EBSD and CSL boundaries analysis of the Alloy 230 in the as-received condition

Figure 2

EBSD and CSL boundaries analysis of the Alloy 617 in the as-received condition

Figure 1

Geometry and dimensions of tensile specimens

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